A COMMENTARY ON CLIMATE SCIENCE DEBATE. ANALYSIS OF THE ROYAL SOCIETY GUIDE AND A GWPF AUTHORS SCEPTICAL RESPONSE.
John Rhys. March 2016.
INTRODUCTION
To be
properly informed on one of the most important and politically charged issues
of this century any engaged citizen needs to consider the facts, opinions and
predictions emanating from climate science, as we would in any comparable area
(such as public health). This means asking
the general questions of what is to be accepted as valid, what confidence can
be placed in “expert” scientific opinion, and what additional conclusions we
might draw from examining any controversies around the issue.
Given that
the science is central, a starting point is the information available from, and
the assessments made by, the various bodies with responsibilities for
developing scientific understanding on climate. These include the
Meteorological Office in the UK, NASA and the NOAA in the US, and the IPCC, the
inter-governmental panel charged with providing summaries and synthesis of the
totality of the available research. The briefings provided by other bodies,
such as The Royal Society and The American Academy of Sciences, represent
perspectives endorsed by bodies [representing science and engaged in
maintaining standards wrt science and public policy]. Finally one can take note of the positions on
climate science taken by other entities engaged with the sector, who will also
have examined the science as part of their responsibilities. These include the International Energy
Agency, the UK Committee on Climate Change, and others.
All these
bodies endorse what one might loosely call the “informed consensus” on climate change.
However it is worth testing opinions and judgements against some of the known
sceptic arguments which dispute the “mainstream” or “consensus” view. Not
least the quality of the arguments
advanced in the public debate may be a guide to the confidence that should be
attached to a mainstream view
In December
2014 the Royal Society published A Short Guide to Climate Science[1], a layman’s introduction to the
subject covering 20 separate questions on climate issues. It may be generally assumed that, on this
subject, the Society represents a wide body of opinion in the science community
that broadly endorses the view that anthropogenic or man-made climate change is
a demonstrable fact, a major threat and hence a challenge for public policy. This
short guide was in turn condensed from a longer document.[2]
The Global
Warming Policy Foundation (GWPF), in contrast, is associated with a much more
sceptical view of the underlying science associated with this position, and commissioned
a response to the “Short Guide” from a number of academics[3],
dealing with its content on a point by point basis, and offering what it
described as a “fuller picture”. The response does not represent a corporate
position of the GWPF itself, but the authors are all members of the Academic
Advisory Council of the GWPF.
This
exchange therefore provides an opportunity to examine directly both sides of
the case, without going into areas of ongoing scientific inquiry for which we
are not equipped. We can conduct this examination as “informed” lay opinion,
starting from the understanding that we already have of the fundamentals of
climate science and the basic points at issue. To this we can add any
professional familiarity with, for example, the interpretation of statistical
trends, with the use of mathematical models, and with some of the general
science that is a necessary part of understanding the issues in the first place.
This paper
therefore takes each of the 20 summary points in the Royal Society guide in
turn, together with the “fuller picture” presented by the GWPF, and adds our
commentary. In some cases we have simply commented on the difference of view
between the two, or drawn attention to matters of logic and consistency, or to
assumptions implicit in the comment. In
others we have drawn on a wider range of opinion, including for example our own
reading of the IPCC or other reports, or have explored the literature to a
limited degree to determine whether a particular issue is the subject of a
consensus or not. There are also a few points that, even if implicit, are not
brought out fully or sufficiently clearly in the exchange between the RS and
the GWPF authors. These points are in our view essential to understanding the
discussion and the wider policy issues.
It is
apparent that in many instances it is possible to form a view as a reasonably
well informed lay person, and this document is intended to assist anyone who wants
to improve their understanding of the science and related issues at stake.
PRELIMINARY OBSERVATIONS
In heat balance terms it is estimated that changes
in this measure are only capturing about 1% of the change and are attempting to
do so with sampling points that sit within chaotic weather systems. This means
there are two major sources of measurement error and hence variability in
temperature data. One is simply the sampling problem. The other is heat
exchanges between air, land and ocean, and within those categories, which may
be subject to quite substantial dynamic changes over quite long periods
The second is time
lags that stem from the thermal inertia of a very large mass of land and
ocean. A hypothetical permanent step change increase in greenhouse gases (GHG)
concentration would tend, all else equal, to result in gradual warming until a
new overall equilibrium was reached. Of course finding a way to measure time
lags against a background of constantly changing GHG may be impossibly complex,
but prima facie one might expect it to be measured in decades. One source
suggests at least 25 years[4].
Inter alia this makes it harder to gauge simple sensitivities of temperature to
GHG increase. It also implies that, at any given time, more future change is
already “baked in” than is already apparent.
The third is irreversibility.
This does feature in discussion of how quickly climate change might reverse if GHG emissions halted. But
its main relevance ought to be in the area of policy. Theories of decision
making under uncertainty (eg options theory), and indeed ordinary common sense,
tend to counsel against irreversible decisions with potentially high cost. The
cumulative nature of CO2, which seems to be generally accepted,
makes current emissions an irreversible choice, to an extent that cannot be
claimed for most economic and policy choices.
The fourth is modelling.
The weaknesses of modelling are
well known and most stem from the near impossibility of modelling systems of
extreme complexity, as well as from significant areas of imperfect knowledge.
This stems not just from the complexity of the numerous physical, chemical and
biological processes involved, but from its combination with features of
physical geography that have no simple mathematical representation (land and
ocean relief maps and coastal indentation). Moreover, in the context of testing
climate hypotheses, the outputs are being compared against observations that
themselves represent only a small and imperfectly measured part of the general
hypothesis of GHG induced change.
However at a more general level, models are doing
no more than represent known or reasonably well estimated physical parameters (eg
“Newton’s Laws of Motion” or the physics of heat transfer). Minimal models might
be said consist of very simple arithmetic calculations, with obvious limitations,
which may then expand to attempt to capture more of reality with more complex
interactions. It is hard to see how progress on the key questions could be made
without some form of arithmetic or mathematical calculation, ie modelling.
The fifth is the notion of a “mainstream” of “consensus science”. Part of the issue for a non-specialist is to
judge where this consensus rests. In most areas we tend to put most weight on
findings endorsed by bodies with explicit responsibilities for work in the
relevant field, including national bodies engaged with weather or climate
matters. But none of these should be above challenge on such an important
issue.
In this context we should take note the role of the
Inter-Governmental Panel on Climate Change, the IPCC, to which we refer on a
few occasions in our comments. The IPCC is not an international body conducting
its own research. It is an inter-governmental body, closely supervised by
representatives of national governments, with its most significant reports
approved in plenary session. Its role is
to review the body of available research on climate within this framework, and
it should be interpreted within this context.
One clear risk in the presentation of IPCC
synthesis reports is that they present an unduly cautious picture of climate
risks, based on a lowest common denominator of what can be agreed in plenary
session of representatives from participating governments, rather than the best
or most respected science. From a risk perspective,
and given the interests of producer and other nations with a strong interest in
continuation of fossil based energy policies, this risk must be treated as
seriously as any risk that climate threats are overstated.
The IPCC role differs therefore from that of
individual bodies charged with climate and related research, such as NASA, or
with national academies of science. But its reports constitute one of the most
useful repositories summarising the current state of knowledge across a wide
spectrum of climate science.
Finally there is risk and uncertainty. We note
that the subject will continue to include substantial uncertainties, our
knowledge is incomplete, as it is in most areas of science, including those
that form the basis of most of our daily lives. Moreover we cannot predict
accurately the human or economic consequences of climate change, although we
can identify very serious and possibly even catastrophic risks. But residual
uncertainties do not detract from the validity of the science as the best guide
to policy and decision making now, and to identification of what may be very
dangerous risks for mankind as a whole.
COMMENTARY.
The remainder of this paper details the 20 points
included in the Royal Society briefing, together with the GWPF authors
response. For each point it aims to comment on the argument as it might appear from
an informed lay perspective, either comparing the arguments or checking on the
extent to which particular statements.
1. Is the climate warming?
Royal Society:
Yes. Earth’s average surface air temperature has
increased by about 0.8◦C (1.4◦F) since 1900, with much of this increase taking
place since the mid-1970s. A wide range of other observations such as sea-level
rise, reduced Arctic sea ice extent and increased ocean heat content provide
incontrovertible evidence of a warming Earth.
GWPF authors. A fuller picture:
This is hardly an important question. The Earth’s
surface is always warming or cooling, or on some occasions barely changing.
What is important is that the change referred to is small and imperfectly
measured. It should also be stressed that the Royal Society guide does not
mention the role of the time window they are using for comparison. The climate
has cooled since the mid-Holocene climatic optimum 8,000 years ago, and the
warming of the past few decades is relatively small in comparison.
Surface temperatures have increased on average by
about 0.8◦C since 1900. There was
a rise of around 0.5◦C at the start of
the twentieth century, followed by a small fall from 1940 to 1970. From then
until the late 1990s temperatures rose by around 0.5◦C. Differences of a tenth of a degree are
insignificant. The temperature is virtually unchanged from that at the
beginning of the century. The two periods of increase are indistinguishable,
although the earlier increase cannot be attributed to increased carbon dioxide.
The relation of other observations such as
sea-level rise, Arctic sea ice extent and ocean heat content all depend on more
factors than global mean temperature, and are hardly incontrovertible evidence
of warming. That said, the possible acceleration of ocean heat content
accumulation and sea level rise are close to the limits of our ability to
detect and the values involved cannot be reconciled to each other. Depending on
the time scale, other observational datasets are still more equivocal: global
sea ice levels declined for several decades but are now above their long-term
mean.
COMMENTS
“This is a hardly an important question.”
The GWPF
authors response appears to disregard the issue at stake, which is not whether
a small change matters per se but whether it tends to support, or not, the
hypothesis that there is a long term threat from a much larger change. Interpretation
and attribution of the measured warming is therefore important and the
subsequent responses of the authors pay a lot of attention to it.
The profound
threat described by the Royal Society, and that “mainstream” climate science claims
to identify, is based on the analysis of real physical phenomena, notably the undisputed
physics of the greenhouse effect itself and the empirical reality of rising CO2
concentrations. Gauging the extent of that threat, and the validity of the
climate predictions, must surely be an important task, to which observations of
actual temperature change will be an important contribution. Observations of an
equivalent fall would surely have provoked a major re-examination of climate
models, and of the state of climate science, and a search for negative
feedbacks to better explain climate. Perhaps unfortunately from a human
perspective, this is not where we find ourselves.
To be
specific, the threat is that we are changing the climate and will in the future face much larger changes both from past and future emissions. The value of firm evidence to support or dismiss
the science will necessarily manifest itself in the first instance as small
changes. Waiting for large changes, which will impose much larger consequences,
will mean that we continue with decisions that promote increases in GHG that
are irreversible. Given the lengthy time lags, these in turn may only be the
pre-cursor of further changes already “baked in” to the system. Prima facie
this seems irresponsible.
“The
climate has cooled since the mid-Holocene climatic optimum 8,000 years ago, and
the warming of the past few decades is relatively small in comparison.”
Systematic measurements capable of
interpretation as direct measures of global temperature do not pre-date 1850,
and earlier periods rely on reconstructions of various kinds, increasing the
scope for differences in scientific opinion. This certainly seems to be true of
the Holocene period. At least one paper
argues the exact opposite “In terms of the global average, temperatures
were probably colder than present day (depending on estimates of latitude
dependence and seasonality in response patterns). While temperatures in the
Northern Hemisphere were warmer than average during the summers, the tropics
and areas of the Southern Hemisphere were colder than average.”[5] Note that this comparison is suitably qualified with the word “probably”.
Even if the statement about Holocene
temperatures is correct, it seems largely irrelevant to the argument about
whether future significant changes in temperature, from the period in which we
now live, and as increases above what would otherwise have occurred, are a
matter of importance or not.
“The
temperature is virtually unchanged from that at the beginning of the century
(1998).”
This is a key statement in the GWPF
briefing since it is treated as a given in a number of the subsequent comments,
which rely on it heavily to support later arguments. However its validity depends mainly on
selection of 1998 as the year on which to base interpretation of the most
recent period. 1998 was an el Nino year which is associated with higher estimated
global average surface temperatures, at least on current methods of measurement.
In statistical terms 1998 appears as an outlier in the time series. The point
is explained in the fuller RS document. The chart below shows this.
A mischievous and similarly misleading
interpretation of this chart, biasing by selecting “outlier” years to support a
particular interpretation, could also restate the conclusion as follows:
There was no discernible change in global average temperature between 1878 (selecting another obvious outlier) and the 1970s. After that it increased sharply.
There was no discernible change in global average temperature between 1878 (selecting another obvious outlier) and the 1970s. After that it increased sharply.
This alternative interpretation chooses
to ignore the significant movements in the first half of the 20th
century. In reality serious science and
serious debate should try to avoid bias or “cherry picking” in interpreting
time series. It often uses, as most informed readers with a statistical bent
will know, smoothing techniques like moving averages to interpret time
series. This aims to reduce underlying
statistical error or “noise” in the data.
Interdecadal averages tell a different
story (below). It is certainly possible
that there has been some slowing in the rate of growth, but it is equally
possible that the small decline in interdecadal growth reflects statistical
noise or minor data bias. Inter alia the inclusion of 2014 and 2015 in the data
set (hottest year and hottest YTD respectively) may confirm the impression of a
steadier trend.
[source: IPCC]
Finally the GWPF authors dismiss other
sources of corroborative evidence. While it is correct to point out that sea
levels and Arctic ice are subject to other complex influences, they rather
obviously cannot be disregarded as pieces of evidence. Falling sea levels or
increasing Antarctic ice mass, for example, would surely have been seen as
evidence tending to contradict any warming hypothesis. Some of these particular questions are
discussed in more depth in later comments.
2. How do scientists know that recent climate change
is largely caused by human activities?
Royal Society:
Human activity leads to emissions of greenhouse
gases (causing warming), and of other pollutants that produce small particles
in the atmosphere (which can have both cooling and warming effects). The
dominant influence of human activities on recent climate change is clear from
an understanding of the basic physics of the greenhouse effect and from
comparing the detailed patterns of recent climate change with those expected
from different human and natural influences. Only when human influences on the
composition of the atmosphere are incorporated can models reproduce observed
changes in climate.
GWPF authors. A fuller picture:
The warming effect of greenhouse gases is widely
recognised. However, the direct effect is known to be relatively small: about
1◦C for a doubling of carbon dioxide levels. Most of the warming predicted in
climate models arises from knock-on effects (‘feedbacks’) associated with
changes to cloud cover, atmospheric humidity and so forth. Feedback processes
are mostly hypothetical and are therefore much more uncertain, and some may
even have cooling effects.
The Royal Society guide claims that models fail to
explain recent warming unless they incorporate anthropogenic forcing. This
assertion depends on the readily falsifiable claim that models correctly
replicate natural variability. Models fail on natural variability, therefore the
Royal Society’s claim fails in the real world. However, even if the conclusion were
correct, it would still be consistent with the view that the climate is not
very sensitive to greenhouse gases since the observed changes have been small (to
the point of being indiscernible for the past 15 years).
COMMENTS
“Feedback
processes are mostly hypothetical ….”
In the early days of efforts to estimate
the impact of CO2 emissions on climate, this was certainly true.
Numerous propositions were advanced, very reasonably, on ways that negative
“dampening” feedbacks might act as automatic stabilisers, including
re-absorption through the carbon cycle and increased plant growth.
Unfortunately some of these, notably
reliance on parts of the carbon cycle, seem to have been largely discounted,
but there are others that would clearly be positive and, in the absence of
countervailing influences, would normally be assumed to accelerate or magnify
change. Examples include increases in water vapour content of the atmosphere
(for which there appears to be some evidence[6]), the prospect of reduced albedo
from falling ice cover (evident in reducing Arctic sea ice), and the risk of methane
release from a melting permafrost. Prima facie these are far from being purely
hypothetical.
The effect of changes in clouds remains a
complex and uncertain issue, with evidence that in different aspects clouds can
have both warming and cooling effects [7] but, on the basis of
existing knowledge it would be hard to state with confidence that clouds offer
the firm prospect of a substantial negative feedback. At the very least there
must be a substantial probability that it does not provide a significant
stabilising feedback.
“This
assertion depends on the readily falsifiable claim that models correctly
replicate natural variability. Models
fail on natural variability, therefore the Royal Society’s claim fails in the
real world.”
Models typically generate a range of
possible outcomes, based on different but credible initial or boundary
conditions for particular physical parameters, and other uncertainties within
chaotic systems, as well as limitations to the granularity or complexity of the
modelling. If outcomes continue to lie within the predicted range, they can be
said, as the Royal Society claims, to “reproduce” outcomes, and do not
”fail”. This can obviously be a rather
undemanding test under some circumstances, but it is combined with the claim
that no alternative explanation has been proposed which is capable of providing
a physical explanation of the significant observed changes in recent years.
In principle there should be numerous
possible candidates for alternative “explanations”, including solar activity,
changes in orbit, or changes in volcanic activity. So far none of these appears
to be capable of providing a convincing physical explanation of the changing
climate in recent years (post 1970). A prima facie case certainly exists more
generally for solar activity, but there has been no change in solar radiation
post 1970. GHG on the other hand do meet
the criterion for explaining this period. There is a known physical mechanism
and a known increase in the quantity of GHG.
Given that natural variability (over all
timescales) and measurement error exist and are recognised as part of the
overall picture, models do not “fail” through inability to “explain” the
totality of natural variability. Inability to explain everything does not imply
inability to explain anything.
“It
would still be consistent with the view that the climate is not very sensitive
to greenhouse gases since the observed
changes have been small (to the point of being indiscernible for the past 15
years).”
Consistency might well be possible if relevant
observed changes were small, but a demonstration that climate is “not very
sensitive” depends on two propositions,
first that there has been “indiscernible” temperature increase in recent years,
and second that we can ignore any time lags due to thermal inertia of the
planet as a whole. The first proposition has been discussed above and is clearly false. The second is highly improbable. Thermal inertia for the planet as a whole
implies substantial time lags[8] before even the first
round effects of a hypothetical step change in CO2 would have fully
worked through to a new equilibrium of atmospheric concentration and ocean,
land and atmospheric temperatures. It follows that we are not yet observing,
and may still be decades away from experiencing, the full impact of the
increase to even the current level of GHG concentration.
3. Carbon
dioxide is already in the atmosphere naturally, so why are emissions from human
activity significant?
Royal Society:
Human activities have significantly disturbed the
natural carbon cycle by extracting long-buried fossil fuels and burning them
for energy, thus releasing CO2 to the atmosphere. The concentration
of CO2 has increased by 40% since the Industrial Revolution.
GWPF authors. A fuller picture:
Carbon dioxide levels have been increasing
steadily. A body of evidence points to this being due to human effects –
emissions from burning of fossil fuels and land-use changes – although the
Earth’s carbon dioxide budget is not sufficiently understood to accurately quantify
the human and natural contributions. Natural fluxes in the carbon cycle are an
order of magnitude higher than manmade emissions, so any natural imbalances,
perhaps as a result of temperature changes, can swamp human contributions.
Regardless, given the aforementioned evidence that the sensitivity to carbon
dioxide is low, anthropogenic GHGs cannot by themselves explain 20th century
warming.
COMMENT
“…
the Earth’s carbon dioxide budget is not sufficiently understood. Natural
fluxes in the carbon cycle are an order of magnitude higher.”
Prima facie this is very misleading.
Annual emissions may indeed be small (c 3%) in relation to the large annual
flux, but unless they are re-absorbed within the natural carbon cycle, they are net
additions, and are cumulative. This means that they have and will become
significant as they build up over several decades.
The fact that we are now 40% above the
observed 800,000 year range suggests substantial anthropogenic influence and that
there has been limited re-absorption of any excess above natural carbon cycle
levels. Exact quantification would obviously
require a counterfactual which could not be directly verified.
“so
any natural imbalances, perhaps as a result of temperature changes, can swamp
human contributions”
Given that the GWPF authors are
dismissive of amplifying feedback effects, necessarily so in order to claim low
climate sensitivity, this suggestion is strange. Having earlier dismissed
feedback mechanisms as purely hypothetical, the authors now introduce, admittedly
hypothetically, a powerful feedback from temperature rise to net CO2
gain. If this feedback exists, and in principle at least it is quite credible
that some changes could reduce the absorption capacity of carbon sinks (eg
through impacts on vegetation), then it is akin to the methane release which is
a major risk factor for “worse than predicted “ outcomes, which the authors later
dismiss in 19 below. It also undermines the case for limited feedbacks described
in 2 above.
“given
the aforementioned evidence that the sensitivity to carbon dioxide is low, anthropogenic
GHGs cannot by themselves explain 20th century warming.”
The GWPF authors have not shown low
sensitivity, for the reasons discussed in 1 and 2 above, and CO2
does not have to explain everything. The authors introduce an alternative
factor, solar variations, in the next section, suggesting it has a significant
role in the 20th century. Prima
facie there does appear to be at least a superficial statistical correlation in
the early 20th century. This might have been argued to complement
the explanation of a larger CO2 driven warming post 1970. Given that the authors have introduced solar
variations as an explanatory factor, one might ask whether this “two factor”
explanation has been investigated and endorsed or discarded by climate
specialists. This is discussed again below in 4.
4. What role has the Sun played in climate change
in recent decades?
Royal Society:
The Sun has not played a major role in recent
climate change. The Sun provides the primary source of energy driving Earth’s
climate system and variations in the energy emitted by the Sun affect Earth’s
climate. However, satellite measurements since the late 1970s show no overall
increase in the energy emitted by the Sun, while the climate system has warmed.
GWPF authors. A fuller picture:
It is frequently claimed that the Sun has not
played a major role in recent climate change because the overall energy emitted
by the sun has changed little. This is simplistic. There is significant
evidence that the Sun has played an important role in climate change, and over
the 20th century in particular. Quantifications of these changes suggest
forcing comparable to anthropogenic forcing. While variability of total solar
irradiance may be small, variability of specific components of solar output can
be large, and some of these are believed to affect the climate through mechanisms
other than direct heating, for example by influencing cloud formation. These effects
are a matter of current inquiry.
COMMENTS
The Royal Society makes its claim only in
relation to recent climate change,
based on satellite measurements since the 1970s. The GWPF authors discuss a
possible role in relation to 20th century warming (as a whole), and
prima facie this does seem to be a hypothesis worth considering. The link below[9] presents a graph which
shows at least a superficial correlation between solar activity and temperature
for the first part of the century, although it breaks down thereafter, and as
the Royal Society says, does not appear to explain post 1970 changes.
If we were to accept this connection as adequately
supported by the evidence, then we would seem to have an explanation of the
first part of the century with solar activity as possibly the major influence,
with GHG predominating thereafter. In other words this would appear to deal
with the alleged failure of climate science to explain the whole of 20th
century warming in terms of anthropogenic GHG. And the combined
effect of both factors would appear to offer a powerful explanation of the
whole of the century.
A non-scientist might however be forgiven
for remaining agnostic on the solar connection, at least in the absence of
demonstrable direct radiation or other explicable physical effects. The authors
suggest some specific components of solar radiation are believed to be
important, but it is not suggested that these beliefs are anything other than unspecified
hypotheses. Generally they have decried hypotheses in relation to feedbacks,
some of which seem prima facie more substantial.
For these reasons, it is hard to see why
acceptance of the potential influence of the sun should diminish either the
credibility of GHG related theory or its significance for the future.
5. What do
changes in the vertical structure of atmospheric temperature – from the surface
up to the stratosphere – tell us about the causes of recent temperature change?
Royal Society:
The observed warming in the lower atmosphere and
cooling higher up in the stratosphere is the result expected from increases in
CO2 and decreases in stratospheric ozone. Natural factors alone
cannot explain the observed changes.
GWPF authors. A fuller picture:
Not so: basic physics implies that increasing
levels of carbon dioxide will lead to increased cooling in the stratosphere.
This is quite separate from the greenhouse impact in the troposphere of
increased carbon dioxide. However, measurements in the stratosphere indicate
that although the overall trend is down, any cooling is only seen in the
immediate aftermath of volcanic eruptions. Between such eruptions,
stratospheric temperatures have been rising. This merely indicates that carbon
dioxide levels here as elsewhere are not the only factor determining
temperature. Similarly, temperatures in the troposphere over the tropics are
predicted to rise faster than anywhere else, including at the surface. This too
is a matter of basic physics, where the temperature profile follows what is
known as the moist adiabat. Models are, indeed, consistent with this. However,
observed warming in the tropical troposphere is very weak compared to warming
at the surface, suggesting problems with observations at the surface or in the
troposphere or both. Given the small changes that are being studied, neither
possibility is implausible.
The fuller RS overview is more nuanced. “It is now known that the observed pattern
of tropospheric warming and stratospheric cooling over the past 30 to 40 years
is broadly consistent with computer model simulations that include increases in
CO2 and decreases in stratospheric ozone, each caused by human
activities. The observed pattern is not consistent with purely natural changes
in the Sun’s energy output, volcanic activity, or natural climate variations
such as El Niño and La Niña. Despite this agreement between the global-scale
patterns of modelled and observed atmospheric temperature change, there are
still some differences.“
Similarly, and unlike some sceptic
commentators, the authors treat this as essentially uncertain – “neither
possibility is implausible”. Elsewhere
it has been claimed that elements in this controversy are critical tests of the
validity of the mainstream science, but given the nature of the multiple uncertainties
regarding both inadequate data and disputed understanding of the processes
involved, there is little reason to suppose that much more can be said at this
stage. [More information may well at
some stage provide further confirmation.]
Without further research and exposition
on the subject, it is not a subject on which it is currently easy or
appropriate for a non-specialist to comment without significant further reading.
We are not aware currently of a final compelling resolution of these differences
in analysis and opinion.
Nothing in a limited search does other
than tend to confirm that this is still a complex issue, governed by incomplete
information and understanding, on which opinions differ, and that there has
been a paucity of data. At least one
recent article[10], has cited new data and in the process cast
doubt on earlier general understanding
of these issues, while another[11] casts doubt on the view
that volcanic activity can explain the changes. Overall, volcanic activity is
believed to promote cooling, and is one of the factors contributing to natural
variability.
Overall this appears to be an issue of secondary significance, from either perspective.
6 Climate is always changing. Why is climate change
of concern now?
Royal Society:
All major climate changes, including natural ones,
are disruptive. Past climate changes led to extinction of many species,
population migrations, and pronounced changes in the land surface and in ocean
circulation. The speed of the current climate change makes it more difficult
for human societies and the natural world to adapt.
GWPF authors A fuller picture:
The Earth has many and hugely varied climates. The
climate also changes naturally on every timescale. Mankind is remarkably
adaptable, living in almost all of these climates. It is impossible to know how
rapidly climate changed in the distant past since the time resolution of the
data we have is mostly inadequate for resolving the timescales that we are
currently concerned about. However, there is ample evidence of rapid climate
change associated with cold periods during the most recent glaciation (more
than 12,000 years ago). Climate change is only one concern among many at the
present time, and a disproportionate focus on it and its possible impacts
detracts from our ability to address many other more pressing matters.
COMMENT
Historic evidence of actual climate
change in the distant past does not relate to any period with a comparable need
to feed 9 billion people. Nor does
history tell us in any detail what the many impacts of climate change may have
been, even then, in terms of conflict or population decline. (Although in some
instances modest changes in climate have been linked by historians to
migrations, disease and population decline.)
The myth of Prometheus Unbound may
suggest that mankind, unlike other species, is infinitely adaptable, but
science and common sense suggest that ultimately there are or may be physical
and biological limits to what is achievable, and to changes which will continue
to accommodate 9 billion people.
“only
one concern among many”
It is certainly true that there are plenty
of other pressing and dangerous problems, such as the risk of global pandemics
or the problem of antibiotic resistance, as well as the widespread nature of
human conflict. Many of these are
intimately linked to climate change in the sense that they may be intensified
by climate phenomena, particularly if climate affects land, water or other
resource pressures – all of which are natural sources of conflict.
A distinguishing and fundamental feature
of the climate issue is that decisions taken now – to continue high levels of
GHG emissions, are essentially irreversible on less than geological timescales.
This is much less true of the other threats.
Failures in planning now for pandemics or ebola type outbreaks, can, and
almost certainly will, be remedied in response to a major public health
incident. Failure to take mitigating
action in relation to climate simply means building in an increasing problem,
and with less time to adapt to the consequences.
Finally the dichotomy is a false one. It
is not obvious why attention to climate policy should prevent efforts to deal
with other pressing dangers. It may indeed complement them, or be a necessary
precondition to managing these other risks in the longer term.
7. Is the
current level of atmospheric CO2 concentration unprecedented in
Earth’s history?
Royal Society:
The present level of atmospheric CO2
concentration is almost certainly unprecedented in the past million years, during
which time modern humans evolved and societies developed. The atmospheric CO2
concentration was however higher many millions of years ago, at which time
temperatures and sea levels were also higher than they are today.
GWPF authors. A fuller picture:
While carbon dioxide levels appear to be higher
than they have been for hundreds of thousands of years, they are relatively low
compared to most of the last 600 million years (when most lifeforms evolved),
during which time levels were often from 2–20 times greater than today. Counter
to the Royal Society, there were periods during which the carbon dioxide level
was as much as 10 times higher than today but the climate was colder, for
example the Silurian Period (about 443–420 million years ago). The fact that
most plant life evolved during these periods is because plants thrive when
carbon dioxide is increased. Moreover, our present estimates of carbon dioxide
variations over the past 700,000 years are based on the analysis of ice cores,
and these analyses may have inadequately dealt with diffusion, which could cause
major adjustments to our estimates of early carbon dioxide levels.
COMMENT
The Royal Society statement focuses on
the last million years. The GWPF authors
in contrast focus on astronomical measures of time when the Sun and Earth would
have been very different, in respect for example of the strength of solar
radiation – a different strength being consistent with higher “equilibrium” CO2
levels. So this is not a direct “counter” to the Royal Society.
The observation that the first life forms
evolved in these earlier periods tells us little about how today’s humans, and
today’s flora and fauna, would cope with what is (in geological terms) rapid
change. Today’s life will have evolved to meet the environment of the last
million years, or in many instances much less, rather than that of the last 400
million.
The Royal Society confines itself to a
period that includes human history, and points out the evidence, presumably
based on reconstruction from ice core samples, that actual CO2 has
remained in a comparatively narrow range. The authors dispute this with the
speculative possibility that there may have been flaws in this analysis, but it
is not evident that there is any empirical support for this possibility.
8. Is there
a point at which adding more carbon dioxide will not cause further warming?
Royal Society:
No. Adding more CO2 to the atmosphere
will cause surface temperatures to continue to increase. The addition of extra
CO2 becomes progressively less effective at trapping Earth’s energy,
but surface temperature will still rise.
GWPF authors. A fuller picture:
Each additional increase of carbon dioxide levels
is expected to produce less and less greenhouse warming, so it takes far more
emissions to produce the second degree of warming than the first. Thus unless
carbon dioxide emissions rise exponentially in the long term, warming should
slow down. In theory temperatures will always keep rising, but eventually at a
rate indistinguishable from zero. As usual, the question is not about warming
per se but about how much warming there will be compared to natural
variability. The available evidence is entirely consistent with the answer ‘not
much.’
COMMENT
The relationship is a log-linear function.
If doubling were to produce one unit of warming, then doubling again would
produce one more unit. This is potentially quite dramatic as a stabilising
mechanism, so it is worth discussing and the GWPF authors’ comment is
informative.
The main problem, intuitively and
computationally, lies in establishing where we are in the process, given the
very long time lags to which we referred earlier, and the fact that CO2 concentration
does not proceed through step changes followed by decades when it is static.
Today’s temperature cannot be interpreted as the outcome of today’s CO2 concentration. It is the outcome of concentrations over
previous decades. Similarly we can only
estimate (eg through climate modelling) what future “equilibrium” temperature,
holding all else equal, would result from holding CO2 concentration
at today’s level.
Recognition of a time lag effect will
inevitably amplify a sensitivity calculated as if the time lag did not exist.
And estimates of the time lag span several decades.[12]
It is worth noting that the loglinear
effect does not necessarily translate through to feedback effects; these may move
towards equilibrium at faster or slower rates.
If we look instead at the damage function, the impact from temperature
rise in terms of adverse consequences of change are likely to increase faster
as temperature rises. Many if not most
natural systems have threshold effects, where they can tolerate change or
variation, but only up to a certain threshold.
Royal Society:
Yes. The observed warming rate has varied from year
to year, decade to decade, and place to place. These shorter-term variations
are mostly due to natural causes, and do not contradict our fundamental
understanding that the long-term warming trend since the mid-20th century is
primarily due to human-induced changes in the atmospheric levels of CO2 and
other greenhouse gases.
GWPF authors. A fuller picture:
Temperature and many other climatic measurements
vary naturally on all timescales, from decades to centuries and longer. Long
periods in which the climate warms or cools naturally are therefore to be
expected. Because climate models do not incorporate all of the different
factors that might affect the climate, many of which are as yet unquantified,
unequivocal attribution of recent warming is not possible, although at least
part of it may be due to human emissions of greenhouse gases.
A major error in modelling is the failure to
account for natural variability. For the Royal Society to use this variation as
an excuse for the obvious mismatches in models is strange indeed. Rationally,
the fact that current models have greatly overestimated observed warming would
suggest that models are too sensitive – a possibility that the Royal Society
should have pointed out.
COMMENT
“unequivocal
attribution of recent warming is not possible”
This is likely to be the case in any system
with natural variation, and the Royal Society says cautiously that this is primarily due to human-induced changes,
while the GWPF authors acknowledge that part of it may be so.
“have
greatly overestimated observed warming”
Prima facie, as argued earlier, this is
an exaggeration based on selective interpretation of recent trends. It has also
been suggested that adjustments to historic data, in the light of improved
knowledge, may also make the models appear more accurate.
Recent findings, described in more detail
below, suggest the possibility of direct verification of the sensitivities used
in the models.
“A
major error in modelling is the failure to account for natural variability.”
This reflects a different conception of the
nature and function of modelling. Climate models can project forced trends but
they can only simulate stochastic (random) variability. This means they cannot
be expected to predict global temperatures accurately over short periods, since
these are dominated by stochastic and unforced variability. This is discussed
again in 10 below.
Empirical
verification
Hitherto it has not been possible to obtain
direct empirical verification of the calculations used in climate models. But according
to a recent (2015) report,
“Scientists have observed an increase in carbon dioxide’s greenhouse
effect at the Earth’s surface for the first time. The researchers, led by
scientists from the US Department of Energy’s Lawrence Berkeley National
Laboratory (Berkeley Lab), measured atmospheric carbon dioxide’s increasing
capacity to absorb thermal radiation emitted from the Earth’s surface over an
eleven-year period at two locations in North America. They attributed this
upward trend to rising CO2 levels from fossil fuel emissions.
The influence of atmospheric CO2 on the balance between
incoming energy from the Sun and outgoing heat from the Earth (also called the
planet’s energy balance) is well established. But this effect has not been
experimentally confirmed outside the laboratory until now. The research was
reported Wednesday, Feb. 25, in the advance online publication of the journal Nature,
and is claimed to detect the unique spectral signature of
infrared energy from CO2.
The results agree with theoretical predictions of the greenhouse effect
due to human activity. The research also provides further confirmation that the
calculations used in today’s climate models are on track when it comes to
representing the impact of CO2.”[13]
10. Does the
recent slowdown of warming mean that climate change is no longer happening?
Royal Society:
No. Since the very warm surface temperatures of
1998 which followed the strong 1997–98 El Niño, the increase in average surface
temperature has slowed relative to the previous decade of rapid temperature
increases, with more of the excess heat being stored in the oceans. Despite the
slower rate of warming, the surface temperatures in the 2000s were on average
warmer than the 1990s.
GWPF authors. A fuller picture:
Surface temperatures have exhibited no warming
since the start of the century. Weather satellite records suggest the pause has
been going on even longer. The reasons for the pause are unknown. Numerous
explanations have been proposed, the most high profile being a suggestion that
the missing heat has found its way to the deep ocean. However, this is simply
an obscure way of blaming natural internal variability, for which the ocean
circulations (which are always exchanging heat between surface and deep water)
are a major cause. There is no known way to distinguish these natural exchanges
from the notion that ‘heat is hiding in the ocean’. What we do know is that
these major ocean circulations are not correctly captured in the current
climate models.
COMMENT
The GWPF authors repeat the assertion
criticised earlier. Nevertheless, although
the GWPF authors have exaggerated the slowdown in warming, by focusing on 1998
as a starting point for comparison, it was true that there appears to have
been some slowing in the rate of warming at least of surface temperatures.
However since these were well within the range of outturns projected by the main
models it would be foolish to conclude that the model sensitivities were wrong
without further examination. Moreover the actual temperature observations for 2014 and 2015 make it much harder to justify the GWPF interpretations of the data that were already questionable. The numbers for these years suggest an objective interpretation much closer to the inter-decadal trend shown above.
One possible test is to examine the
performance of the models over much longer periods, to see whether there is any
systematic bias or failure. One recent paper[14] looks back over the past
century and claims that global average temperature is extremely well captured
by models, with no obvious pattern showing temperature trends are closer to the
upper or lower end of model projection. In other words, while the models may not
capture all the natural variability along the path of rising temperatures, they
are slightly too cool just as often as they're slightly too warm.
To
avoid circularity, if some of the models were based on statistical estimation
over the same period, one would require the test to be carried out over a
different period, but to the extent that models use physical parameters
estimated independently of the temperature data, this is less of an issue.
Ideally the global warming hypothesis should
be expressed as a global heat gain balance, of which we know surface
atmospheric temperatures are likely to be a very small part. Intuitively one
would expect the much larger quantities involved to show much more stable trends in net heat gain or loss. It would
also eliminate much of the time lag issue which we have identified as very
important.
Worryingly, in terms of concern about
warming, there have been proposals that, using surface temperatures only, data
revisions are necessary to reflect a changing appreciation of the details of
climate effects, such as adequate sampling of polar regions. Some of these
suggest that the recent hiatus in warming has been overstated.
11. If the
world is warming, why are some winters and summers still very cold?
Royal Society: Global warming is a long-term trend,
but that does not mean that every year will be warmer than the previous one.
Day to day and year to year changes in weather patterns will continue to
produce some unusually cold days and nights, and winters and summers, even as
the climate warms.
GWPF authors. A fuller picture:
Global warming refers to a long-term trend –
spanning periods of decades to centuries – which has been very small compared
to the weather, which varies a great deal from year to year. Cold weather is
therefore not unexpected in a warm climate. By the same token, one should
expect warmer episodes from time to time even if there were no global warming.
COMMENT
No real difference of view is discernible
in these observations, since this is essentially a statement drawing a
necessary distinction between climate and weather. The GWPF authors correctly
point out the converse, warmer episodes in times that are stable or cooling.
Royal Society:
Sea ice extent is affected by winds and ocean
currents as well as temperature. Sea ice in the partly-enclosed Arctic Ocean
seems to be responding directly to warming, while changes in winds and in the
ocean seem to be dominating the patterns of sea ice change in the Southern
Ocean around Antarctica.
GWPF authors A fuller picture:
There is no basis for the assertion that winds are
less important in the Arctic, and evidence exists that summer sea ice has often
been low. Most climate models predict fast reductions in both Arctic and
Antarctic sea ice, although the two are very different systems. The steady
record rise in Antarctic sea ice is therefore not predicted by models, although
there has been some speculation as to the reasons for the failure. In any case, Arctic ice remains fully with us
in winter despite summer lows. Even in the height of summer substantial ice
remains (many millions of square kilometres).
COMMENT
The real
distinctions are not brought out fully by either party in the above,
abbreviated, discussion. As the GWPF authors say, these are very different
systems.
Sea ice is
the more important in the Arctic. Melting sea ice does not increase sea levels,
but is significant as a potential climate feedback because it reduces albedo in
summer, ie causes the oceans to absorb more heat.
Land ice
is a much more relevant factor in the Antarctic, because of the sheer quantity
of ice on the Antarctic land mass. Melting land ice matters as a consequence
effect of warming, because it does raise sea levels.
Viewed
purely as indicators or measures of actual warming, the target measure has to
be to an estimate of changes in total heat content for the planet. In very
simple terms Arctic sea ice is a useful indicator, but in the Antarctic, any
changes in land ice (including temperature change within the land ice) need to
be taken into the equation as well. (And of course temperatures in the
immediately surrounding oceans matter too.)
Unfortunately
available measures of Antarctic land ice appear to show significant reductions
in volume, a further indicator of rising heat content for the planet as a whole.
Viewed as
feedback effects and consequences, the albedo effect and the consequences for
sea levels are probably the key issues.
“Arctic ice remains fully with us in winter despite
summer lows.”
This is
very little comfort since the main impact of the albedo effect is in summer. It
might be thought that additional Antarctic sea level ice might be a
countervailing effect, but if this were predominantly a winter effect then it
would be less important than in the Arctic. It would be useful to confirm
whether this is a reason and why it has not attracted much coverage.
The West Antarctic
ice sheet has been identified as posing a major risk of much higher sea level
rises, but this possibility is not included in the mainstream IPCC projections.
13 How does climate change affect the strength and
frequency of floods, droughts, hurricanes and tornadoes?
Royal Society:
Earth’s lower atmosphere is becoming warmer and
moister as a result of human-emitted greenhouse gases. This means that more
water is likely to be drawn into major rain storms, which could lead to more
flooding events. There is considerable uncertainty over changes in hurricanes
and tornadoes, but the extra energy available may make the strongest hurricanes
stronger. Dry areas of the subtropics are expected to become drier in the
future.
GWPF authors A fuller picture:
Climate models can have little to say about what
happens below their level of resolution, which remains coarser than most
storminess. There is no evidence of any increase in either intensity or
frequency during the recent period of global temperature average rises. In
fact, there has been a remarkable lack of landfalling hurricanes in the
Atlantic. Tornadoes are unlikely to be affected by any global warming.
Extra energy does not cause storms. Nor does it
necessarily increase their strength. Energy differences and gradients cause
storminess. Changes in internal energy and moisture that do not affect
gradients and differences can have little effect. Speculation that wet areas
become wetter and dry areas become drier are claims about increases in
gradients and differences, which the global warming hypothesis does not contain.
In fact models call for a decrease in gradients between equator and poles, which
would imply a reduction in storminess. Drought levels have, if anything, fallen
worldwide in recent decades and there is little evidence of global changes in
floods.
COMMENT
The IPCC, which attempts to summarise and
synthesise the body of climate research, and whose reports are agreed by
government representatives in plenary session, makes statements stronger than
the rather cautious Royal Society guide statement above. It considers that some of the changes in extreme weather and climate
events observed since about 1950 have been linked to human influence. Other
individual climate scientists have expressed similar views.
“a
decrease in gradients between equator and poles”.
The GWPF authors’ argument here depends
on the assumption that it is this polar to equatorial gradient which is
relevant to storminess. But this does not appear to be the only
credible view of how hurricanes form. To quote NASA, “Tropical
cyclones … use warm, moist air as fuel. That is why they form only over warm
ocean waters near the equator.” This argument seems to represent quite a
fundamental difference from the professional meteorological view.
Intuitively one might therefore expect
some link between temperature, ie the levels of heat energy in the tropics, and
the kinetic energy in storms. Higher
overall levels of energy, on this more local scale, would then tend to larger local
“gradients”. It is this intuition that
the Royal Society seems to be expressing. It would be interesting to hear a
contrary view from a meteorologist.
Royal Society:
Best estimates of the global-average rise over the
last two decades suggest 3.2 mm per year (0.12 inches per year). The overall
observed rise since 1901 is about 20 cm (8 inches). If CO2 and other
greenhouse gases continue to increase on their current trajectories, it is
projected that sea level may rise by a further 0.5 to 1 m (1.5 to 3 ft) by 2100.
GWPF authors. A fuller picture:
In a warming planet sea levels would necessarily
rise due to thermal expansion of the oceans and melting of glaciers and ice
sheets. But sea level has been rising for thousands of years – since long
before GHG emissions became significant. Claims of an acceleration in sea level
rise from 2 to 3mm per year and its attribution to mankind must be treated with
caution. In particular, it is not currently possible to reconcile estimates of
sea level rise with estimates of the factors that are thought to contribute to it.
The picture is even more unclear at the local scale where, depending on the
location, many contributions have nothing to do with climate, such as
tectonics, vegetation cover, hydrology, etc.
COMMENT
There is no direct contradiction here of the
Royal Society position, as set out in their guide, and the GWPF authors’
identification of numerous other factors, and local variations, may be quite
correct. However it is not necessary to assume precise attribution of sea level
changes in order to regard the subject as potentially important.
First, the measurement of long-term changes
in global mean sea levels can provide an important corroboration of predictions
by climate models of global warming. This has certainly been a position taken
by the NOAA.[15] Falling sea levels would certainly have been
a contrary indication.
Second, calculations for the future cover
relatively new phenomena, including melting land ice (Antarctic), associated
with radiative forcing and rising temperatures. These could result in a
substantial increase in the rate of sea level rise and do form a major concern,
with which the GWPF authors do not engage directly.
In terms of risk, some scientists have
expressed fears over the stability of Antarctic ice sheets, which if realised
could result in substantially higher and faster sea level rises. Even the smaller rises projected in the RS
guide would have very substantial consequences for low lying regions and
coastal cities.
15. What is ocean acidification and why does it matter?
Royal Society:
About a quarter of the emissions of carbon dioxide
from human activities are soaked up by oceans each year. The extra CO2
causes the chemical balance of seawater to shift to a more acidic state (lower
pH) and some corals and shellfish have shells composed of calcium carbonate
which dissolves more readily in acid. Acidification is likely to shift the
competitive advantage among species, with as-yet-to-be determined impacts on
marine ecosystems and the food web.
GWPF authors A fuller picture:
The oceans absorb some of the extra carbon dioxide
released into the atmosphere. It would form a weak acid if it were not already
mostly alkaline. Human emissions of carbon dioxide will tend to make sea water
less alkaline and more chemically neutral. The projected change over the next
century is between 0.1 and 0.5 pH units. However, seawater pH naturally varies
from 7.5 to 8.5 between regions of the ocean, between habitats, between days,
and even between times of day. It is therefore misleading to talk of ‘ocean
acidification’. Shallow-water coral reefs are already subjected to hourly,
daily and seasonal changes in pH that encompass the full range of ocean
variability, hence the effects of changes in pH can be studied. Claims that
corals and shellfish will find it harder to grow in acidic water are overly
simplistic, not only because the water is not expected to be acidic but because
the dissolved carbon dioxide forms bicarbonate and carbonate ions, the raw
material for shellfish shells. Most studies find mixed effects, with some
groups of organisms thriving as a result of increased dissolved carbon dioxide
and some doing less well.
COMMENT
Some scientists appear to attach much more
weight to this acidification than does the Royal Society guide, which is rather
low key in this briefing. The shift in
competitive advantage between species reflects a very general phenomenon in
terms of the natural world and would apply to even the smallest variation in
climate. Almost any change will shift competitive balance[16], but is not necessarily
disastrous except from a very static and unrealistic perspective on
conservation of nature (which has always been changing and evolving).
The GWPF authors however appear to be
responding to scientists who have expressed much greater and possibly
legitimate concern than has the RS on this occasion. On a simple technical
point the GWPF authors’ response lacks arithmetic logic. It appears to confuse
the measures of average and range. The effect of any change on marine life, if
it exists, is prima facie most likely to depend on the average or, possibly, on
the extreme to which the organism is subjected.
An increase of 0.5 units (presumed to be an average) will either have a
direct effect on the relevant chemical or biological process, or it will change
the range from (7.5, 8.5) to (8.0, 9.0).
But neither party appears to treat this
as a particularly important point. Seen purely in terms of this exchange, the
ordinary reader might be forgiven for remaining agnostic or treating this as of
lesser importance than other threats. But, if it is a serious issue, it negates
to a significant degree any positive aspects of increased CO2 absorption by the
oceans, whether through natural causes or through geo-engineering initiatives.
16. How confident are scientists that Earth will warm
further over the coming century?
Royal Society:
Very confident. If emissions continue on their
present trajectory, then warming of 2.6 to 4.8◦C (4.7 to 8.6◦F), in addition to
that which has already occurred, would be expected by the end of the 21st
century. The range of values accounts for the fact that there are open
questions as to how exactly some natural processes such as cloud formation
amplify or reduce the direct warming effect of increasing levels of CO2.
GWPF authors A fuller picture:
Increasing carbon dioxide levels are likely to
bring some warming. Climate models predict 0.6–1.8◦C by mid-century, but
observational evidence indicates that they substantially overestimate how
sensitive the climate system is to increasing carbon dioxide levels, and may well
also overestimate how much of the emitted greenhouse gases will remain in the
atmosphere. The failure of models to make correct predictions over the recent
period diminishes our confidence in their ability to make correct predictions
of the far distant future.
COMMENT
This repeats the authors’ earlier
assertions on the overestimation of climate sensitivity, and on the weaknesses
of modelling, which have been discussed earlier. Quite simply these assertions
do not seem to be correct or to be supported by a fuller analysis.
17 Are climate changes of a few degrees a cause for
concern?
Royal Society:
Yes. Even though an increase of a few degrees in
global average temperature does not sound like much, global average temperature
during the last ice age was only about 4 to 5◦C (7 to 9◦F) colder than now.
Global warming of just a few degrees will be associated with widespread changes
in regional and local temperature and rainfall as well as with increases in
some types of extreme weather events. These and other changes (such as sea
level rise and storm surges) will have serious impacts on human societies and
the natural world.
GWPF authors. A fuller picture:
There is little indication of serious problems in
the short-term. Links to extreme weather are not supported by observational,
theoretical or even model evidence, and suggestions that rainfall patterns
would vary are no more than hypotheses (and counterfactual hypotheses at that).
A warmer climate would also bring substantial benefits, for example longer
growing seasons and fewer cold-related deaths. Higher carbon dioxide levels
will fertilise plants, including many important crops. Estimates of the
economic impact of temperature changes suggest little net impact until the
temperature is several degrees above pre-industrial levels.
As concerns the ice age comparison, the Royal
Society guide is patently absurd. Changes in temperature averages represent
effects, not causes. They cannot discriminate between very different processes
of change. It is even possible for there to be climate change where the global
mean temperature doesn’t change at all. It is well known that the ice ages were
driven by huge changes in Arctic insolation in summer (changes that are of the
order of 50 times larger than changes in the mean radiative budget), and that
changes in mean temperature are simply the small residue of the larger
high-latitude changes. Any familiarity with fluid dynamics would show that the Royal
Society has things backwards in asserting that the small changes in the mean drive
the much larger regional changes.
COMMENT
The fuller RS publication claims that
both theory and direct observations confirm that global warming is associated
with greater warming over land than oceans, moistening of the atmosphere,
shifts in regional precipitation patterns and increases in extreme weather
events. There is no obvious reason to assume that changes expressed in
temperature terms would be uniform, particularly in complex dynamic systems
within which there is little uniformity (eg by latitude) in any case.
“the
ice age comparison”
Surely this is intended as a simple
illustration that a (relatively) small average temperature difference can be
associated with a world that looks completely different. In this context the causes of ice ages are
irrelevant.
“Any
familiarity with fluid dynamics would show that the Royal Society has things
backwards in asserting that the small changes in the mean drive the much larger
regional changes.”
The relevance of fluid dynamics is
unclear, since the physics of climate is not confined to fluid dynamics.
Moreover a well-known counter example to
the authors’ view is the el Nino climate phenomenon. It is generally held that a
“small” change in ocean current temperatures in one part of the world (the NOAA definition is a 3-month average
warming of at least 0.5 °C), is associated with or has substantial
consequences for climate and rainfall around the globe, occasionally
manifesting as or at least accentuating events such as droughts. These may be
both beneficial and otherwise, and appear to affect crops and commodity prices.
……..
Others are far less sanguine than the GWPF authors about the future. It is however much
harder to be specific about particular regional impacts and their economic
consequences. Some of these may well be beneficial, at least on some
timescales, as the authors correctly claim. Others, particularly with dramatic
effects such as sea level rise, but also lesser changes disrupting agricultural
patterns, could write off huge amounts of physical and human capital and real
estate.
The real issue here is the nature and
scale of the risks that will be imposed on the world as a whole, and the disruptive
changes implied.
18. What are
scientists doing to address key uncertainties in our understanding of the climate
system?
Royal Society:
Science is a continual process of observation,
understanding, modelling, and testing. The prediction of a long-term trend in
global warming from increasing greenhouse gases is robust and has been
confirmed by a growing body of evidence. Nevertheless, understanding (for
example, of cloud dynamics) remains incomplete. All of these are areas of
active research.
GWPF authors. A fuller picture:
Scientists continue to address some of the unknowns
regarding the climate system. Some are concerned that funding continues to be
focused on characterizing human influences on the climate rather than
investigating natural variability, and on developing complex computer models
rather than improving observational data-gathering systems or fundamental
theory. One would be hard-pressed to identify the ‘growing body of evidence’
that the Royal Society guide refers to. Certainly, the evidence of the past 40
years points clearly to exaggeration by existing models. Moreover, the
‘incomplete understanding’ that the Royal Society guide so glibly acknowledges happens
to be fundamental to the crucial question of climate sensitivity. ‘Nullius in
Verba’, the society’s motto, means we do not even take the word of the Royal Society
guide on these things. We don’t.
COMMENT
Again the authors’ comments are assertions
that have been discussed earlier. Most readers of IPCC summaries will probably
view their reviews as suggesting a “growing body of evidence”, leading to
stronger statements, and recent evidence as tending to reduce uncertainties
around climate sensitivity.
The idea that “incomplete understanding”
invalidates useful analysis is not self-evident. It is certainly and obviously not
true in fields as diverse as quantum theory and evolutionary biology.
The GWPF authors’ views on research
priorities might be taken to imply that important areas such as focusing on precise
measurement and data accuracy were being neglected, or that the bulk of
research consisted of computer model building.
The reality is that research and continuous advance is evident across
the board, some of which is instanced in these comments, in areas as diverse as
satellite measurement of Antarctic ice and direct measurement of warming.
Royal Society:
Results from the best available climate models do
not indicate any abrupt changes or ‘tipping points’ in the climate in the near
future. However as warming increases, the possibilities of major abrupt change
cannot be ruled out.
GWPF authors. A fuller picture:
While these disaster scenarios are raised from time
to time and have been discussed in previous IPCC reports, they are largely
discounted in the current IPCC report,
as is appropriate.
COMMENT
These two comments differ mainly in
emphasis, with the Royal Society refusing to rule out “tipping points”.
One of the most notable tipping points is
the potential feedback associated with methane release from Arctic permafrost. Implicitly the Royal Society says this is not
indicated from the best current models.
The most recent IPCC reports support a similar view.
However if we accept that there are
significant possibilities of current science and “best estimates” overstating
risks, then we should also recognise the possibility that they are understated. Certainly some
scientists continue to maintain that this particular risk has been understated.
20. If
emissions of greenhouse gases were stopped, would the climate return to the conditions
of 200 years ago?
Royal Society:
No. Even if human emissions of greenhouse gases
were to suddenly stop, Earth’s surface temperature would not cool and return to
the level it was at before the Industrial Revolution for thousands of years
because CO2 is only removed from the atmosphere over these very long
time scales.
GWPF authors. A fuller picture:
This question insinuates that there was some sort
of ‘steady state’ of the climate before industrialisation. Indeed, before
industrialisation, the Earth was in the Little Ice Age, and few would want to
return to such a period. However, because the Earth’s climate varies naturally
on all known timescales, it is not possible to make definitive statements about
what the climate would be like today had there been no manmade greenhouse gas
emissions. Similarly, it is not possible to say what will happen in the future,
regardless of the levels of future GHG emissions. Moreover, the statement that
carbon dioxide is only removed from the atmosphere over timescales of thousands
of years is highly misleading. The majority of the excess carbon dioxide over
preindustrial levels should be removed from the atmosphere within a century after
a sudden halt to emissions, assuming that there are no long-term changes in the
natural carbon cycle, which would swamp human contributions even for small changes. It is only a modest proportion that would
take thousands of years to be removed.
COMMENT
The Royal
Society does not “insinuate” a steady state, and earlier points in the guide
discuss other natural variations in climate.
“the excess carbon dioxide … should be removed
… within a century after a sudden halt to emissions, assuming that there are no
long-term changes in the natural carbon cycle”
CO2 does not “decay” of its
own accord and can therefore only be removed as part of processes in the
natural cycle. This statement therefore places a remarkable degree of
confidence in an implicit ability to predict the future behaviour of the
natural carbon cycle, which is in contrast with the authors’ comments on
ability to predict future climate more generally.
Moreover the presumption of continuing
net absorption within the natural cycle implicitly accepts that this is a
further addition to carbon within the oceans (as a major carbon sink),
exacerbating potential adverse impacts there.
If the carbon cycle itself returned
quickly to a new equilibrium position, ie with a zero balance of entry and
exit, then CO2 would persist in the atmosphere for a very long time,
or indefinitely.
“it
is not possible to make definitive statements …”
This seems to confuse precise statements
about “exactly what might have happened otherwise”, which can never be known,
with statements about impact or likely impact, albeit imprecise, which can
reasonably be deduced from known elements in the science.
CONCLUSIONS
This
analysis, and the 20 points, have focused primarily on matters of science. Any
assessment of the impacts of climate change, its human and economic
consequences, and possible policy implications are only covered
tangentially. These conclusions are
therefore confined to the discussion of the science.
It should be
clear from the above statements and comments that, at least in the context of
this exchange and its implications for acceptance or otherwise of the main propositions
of mainstream climate science, that there are quite a small number of key issues.
Both parties clearly accept the science underpinning the principle that GHG can
drive warming, although the GWPF authors seek to qualify this in a number of
ways.
The most
important single issue, at least in this exchange, is the interpretation of recent
(post 1970) data on actual global surface temperatures, both as evidence of an
actual impact and as a measure of climate sensitivity to increasing GHG. A
neutral party looking at the statistics for the first time, and without any
preconceptions as to the theoretical underpinnings, would see a clear increase
since 1970, but with a less clear cut trend since about 2000. However attempts
to base comparison on an obvious statistical outlier such as 1998, should
automatically invite suspicion. Moving or interdecadal averages tell a steadier
story. Purely in terms of risk, it would be impossible to conclude from this
data that we could rely on the assumption that warming had now paused and would
only continue, if at all, at very low levels. (Question 1.)
We might
expect that additional data will increasingly tend to resolve any residual
doubt on this issue, both through the passage of time, for example if the
trends through 2014 and 2015 YTD (hottest on record) are continued, and,
perhaps more importantly, with improving data on new approaches to estimating
other elements in the global heat balance.
In terms
of climate sensitivity to GHG, the discussion fails to bring in time lags and
thermal inertia. It should be clear that a simple division of temperature change
by CO2 change over the same
period, which is implicit in the GWPF arguments, is fallacious, and that
such a calculation has the potential to seriously and systematically understate
sensitivity, even ignoring selective bias in choice of base years. (Comment on
Question 2.) We might argue that this
intuitively rather simple phenomenon, the time lag between changes in GHG
concentration and the full effect of that change, is not stressed sufficiently
in the RS briefing, and is simply ignored by the GWPF authors. The ratio of
committed to observed warming has certainly been stressed by other IPCC
authors.
A second
issue is whether the GHG increase is predominantly attributable to human
activity, but the attempt to cast doubt on this proposition is not supported by
any convincing argument or evidence. (See comment on Question 3.)
Other arguments
are essentially around questions of corroboration for the basic propositions
presented by a mainstream view of CO2 induced warming, and
particular consequences such as sea level rise or extreme weather which are
important per se. While some of these
indicators and corroborations may not be clear cut, are subject to additional
explanatory factors, and fall well short of an absolute proof, they remain as
bits of evidence that appear to point consistently in one direction.
Finally there is scope for discussion of
rather philosophical questions, on the nature of truth in scientific inquiry.
This perhaps deserves a much longer discussion, but the current issues are
about what practical judgements are to be made about balances of risk, and what
policy measures and what strategies are appropriate to deal with them.
Residual uncertainties and incompleteness
in science will remain, but increasingly it appears that these are much less
relevant than what we do now know. The
Royal Society statements, which are intended for a wide public consumption and
not for more specialist audiences, may well be less than complete, but they do
offer at least a good description of a very large, complex and fundamentally
important subject.
US
National Academy of Sciences. February 2014.
[3]The Small Print. What the Royal Society
Left Out. The GWPF report was
prepared by, and endorsed by the following authors: Professor Robert Carter, Professor
Ross McKitrick, Professor Vincent Courtillot, Professor Ian Plimer, Professor
Freeman Dyson, Dr Matt Ridley, Professor Christopher Essex, Sir Alan Rudge, Dr Indur Goklany, Professor Nir
Shaviv, ProfessorWill Happer, Professor Fritz Vahrenholt, Professor Richard
Lindzen,
[4]
Reference to be added
[5]
Kitoh, Akio;
Murakami, Shigenori (2002). "Tropical Pacific climate at the mid-Holocene and the
Last Glacial Maximum". Paleoceanography 17 (3): 1047.
[7]
Reference
[8]
One source suggests several decades. http://www.skepticalscience.com/Climate-Change-The-40-Year-Delay-Between-Cause-and-Effect.html
[14] a
collaboration between scientists at the Max Planck Institute in Germany and the
University of Leeds, is published in the journal Nature. http://www.sciencemag.org/content/348/6242/1469
[16]
Eg el Nino and Darwin’s finches
