What
do Scientists Really Know? Why the Philosophy Really Matters.
This
column does not often stray into the philosophy of science, but there are
occasions when it is useful to reflect on just why we consider certain things
to be true and with what evidence. Nowhere is this more true than in evaluation
of what science tells us on climate change. Given the superficial and
inaccurate material that continues to flow from the many political opponents of
action on climate issues, it is worth dissecting some of the fallacies and
misunderstandings that find their way into popular debate. One of these is the notion
that the nature of scientific knowledge is always provisional, with the
additional assertion that it cannot therefore be relied upon in matters of
policy. This is a misreading of the nature of scientific method and the
philosophy of science. It is often combined with the false claim that climate
science has lacked predictive power and in particular failed to anticipate the
actual warming that we are now observing. These arguments owe little to logic or fact.
…………………………………………………………..
A
lot of the popular discussion on climate (and other) science stems from low
level interpretations of the work of Karl Popper, and in particular the
criterion of falsifiability as a necessary condition for any proposition to be
considered as science. So it is worth describing briefly the nature and status
of Popper's philosophy. Loosely summarised, Popper's essential thesis was that
no proposition could ever be finally proved, but that proper science could be
defined by our ability to set tests, often of a predictive nature, for it to
pass. Hence falsifiability, or the capability of being disproved, was the test
of proper science. Popper has always been popular among political commentators,
especially on the Right, because he usefully demolished the pretensions to science
status of many Marxists. He observed that they failed, or refused, to produce
testable, and hence falsifiable, propositions based on their ideas.
These
ideas, taken in isolation, characterise science as proceeding by a series of
hypotheses, each of which may or will in turn be falsified and replaced by a better
hypothesis. This is the feature that excites
the interest of climate science sceptics. The idea (incorrect, as we shall
argue later) that scientific propositions are always provisional supposedly
implies that they can and will be found to be false, and are therefore not
reliable as a basis for policy. Needless to say, this is an attractive argument
for anyone faced with what they may regard as an “inconvenient scientific
truth”.
So
far, so good. Popper made an important contribution, at the very least as a
codification of what had always been present in de facto practice of science
since the days of Isaac Newton[1]. But
his insight is not the whole story, although it is sometimes treated as such in
a political context. Nor is it a complete description of how science works, and
Popper is certainly not the ultimate court of appeal or the last word on
scientific method.
One
excellent source on this subject is the work[2]
of Brian Davies, referenced below, which gives a much more coherent and
comprehensive account of the nature of proof and knowledge in mathematics and
science, fully acknowledging the contribution of Popper among others, but
putting it in its proper historical, scientific and philosophical perspective.
Another interesting article by Richard Lawson[3]
makes a further interesting contribution on the application of Popper’s
approach to validation of climate science
Popper and Evolution. Scientific understanding of evolution has
had an enormous impact on human thought and on practical science since these
ideas developed more than 150 years ago. Comparison with climate science, which
threatens to be an issue of similar scale, is therefore instructive, not least
because there is some overlap[4]
between the sceptics on both issues. However, Popper’s judgement on matters
scientific is called into question by his earlier failure to recognise the
theory of evolution as science under his criterion. JBS Haldane is famously attributed
the answer: “Show me a pre-Cambrian rabbit, and my confidence in the theory of
evolution is lost.” Popper later and sensibly retracted.
Not all science provides a basis for future
prediction. Falsifiability
does not depend on and cannot be equated with the ability to make accurate
future predictions. Evolutionary biologists may understand perfectly the
mechanisms of genetic mutation but there is no way they can predict, or we
test, exactly how random mutations might lead over many millennia to the
evolution of new species under the same or changed environmental conditions. Similarly,
weather, the day-to-day manifestation of climate, is intrinsically
unpredictable for more than a few days ahead. But this is much less likely to
be true of climate, the composite or “average” of weather over a long period.
Prediction and falsifiability. The reality of science is in practice much more
nuanced and complex than a simple move from predictive failure[5]
to falsification. Where a prediction made from an apparently well-established
theory fails, the first response should normally be to look for what has gone
wrong with the data or the experiment, or what other factors have affected the
result. It should not be immediate rejection of a well-established theory. Otherwise the laws of chemistry and physics
would be disproved on a daily basis in school laboratories.
At
a higher level, discrepancies in the orbit of Uranus revealed the existence of
Neptune, not the failure of Newton’s Laws. Small discrepancies for Mercury, on
the other hand, could only be explained after Einstein’s theory of relativity
had overtaken Newtonian physics as a more complete description of the universe.
The clear parallels in climate science have been critical examination of
apparent anomalies in global temperature data (compared to model predictions), together
with the impact of unpredictable events such as particular large volcanic
eruptions. The normal scientific process of seeking increased understanding
has, in this context, absurdly been characterised as data fraud, as part of the
politicisation of the policy debates. Perhaps fortunately for Einstein and the
general theory of relativity, views on the orbit of Uranus did not disturb as
many vested interests.
Science may never be complete, but it is not
always provisional. The absence
of complete knowledge and understanding does not imply the absence of useful
knowledge and understanding. Most of conventional science is for all practical
purposes providing facts that we can and do treat as certain. Our understanding, even of the
principles of quantum physics, and however incomplete, enables most of the
advanced technologies of the modern world that we take for granted.
Popper’s
characterisation of scientific knowledge as always provisional, is more
relevant to particular parts of physics (quantum mechanics or astrophysics)
than it is to many other sciences. Theoretical
physics does indeed include speculative interpretations, such as string theory
or parallel universes (though it is questionable whether either is capable of
being tested and meeting Popper’s falsifiability test). But much of science,
especially in relation to the natural world, is descriptive and observational.
Science gives us a huge amount of fact that
is certain. There are many
more things that we “know” with certainty as a result of scientific
observation, that do not need to be regarded as “provisional”, and are
fundamental to any sensible consideration of public policy. This is true of
much of climate science, which will be essentially concerned with careful
observation of known phenomena such as parts of the carbon cycle or heat
exchange within the oceans and the atmosphere.
“Science
is never settled. History tells us that!
“
This is an absurd
generalisation and history tell us nothing of the kind. Science provides vast
amounts of knowledge that we can and do, for all practical purposes, treat as
certainty. We know that the basic theory of tectonic plates is true. We know
that AIDS is caused by the HIV virus, and malaria by mosquitoes. We know that
mass vaccination can protect populations from lethal diseases.
The
anti-science brigade, from the Trump and Pence core vote on measles, or tobacco
companies denying the links between smoking and lung cancer, or Melanie
Phillips on MMR vaccines, or African leaders in denial on HIV/AIDs, and more
recently anti-vaccination activists on Ebola, must over the years bear
responsibility for huge amounts of human suffering.
The basic building blocks of
climate science, in terms of the radiative forcing effects of various
greenhouse gases, have well established parameters, and we have, at a minimum,
an awareness of most of the other major factors involved in the carbon cycle
and the climate system. And the knowledge is constantly improving. Climate
science as a distinct discipline consists of the application of knowledge from
a large number of separate but related fields of knowledge and observation.
Putting the pieces together to form a full understanding of climate variation
is a complex application of known science along with some known uncertainties.
And of course it necessarily includes numerous year-on-year effects such as
variations in solar variation and climate cycles such as el Nino, which do not
have a human cause, as well as the possibility of sampling error in climate
measurement.
“We
can’t even find models that forecast tomorrow’s weather, so there cannot be any
basis for predicting the climate decades ahead.”
This
is a popular myth with no basis in reality. Today’s short term weather forecasting, along with associated probabilities,
is good enough to be extremely useful. In farming and shipping, not to mention
storm alerts, it is regarded as a crucially important service. Forecasts will
always have a margin of error, and will always be revised to reflect additional
information and unforeseen extraneous factors, but in various forms it is an
essential part of almost every human endeavour.
The
reality is that scientists have also proved remarkably consistent in their
assessment of the determinants of climate, which is necessarily measured over
much longer time scales than weather. This includes the global temperature
impacts of greenhouse gases. These forecasting efforts are very well summarised
in a Carbon Brief article that starts with some relatively simple
calculations in the early 1970s.
In
a paper published in Nature in 1972, Sawyer hypothesised that
atmospheric CO2 would increase by 25% and that the world would warm
0.6oC between 1969 and 2000. Sawyer argued for a climate
sensitivity – how
much long-term warming will occur per doubling of atmospheric CO2
levels – of 2.4oC, which is not too far off the best estimate of
3oC used by the Intergovernmental Panel on Climate Change (IPCC)
today, on the basis of much more information and sophisticated analysis.
In
some instances, the forecasts have under or overestimated current observed
warming because they were based on assumptions that under or over overestimated
key parameters such as CO2 emissions, and other factors such as
unusual volcanic activity. But of course the real purpose of forecasts is not
absolute precision but a reasonably accurate picture, including the risks and
uncertainties, of the impact of policy alternatives, such as the effect of
allowing uncontrolled emissions or adopting measures for their limitation.
Rejection
of known science is both foolish and unjustified. It has also become perhaps
the most dangerous intellectual fallacy of our age.
[1]
Popper had never read Principia Mathematica. Had he done so he might have found
Newton’s ideas on science closer to his own.
[2] Science
in the Looking Glass: What Do Scientists Really Know? E. Brian Davies Oxford
University Press, 2003. 288 pages, ISBN 0198525435. (Useful review in Notices of the
American Mathematical Society.) Inter alia this remarkable book provides a
good description of Popperian ideas on falsifiability, both their positive
contribution and their limitations.
[3] Climate
Science and Falsifiability. Philosophy Now, 2014. Richard
Lawson shows how Karl Popper can help settle the climate debate. This
article by Richard Lawson provides a usefully brief discussion and turns the
sceptic argument on its head by imposing a falsifiability test on the sceptic
position.
[4]
Christopher Booker. Trump and Pence.
[5] It
is of course only in very specific conditions, such as astronomical observation
or highly controlled laboratory experiments, that truly precise predictions and
measurements are relevant. In most practical circumstances outcomes can be
significantly affected by complex boundary conditions, eg the precise shape of
the land mass and its contours.