What Matters Most? Population, GDP Growth or Technology.
A common theme in popular discussion of climate change, or rather of whether mitigation is feasible, is its attribution to different factors, notably population growth or economic growth, and the reliance of solutions on technology. This also affects any discussion of historic responsibility for CO2 emissions. It is a highly emotive subject, particularly in relation to population control or the limitation of growth, so it is at least worth a cursory look at what the hard statistics tell us.
The so-called IPAT equation represents a general description of human influence on the environment: IMPACT (of CO2) = [POPULATION] X [AFFLUENCE] X [TECHNOLOGY]. A popular and useful way of interpreting this for CO2 emissions for the energy sector is the so-called Kaya Decomposition. Affluence is measured as GDP per capita and technology is further decomposed as energy per unit of GDP, and CO2 emitted per unit of energy. The Kaya identity is:
Global Picture. The IPCC Fifth Assessment Report (2014) provided a useful breakdown of changes in global CO2 emissions over several decades, based on this identity:
In the three decades from 1970 to 2000, population growth and increasing incomes contributed similar amounts to the rise in emissions, but the energy intensity of GDP fell quite sharply contributing a significant saving to the level of emissions that might otherwise have been expected.
The energy intensity of GDP was a significant offsetting factor, whose importance rose in 1990-2000, possibly reflecting the longer term impact of higher energy prices and uncertainties in the 1970s and 1980s. However efforts to reduce the carbon emissions associated with energy use played only a limited role in reducing emissions. This is unfortunate since reduction of dependence on fossil fuels this is a key component of emissions reduction hopes, and this factor actually moved in the wrong direction from 2000-2010, again reflecting in part the Chinese dependence on coal.
From 2000 to 2010 the importance of rising incomes rose relative to population factors, reflecting inter alia the rapid growth of the Chinese economy. The overall outcome was particularly depressing as the decade showed a sharp increase in emissions and lessening impact of the mitigating factors.
Major regional and temporal differences
But this decomposition can change significantly over time. Global averages also conceal major differences between countries, and there are some optimistic signals. A similar but more recent chart for China (Safonov reference below) shows overall reductions (to 2016), and significantly more reductions attributable to less energy intensive GDP and less carbon intensive energy. For China, population growth has not been a significant factor over this period, but income growth continues to be so.
Similarly more optimistic trends have been observed in the USA to 2015, but with higher influence from population, less from economic growth, and significant reductions attributable to less energy intensive GDP and less carbon intensive energy consumption.
An interesting comparison of country by country decomposition for periods before and after the financial crash of 2008 is given in a fairly recent paper by Sadorsky, referenced below. It shows huge diversity in findings between countries, exemplified in the following chart for four countries:
NB. This chart has a rather more complex interpretation, as it represents the changes between two very distinct periods. The reader is referred to the Sadorsky article
Kaya factors. The future.
Given the pace of reduction required to reach net zero by 2050, the Kaya emphasis will have to shift to much greater emphasis on decarbonising energy. Population cannot be subject to substantial percentage reduction, and the drive for higher incomes is unlikely to stop. There is some scope for further weakening of the link between affluence and energy use, but the heavy lifting will depend very substantially on decarbonisation of energy, starting with the power sector and expanding the power sector into transport and heating.
IPCC Fifth Assessment Report.
George Safonov's Lab. National Research University Higher School of Economics, Moscow. Long-term, Low-emission Pathways in Australia, Brazil, Canada, China, EU, India, Indonesia, Japan, Republic of Korea, Russian Federation, and the United States. December 2018.
Sadorsky, P. Energy Related CO2 Emissions before and after the Financial Crisis. Sustainability 2020, 12, 3867. https://doi.org/10.3390/su12093867
Dr Ajay Gambhir, Neil Grant, Dr Alexandre Koberle, Dr Tamaryn Napp. The UK’s contribution to a Paris-consistent global emissions reduction pathway. Grantham Institute. Imperial College. 2 May 2019.
Public Utilities Fortnightly. First Look at 2015 CO2 Emission Trends for the U.S.
For a fuller “actuarial explanation and justification for the Kaya identity, this reference may help Kaya identity_JC Final 050219.pdf (actuaries.org.uk)
 Since the identity is multiplicative, a logarithmic transformation is usually used in the calculation of the factor contributions.
Here are some back of the envelope calculations that demonstrate the credibility of the assertion that action to mitigate climate change, and progress to a low carbon economy, can be achieved at a containable cost. It aims to provide a simple intuitive defence of conventional estimates for the general reader, but serious students of the subject are invited to delve deeper into some of the excellent material produced under the aegis of the Committee on Climate Change.
One of the arguments mounted against taking effective action on climate is that the economic cost is unaffordable. The obvious response is that this has to be compared with the cost of not taking action, the costs of adaptation, and the possibility of existential climate threats on an unimaginable scale. However rather than engage with the occasionally hysterical accusations of alarmism from those in denial on the climate science, it is worth trying to get a sense of the scale of what may be involved in meeting a UK zero carbon target by 2050. Some sense of proportion should start to defuse the issue and calm any fears of national bankruptcy.
This can be a confusing exercise, not least because estimates (of mitigation costs) tend to get tossed around in very different contexts. For example, it’s most common for costs to be discussed in very broad terms as a percentage of GDP. The Stern Review indicated costs of up to 2.0 % of GDP per annum, and some people have argued that this would be a very damaging and unsustainable burden in macro-economic terms. The Committee on Climate Change currently makes a similar estimate (of 1-2 % of GDP). Others argue that Green investment can actually be used to boost economic growth and domestic employment. There can be at least a partial truth in this argument, even if it can be misrepresented as arguing that the low carbon economy pays for itself. It is not an argument I intend to deploy here.
Some will be more concerned with the public expenditure implications, although that issue should be seen much more in terms of more political questions of how we choose to fund transformational change. For example, much of the cost of transition to low carbon may be carried by private consumers, in their utility bills or more expensive motoring choices, or it may include publicly funded infrastructure investment and extensive grants and subsidies.
Macro-economic shocks and UK GDP numbers
2019 GDP (last year before pandemic) £ 2170 billion pa
Estimated permanent loss of
GDP due to 2008 financial crisis £
300 billion pa
The economy is 16%, or £300 billion, smaller than it would have
been had it followed the pre-crisis trend. (IFS 2018)
Typical impact of an oil price
shock in 1970s, 1980s and 1990s. £ 100 billion pa
(an order of magnitude estimate, based on spikes and falls in
the oil price of $100/ bbl, UK consumption of 100 mn tonnes pa,
and scaling up to an equivalent percentage of 2019 GDP)
I have not included the significantly larger shifts in resources associated with different government priorities on taxation and spending. Even so, the conclusion we might draw here is that the expenditure on a low carbon economy, while substantial, is far from catastrophic and unmanageable when viewed in macro-economic terms. We have coped with much larger and less predictable economic shocks than what we now face in eliminating emissions.
Public expenditure choices
Expenditure budget 2021: £ 908 bn.
Defence £ 54 bn pa
Defence in 1951 (Korean War) accounted
10% of GDP. Equivalent percentage of 2019 GDP £ 217 bn pa
Overseas aid (0.7% of GDP target) £ 15 bn pa
Overseas aid (after current cuts) £ 10.85 bn pa
Reported cost of UK Track and
Trace system £ 37 bn
(spread over two years but seems to be essentially
a 12 month figure). Minimal identified benefit.
Assumption of a 2% of 2019 GDP
devoted to GHG £
43 bn pa
reduction and low carbon transition. (as above)
But what can you buy for 2% of GDP?
It turns out you can do quite a lot for decarbonisation with around £ 40 billion a year. Here is one allocation of that money:
Decarbonising the power sector. £ 18 bn pa
Retrofitting UK housing stock.
28 million households £
20 bn pa
Grant of £ 20,000 per household for retrofitting, at one million
households a year for 28 years
Charging infrastructure for electric vehicles (EVs) £ 2.5 bn pa
Total £ 40.5 bn pa
This covers the three main sources of UK emissions, and the main areas for investment to achieve net zero by 2050. Assumptions to justify the plausibility of these numbers are as follows
Sizewell C has an estimated capital cost of around £ 18 billion for 3.2 GW of capacity. Nuclear is currently regarded as one of the more expensive options for low carbon capacity, and Sizewell is “first of a kind” but this at least gives us an order of magnitude. The equivalent of one Sizewell a year for 25 years delivers around 80 GW of capacity and more than 600 TWh pa of energy, more than enough, even after allowing for significant growth, to effectively decarbonise a power sector which already has a significant proportion of renewable low carbon energy. [Current UK annual consumption less than 350 TWh]
Alternative renewable sources are also widely seen as likely to be much cheaper than this, although there will be other major costs associated with energy storage. However we might interpret this as at least a first approximation, or an upper limit to the capital cost for low carbon generation. A great deal of new investment would of course be required in any case, so much of this will not be a truly incremental cost.
Heating of buildings
Retro-fitting of buildings, especially residential property, for energy efficiency and low carbon heat pumps or heat network solutions, is one of the biggest problems for achieving zero carbon. The cost of air or ground source heat pump installations are currently advertised at around £ 6000-8000 and up to £ 16000 respectively, while heat networks are collective typically municipal investments which can also be quite costly. But even adding on a substantial allowance for insulation improvement, £ 20000 per household would look like an extremely generous grant to a householder, especially as there would be a continuing benefit in lower running costs.
“The UK by 2040 needs 1-2.5 million new charging points. An average public charging point costs 25-30,000 euros so it would need to invest 33-87bn euros from now until 2040,” said Wood Mackenzie’s Wetzel. Interpreting this as two million over twenty years and assuming a cost per installation of £ 25000, this implies an annual investment of £ 2.5 billion.
The price of EVs is likely to fall dramatically with increasing scale, so we should not need to worry unduly about the capital costs of fleet replacement, which will be borne by motorists as they retire their existing vehicles.
Current estimates of expenditure required for a zero-carbon economy are plausible. In no sense can they be considered unattainable or damaging in macro-economic terms, as the sums are smaller and more predictable than the much bigger economic shocks we have endured in recent decades from other sources. Viewed as public expenditure choices the sums are commensurate with other choices we make and have made, such as the unfortunate “test and trace” scheme. An it is quite easy to hypothesise major elements in the composition of that expenditure.
Caveat. Sharp-eyed readers will have noticed that I have omitted some of the notoriously difficult, but smaller, sectors, such as aviation and shipping. But I believe the biggest additional issue will be the funds that high income countries will need to find in order to support low carbon strategies in the developing world. That is a different story, and one that I have addressed in earlier posts this year.
 This post concentrates on UK statistics but the same arguments, and similar orders of magnitude, will apply to most developed economies.
 Retrofitting the UK housing stock, and many other infrastructure investments, will be labour intensive.
 10 years on - have we recovered from the financial crisis? - Institute For Fiscal Studies - IFS. Paul Johnson and Jonathan Cribb. 2018
 The UK became a net oil exporter during this period, so the macro-economic consequences for the UK relate both to price shocks and significant changes in production.
 “Chancellor Rishi Sunak’s Budget last week included an additional £15bn for test and trace, taking the total bill to more than £37bn over two years.” [Independent. 10 March 2021]