Concerning Climate
Why we musn’t give up on climate change mitigation and an analysis of how it’s going so far.
Motivation
Often when I think about about climate change and what we might do to mitigate it I become forlorn with the hopelessness of it all. It seems so important and yet so insoluble.
Emitting large amounts of CO2 gives us an incredible lifestyle. When we emit there is no immediate feedback mechanism — no way for us to directly feel the cost of our emissions. What’s more, the cost is mostly born by other people. The big, immediate benefits and the lack of direct negative feedback make it hard to persuade ourselves, or our governments, to curb emissions. So hard in fact that I think it is tempting to give it up as a bad job and to get on with our lives. We feel like there is no chance our governments and industries will make the changes needed to meet the Paris Agreement’s aim of limiting global warming to ‘well below 2°C above pre-industrial levels’ — and so we give up.
But we shouldn’t. Because 2°C is better than 3°C and 3°C is better than 4°C. I think this is a really key point that gets missed. The more CO2 that gets emitted, the hotter it gets and the worse the ramifications become. The late David Mackay — a hero of mine — described the area under a graph of CO2 emissions against time as being equal to ‘suffering’. The bigger the area, the more suffering. So we should do what we can to limit those emissions and the resulting suffering, even if we suspect that the temperature increase will reach 2°C.
Before looking more into what action we should take I think its worth understanding where we are now. How much damage has climate change already done and how much more might it do? How are we doing in our efforts to reduce emissions? These questions (and my current unemployed and hence time-unlimited status) have prompted me to do some research and some data analysis. On the whole I’ve tried to use open source data sets to produce my own figures. On occasion I have failed to do so and so have replicated other people’s figures — in which case I say so in the caption. If you would like to see the code for the data manipulation and plots while reading the article you can do so here.
Climate impacts
The Intergovernmental Panel on Climate Change’s latest report and the recently publicized US Global Change Programme’s Climate Science Special Report describe the impacts that climate change has already had. These include: a temperature increase of about 0.78°C from the period 1850–1900 to the period 2003–2012 (IPCC); a global mean sea level rise of about 19 cm over the period 1901–2010 (IPCC); and an increasing intensity and frequency of extreme temperatures and heavy precipitation events in most continental regions of the world (USGCP).
These reports also include projections of what impacts climate change will have in the future under different emissions scenarios. The IPCC uses four scenarios called “Representative Concentration Pathways” (RCPs). These are RCP2.6, RCP 4.5, RCP 6.0 and RCP 8.5. The numbers in the names represent ‘radiative forcing’ — a measure of how the gases in the atmosphere affect the balance between the energy absorbed by the Earth and the energy radiated back out to space. The bigger the number, the bigger the ratio of radiation in to radiation out — so the hotter it gets. Specifically the numbers relate to what the radiative forcing would be in 2100 in each scenario. Annual CO2 emissions from fossil fuel use and industry under each of the 4 scenarios are shown below.
In RCP 8.5 annual CO2 emissions continue to increase. High population and modest rates of technological change result in long term high demand and high emissions.
In RCP 6.0 annual CO2 emissions peak in 2080 and then decline. Population stabilizes, growth is relatively slow and the energy intensity of the economy (CO2 emitted/$) gradually improves.
In RCP 4.5 annual CO2 emissions peak in 2040 and then decline. The slow growth and then reduction in emissions is achieved through large scale adoption of Nuclear power and Carbon Capture and Storage (CCS) as well as significant reforestation.
In RCP 2.6 annual CO2 emissions peak in 2020 and then decline, becoming negative after 2070. This scenario relies heavily on the use of CCS and biofuels to allow carbon negative power generation (by growing plants, burning them and then capturing and storing the CO2 emitted in the process). This is an unproven technology.
The likely projected global temperature changes under each of the RCP’s are shown in the figures below. The temperature changes shown are relative to the 1986–2005 average. It is worth mentioning that this is not the ‘pre-industrial’ baseline to which the Paris Agreement refers. I looked a little more into what the ‘pre-industrial’ baseline is and wrote about it here. The conclusion is that we need to add somewhere between 0.55°C and 0.8°C to the temperature changes reported below if we want them to be relative to pre-industrial levels.
Adding between 0.55°C and 0.8°C to the reported temperature changes we see that, even if we follow RCP2.6, we might well exceed 2°C of warming by 2010. The scale and speed of warming under the higher emissions scenarios is terrifying. I don’t have a good idea of what a further 3.7°C of warming by 2100 would look like but I do have some grasp of the suffering that 0.78°C of warming is already causing (famine, flooding, fires, hurricanes). Looking at those temperature estimates I vehemently hope that we are well clear of RCP 8.5.
Reality check
With those temperature changes in mind, let’s have a look at the data. For the past few years there has undoubtedly been efforts to reduce our CO2 emissions — what impact have they had? Which scenario do we seem to be following?
The RCP scenarios start in 2000. Detailed data on CO2 emissions from fossil fuels and industry are available up to 2015. We therefore have 15 years of overlap between historical data and ‘future scenarios’. That overlap allows us to figure out how reality has shaped up compared to the scenarios. In the figure below I have plotted historical emissions against the predicted emissions for each of the 4 scenarios. I have replaced the scenario names with the mean temperature increase estimate for each scenario (from the table above). I find temperature change estimates far more understandable than radiative forcing estimates. Note however that the temperature numbers are just the mean outputs of the models. They do not capture the whole range of possible temperature increases under each scenario.
Depressingly it looks like Global CO2 emissions have largely followed the RCP 8.5 — unabated growth scenario. Recently however, emissions growth has slowed and diverged from the RCP 8.5 scenario. In 2015 CO 2 emissions decreased by 0.1% despite a 3% increase in GDP so it would appear that efforts to decarbonize are having some impact.
The exact trajectory of our annual emissions need not follow any of these scenarios exactly — they are merely indicative of some possible futures. The most important thing is the quantity of CO2 emitted overall — not the exact way our emissions change over time. The plot below shows cumulative emissions since 2000 compared to the cumulative emissions in each scenario.
So our cumulative emissions exceed those in the lower temperature scenarios. It is therefore not enough to bring our annual emissions into line with those in the lower temperature scenarios. We would need to reduce our annual emissions even more sharply that those scenarios suggest in order to make up for the overshoot we have already committed. That means that the longer we leave it to curb emissions, the more stringent the emissions limits will need to become. We need to figure out how to dramatically curb emissions and we need to do it soon. If we don’t, we may well see temperature rises much bigger than we currently dare to consider.
In future posts I’ll dig a little more into the emissions of a few key countries and try to figure out what effect different policy approaches are having on CO2 emissions. Hopefully the results will tell us something about how to move forward pragmatically to minimize how much hotter it gets.
Postscript: Why only CO2 emissions from fossil fuels and industry?
This analysis only looks at CO2 emissions from fossil fuel use and from industrial processes. I didn’t look at other anthropogenic sources of CO2 such as land use change. I also didn’t look at other greenhouse gases besides CO2 . The RCP scenarios include projections for other emissions types but I was unable to find up-to-date historical data sets for them. As such I omitted them from this analysis. In order to see if that omission wa justified I looked at the breakdown of anthropogenic greenhouse gas emissions. The figure below shows that breakdown for 2010.
CO2 emissions from fossil fuels and industry form the majority of anthropogenic greenhouse gas emissions. Methane emissions and CO2 emissions from land-use change are also significant contributors and it would be interesting to see how they are evolving. In the absence of up to date emissions data however, I think it’s reasonable to neglect them and focus instead on the biggest factor.
