‘Four degrees and beyond’ - A Look At Significant Climate Change
In September of 2009, in the UK, a scientific meeting was held to discuss the effects of a 4C rise in global mean surface temperatures, and the participants in that conference have now published their results in the latest edition of the Royal Society’s journal Philosophical Transactions A.
Also starting today is the 16th meeting of the parties to the UNFCCC, and the release of these papers are of course to try and influence the parties to that convention. The authors of the papers in Phil. Trans. A make it clear that a 4C rise would be “transformational” for many societies around the globe.
Several of the papers in this issue of Phil. Trans. A are open to public access, including:
Four degrees and beyond: the potential for a global temperature increase of four degrees and its implications (Mark New, Diana Liverman, Heike Schroder and Kevin Anderson)
At the same time that science was suggesting that 2°C might not be as safe a guardrail as previously thought, there was growing evidence suggesting that dramatic emission cuts were required to have any reasonable chance of staying below the 2°C target. For example, Rogelj et al. argued that having a 50:50 chance of constraining warming to 2°C would require developed countries to cut emissions by up to 80 per cent below 1990 levels by 2050, but that even the best case commitments prior to Copenhagen only resulted in a 4 per cent cut by 2020 and a 63 per cent cut by 2050. They concluded that there was ‘virtually no chance of limiting warming to 2°C above preindustrial temperatures’.
The challenges involved in keeping below 2°C have if anything increased since the 2009 Copenhagen meeting. […] At the UNFCCC negotiations in Bonn in June 2010, the first formal negotiations after Copenhagen, expectations were expressed that a legally binding agreement would not be reached before 2012 at COP17 in South Africa. Yvo de Boer, in his final remarks as head of the UNFCCC before stepping down, said that it could take up to 10 years for negotiations to deliver a robust and effective agreement .
It’s pretty clear that in the opinion of these climatologists that the likelihood of staying under a 2C change is remote. They continue:
In this issue, Bowerman et al. build on earlier work to illustrate clearly the importance of cumulative carbon emissions budgets as a determinant of peak global temperature. They show that a total of 1 trillion tonnes of carbon (TtC) from 1750 to 2500 will produce a ‘most likely’ peak warming of 2°C. Importantly, the uncertainties in carbon cycling and climate system response to atmospheric CO2 mean that there is considerable likelihood of exceeding the most likely figure of 2°C. Bowerman et al. also demonstrate that the relationship between cumulative emissions and peak temperature is largely insensitive to the emissions pathway; therefore, a continued steep rise of emissions after 2010, with a high peak and steep post-peak decline, can produce the same peak temperature as a flatter emissions profile, provided they both keep to a 1 TtC cumulative total. Bowerman et al. extend their earlier work by showing the likelihood range for peak temperatures under cumulative carbon budgets arising from less aggressive emissions reduction policies: 2 and 3 TtC result in most likely peak temperatures of 3°C and 4°C over preindustrial.
Unpacking the above: the end results (that is, the peak in global mean surface temperature) does not depend upon how fast we use fossil fuels to spew out CO2 into the atmosphere; what matters is how much total we output. The rate of warming is affected by the emissions rate.
The question is not whether we will end up putting 1 teratonne (Tt) of Carbon (C) into the atmosphere, but if it will be 2 or 3 TtC.
This paper does not address the policy and economic issues of whether 2 or 3 TtC will actually come about. Besides the obvious (but remote) possibility of CO2 mitigation policies coming into being, there are questions about the actual economically feasible reserves of fossil fuels. However, from a purely physical view, there does exist several TtC in various geological deposits around the world.
Some of the other papers in this issue:
In Beyond ‘dangerous’ climate change: emission scenarios for a new world the authors write:
From a mitigation perspective, the gap between the scientific and policy understanding of the challenge needs urgently to be addressed. What is perhaps less evident is the implication of this gap for adaptation. As it stands and in keeping with the dominant policy discourse, the framing of much of the detailed research and practice around adaptation, if guided quantitatively at all, is informed primarily by the 2°C characterization of dangerous climate change. Yet, as the impacts of rising temperatures are unlikely to be linear and also given rising temperatures are increasingly likely to be accompanied by additional feedbacks and hence further temperature rises, adaptation must consider more extreme climate change futures than those associated with 2°C.
There really is a significant chasm between what we have in our public policy and what the scientific community has discovered. I wonder if that chasm will ever be overcome. This paper has further analyses of emission scenarios that would be necessary to reach a 2C change limit, and the results show that peak emissions would have to be now, and as that is very unlikely….
Anyway, to try and answer the question When could global warming reach 4°C? Richard Betts et. al. tackles the problem of the varying outputs from the global coupled climate models used to simulate Earth’s climate system, and concludes:
This paper presents simulations of climate change with an ensemble of GCMs driven by the A1FI [fossil intensive] scenario, and also assesses the implications of carbon-cycle feedbacks for the climate-change projections. Using these GCM projections along with simple climate-model projections, including uncertainties in carbon-cycle feedbacks, and also comparing against other model projections from the IPCC, our best estimate is that the A1FI emissions scenario would lead to a warming of 4°C relative to pre-industrial during the 2070s. If carbon-cycle feedbacks are stronger, which appears less likely but still credible, then 4°C warming could be reached by the early 2060s in projections that are consistent with the IPCC’s ‘likely range’.
These are the worst case scenarios. Will they come about? My question is still - will it be economically feasible to burn all that carbon in the ground? Betts et. al. don’t address that question. While there are substantial carbon-laden sediments around the world, examples such as the Green River Basin kerogen shale (wrongly called “oil” shale by certain politicians) have shown that large carbon deposits do not translate into viable energy resources.
Among the several papers in this issue is Rethinking adaptation for a 4°C world by Mark Stafford Smith et. al. Adaptation is going to be increasingly the only option as mitigation falls by the wayside. Smith includes this chart (adapted from earlier work) to attempt to put into perspective, by placing on a timeline, various activities which societies undertake. Much of the infrastructure of our society, especially the location of our towns (suburbs), landscapes, bridges, etc. are on a scale that will see significant changes. Adaptation will be challenging.
I posted this today in the hope that even as we see the diplomats wrangle down in Cancun over the minutiae of convention protocol the big picture can be kept in mind.
We are changing the world around us, and doing it quickly.
We will have to live with the changes.