There appears to be little chance of avoiding dangerous levels of climate change. Humanity had better get used to the idea of adapting to a world in which greenhouse gas levels stabilise at 650 parts per million of carbon dioxide equivalent (CO2 e) or more around the end of this century. That implies temperatures rising on average by at least 4°C.
This is the bleak conclusion of a paper by Manchester University-based Kevin Anderson and Alice Bows of the Tyndall Centre for Climate Change Research, published in September by the Royal Society.1 The UN’s Framework Convention on Climate Change calls for controls on the rising levels of greenhouse gases in the atmosphere to an extent that avoids dangerous climate change. Politicians and environmental groups have talked about limiting the average rise in global temperatures to 2°C and stabilising the concentration at 450 or 550ppm CO2 e. It presently stands at 435ppm.
The Tyndall Centre paper uses current global emissions data, up-to-date emission trends and the latest scientific understanding of the link between continuing emissions of greenhouse gases and their eventual concentration in the atmosphere. It also takes a realistic view of how much, and how quickly, nations might be able to cut emissions. The findings pour a large bucket of cold water on the idea that very significant man-made climate change can still be forestalled.
"The rhetoric of 2°C is subverting a meaningful, open and empirically informed dialogue on climate change," say the authors. "While it may be argued that 2°C provides a reasonable guide to the appropriate scale of mitigation, it is a dangerously misleading basis for informing the adaptation agenda.
"In the absence of an almost immediate step change in mitigation (away from the current trend of 3% [global] annual emission growth) adaptation would be better guided by stabilisation at 650ppm," they conclude. "Even this assumes rapid success in curtailing deforestation, an early reversal of current trend in non-CO2 greenhouse gas emissions and urgent decarbonisation of the global energy system."
If total greenhouse gas emissions from developing nations continue rising for the next two decades or more, then stabilisation at 650ppm "demands the majority of OECD (developed) nations begin to make draconian emission reductions within a decade."
They estimate developed nations would have to cut their carbon dioxide emissions by at least 6% a year for decades - much more than the cuts envisaged under the UK’s relatively ambitious Climate Change Bill. "It is difficult to envisage anything other than a planned economic recession being compatible with stabilisation at or below 650ppm."
The authors’ conclusions are based on a variety of global scenarios for cutting emissions, under which total emissions peak no later than 2025. The scenarios cover the six most important man-made greenhouse gases, including CO2 and include emissions from deforestation. They exclude any warming or cooling effect from aerosols.
Their paper was published with a collection of papers in the Royal Society’s Philosophical Transactions on the subject of geo-engineering - deliberately altering the earth’s climate to offset the effects of inadvertent man-made climate change.