New research is claiming that concentrations of carbon dioxide (the main greenhouse gas, CO2) will remain high for at least 1,000 years, even if greenhouse gases are eliminated in the next few decades.
The climate scientists who produced this work assert that the effects of global warming, such as high sea levels and reduced rainfall in certain areas, will also persist over this time scale. (The findings are in a paper published in February in the Proceedings of the National Academy of Sciences by researchers from the USA, Switzerland and France, www.pnas.org/cgi/doi/10.1073/pnas.0812721106 )
Most previous estimates of the longevity of global warming effects, after greenhouse gases were removed, have ranged from a few decades to a century, so this new analysis could represent a development with very serious implications, including political ones. For example, those campaigning for action on climate change could be disheartened and climate sceptics could opportunistically say that nothing should be done because it is now too late.
The authors of the paper make various estimates of CO2 concentrations based on the year emissions are cut, assumed to be from 2015 to 2050. They make optimistic assumptions, for instance, that emissions are cut at a stroke rather than gradually, and that their annual rate of growth before cut-off is 2%, not the 3% plus witnessed from 2000-05. They then estimate what the effects would be on surface warming, sea level rise and rainfall over a 1,000-year period using the latest climate models. The results of the melting of the polar ice caps are not included in the calculations of sea levels, only the expansion of the water in the oceans caused by the surface temperature increase so, as the authors point out, the actual new sea level will be much higher.
The best-case results for surface warming, where action is taken in 2015 to eliminate emissions, show that over 1,000 years the temperature rises from 1.3 to 1.0 degree centigrade above pre-industrial levels. The worst case, where action is delayed to 2050, predicts surface temperatures will increase from just under to just over four degrees by 2320 and then remain approximately constant for the rest of the millennium. High levels of CO2 persist in the atmosphere because, over long timescales, reduction of the gas is dependent on the ability of the oceans to absorb it, but there are limits to this due to the physics and chemistry of deep-ocean mixing. On the other hand, the amount of heat in the atmosphere that can be absorbed by the sea, the key way surface temperatures are decreased, is limited by the same scientific laws. As a result, carbon concentrations cannot fall enough to force temperatures down while there is simultaneously reduced cooling due to limited heat loss to the oceans.
The data for sea level rises are even more disturbing, with the best case showing a small rise over the millennium of 350cms compared to pre-industrial levels and then stabilising. The worst case has sea levels elevated by nearly 2m in the year 3000 and still rising. There is a theoretical possibility that the melting of polar ice could add several metres more, but the very long-term effects of increased CO2 concentrations on melting rates are not well enough understood to make firm predictions in the authors’ opinions.
The research also estimates precipitation (rainfall) changes over the next millennium. As the authors acknowledge, on a small scale and for many regions of the world, it is still not possible to make predictions in this area. Nonetheless, the fundamental physics is well understood that increased temperatures cause increased atmospheric water vapour concentrations and, due to advances in modelling, some long-term trends can be identified. These show a pattern of drying over much of the already-dry subtropics in the latitudes 15 degrees to 40 degrees in both hemispheres. Seven regions are identified as at risk: southeast Asia, eastern South America, southern Africa, the south-western USA, western Australia, northern Africa and southern Europe. The reductions in predicted dry-season precipitation range from 3-6% in the best case, to 15-35% in the worst case. Within these ranges, the worst hit regions are expected to be northern Africa and southern Europe. Impacts of these falls in rainfall would be on wheat and maize production, particularly in Africa, human water supplies, increased fire frequency, eco-system change and desertification.
So, what are the implications of these results? Clearly, predicting so far into the future must be subject to uncertainty given existing climate models, although their accuracy is rapidly improving. But the assumptions made here are conservative and the science the models are based on is well established, so the results must be taken seriously. Seeing this data, climate sceptics may now say it is pointless doing anything to mitigate global warming effects since they are irreversible and will be for 1,000 years at least. However, the analysis shows that the severity of threat will vary enormously depending on when decisive action is taken. So, if emissions are eliminated in 2015, the effects, even if they last for 1,000 years, could be manageable, since temperature rises will peak at less than the widely accepted tipping point of two degrees. But if nothing is done before 2050, a catastrophe will loom since surface temperature is predicted to rise by over four degrees, a level that some have identified as threatening life itself.
Incidentally, this research refutes the market-environmentalist theory that it will be possible to take action to tackle warming only at some unspecified point in the future – when society will be richer and have greater resources to throw at the problem – the so-called ‘environmental Kuznetz theory’, named after the well-known market economist. Leaving aside the highly dubious assumption that society will inevitably be richer in the future on a capitalist basis, clearly if action is delayed for another 40 years a disaster is highly likely.
Extrapolating from the reported data, if emissions had been cut 20 years ago when the danger of global warming was first identified, temperatures would have risen only by about one half of a degree, which would have had relatively easily manageable consequences. Since failure to do this has been due primarily to the refusal of the imperialist powers to come to any meaningful agreement, motivated by a need to protect their own multinationals’ profits, responsibility for the irreversible degradation of the physical environment is laid squarely at the door of the market system.
If the worst effects of global warming are to be avoided emissions must be eliminated by 2015 according to the scientists who wrote this article. But what are the chances of this happening? There is absolutely no indication that agreement is going to be reached to significantly cut greenhouse gases by 2015, never mind eliminating them completely. Indeed, all the signs are that the economic crisis is pushing the important protagonists in the USA, Europe and East Asia further apart. If nothing meaningful is done over the next decades and a climate disaster results then, as has been discussed before in this column, the capitalists may be tempted to resort to ‘emergency’ measures that promise a quick fix to the problem. Such action, like seeding the atmosphere to simulate the cooling effects that follow a major volcanic eruption, could lead to a disaster as bad as global warming, possibly triggering the start of a new ice-age or drought on a vast scale. However, if the current diseased system remains in place, where maximising profits is imperative, then the chance of such desperate measures being seriously contemplated will remain.
This nightmare scenario is not inevitable, but to avoid it will require removing the fundamental cause of the problem – the capitalist market system. The longer the labour movement takes to address this task the worse the prospects will be for the environment.
By Pete Dickenson