On the rise

Carbon dioxide will continue to rise even if current national and international targets for reducing emissions are met, scientists warn.


Carbon dioxide, the greenhouse gas that has had the largest impact on our climate, will continue to rise even if current national and international targets for reducing emissions are met, scientists warn.


But, they say, strong action taken now, such as the 80 per cent target recently announced by the UK government, will continue to have benefits a long time into the future.


The scientists reached their conclusions after combining the outcomes of proposals by the G8 countries and the UK government’s Stern Review with the latest knowledge of climate change feedbacks relating to the carbon cycle.


Their findings show that short term cuts alone will not solve the problem and that policy makers need to plan for hundreds of years into the future.


Working alongside colleagues from the NERC Centre for Ecology and Hydrology, the Met Office Hadley Centre and Exeter University, Jo House, from the Natural Environment Research Council’s QUEST programme at Bristol University, ran computer models to see what would happen under the G8 plans to cut global emissions by 50 per cent by 2050.


The models show that under this scenario, unless emission cuts continue beyond 2050, atmospheric carbon dioxide concentrations will continue to rise rapidly.


By 2100 the models suggest that carbon dioxide concentrations could be as high as 590 parts per million (ppm), more than double the level of 280ppm that persisted for thousands of years before the industrial revolution, and significantly higher than today’s level of 386ppm.


By 2300 the worst-case scenario shows that carbon dioxide levels could be 980ppm with an accompanying rise in global temperature of 5·7°C.


Using the Stern Review proposal of cutting emissions by 25 per cent by 2050 and continuing to make cuts down to 80 per cent towards the end of the century, the models show a more hopeful future.


In this case the carbon dioxide levels would become almost stable, at levels of between 500 and 600ppm by 2100, although they would creep up further into the future if greater cuts were not made.


In this case the temperature by 2100 increase ranges from 1·4°C to 3·4°C depending on the model used, and by 2300 it is almost stable with an increase of 4·2°C.


The Stern Review concluded that, to avoid the worst impacts of climate change, the concentrations of all greenhouse gases should be limited to what is equivalent to between 450 and 550ppm of carbon dioxide concentration.


House and her colleagues said that making cuts in other greenhouse gases is no good if the longer term problem of atmospheric carbon dioxide is ignored.


She said: ‘To achieve long-term stabilisation of carbon dioxide levels at around 550ppm will require cuts in global emissions of between 81 per cent and 90 per cent by 2300 and even more beyond that time.


‘We applaud the government’s new plans to cut UK emissions by 80 per cent by 2050.


‘This is a realistic assessment of the scale of the problem and the action needed.


‘Our research confirms that bringing other countries on board to meet a global target of 80 per cent reductions towards the end of the century will virtually stabilise carbon dioxide levels, but a much longer-term strategy is still needed to reduce future emissions even further.’


The research was supported by the Natural Environment Research Council through the QUEST Programme and the Centre for Ecology & Hydrology and by the Joint Defra/ MoD Integrated Climate Change Programme.