A lower limit for future climate emissions

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A new study finds that the greenhouse gas emissions that the world can emit in order to limit climate change to less than 2°C are severely limited, lending further urgency to the need to address climate change. Researchers from, among others, PBL Netherlands Environmental Assessment Agency and IIASA see a limit to future greenhouse gas emissions - or carbon budget - of 590-1240 billion tons of CO2 from 2015 onwards, as the most appropriate estimate for keeping warming to well below 2°C, a temperature target which aims to avoid the most dangerous impacts of climate change. These numbers are very low compared to today’s annual emissions of 40 billion ton of CO2. The study is published in the journal Nature Climate Change.

Carbon budget

Estimates for a carbon budget consistent with the 2°C target vary widely. A comprehensive analysis of these differences shows that they stem from differences in scenarios and methods, as well as whether or not other human activities that can affect the climate are included, for example the release of other greenhouse gases like methane. This new understanding of the cause of the variations in previous estimates makes it possible to support the policy-making processes better.

Lowering CO2 emissions

The researchers show that a carbon budget of 590-1240 billion tons of CO2from 2015 onwards would limit the increase of global mean temperature to less than 2oC. This budget takes into account all human activities and greenhouse gases and is based on detailed scenarios that simulate low-carbon futures. The range is caused by uncertainty in future non-CO2 emissions and the scientific methods that have been applied to estimate these budgets. However, even the high-end of the range would only allow 30 years of current emissions of 40  billion tons of CO2 before the budget is spent and a sudden transition to zero emissions is necessary.

2°C target

The 2°C target - limiting future average temperature rise well below 2°C over pre-industrial averages - was adopted as a goal by 196 countries at the 2015 climate conference in Paris as a safe limit to prevent dangerous impacts of climate change. Countries also decided in Paris to pursue efforts to further limit warming below 1.5°C; for this target the carbon budget is even lower.

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