Emission pathways consistent with a 2 degree Celsius global temperature limit

The identified range of emissions was found to be significantly below the expected range of emissions resulting from current policies. In other words, if policymakers would not implement mechanisms that enable a peak in global emissions within the next decade or so, there are significant risks of the 2 °C target slipping out of reach. 

In the context of the current climate negotiations, it has been recognised that countries should take urgent action to limit the increase in global average temperature to less than two degrees Celsius, relative to pre-industrial levels. A crucial question here is which emission levels could be regarded as consistent with achieving this target. This requires understanding of both the technical and economic implications of reducing emissions and the processes that link emissions to temperature.

The article in Nature Climate Change aims to contribute to this understanding by evaluating a large number of greenhouse gas emission scenarios, developed by individual modeling teams, in terms of their climate consequences. This evaluation has shown that optimal reduction pathways (e.g. assuming a significant contribution by all important greenhouse gas emitters) need emission levels of the order of 80 percent to 100 percent of the 2010 level, in order to achieve at least a 50 percent probability of meeting the two-degree target (for at least a 66 percent probability, these percentages lie at 65 percent to 95 percent of the 2010 level). Although scenarios that assume reduced participation may have result in slightly higher emissions, overall the analysis confirms that if the mechanisms to enable an early peak in global emissions followed by steep reductions are not put in place soon, there is a significant risk of the 2 °C target not being achieved.