Greenhouse Gas Emissions Targets to Avoid Dangerous Climate Change
Kirsten Zickfeld
School of Earth and Ocean Sciences, University of Victoria
The ultimate goal of climate policies is to reduce the amount of anthropogenic greenhouse gas emissions in order to achieve ?stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system? (United Nations Framework Convention on Climate Change, Article 2). Before being able to specify a stabilization target, scientists and policymakers are thus confronted with the challenging task of defining ?what is dangerous?. Here we derive allowable greenhouse gas emissions compatible with different interpretations of ?dangerous? climate change, e.g. the 2 ?C global mean temperature threshold suggested by the European Union. We use a state-of-the-art climate-carbon cycle model to estimate the probability that any given level of greenhouse gas emissions will exceed specified long-term global mean temperature targets for ?dangerous anthropogenic interference?, taking into consideration uncertainties in climate sensitivity and the carbon cycle response to climate change. Results obtained within this framework can serve as a basis for selecting a greenhouse gas emissions level given a threshold for ?dangerous? climate change and an overshoot probability society is willing to accept. For instance, we show that in order to stabilize global mean temperature increase at 2 ?C above pre-industrial levels with a probability of at least 0.66, cumulative equivalent CO2 emissions from 2000 to 2500 must not exceed a median estimate of 636~PgC (range: 280-930 PgC), independently of the path taken to stabilization.