June, 2016
The climate community does not organize its research nor its modeling activities toward specific temperature targets. We evaluate atmospheric CO2 concentrations that, when incorporated into models with various climate sensitivities, lead to probabilities of global average surface temperatures of a given range at future time periods as one outcome.
We organize and coordinate our work using Representative Concentration Pathways (RCPs, as for CMIP5) or Shared Socioeconomic Pathways (SSPs, new for CMIP6). At the same time we empathize with nations and regions whose aspirations led to the 'well below 2°C and if possible below 1.5C' language of the CoP21 agreement. A letter from Christiana Figueres, outgoing Executive Secretary of UNFCCC, to WCRP attests to the political interest in 2°C and 1.5°C goals. Meanwhile, the climate system of our planet pays no attention to agreements or aspirations and, as clearly evident in various spirals and time series (e.g. the one on the right from NOAA), surges toward warmer and warmer temperatures. Whatever the reality or unreality of staying within a 1.5°C global target, we have an opportunity with the upcoming IPCC Special Report on 1.5°C to delineate serious and very aggressive mitigation steps.
David Carlson, WCRP Director