The Paris Agreement prompted a range of studies that compared the difference to our climate if the global warming target was limited to 1.5°C and 2°C levels above pre-industrial conditions.
However, it can be difficult and time consuming to quantify such a small difference in global average temperatures with global climate model simulations.
For this reason, many researchers have taken a pattern-scaling approach to determine the different impacts at these temperatures, scaling up the impacts at 1.5°C in a linear manner to determine impacts at 2°C.
To determine if this approach is valid, particularly at regional levels, CLEX researchers first produced climate model outputs for 1.5°C and 2°C. They then used a pattern scaling method to take the outputs from the 1.5°C climate model projections to estimate conditions at 2°C.
Climate model projections at 2°C were then compared to pattern scale projections at the same temperature to determine if there was any difference.
While there was variation between the models used, the ensemble mean produced a result very similar to that found in the pattern scaling approach, suggesting a linear relationship was generally consistent.
However, in some regions this relationship did not hold true, such as the North Pacific, northwest Atlantic, northwest Africa and China.
Using East Asia as a case study, the warming simulated by climate models was greater than found with pattern scaling. Analysis of this result suggested reduced aerosol emissions over this region were the prime cause for this difference.
The findings suggest that the differences in results between pattern-scaling and climate model output were primarily due to forcings other than changes to greenhouse gas emissions. So, while pattern-scaling was generally consistent with climate model outputs for 2°C at a regional level, it was a poor predictor of change in regions where forcings beyond greenhouse gas emissions played a role.
- Paper: King, A.D., R. Knutti, P. Uhe, D.M. Mitchell, S.C. Lewis, J.M. Arblaster, and N. Freychet, 0: On the linearity of local and regional temperature changes from 1.5°C to 2°C of global warming. Climate, 0, https://doi.org/10.1175/JCLI-D-17-0649.1