Session: Benchmarking & cross-cutting Group 1 (Isotope modelling, COMPARE)
Author: Julia Hargreaves / email@example.com / Blue Skies Research
Co-author: James Annan, Blue Skies Research;
We have investigated relationships in the PMIP ensembles between the tropical temperature changes for paleoclimate intervals and climate sensitivity for the models. The goal is to use paleoclimate observations to constrain the ensemble and thus narrow our uncertainty on our estimate of climate sensitivity.
For the PMIP2 ensemble we found a correlation between tropical temperature at the Last Glacial Maximum (LGM) and climate sensitivity which is statistically significant and physically plausible (Hargreaves et al,2012). For PMIP3, however, no significant correlation is found, possibly due to the new processes in the models introducing different behaviours in different models at the LGM (Hopcroft and Valdes, 2015). For PMIP3 we additionally have an ensemble of mid-Pliocene runs (PlioMIP). We observe a correlation in the ensemble between their tropical temperature anomalies at the mid-Pliocene and their equilibrium sensitivities. If the real world fits this relationship, then the reconstructed tropical temperature anomaly at the mPWP can in principle generate a constraint on the true sensitivity. Directly applying this methodology using available data yields a range for the equilibrium sensitivity of 1.9–3.7C, but there are considerable additional uncertainties surrounding the analysis which are not included in this estimate (Hargreaves and Annan, 2016).
In terms of this type of analyses, there is much to look forward to in the forthcoming PMIP4 runs: full complexity models will be integrated for the Pliocene experiment, which has been modified to more clearly represent a specific climate time slice, and there is the potential for combining estimates from both LGM and the Pliocene as the same models will (hopefully!) be used for both intervals.
Hargreaves, J. C., Annan, J. D., Yoshimori, M., & Abe-Ouchi, A. (2012). Can the Last Glacial Maximum constrain climate sensitivity? Geophysical Research Letters, 39(24), L24702. http://doi.org/10.1029/2012GL053872
Hopcroft, P. O., & Valdes, P. J. (2015). How well do simulated last glacial maximum tropical temperatures constrain equilibrium climate sensitivity? Geophysical Research Letters, 42(13), 5533–5539. http://doi.org/10.1002/2015GL064903
Hargreaves, J. C., & Annan, J. D. (2016). Could the Pliocene constrain the equilibrium climate sensitivity? Climate of the Past, 12(8), 1591–1599. http://doi.org/10.5194/cp-12-1591-2016