- The climate sensitivity uncertainty of global climate models (GCMs) is partly due to the spread of individual
feedbacks. One approach to constrain long-term climate sensitivity is to use the relatively short
observational record, assuming there exists some relationship in feedbacks between short and long records.
The present work tests this assumption by regressing short-term feedback metrics, characterized by the 20-yr
feedback as well as interannual and intra-annual metrics, against long-term longwave water vapor, longwave
atmospheric temperature, and shortwave surface albedo feedbacks calculated from 13 twentieth-century
GCM simulations. Estimates of long-term feedbacks derived from reanalysis observations and statistically
significant regressions are consistent with but no more constrained than earlier estimates.
For the interannual metric, natural variability contributes to the feedback uncertainty, reducing the ability
to estimate the interannual behavior from one 20-yr time slice. For both the interannual and intra-annual
metrics, uncertainty in the intermodel relationships between 20-yr metrics and 100-yr feedbacks also contributes
to the feedback uncertainty. Because of differences in time scales of feedback processes, relationships
between the 20-yr interannual metric and 100-yr water vapor and atmospheric temperature feedbacks are
significant for only one feedback calculation method. The intra-annual and surface albedo relationships show
more complex behavior, though positive correspondence between Northern Hemisphere surface albedo
intra-annual metrics and 100-yr feedbacks is consistent with previous studies. Many relationships between
20-yr metrics and 100-yr feedbacks are sensitive to the specific GCMs included, highlighting that care should
be taken when inferring long-term feedbacks from short-term observations.
- Dalton, Meghan M., Karen M. Shell, 2013: Comparison of Short-Term and Long-Term Radiative Feedbacks and Variability in Twentieth-Century Global Climate Model Simulations. Journal of Climate, 26, 10051–10070. doi:10.1175/JCLI-D-12-00564.1
|Funding Statement (additional comments about funding)
- This work was supported by National Science Foundation Grant ATM-0904092.