Improved Method Developed to Assess Non-Local Climate Feedback

Summary

One critical issue in climate dynamics is the feedback response of the atmosphere to its lower boundary forcing, e.g. changes in sea surface temperature (SST). This feedback response is usually difficult to quantify because of the overwhelming internal atmospheric variability that occurs independent of the lower boundary forcing. In the real world, climate feedback can be assessed only statistically using observational data. In contrast, climate feedbacks can be assessed dynamically using a climate model with ensemble experiments that are explicitly designed to suppress internal atmospheric variability.

In a study jointly sponsored by DOE, NSF and NOAA, published in the February issue of Journal of Climate, authors Liu et. al, describe a method that assesses the climate feedbacks and apply the technique to assess the feedback response of SST on surface heat flux in a simple ocean–atmosphere model that includes the exchange of heat between the atmosphere and ocean. Feedbacks could be local and non-local, e.g. those due to climate anomalies that are related to each other at large distances, typically thousands of kilometers. Results show that the model simulations capture the major features of non-local climate feedback as long as the spatial resolution of the model is not very large. The sampling error (the error caused by observing a sample instead of the whole population) is also found to increase significantly with the spatial scale of the atmospheric forcing and, in turn, the SST variability. These deficiencies call for further improvements in methods used to assess non-local climate feedbacks.

References

Zhengyu Liu, N. Wen and Y. Liu, 2008: On the Assessment of Nonlocal Climate Feedback. Part I: The Generalized Equilibrium Feedback Assessment. J. Climate, 21, 134-148.