The Importance of Heterogeneous Human Climate Forcings on Skillful Prediction of Regional Climate
27 Jun, 2007 05:42 pm
The role of heterogeneous human climate forcings as they affect skillful prediction of regional climate variability and change was inadequately reported on in the 2007 IPCC WG1 Report. This column briefly discuses why these forcings are so important in altering tropospheric weather patterns.
He wrote with respect to climate science that, “….. the science is not done because we do not have reliable or regional predictions of climate. But we need them. Indeed it is an imperative! So the science is just beginning.”
He is absolutely correct on this issue.
As concluded in the 2005 National Research Council report
National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties. Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., 208 pp.
“regional variations in radiative forcing may have important regional and global climate implications that are not resolved by the concept of global mean radiative forcing.”
“Regional diabatic heating can cause atmospheric teleconnections that influence regional climate thousands of kilometers away from the point of forcing.”
This regional diabatic heating produces temperature increases or decreases in the layer-averaged regional troposphere. This necessarily alters the regional pressure fields and thus the wind pattern. This pressure and wind pattern then affects the pressure and wind patterns at large distances from the region of the forcing which we refer to as teleconnections.
The regional diabatic forcing can be caused by land-use/land-cover change (e.g.
Pielke Sr., R.A., G. Marland, R.A. Betts, T.N. Chase, J.L. Eastman, J.O. Niles, D. Niyogi, and S. Running, 2002: The influence of land-use change and landscape dynamics on the climate system- relevance to climate change policy beyond the radiative effect of greenhouse gases. Phil. Trans. A. Special Theme Issue, 360, 1705-1719
or by aerosol emission (e.g.
Matsui, T., and R.A. Pielke Sr., 2006: Measurement-based estimation of the spatial gradient of aerosol radiative forcing. Geophys. Res. Letts., 33, L11813, doi:10.1029/2006GL025974)
Even natural surface variations such as in ocean color produce such teleconnections in a general circulation model; e.g.
Shell, K. M., R. Frouin, S. Nakamoto, and R. C. J. Somerville, Atmospheric response to solar radiation absorbed by phytoplankton, J. Geophys. Res., 108(D15), 4445, doi:10.1029/2003JD003440, 2003.
There is debate, however, regarding whether the magnitude of the regional diabatic forcing is large enough to result in long distance teleconnections. However, observed multi-decadal trends in tropospheric-averaged temperatures are large enough to result in large-scale circulation trends (see, for example,
Chase, T.N., R.A. Pielke Sr., J.A. Knaff, T.G.F. Kittel, and J.L. Eastman, 2000: A comparison of regional trends in 1979-1997 depth-averaged tropospheric temperatures. Int. J. Climatology, 20, 503-518.).
Thus land-use/land-cover changes and aerosol clouds that produce regional tropospheric temperature anomalies of a similar magnitude (or larger magnitude) would be expected to have significant teleconnection effects. These heterogeneous climate forcings can result in major alterations in regional weather both in the region where the climate forcing is occuring as well as at long distances through teleconnection, even in the absence of any long term trend in global warming or cooling!
Regional tropopsheric diabatic heating due to human activities represents major, but under-recognized climate forcings on long-term global weather patterns. Indeed, this heterogeneous climate forcing may be more important on the weather that we experience than changes in weather patterns associated with the more homogeneous spatial radiative forcing of the well-mixed greenhouse gases (see this NASA press release).
The 2007 IPCC WG1 Report did not properly communicate the important role of these regional climate forcings, nor the lack of reigonal predictive skill to the public and to policymakers.