The Human Effect On The Climate System Involves A Diverse Set Of Heterogeneous Climate Forcings – A Focus On Carbon Dioxide Is Too Narrow

There continues to be a focus on carbon dioxide as the dominate human climate forcing (e.g. see). This is too narrow an approach to how society should reduce its risk to climate, and will have little actual affect on the weather and climate.

In July 2005, Climate Science published a weblog that highlighted the importance of spatial variations in  climate forcings on the weather and climate that we experience. This perspective emphasized that the correct approach to climate policy is to recognize and respond to the actual diversity of human climate forcings. The scientific literature supports the conclusion given below:

The human influence on climate is significant and involves a diverse range of first-order climate forcings, including, but not limited to the human input of CO2.

These forcings include

• The influence of human-caused aerosols on regional (and global) radiative heating
• The effect of aerosols on clouds and precipitation
• The influence of aerosol deposition (e.g. soot; nitrogen) on climate
• The effect of land cover/ land use on climate
• The biogeochemical effect of added atmospheric CO2

This July 2005 weblog What is the Importance to Climate of Heterogeneous Spatial Trends in Tropospheric Temperatures? is repeated today

“The 2005 National Research Council report concluded that:

“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.”

And furthermore:

“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. , Chase et al. 2000) or by aerosol emissions. Even natural surface variations such as in ocean color produce such teleconnections in a general circulation model (see Atmospheric response to solar radiation absorbed by phytoplankton )

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, A Comparison of Regional Trends in 1979-1997 Depth-Averaged Tropospheric Temperaturesfor the magnitude of the 1979-1997 regional trends). 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.

If this is true, than regional diabatic heating due to human activities represents a major, but under-recognized climate forcing, on long-term global weather patterns. Indeed, this heterogenous 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 the NASA press release, which is based on the multi-authored paper 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).