People with interest in radiative forcing, aerosols, climate and geoengineering may be interested in the following paper:
"An explanation for the difference between twentieth and twenty-first century land–sea warming ratio in climate models" Joshi, Lambert and Webb (2013) http://link.springer.com/content/pdf/10.1007%2Fs00382-013-1664-5.pdf "A land–sea surface warming ratio (or u) that exceeds unity is a robust feature of both observed and modelled climate change. Interestingly, though climate models have differing values for u, it remains almost time-invariant for a wide range of twenty-first century climate transient warming scenarios, while varying in simulations of the twentieth century. Here, we present an explanation for time-invariant land–sea warming ratio that applies if three conditions on radiative forcing are met: first, spatial variations in the climate forcing must be sufficiently small that the lower free troposphere warms evenly over land and ocean; second, the temperature response must not be large enough to change the global circulation to zeroth order; third, the temperature response must not be large enough to modify the boundary layer amplification mechanisms that contribute to making u exceed unity. Projected temperature changes over this century are too small to breach the latter two conditions. Hence, the mechanism appears to show why both twenty first century and time-invariant CO2 forcing lead to similar values of u in climate models despite the presence of transient ocean heat uptake, whereas twentieth century forcing which has a significant spatially confined anthropogenic tropospheric aerosol component that breaches the first condition—leads to modelled values of u that vary widely amongst models and in time. Our results suggest an explanation for the behaviour of u when climate is forced by other regionally confined forcing scenarios such as geo-engineered changes to oceanic clouds. Our results show how land–sea contrasts in surface and boundary layer characteristics act in tandem to produce the land–sea surface warming contrast. ... The conceptual model shows how the land–sea warming contrast in climate models does not arise directly from continental-scale land–ocean contrasts in surface properties such as evaporative fraction, since such effects are spread between land and ocean, but instead arises indirectly from the effects of these same land–ocean contrasts on moisture supply to the boundary layer. Future work might involve separating these direct and indirect effects in climate models to estimate the model robustness of climate response to each effect." Simon ________________________________________________ Simon Driscoll Atmospheric, Oceanic and Planetary Physics Department of Physics University of Oxford Office: +44 (0) 1865 272930 Mobile: +44 (0) 7935314940 http://www2.physics.ox.ac.uk/contacts/people/driscoll -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to geoengineering+unsubscr...@googlegroups.com. To post to this group, send email to geoengineering@googlegroups.com. Visit this group at http://groups.google.com/group/geoengineering?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
