There is a new paper out (Transient Climate Simulations with the HadGEM1 Climate Model: Causes of Past Warming and Future Climate Change) in J Climate on climate change – past century and next – as simulated by HadGEM1. This reaches the standard conclusions: whereas the effects of a combination of anthropogenic and natural forcings on the climate system could explain the evolution of global mean temperatures over the twentieth century, natural factors failed to explain the warming observed over the second half of the century.
However, they also appear to have taken seriously some other proposed mechanisms, because they also say the new model can demonstrate that black carbon and land use changes are relatively unimportant for explaining global mean near-surface temperature changes. Land use changes are RP Sr’s thing; black carbon I’ve seen pushed elsewhere, but I forget by whom. Which brings up Many open questions remain, for example, the role of forcings not yet fully included in CGCM simulations, such as land use change or forcing by black carbon and nonsulfate aerosols, which is from Detecting and Attributing External Influences on the Climate System: A Review of Recent Advances by THE INTERNATIONAL AD HOC DETECTION AND ATTRIBUTION GROUP. So thats one solved, then :-)
The 40-70’s “cooling” (fig 4) works moderately well in the natural-forcings version (though not as well as in the anthro-forced) so presumably there is a natural component to this, as well as the more familiar sulphate aerosol (which they can’t spell :-(). And it still doesn’t seem to be clear if the early 20th warming is natural or anthro or some (what?) mixture.