Here in the UK, Channel 4 just screened an interesting documentary. Good viewing and challenges what seems to have become the accepted view that global warming is caused by man-made CO₂ emissions. Instead, the programme points out that climate change has always been with us (including a medieval warm period, even balmier than today, and a mini ice-age in the seventeenth century when the River Thames froze so solid that fairs were regularly held on the ice). The programme presents some evidence to suggest that the rise in carbon dioxide lags behind temperature rises by 800 years and therefore can't be the cause of it. It also suggests that man-made sources of carbon dioxide are dwarfed by natural sources and that the source of variation in temperature is really linked to variations in sun activity.

The programme suggests that we can hardly be surprised when "environmental journalists" whose continued employment requires publication of stories produce newsworthy doom-laden stories. After all, why would the media publish stories from such journalists the gist of which is there is no need to panic because climate variation is nothing to do with us.

Anyway, if you are able, see the programme again in the UK on More4 (Monday 12 March 2007, 10.00pm): "Polemical film challenging the consensus that man-made CO2 is heating up the earth. Featuring leading academics, the film questions the science behind the accepted reasons for global warming and argues other explanations for climate change are not being properly aired".

The observation that soot makes global warming "worse" is well covered today. The BBC covers this - largely because it appears that soot is more important for global warming than realised earlier. Dr James Hansen and Larissa Nazarenko, (Goddard Institute for Space Studies, NASA, and Columbia University Earth Institute) suggest that trying to reduce the amount of soot produced would be easier than cutting carbon dioxide and other greenhouse gas emissions. Concentrations of soot are often high over China and India, where coal and organic fuels are used domestically, and over Europe and North America, where the main source is diesel oil.1

• 1. Soot climate forcing via snow and ice albedos,
  Hansen, J.
  , Proceedings of the National Academy of Sciences, 01/2004, Volume 101, Issue 2, p.423 - 428, (2004)
  

Abstract: plausible estimates for the effect of soot on snow and ice albedos (1.5% in the Arctic and 3% in Northern Hemisphere land areas) yield a climate forcing of +0.3 W/m² in the Northern Hemisphere. The “efficacy” of this forcing is ∼2, i.e., for a given forcing it is twice as effective as CO₂ in altering global surface air temperature. This indirect soot forcing may have contributed to global warming of the past century, including the trend toward early springs in the Northern Hemisphere, thinning Arctic sea ice, and melting land ice and permafrost. If, as we suggest, melting ice and sea level rise define the level of dangerous anthropogenic interference with the climate system, then reducing soot emissions, thus restoring snow albedos to pristine high values, would have the double benefit of reducing global warming and raising the global temperature level at which dangerous anthropogenic interference occurs. However, soot contributions to climate change do not alter the conclusion that anthropogenic greenhouse gases have been the main cause of recent global warming and will be the predominant climate forcing in the future.

Soot climate forcing via snow and ice albedos, Hansen, J. , Proceedings of the National Academy of Sciences, 01/2004, Volume 101, Issue 2, p.423 - 428, (2004)