There are some who remain skeptical about global warming. As I reported in a recent posting, "The Great Global warming Swindle", which was the title and subject of a documentary run on the British television station Channel 4, there are those who are of the opinion that climate change is not "all our fault", and that the warming of the globe is driven by other forces than the greenhouse effect, enhanced by rising levels of CO2 in the atmosphere. One theory is that the power output of the Sun varies over time, and has been offered in some quarters as an explanation for the geologic record, that temperatures and CO2 concentrations rise in spikes during the interglacial periods, with a time interval of around 100,000 years, before the Earth runs-into the next ice-age. It seems clear enough that the current "concentration" of 390 parts per million (which should strictly be defined as a mixing ratio rather than a concentration) is unprecedented, certainly for some millions of years, although there is credible debate about the Medieval Warm Period, and why that should have happened during a time when there was comparatively little CO2 being pumped into the air by humans and their activities.
The Channel 4 documentary has come under severe attack - not surprisingly, given that its message is practically heresy! - but it now transpires, and the makers of the programme have acknowledged, that some of the graphs shown were out of date, and that there had been an element of selectivity in what data were shown. Nonetheless, it is not absolutely certain that the sole underlying cause of global warming is human-induced (anthropogenic) greenhouse gas (mainly CO2) emissions, and there is clearly an underlying cycle of warming and cooling, which our actions may exacerbate.
My own fear is that the full influence of the rising CO2, which is exceeding the capacity of the planet to absorb it by about 2 - 3 ppm per year, is yet to kick-in, and the Earth might in subsequent decades become very hot indeed, resulting either in a runaway greenhouse effect, or by melting the arctic ice and diluting the dense, saline waters from the tropics switch-off the Atlantic conveyor (which includes the Gulf Stream), resulting in a North European ice-age. If the geologic record holds true in the future, we must be due another ice-age at some relatively near point, as the "width" of the present warm interglacial period is about as wide as interglacial periods have been in the past, before the climate plunges into the next 100,000 year cold-snap! My own feeling is that running out of oil and gas will hit us before global warming does, and then our CO2 emissions will inevitably be cut, once we have far less of these carbon fuels available to burn. While that might sound good to some ears, it also raises the disquieting possibility that civilization will collapse, once there is insufficient energy to maintain its integrity.
Interestingly, another piece of evidence has been gleaned which will rally the anti-global warming camp. I should really call them the "it's all our fault" skeptics. This is the news that the planet Mars is warming-up too! The evidence is from research done by planetary scientists in the US, who believe that the Red Planet has warmed by around 0.65 degrees C during the past three decades (1970's to the 1990's), and is in similar amount to the Earth's temperature rise of 0.6 degrees C during this same period. In a recent paper published in Nature, describing the research, it is suggested that the warming of the Earth could be down to natural climate variability. This view has been opposed however by Neville Nicholls, a climate scientist at Monash University in Melbourne, who said: "The paper is interesting, but it hasn't got anything to do with the question of human impact on global warming on Earth. It is not an excuse to argue that humans are not causing global warming on Earth."
The research itself was carried out by a group led by Lori Fenton of the NASA Ames Research Centre in California. They used a computer model, similar to those devised to simulate global warming on Earth, into which were added particular Martian features such as a cold "airless" (significant - no atmosphere!) surface and a southward-moving polar ice-cap, but with the contribution from the Earth's atmosphere and its oceans removed. The study also "found" (it is a simulation) that annual variation in the amount of the Sun's radiation reflected from the Martian surface contributed to the temperature rise of the planet by increasing the amount of dust blowing in the atmosphere. Apparently, over the past 30 years the dust scourged large areas of the planet's surface making it less reflective (lower albedo) , and hence more warming occurred. The outcome of this was a positive feedback loop between dust, wind, albedo and temperature. At the University of New South Wales, climate scientist Andy Pitman commented, "It's a nice piece of work, but there are no implications for Earth."
The paper in Nature is published on the eve of the second report from the fourth IPCC review, due to be released tonight. It is also noted that computer models include the effects of changes in albedo, but might there be another explanation - for example, a change in the output of the Sun, which is not included in the models? In general, computer simulations, if they do not include a particular dominant parameter in the model, will "absorb" an effect (like rising temperature) into other parameters that are included. If there is a variation in solar output, that might result in false weightings of the importance of other effects, like wind and dust? The comparable warming of Earth and Mars may be a complete coincidence, especially given the completely different characters of their atmospheres; however, the possibility that it is not is fascinating and may point to an external cause - like the Sun.