CMAR aims to advance Australian climate, marine, and earth systems science.
Dr Raupach responds to the UK television program The Great Global Warming Swindle, airing on ABC television on Thursday 12 July 2007.
The Great Global Warming Swindle has sent a shiver of excitement through those for whom global warming is somewhere between a bad dream and a dangerous plot. Can we breathe a sigh of relief and forget climate change?
To assess this, let's start with what can be called the consensus view.
Through careful evaluation of evidence, most climate scientists have reached three major conclusions:
the concentrations of carbon dioxide (CO2) and other greenhouse gases are increasing rapidly, mainly due to human activities
these increases will lead to global warming, rainfall changes, sea-level rises, and damage to ecosystems and human populations
the risks posed by unchecked climate change are so great that emissions of greenhouse gases - particularly CO2 - have to be at least halved over coming decades.
This is where the going gets tough, because the biggest source of CO2 is the burning of fossil fuels to generate energy. Hence, these scientists are actually asking for a complete rethink on how human societies do everything involving energy - that is, most things.
The Swindle takes an utterly different view. The program accepts that CO2 concentrations are rising because of human activities, but then diverges radically from most climate science by maintaining that CO2 does not cause global warming, present efforts to reduce CO2 emissions are misplaced and even 'anti-human', and scientists advocating emissions reductions are (to paraphrase) fund-grabbing puppets of a neo-Marxist movement intent on overthrowing western capitalism.
The major scientific claims in the Swindle are either wrong or are true statements so out of context as to create falsehoods. Here are the main assertions, contrasted with the facts.
Swindle: Temperature actually fell between 1940 and 1980 but CO2 concentrations rose, so CO2 cannot cause warming.
Truth: Global average temperatures rose by about 0.3 degrees from 1910 to 1940, stayed approximately constant between 1940 and 1970, and have risen by a further 0.5 degrees since 1970. Three factors have combined to produce this pattern: fluctuations in solar radiation, volcanic activity, and greenhouse gases. Since 1970, the role of greenhouse gases has been dominant as their concentrations have risen sharply.
Swindle: The Medieval Warm Period (from 1000 to 1300 AD) was warmer than today.
Truth: Several recently published climate reconstructions show that there was indeed a warm period back then, but also that temperatures now are warmer than the highest during this period by between 0.5 and 1 degree.
Swindle: Climate models predict that warming occurs faster several kilometres aloft than at the surface, but observations show the reverse; hence the models are wrong.
Truth: Published studies have revealed calibration problems in upper-air temperature data from both balloons and satellites. When these were fixed, the data and the models agreed.
Swindle: Ice cores show that over the last 500,000 years, CO2 rises followed temperature rises by a few hundred years. Hence CO2 can't cause temperature increases.
Truth: The observation is correct but the conclusion is wrong. The observation merely shows that CO2 does not cause the first few hundred years of the warming events that terminate ice ages. This initial warming is due to subtle earth-orbital variations which are too weak to break down the major ice ages alone. The necessary extra leverage is supplied by powerful positive feedbacks including rising atmospheric CO2 as oceans warm, darkening surfaces as ice melts, and increasing water vapour in a warmer atmosphere. All these factors work together to produce glacial cycles. Greenhouse gas emissions from human activities now provide a warming trigger different from the one that broke down past ice ages.
Swindle: The current warming is all due to natural variability caused by the sun.
Truth: Solar fluctuations in both gross energy output and cosmic radiation are nowhere near strong enough to cause the rapid warming since 1970, as confirmed by several recent studies including one published just last week.
Swindle: Volcanoes produce more CO2 than human activities; so does the ocean.
Truth: Volcanoes produce only about 1 per cent of current CO2 emissions from fossil fuels. The oceans, together with vegetation on land, certainly release vast amounts of CO2 to the atmosphere, but they also take up vast amounts. The current net effect is actually a removal of CO2 from the atmosphere by oceans and land vegetation, of about half of all fossil-fuel emissions each year.
Swindle: Climate models are useless.
Truth: Climate models are based on known laws of physics, and incorporate the effects of greenhouse gases together with many other processes. They do a good job of reproducing and explaining past climates, so their predictions of climate trends over coming decades are worthy of respect.
Why, then, do a handful of scientists torture the evidence to claim that human activities do not induce climate change?
The answer often quoted, that these scientists are in the pockets of oil companies, is probably inadequate (like the counterclaim that most climate scientists are in the pockets of neo-Marxists).
A more fundamental reason may be philosophical: those who attack the links between CO2 and human-induced climate change believe that the planetary machinery is too vast and intrinsically variable to be thrown off course by mere humankind, and that the earth's environment is in no way threatened by human exploitation.
Sound science now shows that this view is dangerously misplaced.
We have the power to alter the workings of the planet, and are already doing so through climate change. The leap we must make in just a few decades is to accept global stewardship of our shared environment. The position taken in The Swindle is a dangerous dead weight as we endeavour to face this entirely new and critical challenge.
Read more about CSIRO scientists and the climate change debate.
This article was published in The Canberra Times newspaper on 12 July 2007