The view on AGW from the Australian

HAS global warming stopped? The question alone is enough to provoke scorn from the mainstream scientific community and from the Government, which says the earth has never been hotter. But tell that to a new army of sceptics who have mushroomed on internet blog sites and elsewhere in recent months to challenge some of the most basic assumptions and claims of climate change science.

Their claims are provocative and contentious but they are also attracting attention, so much sothat mainstream scientists are being forced torespond.

The bloggers and others make several key claims. They say the way of measuring the world’s temperature is frighteningly imprecise and open to manipulation. They argue that far from becoming hotter, the world’s temperatures have cooled in the past decade, contrary to the overwhelming impression conveyed by scientists and politicians.

As such, they say there should be far greater scepticism towards the apocalyptic predictions about climate change. Even widely accepted claims, such as that made by Climate Change Minister Penny Wong that “the 12 hottest years in history have all been in the last 13 years”, are being openly challenged.

“She is just plain wrong,” says Jennifer Marohasy, a biologist and senior fellow of the Institute of Public Affairs. “It’s not a question of debate. What about the medieval warming period? The historical record shows they were growing wine in England, for goodness sake; come on. It is not disputed by anyone that the Vikings arrived in Greenland in AD900 and it was warmer than Greenland is now. What Penny Wong is doing is being selective and saying that is a long time ago.”

But selective use of facts and data is fast becoming an art form on both sides of the climate change debate now that real money is at stake as the West ponders concrete schemes to reduce carbon emissions. So what is the validity of some of the key claims being made by these new blogger sceptics?

Their first claim is that the most basic aspect of climate change science – the measurement of global warming – is flawed, imprecise and open to manipulation.

The earth’s temperature is measured using land-based weather stations – in effect, a network of thermometers scattered unevenly across the globe – as well as via satellites and ocean-based weather sensors. There are four agencies that measure the world’s temperatures and each has different methodology and produces varying, although not dramatically different, results.

Sceptics accuse climate change believers of always quoting the agency that shows the highest level of warming, the US National Aeronautic and Space Administration’s Goddard Institute for Space Studies run by prominent climate change scientist and activist James Hansen.

An independent study by Yale University in the US shows GISS says the earth has warmed by 0.025C a year during the past eight years while the other best-known measurement agency, London’s Hadley Centre, says it warmed by only 0.014C a year during the same period. Not surprisingly, the Hadley figures are the most quoted by climate change sceptics while the GISS figures are most popular with climate change believers.

David Evans, former consultant to the Australian Greenhouse Office, says Hansen’s GISS is unreliable because it is the only measurement agency that relies almost wholly on land-based data instead of satellites.

“Land-based temperature readings are corrupted by the urban heat island effect,” he says. “Urban areas encroaching on thermometer stations warm the micro-climate around the thermometer due to vegetation changes, concrete, cars and houses.”

As such, he alleges that the GISS figures – which are enormously influential in the climate change debate – are “hopelessly corrupted” and may even be manipulated to suit Hansen’s views on global warming.

A group of weather buffs in the US also has attacked GISS’s methodology, putting together an online photo gallery of US weather stations at website www.surfacestations.org that shows some thermometers situated next to asphalt runways and parking lots where they would pick up excess warming.

But GISS says the distorting impact of this urban warming is negated because data from these stations is modified to remove these effects and give a true reading. Hansen acknowledges there may be flaws in the weather station data because temperature measurement is not always a precise science. But he says this does not mean big-picture trends can’t be drawn from the data.

He says: “That doesn’t mean you give up on the science and that you can’t draw valid conclusions about the nature of earth’s temperature change.”

Hansen has been infuriated by the attacks on GISS by climate change critics. Last year Canadian blogger and retired businessman Stephen McIntyre exposed a minor mistake in Hansen’s figures that had caused GISS to overstate US temperatures by a statistically small 0.15C since 2000.

Sceptics were energised. “We have proof of man-made global warming,” roared conservative American radio host Rush Limbaugh. “The man-made global warming is inside NASA.”

Hansen struck back, saying he would “not joust with court jesters” who sought to “create a brouhaha and muddy the waters in the climate change story”.

What the bloggers have succeeded in doing is to highlight that measuring climate change is an evolving science. But their success has been at the margins only. So far they have failed to prove that these discrepancies negate the broader core arguments about the trends of global warming.

However, the second argument being put forward by blogger sceptics is more accessible to the public and therefore is having a greater impact. They argue that, contrary to the impressions given about global warming, the earth’s temperatures have plateaued during the past decade and may have cooled in recent years. This, they argue, should not be happening when carbon emissions are growing rapidly. This was not what the climate change modellers predicted. Their conclusion therefore is that carbon emissions are not the driver of warming and climate change and that the earth is not heading for a climate change apocalypse caused by greenhouse gases.

“All official measures of global temperature show that it peaked in 1998 and has been declining since at least 2002,” says climate change sceptic Bob Carter, a science adviser to the Australian Climate Science Coalition. “And this is in the face of an almost 5 per cent increase in atmospheric carbon dioxide since 1998. Spot the problem?”

A careful analysis of global temperature graphs from each of the measurement agencies confirm that – despite variations between them – there has not been any notable warming since 2000. Depending on which graphs you use, global temperatures since 2000 have been more or less flat. Some, such as the GISS data, show a modest rise, while others show negligible movement and even a small fall in recent years.

Sceptics like to use graphs that date from 1998 because that was the hottest year on record due to El Nino influences and therefore the temperature trends for the decade look flattest when 1998 is the starting point.

But ultimately this is a phony war because most mainstream scientists do not dispute that global temperatures have remained relatively flat during the past decade. Where they differ with the sceptics is on how this outcome should be interpreted.

“The changes in temperature over the past 10 years have basically plateaued,” says Andy Pitman, co-director of the Climate Change Research Centre at the University of NSW. “But scientists did not anticipate a gradual year-by-year warming in temperature. What matters is the long-term trend. This outcome does not change any of the science but it does change the spin climate deniers can put on it.”

The sceptics are having a field day with this trend. The IPA’s Marohasy says: “In the last 10 years we have seen an increase in carbon dioxide levels yet temperatures are coming down. That, if anyone looks at the actual data, is not disputable. Carbon dioxide is not driving temperatures because there are other important climatic factors at play.”

Most scientists are adamant that any assessment of climate change based on only 10 years of data is not only meaningless but reckless.

“From a climate standpoint it is far too short a period to have any significance,” says Amanda Lynch, a climate change scientist at Melbourne’s Monash University. “What we are seeing now is consistent with our understanding of variability between decades. If we hung about for another 30 years and it kept going down, then you might start to think there is something we don’t understand. But the evidence at this point suggests this is not something we should hang around and wait for.”

Climate change scientists say we must go back much further than the past decade and pay attention to the longer-term trend lines that run through the temperature data and clearly trend upwards. Lynch says other factors beyond temperature are also relevant. “In the last 10 years there has been a catastrophic and massive Arctic sea ice retreat. We’ve seen glacial retreat, permafrost thaw and ocean thermal expansion, so temperature is not the whole story.”

But the sceptics are undeterred. “It is widely alleged that the science of global warming is settled,” says the US-based Science and Public Policy Institute. “This implies that all the major scientific aspects of climate change are well understood and uncontroversial. The allegation is profoundly untrue … even the most widely held opinions should never be regarded as an ultimate truth.”

Matthew England, from the Climate Change Research Centre, describes the latest blog war by climate change sceptics as an amazing phenomenon. “Climate change is a robust area of science and there is plenty that is still being debated and new discoveries are still being made,” he says. “It is a topic (that) will keep attracting different opinions from enthusiasts and from bloggers. They are a minority but they are proving to be a very vocal group.”