UK Met Office analysis reveals 'clear fingerprints' of man-made climate change

Climate scientists say the 100 studies of sea ice, rainfall and temperature should help the public to make up their own minds on global warming
Alok Jha, The Guardian 5 Mar 10;

It is an "increasingly remote possibility" that human activity is not the main cause of climate change, according to a major Met Office review of more than 100 scientific studies that track the observed changes in the Earth's climate system.

The research will strengthen the case for human-induced climate change against sceptics who argue that the observed changes in the Earth's climate can largely be explained by natural variability.

Climate scientists and the UN's climate body, the Intergovernmental Panel on Climate Change (IPCC), have come under intense pressure in recent months after the IPCC was forced to admit it had made two errors in its fourth assessment report published in 2007. Emails hacked from climate scientists at the University of East Anglia in November have also sparked a series of inquiries into allegations of a lack of transparency by researchers and manipulation of the peer review process.

Asked whether his study was specifically scheduled as a fightback, Peter Stott, who led the review, said that the paper was originally drafted a year ago. But he added: "I hope people will look at that evidence and make up their minds informed by the scientific evidence."

Scientists matched computer models of different possible causes of climate change - both human and natural - to measured changes in factors such as air and sea temperature, Arctic sea ice cover and global rainfall patterns. This technique, called "optimal detection", showed clear fingerprints of human-induced global warming, according to Stott. "This wealth of evidence shows that there is an increasingly remote possibility that climate change is being dominated by natural factors rather than human factors." The paper reviewed numerous studies that were published since the last IPCC report.

Optimal detection considers to what extent an observation can be explained by natural variability, such as changing output from the sun, volcanic eruptions or El Niño, and how much can be explained by the well-established increases in carbon dioxide and other greenhouse gases in the atmosphere.

According to Nasa, the last decade was the warmest on record and 2009 the second warmest year. Temperatures have risen by 0.2C per decade, over the past 30 years and average global temperatures have increased by 0.8C since 1880.

The evidence that the climate system is changing goes beyond measured air temperatures, with much of the newest evidence coming from the oceans. "Over 80% of the heat that's trapped in the climate system as a result of the greenhouse gases is exported into the ocean and we can see that happening," said Stott. "Another feature is that salinity is changing - as the atmosphere is warming up, there is more evaporation from the surface of the ocean [so making it more salty], which is most noticeable in the sub-tropical Atlantic."

This also links into changes in the global water cycle and rainfall patterns. As the atmosphere warms, it has been getting more humid, exactly as climate modellers had predicted. "This clear fingerprint has been seen in two independent datasets. One developed in the Met Office Hadley Centre, corroborated with data from satellites."

Arctic sea ice is also retreating - the summer minimum of sea ice is declining at a rate of 600,000 km² per decade, an area approximately the size of Madagascar. Again, decreasing sea ice is predicted by climate models.

Rainfall is also on the rise in the higher latitudes of the northern hemisphere and large swaths of the southern hemisphere, while in the tropics and sub-tropics, there are decreases. "The already-wet regions are getting wetter and the dry regions are getting drier," said Stott. "We now have studies that can identify this fingerprint in the observational data."

The review, published in Wiley Interdisciplinary Reviews: Climate Change, found that the natural causes of climate variation, including changing energy output from the sun and volcanic eruptions, could not explain the observed changes by themselves. "There hasn't been an increase in solar output for the last 50 years and solar output would not have caused cooling of the higher atmosphere and the warming of the lower atmosphere that we have seen," said Stott.

If the observed climate change was entirely due to solar activity, the Earth's atmosphere would have warmed more evenly - both the troposphere and stratosphere would have been affected. Warming due to the Sun would also have meant temperatures should have increases more quickly early than late in the 20th century, which is the reverse of what was actually measured.

The review is published as scientists also report a rise in methane emissions from a section of the Arctic Ocean sea floor. That study, published today in the journal Science, shows that the permafrost under the East Siberian Arctic shelf, once considered an safe store of methane, is leaking large amounts of the gas into the atmosphere. Release of even a fraction of the methane stored in the shelf could trigger abrupt climate warming as this is a greenhouse gase around 30 times more potent than CO2.

"The amount of methane currently coming out of the East Siberian Arctic shelf is comparable to the amount coming out of the entire world's oceans. Sub-sea permafrost is losing its ability to be an impermeable cap," said Natalia Shakhova, a researcher at the University of Alaska Fairbanks's International Arctic Research Centre. "The release to the atmosphere of only one percent of the methane assumed to be stored in shallow hydrate deposits might alter the current atmospheric burden of methane up to three to four times. The climatic consequences of this are hard to predict."


'Case stronger' on climate change
Pallab Ghosh, BBC News 5 Mar 10;

A review from the UK Met Office says it is becoming clearer that human activities are causing climate change.

It says the evidence is stronger now than when the Intergovernmental Panel on Climate Change carried out its last assessment in 2007.

The analysis, published in the Wiley Interdisciplinary Reviews Climate Change Journal, has assessed 110 research papers on the subject.

It says the Earth is changing rapidly, probably because of greenhouse gases.

In 2007 the IPCC's report concluded that there was "unequivocal" evidence that the Earth was warming and it was likely that it was due to burning of fossil fuels.

Since then the evidence that human activities are responsible for a rise in temperatures has increased, according to this new assessment by Dr Peter Stott and colleagues at the UK Met Office.

The Met Office study comes at a time when some have questioned the entire basis of climate science following recent controversies over the handling of research findings by the IPCC and the Climate Research Unit at the University of East Anglia.

Dr Stott denies that the study has been published as part of a fight back by the climate research community.

"We started writing this paper a year ago. I think it's important to communicate to people what the science is showing and that's why I'm talking about this paper."

'Consistent picture'

The study, which looks at research published since the IPCC's report, has found that changes in Arctic sea ice, atmospheric moisture, saltiness of parts of the Atlantic Ocean and temperature changes in the Antarctic are consistent with human influence on our climate.

"What this study shows is that the evidence has strengthened for human influence on climate and we know that because we've looked at evidence across the climate system and what this shows very clearly is a consistent picture of a warming world," said Dr Stott.

The study brings together other research from a range of disciplines.

"We hadn't [until now] looked in detail at how the climate system was changing," says Dr Stott.

"[Our paper looks at] not just the temperatures but also the reducing Arctic sea ice and it includes changing rainfall patterns and it includes the fact that the atmosphere is getting more humid.

"And all these different aspects of the climate system are adding up to a picture of the effects of a human influence on our climate."

The Met Office study said that it was harder to find a firm link between climate change and individual extreme weather conditions - even though models predicted that extreme events were more likely.

According to the report: "Extremes pose a particular challenge, since rare events are by definition, poorly sampled in the historical record and many challenges remain for robustly attributing regional changes in extreme events such as droughts, floods and hurricanes."

New evidence for man-made global warming
Man is responsible for global warming, according to a new report that hits back at the growing scepticism around climate change.
Louise Gray, The Telegraph 5 Mar 10;

The Met Office-led report looked at the latest figures on global temperatures, melting sea ice and humidity. It also considered new evidence on the extent of warming in the Antarctic, rainfall patterns and salinity of the oceans.

It concluded that is was "human influence" that is changing the climate.

However, sceptics insisted the new report did little to back up the case for spending billions of pounds on tackling global warming.

The recent 'climategate' scandal around stolen emails from the University of East Anglia has cast doubt on the science around climate change. Sceptics claim that the emails show scientists were willing to manipulate the data to show that global warming is a man-made phenomenon.

The UN body in charge of climate science, the Intergovernmental Panel on Climate Change, is also under fire after being forced to retract claims that the Himalayan glaciers could melt by 2035.

The IPCC won the Nobel Peace Prize in 2007 for their seminal report that claimed global warming is almost certainly caused by man-made green house gases.

The latest report, published in Wiley Interdisciplinary Reviews Climate Change, found that since then even more evidence has emerged to back up the case.

The study, by six IPCC scientists from around the world, looked at 101 papers including evidence that was not in the earlier report. This included some of the first evidence of rising temperatures in Antarctic and new analysis of changing rainfall patterns across the world. There have also been fresh studies of humidity and salinity in the oceans, that increases with global warming because water is evaporating faster.

Dr Peter Stott, from the Met Office Hadley Centre in Exeter, who co-led the study, said all the new evidence on melting sea ice in the Arctic and rising global temperatures point to man made global warming.

"It shows that evidence has strengthened over the last two or three years that human influence is changing the climate," he said.

Dr Stott hoped the study would add to the ongoing debate about whether mankind is to blame for global warming.

"I just hope people look at the evidence," he said. "This is really what it is up to scientists to do - to show the climate is changing in such a systematic way it is consistent with understanding and with the expected response to human activities. I just hope people will look at that evidence and make up their minds informed by the scientific evidence."

However well known sceptic Professor Bjorn Lomborg, said people remain confused about the impacts of climate change and what the world should do about it.

"If the study confirms what the UN has been telling us - that global warming is real and man made and really happening - that would be great. But the scepticism is much more on the actual impacts and what we are doing," he said. "Just like other serious problems we should not magnify global warming for affect."

Godfrey Bloom, the UKIP MEP and member of the European Parliament Environment Committee, questioned the study itself.

"I have seen no published evidence that goes beyond a rather unlikely hypothesis that man caused global warming and it is getting thinner by the day," he said. "So before we disturb the global economy we need to take a step back and re-evaluate."