/ 4 October 2009

Warning on warming

Unchecked global warming could bring a temperature rise of 4ºC within many people’s lifetimes, according to a new report for the British government that significantly raises the stakes on climate change.

The study, prepared for the department of energy and climate change by scientists at the Met Office [the UK’s national weather service], challenges the assumption that severe warming will be a threat only for future generations and warns that, without strong action on emissions, a catastrophic 4ºC rise in temperature could happen by 2060.

Officials from some 190 countries gather this week in Bangkok to continue negotiations on a new global deal to tackle global warming, which they aim to secure at United Nations talks in December in Copenhagen.

“We’ve always talked about these very severe impacts affecting only future generations, but people alive today could live to see a 4ºC rise,” said Richard Betts, the head of climate effects at the Met Office Hadley Centre, who will announce the findings at a conference at Oxford University. “People will say it’s an extreme scenario and it is an extreme scenario, but it’s also a plausible scenario.”

According to scientists, a 4ºC rise above pre-industrial levels could threaten the water supply of half the world’s population, wipe out up to half of animal and plant species and swamp low-lying coastlines.

A 4ºC average would mask more severe local effects: the Arctic and Western and Southern Africa could experience warming of up to 10ºC, the Met Office report warns.

The study updates the findings of the 2007 report of the intergovernmental panel on climate change (IPCC), which said the world would probably warm by 4ºC by 2100 if greenhouse gas emissions continued to rise. The IPCC listed a more severe scenario, with emissions and temperatures rising further because of more intensive fossil-fuel burning, but this was not considered realistic.

“That scenario was downplayed at the time because we were more conservative a few years ago. But the way we are going, the most severe scenario is looking more plausible,” Betts said.

A report last week from the United Nations Environment Programme said emissions since 2000 have risen faster than even this IPCC worst-case scenario.

“Created in the 1990s, these scenarios all assumed political will or other phenomena would have brought about the reduction in greenhouse gas emissions by this point. In fact, carbon dioxide emissions from fossil-fuel burning and industrial processes have been accelerating on a global scale.”

The Met Office scientists used new versions of the computer models used to set the IPCC predictions, updated to include so-called carbon feedbacks.

Often called tipping points, these feedbacks occur when warmer temperatures release more carbon, such as from soils.

When they ran the models for the most extreme IPCC emissions scenario, they found that a 4ºC rise could come by 2060 or 2070, depending on the strength of the feedbacks.

Betts said: “It’s important to stress it’s not a doomsday scenario. We do have time to stop it happening if we cut greenhouse gas emissions soon.”

Emissions must peak and start to fall sharply within the next decade to head off a 2ºC rise, he said. To avoid the 4ºC scenario, that peak must come by the 2030s.

Earlier this year, a poll of 200 climate experts found that most of them expected a temperature rise of 3ºC to 4ºC by the end of the century.

The implications of a 4ºC rise for society, agriculture, water supplies and wildlife will be discussed at the Oxford conference, which organisers have billed as the first to give proper consideration such a dramatic scenario. Mark New, a climate expert at the university who organised the conference, said: “We are now getting to the stage that if we get a weak agreement at Copenhagen, then there is not just a slight chance of a 4ºC rise, there is a really big chance.”

He said: “It’s only in the last five years that scientists have started to realise that 4ºC is becoming increasingly likely and something we need to look at seriously.”

The target to limit global warming to 2ºC was “pie in the sky”, he said, and could be achieved only with new technology to suck greenhouse gases from the atmosphere. “I think the policymakers know that. I think there is an implicit understanding that they are negotiating not about 2ºC, but 3ºC or 5ºC.” —