Global warming could be less extreme than feared

By Tim Radford

New findings by Norwegian scientists, which include data from this century, suggest that global average temperatures may not rise as much as many climatologists believe likely.

The Copenhagen target of no more than a 2°C average warming for the planet might be achievable after all, according to new research from Norway.

A team backed by the Norwegian research council harnessed multiple sources of data to a single climate model, ran it millions of times and found that, even if carbon dioxide levels in the atmosphere double by 2050, warming might still be no greater than 1.9°C.

Such calculations come with the routine health caution: the range of warming could be as low as 1.2°C, or as high as 2.9°C; the figures represent a global average, so different regions might experience much warmer or colder climates; and finally they are the conclusions of just one climate group.


Climate Change Map

This projected warming is lower than the forecast by the Intergovernmental Panel on Climate Change (IPCC), which foresees a range of warming between 2°C and 4.5°C, and is considerably lower than the worst fears of some climate scientists.

The IPCC figures are themselves a compromise, based on calculations by a global network of national and international research teams.

Even so, the findings surprised the Norwegians themselves.

Terje Berntsen, of the Centre for International Climate and Environmental Research at the University of Oslo, and his colleagues took a new approach: they entered measurements taken from the air, the ground and the oceans; they incorporated all known feedback mechanisms that might either accelerate or slow the rate of warming, such as the release of sulphate particulates that may indirectly cool the climate; and they entered into their model all the data from the 21st century.

Hopeful prospects?

“The Earth’s mean temperature rose sharply in the 1990s,” said Professor Berntsen.

“This may have caused us to overestimate climate sensitivity. We are most likely witnessing natural fluctuations in the climate system – changes that can occur over several decades – which are coming on top of a long-term warming. The natural changes resulted in a rapid global temperature rise in the 1990s, whereas the natural variations between 2000 and 2010 may have resulted in the levelling-off we are observing now.”

He warned that the group’s findings should not be used as an excuse for complacency in addressing human-induced global warming.

They do however show that the pessimists may not be right: it may be possible to achieve the global climate targets agreed at the  Copenhagen climate change summit in 2009.

Berntsen’s is not the only group to see an apparent slowdown in the rate of warming. John Christy and Roy Spencer of the University of Alabama at Huntsville, USA, issued their own report on the world climate in 2012.

They included satellite microwave readings over regions – deserts, oceans and rainforests – where standard data is not collected, compared figures with a 30-year average from 1981-2010, and reported in January that there was no measurable long term warming trend.

No time to waste

The Huntsville team – in contrast to the UK Met Office and the Goddard Space Science Institute of Nasa, which scored 2010 and 2005 as joint winners in the hottest-ever years – recorded 1998 as the warmest year in history.

However, even on the Huntsville scorecard, 11 of the 12 warmest years ever recorded happened within the present century.

And the general conclusion remains: rising carbon dioxide levels impose a threat of planetary warming, and the longer governments delay, the harder it will be to contain warming to within 2°C.

In the journal Science of 18 January Thomas Stocker of the University of Bern, Switzerland, warns: “Even well-intentioned and effective international efforts to limit climate change must face the hard physical reality of certain temperature targets that can no longer be achieved if too much carbon has been emitted to the atmosphere.

Both delay and insufficient mitigation efforts close the door on limiting global mean warming permanently.”

This article was produced by the Climate News Network

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