'Pause' in heating of atmosphere detected

Slower warming may alter models

AFP-JIJI, Kyodo

A “pause” in global warming over the past decade may invalidate the harshest climate change predictions for the next 50 to 100 years, a study said Sunday — though levels remain in the danger zone.

Writing in the journal Nature Geoscience, an international team of climate scientists said a slower rate of warming that was observed between 2000 and 2009 suggested a “lower range of values” that should be taken into account by policymakers.

While the past decade was the hottest since records began in 1880, the rate of increase showed a stabilization despite ever-rising levels of Earth-warming greenhouse gases in the atmosphere.

Scientists have alternatively explained the flatter curve by oceanic heat capture, a decline in solar activity or an increase in volcanic aerosols that reflect the sun’s rays.

Because of the hiatus, warming in the next 50 to 100 years “is likely to lie within the range of current climate models, but not at the high end of this range,” said study coauthor Alexander Otto of Oxford University’s Environmental Change Institute.

Otto and his team used up-to-date data on temperatures and levels of solar radiation trapped in the atmosphere by greenhouse gases to map out new projections for climate warming.

The United Nations is targeting a global average maximum temperature rise of 2 degrees Celsius on preindustrial levels, for what scientists believe will be manageable climate change.

In 2007, the U.N.’s Intergovernmental Panel on Climate Change (IPCC) warned in a report of the temperature rising by as much as 6.4 degrees in the worst emissions scenario.

Study coauthor Reto Knutti of ETH Zurich said that being able to rule out the most extreme scenarios for near-term warming is clearly welcome news.

“But even if the response is at the low end of the current range of uncertainty, we are still looking at warming well over the 2-degree goal that countries have agreed upon,” Knutti said.

To meet the 2-degree goal, countries are negotiating curbs to emissions of Earth-warming greenhouse gases released by fossil fuel burning.

But in a turnaround for European energy policy, EU leaders meeting Wednesday plan to prioritize the supply of energy at affordable prices over cutting greenhouse gas emissions that impose burdens on industries, an EU official said Saturday. The change reflects requests from businesses amid the region’s prolonged economic slump.

Earlier this month, the level of carbon dioxide in the Earth’s atmosphere breached a threshold of 400 parts per million — a level never before experienced by humans and considered the absolute maximum for the 2-degree target to remain within reach.

Many scientists believe that on current trends, Earth is set for warming much higher than the 2-degree target.

Commenting on the publication, University of New South Wales climate researcher Steven Sherwood said the conclusions “need to be taken with a large grain of salt until we see what happens to the oceans over the coming years.”

The authors had partly based their finding on a higher-than-expected absorption of heat by the world’s oceans, he said, but other research has suggested this storage may reverse due to natural phenomena such as El Nino.

  • John Watt

    “Because of the hiatus, warming in the next 50 to 100 years “is likely to lie within the range of current climate models, but not at the high end of this range,” said study coauthor Alexander Otto of Oxford University’s Environmental Change Institute.”

    Currently, the lack of warming over the last decade means that observed temperatures are actually well below any of the predictions of current climate models. Until they can figure out what actually causes rises and falls in global temperatures, it might be a bit premature to go making another prediction…

  • John Watt

    It is interesting to note that the current climate models made their exaggerated predictions based on assumptions about the role of CO2 in the 0.8C warming over the last 100 years. Obviously those assumptions have turned out to suspect as best, and clearly faulty to some extent. That means we really don’t know how much of a role CO2 played in that previous warming. Thus, even if there is more warming in this century, we still have no idea how much CO2 might be involved. Nor do we have any idea what the effects of reducing CO2 output might have on temperatures.

    This article simply highlights the enormous amount of uncertainty that exists in this area.