Global warming less extreme than feared?

Policymakers are attempting to contain global warming at less than 2°C. New estimates from a Norwegian project on climate calculations indicate this target may be more attainable than many experts have feared.
Internationally renowned climate researcher Caroline Leck of Stockholm University has evaluated the Norwegian project and is enthusiastic.
“These results are truly sensational,” says Dr Leck. “If confirmed by other studies, this could have far-reaching impacts on efforts to achieve the political targets for climate.”

Temperature rise is levelling off

After Earth’s mean surface temperature climbed sharply through the 1990s, the increase has levelled off nearly completely at its 2000 level. Ocean warming also appears to have stabilised somewhat, despite the fact that CO2 emissions and other anthropogenic factors thought to contribute to global warming are still on the rise.
It is the focus on this post-2000 trend that sets the Norwegian researchers’ calculations on global warming apart.

Sensitive to greenhouse gases

Climate sensitivity is a measure of how much the global mean temperature is expected to rise if we continue increasing our emissions of greenhouse gases into the atmosphere.
CO2 is the primary greenhouse gas emitted by human activity. A simple way to measure climate sensitivity is to calculate how much the mean air temperature will rise if we were to double the level of overall CO2 emissions compared to the world’s pre-industrialised level around the year 1750.
If we continue to emit greenhouse gases at our current rate, we risk doubling that atmospheric CO2 level in roughly 2050.

Mutual influences

A number of factors affect the formation of climate development. The complexity of the climate system is further compounded by a phenomenon known as feedback mechanisms, i.e. how factors such as clouds, evaporation, snow and ice mutually affect one another.
Uncertainties about the overall results of feedback mechanisms make it very difficult to predict just how much of the rise in Earth’s mean surface temperature is due to manmade emissions. According to the Intergovernmental Panel on Climate Change (IPCC) the climate sensitivity to doubled atmospheric CO2 levels is probably between 2°C and 4.5°C, with the most probable being 3°C of warming.
In the Norwegian project, however, researchers have arrived at an estimate of 1.9°C as the most likely level of warming.

Manmade climate forcing

“In our project we have worked on finding out the overall effect of all known feedback mechanisms,” says project manager Terje Berntsen, who is a professor at the University of Oslo’s Department of Geosciences and a senior research fellow at the Center for International Climate and Environmental Research – Oslo (CICERO). The project has received funding from the Research Council of Norway’s Large-scale Programme on Climate Change and its Impacts in Norway (NORKLIMA).
“We used a method that enables us to view the entire earth as one giant ‘laboratory’ where humankind has been conducting a collective experiment through our emissions of greenhouse gases and particulates, deforestation, and other activities that affect climate.”
For their analysis, Professor Berntsen and his colleagues entered all the factors contributing to human-induced climate forcings since 1750 into their model. In addition, they entered fluctuations in climate caused by natural factors such as volcanic eruptions and solar activity. They also entered measurements of temperatures taken in the air, on ground, and in the oceans.
The researchers used a single climate model that repeated calculations millions of times in order to form a basis for statistical analysis. Highly advanced calculations based on Bayesian statistics were carried out by statisticians at the Norwegian Computing Center.

2000 figures make the difference

When the researchers at CICERO and the Norwegian Computing Center applied their model and statistics to analyse temperature readings from the air and ocean for the period ending in 2000, they found that climate sensitivity to a doubling of atmospheric CO2 concentration will most likely be 3.7°C, which is somewhat higher than the IPCC prognosis.
But the researchers were surprised when they entered temperatures and other data from the decade 2000-2010 into the model; climate sensitivity was greatly reduced to a “mere” 1.9°C.
Professor Berntsen says this temperature increase will first be upon us only after we reach the doubled level of CO2 concentration (compared to 1750) and maintain that level for an extended time, because the oceans delay the effect by several decades.

Author: Bård Amundsen/Else Lie. Translation: Darren McKellep/Carol B. Eckmann
Source:
 http://www.forskningsradet.no/en/Newsarticle/Global_warming_less_extreme_than_feared/1253983344535/p1177315753918

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