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" 1.9C.
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.
Natural changes also a major factor
The figure of 1.9C as a prediction of global warming from a doubling of atmospheric CO2 concentration is an average. When researchers instead calculate a probability interval of what will occur, including observations and data up to 2010, they determine with 90% probability that global warming from a doubling of CO2 concentration would lie between 1.2C and 2.9C.
This maximum of 2.9C global warming is substantially lower than many previous calculations have estimated. Thus, when the researchers factor in the observations of temperature trends from 2000 to 2010, they significantly reduce the probability of our experiencing the most dramatic climate change forecast up to now.
Professor Berntsen explains the changed predictions:
"The Earth's mean temperature rose sharply during the 1990s. 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 and 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."
Climate issues must be dealt
|Contact: Thomas Keilman|
The Research Council of Norway