By Alton Parrish.
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.
In the Norwegian project, however, researchers have arrived at an estimate of 1.9°C as the most likely level of warming.
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.
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. The researchers have arrived at an estimate of 1.9°C as the most likely level of warming.
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 with
Terje Berntsen emphasises that his project’s findings must not be construed as an excuse for complacency in addressing human-induced global warming. The results do indicate, however, that it may be more within our reach to achieve global climate targets than previously thought.
Regardless, the fight cannot be won without implementing substantial climate measures within the next few years.
But the findings of the Norwegian project indicate that particulate emissions probably have less of an impact on climate through indirect cooling effects than previously thought.
So the good news is that even if we do manage to cut emissions of sulphate particulates in the coming years, global warming will probably be less extreme than feared.
About the project
Geophysicists at the research institute CICERO collaborated with statisticians at the Norwegian Computing Center on a novel approach to global climate calculations in the project “Constraining total feedback in the climate system by observations and models”. The project received funding from the Research Council of Norway’s NORKLIMA programme.
The researchers succeeded in reducing uncertainty around the climatic effects of feedback mechanisms, and their findings indicate a lowered estimate of probable global temperature increase as a result of human-induced emissions of greenhouse gases.
The project researchers were able to carry out their calculations thanks to the free use of the high-performance computing facility in Oslo under the Norwegian Metacenter for Computational Science (Notur). The research project is a prime example of how collaboration across subject fields can generate surprising new findings.
Contacts and sources:
Thomas Keilman
The Research Council of Norway
