OSLO – A temperature goal set by almost 200 governments as the limit for global warming is a poor guide to the planet’s health and should be ditched, a study published in the journal Nature said on Wednesday.
The world’s environment ministers agreed in 2010 to cap a rise in average surface temperatures at 2 degrees Celsius (3.6 Fahrenheit) above preindustrial times as the yardstick to avoid more floods, heat waves, droughts and rising sea levels.
“Politically and scientifically, the 2 degree C goal is wrong-headed,” David Victor and Charles Kennel, both professors at the University of California in San Diego, wrote in the Nature article, titled “Ditch the 2C Warming Goal.”
Among their objections, they said the goal is “effectively unachievable” because of rising emissions of greenhouse gases, led in recent years by China’s strong economic growth.
They said the target is also out of line with recent trends. Temperatures have risen about 0.85 degree Celsius (1.5 F) since about 1900 but have been virtually flat since about 1998 despite higher emissions from factories, power plants and cars.
Using a metaphor, they said that blood pressure, heart rate and body mass are all vital signs of health for a person, not just temperature. “A similar strategy is now needed for the planet,” they wrote.
The study urged a shift to other yardsticks to gauge the planet’s health, such as concentrations of greenhouse gases in the atmosphere and changes in the heat content of the oceans.
Some other scientists said the 2-degree target is still the best goal to guide U.N. talks on a deal to limit climate change, due to be agreed on by governments in late 2015 at a summit in Paris.
“Their arguments don’t hold water,” said Stefan Rahmstorf, a scientist at the Potsdam Institute for Climate Impact Research.
He said that a shift to tracking carbon dioxide concentrations in the atmosphere, for instance, would not help because no one knows exactly how far rising carbon concentrations affect temperatures.
And he said that 1998 was an exceptionally hot year, warmed by a powerful El Nino event in the Pacific Ocean. The period since then was not typical of long-term trends.
A German group of experts, Climate Analytics, also defended the 2-degree goal. “Whilst no one is in doubt about the difficulty of limiting warming below 2 degrees C, it is incorrect to claim that achieving this goal is infeasible,” they wrote.
The U.N.’s panel of climate experts said in March that it is still possible to keep temperatures below 2 degrees at a moderate annual cost of about 0.06 percent of economic output.
The panel says it is at least 95 percent probable that man-made greenhouse gas emissions, rather than natural swings in the climate system, are the main cause of global warming since 1950.