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Scientists Dispute 2-Degree Model Guiding Climate Talks
The single most important benchmark underpinning this weekâs talks in Paris on climate changeâtwo degrees Celsiusâhas guided climate-treaty discussions for decades, but scientists are at odds on the relevance of that target.
Many researchers have argued that a rise in the planetâs average global air temperature of two degrees or more above preindustrial levels would usher in catastrophic climate change. But many others, while convinced the planet is warming, say two degrees is a somewhat arbitrary threshold based on tenuous research, and therefore an impractical spur to policy action.
âIt emerged from a political agenda, not a scientific analysis,â said Mark Maslin, professor of climatology at University College London. âItâs not a sensible, rational target because the models give you a range of possibilities, not a single answer.â
Policy makers tend to assume the two-degree target expresses a solid scientific view, but it doesnât. The exhaustive reports published by the United Nations Intergovernmental Panel on Climate Change are considered to be the most comprehensive analysis of the science of global warming. Yet the two-degree limit isnât mentioned in a single IPCC report.
Still, many scientists back the goal because they see it as giving policy makers a clear-cut target to shoot at in the fight against global warming.
The vast majority of climatologists agree that the earth is getting warmer and that the emission of greenhouse gases by human activity is the main driver of this change. But the question of when a catastrophic tipping point might be reached is up in the air.
Some significant phenomena widely attributed to warmingâsuch as dramatic summer melting of Arctic sea ice and glacial retreat in Greenlandâare already evident today, even though the average temperature is one degree Celsius above preindustrial levels and thus some ways from the two-degree benchmark.
On the other hand, some of the more dangerous consequences of warming might not become evident until long after the two-degree line is crossed.
âThe whole apocalyptic metaphor is misleading,â said Carlo Jaeger, chairman of the Global Climate Forum, a German think tank, and a professor at the University of Potsdam. âHell is not going to break loose at two degreesâit will take hundreds of years to unfold.â
William Nordhaus, a professor of economics at Yale University, appears to have been the first to mention the two-degree figure in a paper published in 1977. But rather than making a robust scientific calculation based on the physics of climate change, his paper argued that a rise of two or more degrees would put the earthâs climate outside the observable range of temperature over the last several hundred thousand years.
Thereafter, the two-degree benchmark slowly gained traction. Other scientists argued that global air temperatures hadnât risen beyond 1.5 or two degrees in the course of human history, and that greater temperature shifts eons earlier had triggered cataclysmic changes in sea level. They figured that a two-degree ceiling would therefore amount to a natural safety limit.
âThe idea was, âletâs not move the human enterprise out of an evolutionary regime that we are adapted to,â â said Hans Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research, who helped popularize the two-degree goal.
In 1994, at a meeting in Bonn, Dr. Schellnhuber sat down with Angela Merkel, then Germanyâs minister for the environment. Since both are trained physicists, Dr. Schellnhuber offered complicated charts and figures for Ms. Merkel to peruse.
âI presented what I call âthe tolerable windowsâ approach,â recalls Dr. Schellnhuber, then the German governmentâs chief adviser on climate. âIn terms of temperature, the tolerable window was limited to two degrees.â
Ms. Merkel backed the target. The following year, she persuaded the Council of the European Union to formally endorse it.
More scientists began to support it, too. One 2003 study concluded that beyond two degrees, âthe risks increase very substantially involving potentially large extinctions or even ecosystem collapses, major increases in hunger and water shortage risks as well as socioeconomic damages, particularly in developing countries.â
In October 2014, David Victor, a professor of international relations at the University of California, San Diego, and Charles Kennel, a professor at the Scripps Institution of Oceanography in La Jolla, Calif., wrote a sharp critique of the two-degree benchmark in the journal Nature.
Police clashed with protesters near the Place de la RĂŠpublique in Paris on Sunday ahead of the climate conference in the French capital. Authorities outlawed public gatherings in the wake of the Nov. 13 terror attacks, but thousands flouted the ban.
They argued that the yardstick was scientifically weak because it captured only a tiny portion of the planetâs climate profile. More than 93% of the extra heat, they noted, ends up in the ocean and not in the atmosphere.
For that reason, they said, policy makers should also track ocean heat content and other parameters when setting emission goals. In an article this month in Nature Climate Change, they and a third author said âa new list of planetary vital signsâ is needed to take the full measure of climate change.
Prof. Victor also said the two-degree benchmark should be ditched because it is no longer an achievable target.
âThe trajectory of emissions weâre on now is so steep, itâs too late,â he said. âThereâs no scenario under which this could be contained below two degreesâitâs game over.â
The single most important benchmark underpinning this weekâs talks in Paris on climate changeâtwo degrees Celsiusâhas guided climate-treaty discussions for decades, but scientists are at odds on the relevance of that target.
Many researchers have argued that a rise in the planetâs average global air temperature of two degrees or more above preindustrial levels would usher in catastrophic climate change. But many others, while convinced the planet is warming, say two degrees is a somewhat arbitrary threshold based on tenuous research, and therefore an impractical spur to policy action.
âIt emerged from a political agenda, not a scientific analysis,â said Mark Maslin, professor of climatology at University College London. âItâs not a sensible, rational target because the models give you a range of possibilities, not a single answer.â
Policy makers tend to assume the two-degree target expresses a solid scientific view, but it doesnât. The exhaustive reports published by the United Nations Intergovernmental Panel on Climate Change are considered to be the most comprehensive analysis of the science of global warming. Yet the two-degree limit isnât mentioned in a single IPCC report.
Still, many scientists back the goal because they see it as giving policy makers a clear-cut target to shoot at in the fight against global warming.
The vast majority of climatologists agree that the earth is getting warmer and that the emission of greenhouse gases by human activity is the main driver of this change. But the question of when a catastrophic tipping point might be reached is up in the air.
Some significant phenomena widely attributed to warmingâsuch as dramatic summer melting of Arctic sea ice and glacial retreat in Greenlandâare already evident today, even though the average temperature is one degree Celsius above preindustrial levels and thus some ways from the two-degree benchmark.
On the other hand, some of the more dangerous consequences of warming might not become evident until long after the two-degree line is crossed.
âThe whole apocalyptic metaphor is misleading,â said Carlo Jaeger, chairman of the Global Climate Forum, a German think tank, and a professor at the University of Potsdam. âHell is not going to break loose at two degreesâit will take hundreds of years to unfold.â
William Nordhaus, a professor of economics at Yale University, appears to have been the first to mention the two-degree figure in a paper published in 1977. But rather than making a robust scientific calculation based on the physics of climate change, his paper argued that a rise of two or more degrees would put the earthâs climate outside the observable range of temperature over the last several hundred thousand years.
Thereafter, the two-degree benchmark slowly gained traction. Other scientists argued that global air temperatures hadnât risen beyond 1.5 or two degrees in the course of human history, and that greater temperature shifts eons earlier had triggered cataclysmic changes in sea level. They figured that a two-degree ceiling would therefore amount to a natural safety limit.
âThe idea was, âletâs not move the human enterprise out of an evolutionary regime that we are adapted to,â â said Hans Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research, who helped popularize the two-degree goal.
In 1994, at a meeting in Bonn, Dr. Schellnhuber sat down with Angela Merkel, then Germanyâs minister for the environment. Since both are trained physicists, Dr. Schellnhuber offered complicated charts and figures for Ms. Merkel to peruse.
âI presented what I call âthe tolerable windowsâ approach,â recalls Dr. Schellnhuber, then the German governmentâs chief adviser on climate. âIn terms of temperature, the tolerable window was limited to two degrees.â
Ms. Merkel backed the target. The following year, she persuaded the Council of the European Union to formally endorse it.
More scientists began to support it, too. One 2003 study concluded that beyond two degrees, âthe risks increase very substantially involving potentially large extinctions or even ecosystem collapses, major increases in hunger and water shortage risks as well as socioeconomic damages, particularly in developing countries.â
In October 2014, David Victor, a professor of international relations at the University of California, San Diego, and Charles Kennel, a professor at the Scripps Institution of Oceanography in La Jolla, Calif., wrote a sharp critique of the two-degree benchmark in the journal Nature.
Police clashed with protesters near the Place de la RĂŠpublique in Paris on Sunday ahead of the climate conference in the French capital. Authorities outlawed public gatherings in the wake of the Nov. 13 terror attacks, but thousands flouted the ban.
They argued that the yardstick was scientifically weak because it captured only a tiny portion of the planetâs climate profile. More than 93% of the extra heat, they noted, ends up in the ocean and not in the atmosphere.
For that reason, they said, policy makers should also track ocean heat content and other parameters when setting emission goals. In an article this month in Nature Climate Change, they and a third author said âa new list of planetary vital signsâ is needed to take the full measure of climate change.
Prof. Victor also said the two-degree benchmark should be ditched because it is no longer an achievable target.
âThe trajectory of emissions weâre on now is so steep, itâs too late,â he said. âThereâs no scenario under which this could be contained below two degreesâitâs game over.â
