Close this search box.

Prof. Roger Pielke Jr. on origins of 2 degree temp target: ‘Has little scientific basis’

Via: Roger Pielke Jr.’s The Climate Fix website:

Do you want to know the origins of the 2 degree temperature target that underpins much of climate policy discussions and action?

  • As is often the case, it is an arbitrary round number that was politically convenient. So it became a sort of scientific truth. However, it has little scientific basis but is a hard political reality.
  • Jaeger and Jaeger (2011) explain that it came from “a marginal remark in an early paper about climate policy”
  • That “marginal paper” was a 1975 working paper by economist William Nordhaus (here in PDF and a second version is from 1977, with the figure shown below). At p. 23, “If there were global temperatures of more than 2 or 3 C. above the current average temperature, this would take the climate outside of the range of observations which have been made over the last several hundred thousand years.”nord-1977
  • Nordhaus’ claim was sourced to climatologist Hubert Lamb (1972) who in turn calculated long-term variations in temperature based on record kept in Central England.
  • So: The 2 degree temperature target that sits at the center of current climate policy discussions originated in a local, long-term record of temperature variation in England, which was adapted by an economist in a “what if?” exercise.
  • The 2 degree target is today far more politically “real” than its grounding in science or policy. That won’t change, but it is nonetheless a fascinating look at the arbitrariness of policy and how it is that issues are framed shapes what options are deemed relevant and appropriate.
  • As an example, check out this paper just out today in Nature — it argues that we can emit more than we thought and still hit a 1.5 degree temperature target. People will argue about the results, many because of its perceived political implications. But this argument is only tenuously related to actual energy policies, instead it is related to how we should think about arguments that might be used to motivate people to think about energy policies and thus demand action and so on. Tenuous, like I said.


Related Link: 

Flashback Climategate emails: Phil Jones says critical 2-degree C limit was ‘plucked out of thin air’

German Scientists: ‘2°C Target Purely Political’ – Prof. Dr. Christian Schönwiese told German public television: ‘They formulated a 2°C target. It is not from a climate scientist, or a physicist, or a chemist, but from an outside person who simply plucked it out of thin air and said ‘2°C’

Warmist father Hans Joachim Schellnhuber of 2C temperature limit admits it’s ‘a political goal’– Hans Joachim Schellnhuber, a top German climate scientist who helped establish the 2-degree threshold, stressed it was a policy marker: “Two degrees is not a magical limit — it’s clearly a political goal,” says Hans Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research (PIK). “The world will not come to an end right away in the event of stronger warming, nor are we definitely saved if warming is not as significant. The reality, of course, is much more complicated.” Schellnhuber ought to know. He is the father of the two-degree target. “Yes, I plead guilty,” he says, smiling. The idea didn’t hurt his career. In fact, it made him Germany’s most influential climatologist. Schellnhuber, a theoretical physicist, became Chancellor Angela Merkel’s chief scientific adviser — a position any researcher would envy.

Now in NatureClimate – limiting global warming to 2C target may not save coral reefs