Thread by @Peters_Glen

The latest comprehensive emission scenarios (Shared Socioeconomic Pathways) leads to a temperature increase between 1.3°C & 5.1°C in 2100.

These outcomes are treated as equally likely.

Should experts assign probabilities to different scenarios?

1/

I was reminded about this after rereading "What is 'dangerous' climate change?" by Schneider (2001) nature.com/articles/35075…

Back then (IPCC 3rd Assessment Report) scenarios indicated a range 1.4-5.8°C (basically, 20 years ago).

2/

Schneider was expressing frustration that experts would not assign probabilities: "I urged the expert group to provide a subjective probability assessment for less expert users, but I was not persuasive enough, and the SRES authors
expressed “no preference” for each scenario"

3/

"Because of the divergent views of participants about the
likelihood of each storyline, the final report offered no assessment of the relative likelihoods, in an attempt to avoid endless disputes"

4/

I think Schneider's strongest point: "I strongly argued at the time that policy analysts needed probability estimates to assess the seriousness of the implied impacts; otherwise they would be left to work out the implicit probability assignments for themselves"

5/

I would argue we are at the same place 20 years later, though, the probability assessment is perhaps morphed into the phrase "feasibility"

6/

"In the risk-management dilemma that constitutes climate-change [policy], I would definitely put more
trust in the probability estimates of the SRES team — however subjective — than those of the myriad special interests that have been encouraged to make their own
selection."

7/

I agree, 100%. We need to assign probabilities to scenarios, if we don't others implicitly will.

8/

On a lighter note. Amazing how little changes in 20 years

(Worth a read, if anything, for the very personal style that was used back in the day nature.com/articles/35075…)

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