Why We Won’t Know When We’ve Passed the 1.5-Degree Threshold

e360.yale.edu

Why We Won't Know When We've Passed the 1.5-Degree Threshold

4 comments

Already there. Average has been above 1.5°C since August.
- That just gives you mudslides.
- Warming surpassed the 1.5-degree mark for one month or more in 2016, 2017, 2019, 2020, and again in 2023.
  Measured across the entire year, 2023 will conclude 1.4 degrees hotter than the preindustrial era, and at least one of the next five years is expected to surpass 1.5 degrees. But it’s unclear at what point the world will have officially breached the Paris target, as the pact offers no clear guidance on this matter.
  By Copernicus's metric, we're currently at about 1.25C long-term average and on track to pass 1.5C in about a decade.
All a bit surreal, because it really isn't a physical threshold - just a diplomatic one, lower than 2ºC (too high to save some islands, deltas, food, ecosystems), and higher than 1ºC (already passed when they wanted a lower target). There was originally some paleoclimatic justification for 2ºC, but not with any precision, these round numbers depend on our definition of degrees as 1% of the range from freezing to boiling water.
Sure the physical climate system includes many tipping points, but their thresholds vary by region and sector and we don't know them with precision. So when you try to integrate risk across projected impacts (result of which depends strongly on value judgements) you get a curve, on which nobody has shown that 1.5 marks a special nonlinearity.
Diplomatic thresholds do matter for our social system, but we should acknowledge these for what they are.
Otherwise it tempts the reaction - ok we failed, world's going to end, let's go have another [conference of the] party.