Post COP27 nations are talking about whether or not 1.5C as a global warming target is “dead” or not. I’m not going into the politics of Western nations discussing this now because COP26 was held in a western nation where everyone clubbed together to pretend it was alive and now because it is in Egypt is fine to announce it’s demise, because, you know those African nations…prejudice…etc…etc.
This post is about the target
The original target was “well below 2, preferably to 1.5 degrees Celsius“, compared to pre-industrial levels” 2C. Set in Paris (2015).
This is not a clear cut target of 1.5C.
The secondary target of 2C is also poorly defined, using the term “well below”.
1C is “well below” 2C, so is that the target?
Noting the inclusion of the 1.5C bit was only because several island nations pointed out that they would be wiped out at 2C. So the 1.5C was tagged in as a concession to them.
However what is glaringly missing from this discussion, is the question, “at what temperature will warming bring and end to any state, whether it be a small low lying country in the South Pacific, or an industrialised country in central Europe?
Why should 1.5C be considered a demand by island nations, when no one knows the temperature thresholds that the societies of other countries can withstand. Or if they are any greater than 1.5C. Perhaps Sweden will become uninhabitable at 1.4C.
It does not seem that ANY WORK AT ALL has been done to settle on a global target threshold for
A. Social collapse
B. A Habitable Planet.
This is why we have multiple pathways across a range of outcomes from 1.5C (fudged with anything up to 1186 GtCO2 of CDR) to 5C or more.
In engineering analysis, when considering the failure of a structure (i.e. a steel bridge) the FIRST thing the engineer would do is work out the acceptance criteria. This would usually be a stress level in the steel material, set at a value below the material yield point.
Only with an acceptance criteria set do any of the subsequent calculated stresses from the structural loading make any sense.
If the loads cause a stress greater than the acceptance crieria the bridge design is a fail.
I the absence of any agreed acceptance criteria for global temperature rise, pathways of 5C make as much sense of pathways of 1.5C.
Hoever if we were to realise that 1.8C is threshold for social collpase – based maybe on crop yields falling to a specified level – then we can see that our current predicte pathway towards 2.7C (ish) is a FAIL.
At some point someone should be replacng political targets with scientific ones, because science and politics is a bad mix.