Arbitrarily selected with little to no scientific basis. Check the siblings, it was some random “scientist” that pulled a number out of who knows where, under the consideration “politicians like limits and people tend to go over speed limits, so I said 1.5”. There’s no science to it, just fear mongering and grant seeking.
When this happens in any other “scientific” field HN is quick to jump on it, but when it comes to climate change we love to toe the party line.
1.5° was a good guess as to what we could achieve and what would avoid a good deal of harm. Was there a dictum from objective reality to stay below that threshold? No. It was mostly a cost benefit decision on the part of politicians and scientists.
The baseline was chosen because it had good data and was prior to the vast majority of greenhouse gas emissions.
Pretty much all baselines and goals are chosen to some extent based on circumstances and possibility. That doesn't make them arbitrary. using 1970 as a baseline would ruin the pre-industrial comparison. Aiming to say under 5° would be ridiculously dangerous.
> The baseline was chosen because it had good data and was prior to the vast majority of greenhouse gas emissions.
We have data going back literal hundreds of thousands of years via ice cores. Of course if we picked that data the numbers would look incredibly dumb: depending on what 57 year chunk you took as “baseline” at we’d be a delta of anywhere from -2 to 8 degrees, and where exactly on that range we’d fall would vary more or less randomly with the time of the chunk’s start.
We’re looking at the most minuscule (~100yr) chunk of 500,000 year time series and getting worried about its slope. It’s laughable.
> Aiming to say under 5° would be ridiculously dangerous.
Dangerous how? Because that’s the exact temperature range we were at ~0.4mya, and look how well we’re doing now! Civilization and everything.
> We have data going back literal hundreds of thousands of years via ice cores. Of course if we picked that data the numbers would look incredibly dumb: depending on what 57 year chunk you took as “baseline” at we’d be a delta of anywhere from -2 to 8 degrees, and where exactly on that range we’d fall would vary more or less randomly with the time of the chunk’s start.
You're ignoring that the thing we are trying to track/correct is man made warming. If that's the goal, what's a good anchor? How about the period where we have the most data prior to us causing warming? That'd be the late 19th century.
Furthermore, that data going back hundreds of thousands of years is exactly the reason we know 5° Celsius would be dangerous: we are changing the planet faster than any of those records would indicate has happened previously, outside of massive extinction events. The speed of the change is as important as the degree, so reversing 400k years of cooling in a few hundred seems like an incredibly dangerous thing to do.
[1]https://climatepositions.com/global-warming-pre-industrial-t...