JavaScriptDonkey wrote:Up front and flat out we do not know what impact 'an amount' of CO2 will have on our climate because we do not know how the climate works. We can make predictions but the certainty levels are low.
Anthropogenic climate impact is undeniable. Climate change is undeniable. That there is a linear relationship between emitted CO2 and the temperature in Cardiff in 2050 is less clear.
Yes, this is quite right. "The community" has been generally poor at first understanding and quantifying climate projection uncertainty and secondly communicating uncertainty. For the last few years climate projection uncertainty has had increased research attention.
JavaScriptDonkey wrote:What we do know for an absolute fact is that CO2 levels were higher than they are now for the majority of the period that life has been on this planet and yet we are here.
This is non sequitur, when we start to look millions of years back through time, the very "rules" of the Earth system change. The movements of the continents, and for example the recent closure of the Panama seaway have significant impacts on dynamics, energy distribution, ice sheet mass and ultimately temperature. Even the solar constant changes significantly on timescales of millions of years. In short 2000ppm 200 million years ago is an extremely poor analogue for 2000 ppm today.
JavaScriptDonkey wrote:I find that difficult to square away against the 'we are doomed' claims.
It all depends what you (and others) mean when they say 'we are doomed'. Are we talking about the ability of the planet to support the volume and biodiversity of life that it does today? Or are we talking about the 'collapse' of post-industrial civilisation with a die-off of several billion humans during the coming century? Even with a stable climate, there's a fair chance we won't be able to satisfactorily feed and water this century's population. Change the rainfall distributions, temperatures just a little bit and all bets are off in my opinion.
It's not so much about the magnitude of the changes, it's about the speed of change and our civilisation's degree of investment in the current climate. Our cities built <1m above sea level, our population's reliance on agriculture etc. Map the projected climate changes onto Homo sapiens 100,000 years ago and they'd hardly have noticed. They didn't have multi-generational investments and the world was huge compared to their 'footprint'. Some 10-14k years ago, only just pre-history, our ancestors witnessed a ~120m sea level rise which flooded them out of what is now the southern half the North Sea. It took a few thousand years, they didn't have cities like London - most folk alive then probably didn't even notice! Apply a similar (not that it could happen) sea level to today's civilisation and it would change everything.
JavaScriptDonkey wrote:Change is normal.
Absolutely. Unfortunately, change is just what our civilisation doesn't like. We don't have the slack. 2 degrees hotter or 2 degrees colder, 20% more or 20% less rainfall - change is bad as we're hyper invested in the past few thousand years stability.
"Life" will find a way, even with 4-6C temperature rise by 2100. I'm far less confident of the chances for a thriving 10bn strong human population by 2100 in a 4-6 degree warmer world.