Does anyone here knows what is the temperature value that we are comparing to?
I cannot find that anywhere.
I cannot find that anywhere.
1. If you mean what 1.5 degrees is above, it's an anomaly, which is defined as the difference from an average computed over a somewhat arbitrary time window. I think this one is defined as 1850-1900, which is defined as "pre industrial" times. Britain and America might disagree about that classification, but this is how it's done.
2. If you mean what 1.5 degrees is below, the answer is nothing. A 1.5 degree limit is a goal designed to motivate politicians. It's not justified by any particular research. It is discussed in this interview in Der Spiegel with an IPCC climatologist [1]:
SPIEGEL: Why then have you, as one of the creators of the two-degree target, imposed such a magical limit to which all countries must slavishly adhere?
Schellnhuber: Politicians like to have clear targets, and a simple number is easier to handle than a complex temperature range. Besides, it was important to introduce a quantitative orientation in the first place, which the 1992 Framework Convention on Climate Change managed to elegantly wangle its way out of. And let's be honest: Even if we aim for the two-degree target, we'll end up somewhat higher. Whenever there's a speed limit, most drivers tend to go a little faster.
[...]
And of course the world won't end if temperatures go up by 2.01 degrees, let alone end suddenly. From today's scientific perspective, we could possibly live with a warming of two to three degrees
[1] https://www.spiegel.de/international/world/german-climatolog...
It's strange that we don't a value but a definition of a value.
I totally understand that we need a target to motivate politicians (sad but true).
https://www.ncei.noaa.gov/access/monitoring/monthly-report/g....
In my opinion the only way to slow down involves changing this growth oriented economy. I hope the EU conference "Beyond growth" is a start of a new movement.
But I'm not even sure ratios matter here. The earth is a sensitive system and the amount of change it takes to knock it out of wack is peculiar to it. I don't think you can just look at ratios of (absolute) temperatures.
How sensitive exactly is called equilibrium climate sensitivity (ECS). Climatologists compute it using global climate models and different climatology groups have different models, so they produce different numbers. Unfortunately the span is wide and has been getting wider with time as the simulations become more detailed, so confidence in this value has been falling. This isn't meant to happen and we're rarely directly told it is, actually we're told the opposite (that there is consensus on everything).
IPCC 2013 AR5: "No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence".
The most recent IPCC reports try to solve this by de-weighting the models that compute a high ECS i.e. a highly sensitive climate. They do this because they know the models must be wrong, as they conflict with observational data. The climate can't actually be all that sensitive to CO2 relative to what some climatologists try to claim. Unfortunately most climatological research does not do this and assumes all models are equally valid, so justs averages all of them. It's clearly not valid when error bars are so wide.
Also, this situation leads to the obvious question of why not simply compute ECS from observed data to begin with? Unfortunate answer: because if you do, you get a very low value indeed (see the work of Lewis). With ECS values that low CO2 stops being a significant environmental problem and is probably less important than other environmental problems like e.g. clean rivers, biodiversity. Climatologists don't like to do this and prefer to continue deriving values from models, even though they know that at least some of them cannot be correct.
tl;dr - what you state as fact is actually one of the most bitterly argued and controversial aspects of climate science. They have a way to express it numerically but nobody can agree what the right number is.
If the average temperature were above 40°C there, again, would be no life on this earth, because proteins start coagulating at about that temperature, weird vent hole creatures at the bottom of the oceans exempted.
A temperature change of 1.5°C is a big change in the context of temperatures that support life, let alone temperatures that allow humans to have the foods and outdoor fun that we’ve enjoyed this past few hundred thousand years.