You might like my article on this topic.
How much has the Earth warmed up since the “preindustrial” period? The politics of 1.2C.
It's more complex than you probably think. A LOT of this goes back to the 80's and 90's. When the "Moderates" in Climate Science defined the paradigm for the evolving field.
Always remember, "Climate Science" really only starts in 1957/1958 with the UN sponsored Geophysical Year. Climate Science as a field is only 65 years old.
In the beginning, we knew very little.
The 1.5C-2.0C range of warming BY 2100 was a product of the Moderate Faction of Climate Scientists in conjunction with the Fossil Fuel industry. It's based on the assumption that the Climate System is heavily self correcting and that warming in response to CO2 increases will come in two phases.
Phase One is Immediate Thermal Response
We increased the CO2 level in the atmosphere by 70ppm from 1850-1985 (280ppm to 350ppm). How much hotter did the world get?
About 0.6C. That's what the "Immediate Thermal Response" seemed to be.
Now, based on that, how much warming would you predict by 2100? By 2500?
At that time the Moderates expected around.
0.1C-0.2C Warming by 2100
1.5C-2.5C Warming by 2500
The ARGUMENT between the MODERATES and the EXTREMISTS, like James Hansen, was over HOW FAST the "long tail" warming would happen. The EXTREMISTS argued that we didn't know "for sure" how much warming we would get by 2100 and that caution was indicated.
The EXTREMISTS lost and the paradigm of the MODERATES has prevailed for the last 35 years.
Phase Two is Equilibrium Thermal Response.
This is how much hotter it gets when a new Climate Equilibrium or New Climate Energy State is reached. For example.
The Earthshine and NASA CERES studies observed a diminishment of the Earth's albedo over a 20 year period from 1999 to 2019. During that time "dimming" of the albedo increased the solar forcing by 2X.
Since 2015 the RATE OF WARMING has increased from 0.18C per decade to 0.36C per decade.
The amount of EXTRA ENERGY flowing into the Climate System via the Global Ocean has jumped from about 5 Hiroshima bombs per second to about 10 Hiros per second since 2015.
How much hotter do you think that will make 2100? Or 2500?
The paleoclimate record suggests Thermal Equilibrium of around 5.0C to 6.0C if we go to Net Zero tomorrow. At 0.36C per decade, it won't take us long to find out.
IT LOOKS LIKE THE EXTREMISTS WERE RIGHT.
