@deveraux there is a tonne of different types of reports explaining exactly the type of evidence that you are asking for. I'm finding it a bit disingenuous.
E.g. www.ipcc.ch/sr15/ which outlines various high confidence, medium confidence adn low confidence scenarios, written by these people: www.ipcc.ch/sr15/authors/ (86 Authors and Review Editors from 39 countries)
And this explainer from NASA: NASA has the following: climate.nasa.gov/news/2865/a-degree-of-concern-why-global-temperatures-matter Reviews the SR15 report
climate scientists have very effectively predicted how temperatures will rise based on concentrations of CO2 in the atmosphere: theconversation.com/40-years-ago-scientists-predicted-climate-change-and-hey-they-were-right-120502
probabilities are here: climateactiontracker.org/global/temperatures/
In the absence of policies, global warming is expected to reach 4.1°C – 4.8°C above pre-industrial by the end of the century. The emissions that drive this warming are often called Baseline scenarios (‘Baselines’ in the above figure) and are taken from the IPCC AR5 Working Group III. Current policies presently in place around the world are projected to reduce baseline emissions and result in about 3.0°C1 warming above pre-industrial levels. The unconditional pledges and targets that governments have made, including NDCs2 as of December 2019, would limit warming to about 2.8°C3 above pre-industrial levels, or in probabilistic terms, likely (66% or greater chance) limit warming below 3.0°C.
globalwarming.berrens.nl/globalwarming.htm
BETWEEN TWO AND THREE DEGREES OF WARMING
Up to this point, assuming that governments have planned carefully and farmers have converted to more appropriate crops, not too many people outside subtropical Africa need have starved. Beyond two degrees, however, preventing mass starvation will be as easy as halting the cycles of the moon. First millions, then billions, of people will face an increasingly tough battle to survive.
To find anything comparable we have to go back to the Pliocene – last epoch of the Tertiary period, 3m years ago. There were no continental glaciers in the northern hemisphere (trees grew in the Arctic), and sea levels were 25 metres higher than today’s. In this kind of heat, the death of the Amazon is as inevitable as the melting of Greenland. The paper spelling it out is the very one whose apocalyptic message so shocked in 2000. Scientists at the Hadley centre feared that earlier climate models, which showed global warming as a straightforward linear progression, were too simplistic in their assumption that land and the oceans would remain inert as their temperatures rose. Correctly as it would turn out, they predicted positive feedback.
Warmer seas absorb less carbon dioxide, leaving more to accumulate in the atmosphere and intensify global warming. On land, matters would be even worse. Huge amounts of carbon are stored in the soil, the half-rotted remains of dead vegetation. The generally accepted estimate is that the soil carbon reservoir contains some 1600 gigatonnes, more than double the entire carbon content of the atmosphere. As soil warms, bacteria accelerate the breakdown of this stored carbon, releasing it into the atmosphere.
The end of the world is nigh. A three-degree increase in global temperature – possible as early as 2050 – would throw the carbon cycle into reverse. Instead of absorbing carbon dioxide, vegetation and soils start to release it. So much carbon pours into the atmosphere that it pumps up atmospheric concentrations by 250 parts per million by 2100, boosting global warming by another 1.5C. In other words, the Hadley team had discovered that carbon-cycle feedbacks could tip the planet into runaway global warming by the middle of this century – much earlier than anyone had expected.
Confirmation came from the land itself. Climate models are routinely tested against historical data. In this case, scientists checked 25 years’ worth of soil samples from 6,000 sites across the UK. The result was another black joke. As temperatures gradually rose the scientists found that huge amounts of carbon had been released naturally from the soils. They totted it all up and discovered – irony of ironies – that the 13m tonnes of carbon British soils were emitting annually was enough to wipe out all the country’s efforts to comply with the Kyoto Protocol.” All soils will be affected by the rising heat, but none as badly as the Amazon’s. “Catastrophe” is almost too small a word for the loss of the rainforest. Its 7m square kilometres produce 10% of the world’s entire photosynthetic output from plants. Drought and heat will cripple it; fire will finish it off. In human terms, the effect on the planet will be like cutting off oxygen during an asthma attack.
In the US and Australia, people will curse the climate-denying governments of Bush and Howard. No matter what later administrations may do, it will not be enough to keep the mercury down. With new “super-hurricanes” growing from the warming sea, Houston could be destroyed by 2045, and Australia will be a death trap. “Farming and food production will tip into irreversible decline. Salt water will creep up the stricken rivers, poisoning ground water. Higher temperatures mean greater evaporation, further drying out vegetation and soils, and causing huge losses from reservoirs. In state capitals, heat every year is likely to kill between 8,000 and 15,000 mainly elderly people.
It is all too easy to visualise what will happen in Africa. In Central America, too, tens of millions will have little to put on their tables. Even a moderate drought there in 2001 meant hundreds of thousands had to rely on food aid. This won’t be an option when world supplies are stretched to breaking point (grain yields decline by 10% for every degree of heat above 30C, and at 40C they are zero). Nobody need look to the US, which will have problems of its own. As the mountains lose their snow, so cities and farms in the west will lose their water and dried-out forests and grasslands will perish at the first spark.
The Indian subcontinent meanwhile will be choking on dust. All of human history shows that, given the choice between starving in situ and moving, people move. In the latter part of the century tens of millions of Pakistani citizens may be facing this choice. Pakistan may find itself joining the growing list of failed states, as civil administration collapses and armed gangs seize what little food is left.
As the land burns, so the sea will go on rising. Even by the most optimistic calculation, 80% of Arctic sea ice by now will be gone, and the rest will soon follow. New York will flood; the catastrophe that struck eastern England in 1953 will become an unremarkable regular event; and the map of the Netherlands will be torn up by the North Sea. Everywhere, starving people will be on the move – from Central America into Mexico and the US, and from Africa into Europe, where resurgent fascist parties will win votes by promising to keep them out.
Chance of avoiding three degrees of global warming: poor if the rise reaches two degrees and triggers carbon-cycle feedbacks from soils and plants.
(This is the Hadley Centre) www.metoffice.gov.uk/research/approach/modelling-systems/unified-model/climate-models/hadcm3