From "Climate Wars: The Fight for Survival as the World Overheats"

From "Climate Wars: The Fight for Survival as the World Overheats"
by Gwynne Dyer.  This is a worst case business-as-usual scenario:

'Scenario 1
The Year: 2045
Average global temperature: 2.8 degrees Celsius higher than 1990
Global population: 5.8 billion.

'Since the final collapse of the European Union in 2036, under the stress of mass migration from the southern to the northern members, the reconfigured Northern Union (France Benelux, Germany, Scandinavia, Poland and the old Hapsburg domains in central Europe) has succeeded in closing its borders to any further refugees from the famine-stricken Mediterranean countries. Italy, south of Rome, has been largely overrun by refugees from even harder hit north African countries and is no longer part of an organised state, but Spain,
Padania (northern Italy) and Turkey have all acquired nuclear weapons and are seeking (with little success) to enforce food sharing on the better-fed countries of northern Europe.  Britain, which has managed to make itself just about self-sufficient in food by dint of a great national effort, has withdrawn from the continent and shelters behind its enhanced nuclear deterrent.

'Russia, the greatest beneficiary of climate change in terms of food
production, is the undisputed great power of Asia.  However, the
reunification of China after the chaos of the 2020s and the 2030s poses a renewed threat to its Siberian borders, for even the much reduced Chinese population of eight hundred million is unable to feed itself from the country's increasingly arid farmland, which was devastated by the decline of rainfall over the north Chinese plain and the collapse of the major river systems.  Southern India is re-emerging as a major regional power, but what used to be northern India, Pakistan and Bangladesh remain swept by famine and anarchy, due to the collapse of the flow in the glacier-fed Indus, Ganges and Brahmaputra rivers and the increasingly frequent failure of the monsoon.  Japan, like Britain, has withdrawn from its continent and is an island of relative prosperity bristling with nuclear weapons.

'The population of the Islamic Republic of Arabia, which had risen to forty million, fell by half in five years after the exhaustion of the giant
Ghawar oil field in 2020, and has since halved again due to the exorbitant price of what little food remains available for import from any source.  Uganda's population, 5 million at independence in 1962, reached 110 million in 2030 before falling back to 30 million, and the majority of the survivors are severely malnourished.  Brazil and Argentina still manage to feed themselves, but Mexico has been expelled from the North American Free Trade Area, leaving the United States and Canada with just enough food and water to maintain at least a shadow of their former lifestyles.  The wall along the US-Mexican border is still holding.

'Human greenhouse-gas emissions temporarily peaked in 2032, at 47 percent higher than 1990, due largely to the dwindling oil supply and the Chinese Civil War.  However, the release of thousands of megatons of methane and carbon dioxide from the melting permafrost in Arctic Canada, Alaska and Siberia has totally overwhelmed human emissions cuts, and the process has slid beyond human ability to control.  The combined total of human
and'-neo-natural' greenhouse-gas emissions continues to rise rapidly, and the average global temperature at the end of the century is predicted to be 8 or 9 degrees Celsius higher than 1990.'