[exoverito]

Britain halved their emissions primarily because the West has been deindustrializing and offshoring their production to China. Global CO2 emissions have still increased significantly in the past 35 years, so these national figures are mostly just accounting tricks.

Also if things get bad we can just use stratospheric aerosols to cool the Earth. Terraforming would be like a thousandth the cost of trying to completely replace all energy infrastructure by 2050. I'm not opposed to building more sensible energy production like advanced fission, but given how slow, inefficient, and expensive infrastructure has become in the West I wouldn't bet that net zero happens by 2050, especially without decimating the middle classes.