COP26: What will the world look like at 3C of warming? How different will it be from 1.5C warming?

In the Paris Agreement, countries committed to seek to limit the increase in temperature to 1.5 C above pre-industrial levels. However, even if countries fulfilled their current pledges to reduce emissions, we would still see an increase of around 2.7 C. No wonder that nearly two thirds of Intergovernmental Panel on Climate Change authors who responded to a new survey conducted by the journal Nature expect the increase to be 3 C or more. At the outset, it is important to point out that even if impacts increased in line with temperature the impacts at 3 C warming would be more than twice those at 1.5 C. This is because we already have an increase of around 1 C above pre-industrial levels, so impacts at 3 C would be four times as great as at 1.5 C. In practice, however, impacts do not necessarily increase linearly with temperature. We found that, for example, the global average annual chance of having a major heatwave increases from around five percent over the period 1981-2010 to around 30 percent at 1.5 C but 80percent at 3 C. The average chance of a river flood currently expected in two percent of years increases to 2.4 percent at 1.5 C, and doubles to four percent at 3 C. At 1.5 C, the proportion of time in drought nearly doubles, and at 3 C it more than triples. The chances of what is currently considered a ten-year flood increases in the north west of England from 10 percent each year now to 12 percent at 1.5 C and 16 percent at 3 C. As at the global scale, there is considerable variability in impact across the UK, with risks related to high-temperature extremes and drought increasing most in the south and east, and risks associated with flooding increasing most in the north and west.