Rising temperatures

In August 2021, the IPCC published its most recent report on the Physical Science Basis for Climate Change, representing the global scientific consensus. The report stated that global surface temperature was, on average, 1.09 degrees higher in the last decade (2011-2020) than it was between 1850-1900, before large-scale greenhouse gas emissions started having an effect. It also stated that “each of the last four decades has been successively warmer than any decade that preceded it since 1850”.

These rapid temperature rises are the result of increases in the concentrations of greenhouse gases in the atmosphere since about 1750. These increases, the IPCC report says “are unequivocally caused by human activities”. Having reconstructed temperatures from before human observations started, the scientists behind the report can state that our current level of warming is unprecedented in 2,000 years.

Reconstructing historic global temperatures might sound complicated, but it’s actually a well-established science. Researchers use a variety of methods, including drilling boreholes, studying the records preserved in rocks, tree rings, shells and microfossils and analysing the composition of ancient snow preserved in the ice sheets in Greenland and Antarctica. They cross-reference these with each other to establish a “paleoclimatic record”, allowing us to compare today’s temperatures with those of previous eras.

The rapid increase in global average temperatures is the root cause of many of the other catastrophic impacts of climate change – from the increased frequency of droughts, hurricanes and wildfires, to the melting of glaciers and ice sheets, to the rises in global sea levels. But rising temperatures are also deadly in their own right.

Excess deaths from heat waves is already a concern. The 2003 heat wave in Europe is estimated to have killed around 70,000 people, for example, and it’s estimated that over 1,000 people died in the Western United States and Canada as a direct result of the high temperatures in June and July 2021. As mean temperatures climb, such heat waves will become more common.

“Wet bulb temperature” (WBT) is a measurement that takes into account the cooling effect of evaporation. When the WBT reaches 35 degrees C, the human body can no longer cool itself down by sweating. Even if you’re sitting in the shade with unlimited water to drink, you’ll die of overheating within a matter of hours if the WBT is 35 degrees or higher.

It’s predicted that by later this century, wet bulb temperatures of more than 35 degrees will become common in certain areas of the world, including the Persian Gulf, rendering outdoor work impossible, and making many regions all-but uninhabitable.