Gavin Schmidt

The urgent case for net zero

Earlier this year, a report from climatologists around the world made it clear that climate change is happening now and that it is almost entirely a result of human behaviour. This is not a controversial conclusion and it is not hard to explain how the report’s authors arrived at it.

First, independent observations — from the ocean to the atmosphere, from poles to tropics — all show rapid and significant warming over the past century, particularly over the past few decades. Human activity has simultaneously caused a 50 per cent increase in carbon dioxide concentrations, a more than doubling of methane concentrations, and the appearance of multiple synthetic gases, all of which are potent greenhouse substances.

Who is responsible? Over the past 170 years, carbon dioxide emissions have been led by the United States, followed by China, Russia, and the UK in eighth place. It’s worth noting, however, that UK emissions have fallen faster since 2010 than those of any other major economy.

Even before the warming was distinguishable from the weather, scientists had predicted these increases in greenhouse gases would have some profound effects, namely glacier reduction, the warming of the Earth’s surface, ocean temperatures increasing and sea levels rising.

Scientists have looked at what else could be causing global warming — the sun, volcano eruptions, wobbles of the Earth’s orbit, ozone depletion, air pollution and deforestation. But when it comes to the plus 1ºC global trend in warming, only the human-caused effects — the greenhouse gases, moderated partially by cooling from air pollution — fit the evidence.

The global warming we’ve seen so far is contributing to extreme weather worldwide. Heatwaves are becoming more frequent and more intense; rain is falling harder by about 7 per cent for every degree we warm; and when there are droughts, they are becoming more intense, with decreases in soil moisture 10 to 30 per cent greater.

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