Doubling CO2 compared to the preindustrial era is worth up to +4.8 °C of global warming
The Earth’s climate system is more sensitive than expected to anthropogenic greenhouse gas emissions, with the result that global warming is accelerating more than climate scientists have estimated so far. At this rate, we could steadily exceed the threshold of 1.5 degrees within this decade (instead of the mid-1930s, according to IPCC forecasts) and exceed the maximum limit of the Paris Agreement by bringing us over 2 degrees already around 2050.
This is supported by a study published in Oxford Open Climate Change by James Hansen, long-term climate scientist who already in the 80s warned the United States Congress of the dangerousness of the increase in greenhouse gases in the atmosphere. To a similar conclusion came a study published this week that recalculates the carbon budget and suggests that the overrun year will be 2029.
Why is global warming accelerating?
Hansen’s starting point is a reassessment of the Earth’s climate sensitivity to changes in carbon dioxide in the atmosphere. With a doubling of CO2 compared to the pre-industrial era, the IPCC estimates that global warming is about 3 degrees. Using the most up-to-date paleoclimatic data, Hansen and colleagues come to the conclusion that the increase in global temperature for the same amount of additional CO2 can reach +4.8 ºC.
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If so far the lowest estimates seemed consistent with field observations it is because air pollution – generated by burning fossil fuels – has shielded part of the incoming solar radiation on Earth. But with the fight against pollution and the reduction of emissions, in particular aerosols, the health gain is also accompanied by a greater increase in temperature.
Hansen’s study attempts to quantify the effect of the gradual disappearance of aerosols on global temperatures. And it predicts that the collapse of these particles from 2010 onwards will soon lead to an increase in the rate of global warming well distinguishable from the factors that determine the natural variability of the Earth’s climate system. Thus, if global warming has raced at the rate of +0.18°C per decade between 1970 and 2010, after that date it will soar to +0.27°C. Almost double. With these rhythms, we will exceed 1.5 degrees already before 2030.