Climate models projecting higher warming for a given level of carbon dioxide have been discounted as unrealistic, but a new way of assessing models suggests they may, in fact, turn out to be accurate. The conclusion has enormous implications. For instance, a project called the Climate Action Tracker currently projects that average global surface temperatures will rise by 2.6°C by 2100 if countries implement existing policies.
Gyuleva team’s results suggest we are instead heading for 3.25°C. Why global warming is accelerating and what it means for the future How much the world will warm depends on how much more CO2 we put into the atmosphere and how the planet responds to that CO2. Different climate models vary in how much warming they project for a given CO2 level.
For instance, some models suggest that a doubling of CO2 will result in the average global surface temperature increasing by around 1.6°C in the short term. Others suggest it could be as high as 3°C. The models are fed data on greenhouse emissions over the past century or so, and their projected climate response compared with what actually happened.
For the last report by the Intergovernmental Panel on Climate Change, a lot of these models simulated more warming than had happened, so were discounted. Based on the remaining models, the panel’s last report concluded that a doubling of CO2 would result in between 1.2°C and 2.4°C of warming in the short term, with a best estimate of 1.8°C. Global warming already causing crop losses of over $20 billion a year But there is lots of variability in Earth’s climate.
For instance, during the La Niña climate pattern, cooler seawater from deeper down spreads across the ocean, resulting in cooler surface temperatures. So, Gyuleva and colleagues have filtered the historical climate record to try to remove the effect of variability due to phenomena like La Niña. Their results suggest that natural variability limited temperature rises between 1981 and 2014 – a period that includes the so-called global warming hiatus in the first decade of the 21st century.
But Gyuleva’s team also assessed models using a new approach. Instruments on several satellites have been measuring how much shortwave radiation from the sun enters the atmosphere, and how much longwave radiation is emitted. The difference between how much heat energy enters the atmosphere and how much leaves is the most fundamental measure of global warming.
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