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Most models used in the scientific literature on climate change, especially since the Paris Agreement, are based on a technique called backcasting, that calculates what patterns of CO2 emissions are compatible with a chosen temperature goal, such as a 1.5 °C increase in global temperature. A study in Nature Climate Change took the opposite route, starting from current emission trends and Nationally Determined Contributions (NDCs, that represent each country’s binding commitments for reducing emissions). It combined seven different models to calculate how those trends may evolve beyond 2030, and how they would affect climate. The results1 show that current policies are unlikely to prevent an increase in global temperatures well above the Paris targets.
“The common approach is a bit distant from how mitigation policy happens in reality,” explains Lorenza Campagnolo, co-author of the study and researcher at Ca’ Foscari University in Venice, the European Institute on Economics and the Environment (EIEE) and the Euro-Mediterranean Center on Climate Change (CMCC). “Ours is different because it takes into account implemented policies and NDCs, and builds on them to model emission estimates and temperature increase estimates.”
The study predicts temperature increases to range between 2.2 and 2.9 degrees by 2100. Despite a wide range of possible emissions pathways by 2050, nearly all the scenarios in the study have median warming below 3 °C in 2100. However, even the most optimistic scenario does not allow to limit global warming to less than 2 °C. These findings, said Campagnolo, are in line with other recent studies following COP26 outcomes, such as Climate Action Tracker’s analysis which projects an increase of 2.4 degrees based on current policies.
“We have tried to consider different scenarios and quantify how different models lead to different results” says Campagnolo. For example, some scenarios calculate the effect of mitigation policy assuming reductions in emission intensity (CO2 emissions per unit of GDP) similar to those observed in the past decades, while others focus on increasing carbon prices. “If no other policy instruments are used than the carbon price, models predict the necessity of Carbon Capture and Storage as a key technology to achieve decarbonization,” says Elisa Delpiazzo, co-author of the study and researcher at Ca’Foscari, EIEE and CMCC. By applying the same carbon price to all sectors and all countries, she explains, these models can exaggerate the role of CCS, despite it not being a mature technology yet. “Scenarios that account for current sector-specific mitigation policies, foresee a greater use of electrification and renewables, even in the automotive sector”.
The finding that different models point to different pathways for reducing emissions is indeed a key message of the study. “There is not just one way to get there,” says Delpiazzo. “It is important that we start from today’s trajectories, and see how far we are from the ‘ideal’ we set for ourselves.”
