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Temporary 1.5° Overshoot Would Increase Heat and Drought, Harm GDP, Scientists Warn

Opting for a temporary “overshoot” of end-of-century global temperature targets and the subsequent “Hail Mary” deployment of carbon dioxide removal (CDR) technologies, rather than never permitting global heating to exceed safe limits, would leave both the climate and the global economy very much worse off by 2100, warns new research.

Known as the “end-of-century” pathway, the overshoot + CDR route to capping global heating at 1.5°C (or 2°C) by 2100 is a popular one, but should not be, say the authors of two new studies just published in the journal Nature Climate Change.

By comparison, a true “net-zero” pathway would help keep a lid on both climate havoc and economic distress by reducing emissions early enough to keep global heating below Paris targets, writes Carbon Brief. Climate scientist Dr. Laurent Drouet, lead author of one of the studies, traced the continuing popularity of overshoot models to their tendency to focus primarily on costs of climate change mitigation, rather than accounting for “the geophysical and economic impacts from climate change.”

By that deeply limited logic, it looks like a sound idea to kick the can of emissions reductions down the road until CDR is advanced enough to swoop to the rescue.

In a global research first, Drouet’s team “calculated the probabilistic climate impacts of a range of indicators—including the frequency and duration of heat waves and agricultural drought—in both the end-of-century and net-zero pathways to 1.5°C and 2°C warming,” Carbon Brief reports. The study found a significantly larger probability of “high” heat wave duration on the overshoot pathway. The impacts would land heaviest on western and southern Africa and Brazil.

While net-zero pathways either avoided damage or produced economic benefits, Drouet and his team found that overshoot-dependent pathways delivered both higher mitigation costs and more economic damage by 2050.

A second study led by Dr. Keywan Riahi, program director at the International Institute for Applied Systems Analysis (IIASA), found that “global GDP in 2100 will be up to 2% higher in scenarios that avoid overshoot,” Carbon Brief adds.

While avoiding overshoot through aggressive mitigation efforts will require “higher up-front costs” than embracing offshoot + CDR, the payoff will come once net-zero is achieved and the economy rebounds, the authors reported.

Riahi’s team also found that allowing overshoots would come at a steep climate cost, with the planet warming as much as an extra 0.16°C by 2100.