Emerging compound air-soil heatwaves amplify global vegetation losses

Compound air-soil heatwaves-periods in which extreme air and soil temperatures co-occur-pose a growing threat to terrestrial ecosystems, yet their occurrence and impacts remain poorly understood. Here, we show that compound air-soil heatwaves have become more frequent (0.59 ± 0.07 events decade^-1), longer-lasting (0.18 ± 0.04 days decade^-1) and more intense (4.02 ± 0.77°C × days decade^-1) since 1979. These rates of change far exceed those for independent air and soil heatwaves and are driving increasingly widespread reductions in vegetation productivity. On average, ∼98.5 million km² of land experienced gross primary productivity (GPP) losses during compound air-soil heatwaves. Globally, annual GPP losses have risen by 0.61 gC m^-2 year⁻¹ decade⁻¹, which is a 30.5- and 12.2-fold increase relative to those of independent air and soil heatwaves, respectively. Climate model projections indicate that compound air-soil heatwaves will continue to intensify and expand spatially under future warming, particularly under the high-emission scenario. Given pronounced GPP reductions during compound heatwaves, their projected intensification is likely to pose an increasing threat to terrestrial ecosystem productivity. Our findings highlight the escalating ecological impacts of compound heatwaves and underscore the urgent need for adaptation and preparedness strategies to address this compound hazard in a warming world.