Regional acceleration of climate change

Anthropogenic activity has altered Earth’s climate at a rate unprecedented in millennia. Whether this rate itself has increased in recent decades remains uncertain, partly because natural variability obscures acceleration signals over short timescales. Here, we show that commonly used detection methods can yield different acceleration estimates, helping to explain divergent conclusions in the literature. We then examine whether acceleration emerges more clearly at regional than at global scales using observational, reanalysis, and simulation datasets. We find that large areas of the planet show significant acceleration of surface temperature. Densely populated regions, biodiversity hotspots, and Key Biodiversity Areas are particularly affected, with roughly half of the world’s population already living in areas undergoing accelerating warming. We show that this regional signal is correlated with the emergence of a global acceleration signal, indicating that a detectable global signal is expected around the present decade. We further demonstrate that regional aerosol forcing modulates the timing of acceleration emergence, delaying detection in heavily polluted regions while hastening it where aerosol emissions have declined. Finally, we assess when a deceleration signal is expected to emerge under different emissions pathways over the twenty-first century. Under a stringent mitigation pathway (SSP1-2.6), a deceleration signal in global warming is projected to emerge near mid-century, whereas under a moderate emissions pathway (SSP2-4.5) it is delayed by about three decades, emerging around 2080. These results indicate that the climate system is not only warming, but doing so at an increasing rate in many inhabited regions, underscoring the urgency of rapid mitigation and adaptation.