Tracking Shifts and Uncertainty in Global Climate Space: Holdridge Life Zones Across the CESM2 Large Ensemble

Climate change is altering the “climate space” that ecosystems and species occupy. This multidimensional space defines where biomes can exist, and its rate of change determines whether vegetation can keep pace through processes like migration or adaptation. When climate shifts faster than vegetation can track it, ecological mismatches can emerge, leading to species die-off or invasion by novel communities. Using the Holdridge Life Zone framework, I examine global changes in climate space and life zone distributions through 2100 using a 90-member Community Earth System Model Large Ensemble. This ensemble approach quantifies both the magnitude and uncertainty of projected shifts, revealing where future climate change is most likely to drive biome transitions and where predictions remain uncertain. Results show widespread shifts (50-60% of the landscape) in climate zones. Although strong warming trends indicate that ecosystem change is inevitable, the direction of those changes remains uncertain due to variability in precipitation and aridity projections. These findings highlight where climate-driven ecological change is both most rapid and most uncertain, offering insight into the stability and resilience of global ecosystems under future warming.