Forests may absorb 30 percent less carbon than climate models predict, new study finds

A new study published in Geophysical Research Letters finds that climate models may overestimate how much carbon forests can absorb by as much as 30 percent. Researchers used eight years of daily growth data from 160 trees across 47 sites in Switzerland and found that hot, dry conditions can stall tree growth even when photosynthesis continues. The gap was largest for conifers and broadleaf trees in southern Europe, where drier conditions are expected to intensify. The study challenges a key assumption in most climate models: that photosynthesis and tree growth move together. When air gets hotter and drier, water pressure inside trees drops, limiting cell division and wood formation. Trees keep taking in carbon dioxide but cannot use it to grow. The researchers say climate models need to be rebuilt to reflect this physical limit. The findings could affect how governments plan their climate targets, since forests currently absorb about 27 percent of human CO2 emissions each year.