A new study from Cornell University finds that climate models may overestimate how much carbon forests can store by as much as 30 percent. The research compared a statistical model built from eight years of measured tree growth in Swiss forests with a widely used land surface model. It found that standard simulations overestimate growth by a factor of two for broadleaf trees and three for coniferous trees. The main reason is that warming temperatures and drier air slow tree growth, a mechanism many models do not account for. This matters because land currently absorbs about 27 percent of CO2 from fossil fuel burning. If forests absorb less than expected, more CO2 stays in the atmosphere, leading to faster warming. The study highlights a disconnect between field ecologists and climate modelers, and suggests current projections may be too optimistic about nature's ability to offset emissions. For carbon markets and climate policy, this means relying on forest-based offsets may be riskier than assumed.
