To wonder whether higher levels of carbon dioxide might stimulate more rapid plant growth—perhaps even in the tropics!—is one of those heresies that brings down instant condemnation from the climatistas, and yet a few brave scientists have decided to study and measure the topic. Last week the Proceedings of the National Academy of Sciences (PNAS) published “Effect of increasing CO2 on the terrestrial carbon cycle,” by two professors from CalTech and one from the National Center for Atmospheric Research in Boulder.
According to the article, CO2 “uptake” especially in tropical regions is considered the second-largest uncertainty in climate modeling (after cloud behavior), and most of the models assume limited increased CO2 absorption. But this study suggests otherwise. The abstract is typically dense, but you can make out the problem this poses for the certainty of the climatistas:
Feedbacks from the terrestrial carbon cycle significantly affect future climate change. The CO2 concentration dependence of global terrestrial carbon storage is one of the largest and most uncertain feedbacks. Theory predicts the CO2 effect should have a tropical maximum, but a large terrestrial sink has been contradicted by analyses of atmospheric CO2 that do not show large tropical uptake. Our results, however, show significant tropical uptake and, combining tropical and extratropical fluxes, suggest that up to 60% of the present-day terrestrial sink is caused by increasing atmospheric CO2. This conclusion is consistent with a validated subset of atmospheric analyses, but uncertainty remains. Improved model diagnostics and new space-based observations can reduce the uncertainty of tropical and temperate zone carbon flux estimates. This analysis supports a significant feedback to future atmospheric CO2 concentrations from carbon uptake in terrestrial ecosystems caused by rising atmospheric CO2 concentrations. This feedback will have substantial tropical contributions, but the magnitude of future carbon uptake by tropical forests also depends on how they respond to climate change and requires their protection from deforestation. (Emphasis added.)