Re-appraisal of the global climatic role of natural forests for improved climate projections and policies

Abstract

Along with the accumulation of atmospheric carbon dioxide, the loss of primary forests and other natural ecosystems is a major disruption of the Earth system causing global concern. Quantifying planetary warming from carbon emissions, global climate models highlight natural forests' high carbon storage potential supporting conservation policies. However, some model outcomes effectively deprioritize conservation of boreal and temperate forests suggesting that increased albedo upon deforestation could cool the planet. Potential conflict of global cooling versus regional forest conservation could harm environmental policies. Here we present theoretical and observational evidence to demonstrate that, compared to the carbon-related warming, the model skills for assessing climatic impacts of deforestation is low. We argue that deforestation-induced global cooling results from the models' limited capacity to account for the global effect of cooling from evapotranspiration of intact forests. Transpiration of trees can change the greenhouse effect via small modifications of the vertical temperature profile.Due to their convective parameterization (which postulates a certain critical temperature profile), global climate models do not properly capture this effect. This parameterization may lead to underestimation of warming from the loss of evapotranspiration in both high and low latitidues, and therefore, conclusions about deforestation-induced global cooling are not robust. To avoid deepening the environmental crisis, these conclusions should not inform policies of vegetation cover management. Studies are mounting quantifying the stabilizing impact of natural ecosystems evolved to maintain environmental homeostasis. Given the critical state and our limited understanding of both climate and ecosystems, an optimal policy would be a global moratorium on the exploitation of all natural forests.

Even cooler insights: On the power of forests to (water the Earth and) cool the planet

“…Increasing cloud production, as illustrated by a quick comparison with Figures2 and 3above, leads to increased downward LW radiation toward the land surface and a decline in outgoing LW radiation. Moreover, since increasing concentrations of CO 2 /GHGs and clouds (water vapor) both act as GHGs, their persistent accumulation in the atmosphere appears to weaken any causal pathway (assuming one exists, see, e.g.,Colman & Soden, 2021;Jeevanjee et al, 2021Jeevanjee et al, , 2022Makarieva et al, 2023;Stevens & Bony, 2013) by which a share of the latent heat flux might move beyond the lower atmosphere and out into space. Thus, while Zeng et al, for example, suggest that increased ET is one of the principal drivers of cooling global temperatures(Zeng et al, 2017), the evidence presented here suggests something different: increasing latent heat production, cloud cover, and atmospheric CO 2 /GHG concentrations hinders the potential space-bound release of outgoing LW radiation, further exacerbating the climate problem.Thus, the steadily increasing gap between annual emissions and the CO 2 drawdown likely exacerbates atmospheric feedback, thereby strengthening the EEI.…”