Climate feedbacks of changing forest and grassland areas across the northern hemisphere

Background/Question/Methods

Forest cover has the ability to modify local climate through changes in surface fluxes of energy, water, and momentum. Changes in forest cover over large spatial areas may also have the ability to alter atmospheric circulation patterns globally, leading to consequences for ecology in locations far from the original change in land cover. These downstream impacts on ecology can then force climate locally, leading to ecoclimate teleconnections. Using global climate model experiments we find the mechanisms responsible for both local and global climate responses to changes in forested area across the northern hemisphere mid-latitudes as well as asses the potential for ecological response in regions remote from the original change in forest cover.

Results/Conclusions

An expansion of dark forests relative to grasslands increases the absorption of solar energy and increases surface temperature, particularly in regions where the land surface is unable to compensate with latent heat flux due to water limitation. Atmospheric circulation re-distributes the anomalous energy absorbed in the northern hemisphere, in particular towards the south, through altering the Hadley circulation, resulting in the northward displacement of the tropical rain-bands. Precipitation decreases over parts of the Amazon basin affecting productivity. The magnitude of circulation response to forcing from vegetation scales linearly with area of forest cover added. Clouds decrease in the afforested latitude, but increase over lower latitudes, compensating for some of the energy imbalance between hemispheres. Mid latitude afforestation is found to have a small impact on modeled global temperatures and on global CO2, but asymmetric heating from the increase in forest cover is capable of driving unintended and undesirable changes in circulation and precipitation. The ability of vegetation to affect remote circulation has implications for strategies for climate mitigation.