文献阅读 260325-Global forestation and deforestation affect remote climate via adjusted atmosphere...

Global forestation and deforestation affect remote climate via adjusted atmosphere and ocean circulation来自 https://www.nature.com/articles/s41467-022-33279-9?fromPaywallRecfalse## Abstract:Background:Forests can store large amounts of carbon and provide essential ecosystem services. Massive tree planting is thus sometimes portrayed as a panacea to mitigate climate change and related impacts. Recent controversies about the potential benefits and drawbacks of forestation have centered on thecarbon storage potential of forests and the local or global thermodynamic impacts.What this paper did:Here we discuss how global-scale forestation and deforestation change the Earth’s energy balance, thereby affect theglobal atmospheric circulationand even have profound effectson the ocean circulation.Weperform multicentury coupled climate model simulations in which preindustrial vegetation cover is either completely forested or deforested and carbon dioxide mixing ratio is kept constant.Results:We show that global-scale forestation leads to a weakening and poleward shift of the Northern mid-latitude circulation, slows-down the Atlantic meridional overturning circulation, and affects the strength of the Hadley cell, whereas deforestation leads to reversed changes. Consequently, both land surface changes substantially affect regional precipitation, temperature, clouds, and surface wind patterns across the globe. The design process of large-scale forestation projects thus needs to take into account global circulation adjustments and their influence on remote climate.## Intro:Large-scale tree planting, along withbioenergy with carbon capture and storage, is one of the two most widely discussed land-based options for mitigating climate change complementary to fossil fuel emissions reductions.At the same time, particularly in the tropics, deforestation continues at a rapid pace.Bothforestation[here used as an umbrella term for reforestation and afforestation] and deforestation not only affect the carbon cycle and atmospheric CO2-concentrations, but also influence the local and global climate throughchanges in the surface energy balance (i.e., by changing albedo, evaporative fraction, and surface roughness).These so-calledbiogeophysical effectsstronglydepend on the location where land-use change occursand can oppose the changes in surface temperature that result from changes in land carbon storage6,8,9,10,11. On a global scale,changes in albedo tend to dominate the biogeophysicaltemperature response4,7. This implies that the globalmitigation effectof large-scale forestation could bediminished by the warming effect of a reduced surface albedo and altered radiative balance.In addition to this direct thermodynamic warming effect, there is evidence that a massive change in forest cover also altersatmospheric dynamics, which is an important driver of regional precipitation and temperature patterns. Recent studies suggest that surface temperature changes caused by large-scale forestation or deforestation in the extratropical Northern Hemispherecan lead to a shift in the intertropical convergence zone (ITCZ)and changes in cross-equatorial atmospheric heattransport5,14,15,16,17.Complete deforestation of the tropics may result in reduced tropical convection,which weakens the tropical source of poleward propagating Rossby waves, thereby altering extratropical circulation and surface weather18,19,20.Except for ref. 20, these studies were conducted with a slab ocean or prescribed sea-surface temperatures. However, there is evidence thatocean circulation plays an important role in shaping the climate systems response to large-scale forestation and deforestation4, and a change in ocean circulation may entail a reduced atmospheric circulation response17,21. Recent efforts based on the Land-Use Model Intercomparison Project (LUMIP) contribution to the Coupled Model Intercomparison Project Phase 6 (CMIP6) showed that several models respond to global deforestation with substantial near-surface temperature changes over the oceans10. In fact, the ocean thermohaline circulation appears to respond strongly to global-scale land-use change22. At present, it is unclear how the ocean and atmospheric circulations respond to global-scale forestation and deforestation in simulations with coupled atmosphere-ocean models. Because of their complexity, the remote effects of forestation and deforestation on weather and climate patterns remain unresolved and, inevitably, have not yet been adequately addressed in the related planning and policy-making processes. Given that a controversial recent study advocated for global-scale forestation to mitigate climate change23 and actual plans are currently being pursued (Trillion tree campaign, www.trilliontreecampaign.org), it is important to quantify potential side-effects of large global-scale changes in forest cover on circulation and remote weather patterns.## Results:Impacts on temperature, near-surface winds, clouds, and precipitationFig. 1: Changes of variables relevant to near-surface weather and climate.Changes in the meridional heat transport in the climate systemFig. 2: Changes of the annual mean meridional heat transport in atmosphere and ocean.Fig. 3: Slowdown and acceleration of the Atlantic meridional overturning circulation.Changes in midlatitude westerlies, weather systems and the extratropical jet streamFig. 4: Changes in the extratropical atmospheric circulation.Fig. 5: Seasonal changes in the strength of the Hadley cell.