The Unseen Effects of Deforestation: Biophysical Effects on Climate

Abstract

Climate policy has thus far focused solely on carbon stocks and sequestration to evaluate the potential of forests to mitigate global warming. These factors are used to assess the impacts of different drivers of deforestation and forest degradation as well as alternative forest management. However, when forest cover, structure and composition change, shifts in biophysical processes (the water and energy balances) may enhance or diminish the climate effects of carbon released from forest aboveground biomass. The net climate impact of carbon effects and biophysical effects determines outcomes for forest and agricultural species as well as the humans who depend on them. Evaluating the net impact is complicated by the disparate spatio-temporal scales at which they operate. Here we review the biophysical mechanisms by which forests influence climate and synthesize recent work on the biophysical climate forcing of forests across latitudes. We then combine published data on the biophysical effects of deforestation on climate by latitude with a new analysis of the climate impact of the CO2 in forest aboveground biomass by latitude to quantitatively assess how these processes combine to shape local and global climate. We find that tropical deforestation leads to strong net global warming as a result of both CO2 and biophysical effects. From the tropics to a point between 30°N and 40°N, biophysical cooling by standing forests is both local and global, adding to the global cooling effect of CO2 sequestered by forests. In the mid-latitudes up to 50°N, deforestation leads to modest net global warming as warming from released forest carbon outweighs a small opposing biophysical cooling. Beyond 50°N large scale deforestation leads to a net global cooling due to the dominance of biophysical processes (particularly increased albedo) over warming from CO2 released. Locally at all latitudes, forest biophysical impacts far outweigh CO2 effects, promoting local climate stability by reducing extreme temperatures in all seasons and times of day. The importance of forests for both global climate change mitigation and local adaptation by human and non-human species is not adequately captured by current carbon-centric metrics, particularly in the context of future climate warming.

Forest-based climate change mitigation and adaptation in Europe

“…In tropical regions, the effect is reversed because changes in evapotranspiration resulting from deforestation are more important than changes in albedo. Several studies highlight the need to consider these biophysical effects in climate change mitigation assessments (e.g., Grassi et al 2019;Kalliokoski et al 2020;Lawrence et al 2022). 115 MtCO 2 eq yr -1 (see Figure 1).…”

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“…As forests are not only effective carbon storing entities but play multiple roles in climate stabilisation, the feedback loops involving the loss of ecosystem functions and services are all the more worrying (Lawrence et al 2022). These are examples of how tipping cascades may be starting, or have already started (Steffen et al 2018).…”

The State of Nationally Determined Contributions: 2022

“…For example, mangroves protect coastal lands against rising seas and tidal surges, and inland forests moderate temperature fluctuations and stabilize water supply (GCA 2019). Forests also provide significant additional global and local cooling services beyond their ability to sequester carbon (Lawrence et al 2022). Thus, deforestation has important consequences for the climate at both global and local scales beyond the release of stored carbon.…”