Deforestation involves the deliberate clearing of forests, converting these lands for other purposes such as agriculture, urban development, or mining. This practice contributes to global warming. Human activities, primarily the burning of fossil fuels, have increased heat-trapping greenhouse gas levels in Earth’s atmosphere. Deforestation is a significant contributor to this warming trend.
Forests and the Carbon Cycle
Forests function as natural carbon sinks, absorbing carbon dioxide (CO2) from the atmosphere through photosynthesis. This CO2 is then stored within their biomass, including trunks, branches, leaves, roots, and the surrounding soil. Tropical forests alone hold more than 210 gigatons of carbon, helping regulate atmospheric CO2 levels.
When forests are cleared, particularly through methods like slash-and-burn, this stored carbon is released back into the atmosphere. Burning trees rapidly converts their stored carbon into CO2, while decomposition of felled trees also releases carbon, albeit at a slower rate. Between 2015 and 2017, gross carbon emissions from tree loss were estimated at 4.8 billion tons annually, equivalent to the lifetime emissions of 85 million cars.
The removal of forests also means a significant loss of their future capacity to absorb CO2 from the atmosphere. This reduction in natural carbon absorption, combined with the immediate release of stored carbon, leads to a net increase in atmospheric CO2 levels. This imbalance intensifies the greenhouse effect, directly contributing to global warming. Land use changes, primarily deforestation, are estimated to contribute between 12% and 20% of global greenhouse gas emissions.
Some tropical forests, like the southeastern Amazon Rainforest, have even transitioned from being carbon sinks to becoming net carbon sources due to extensive deforestation and degradation. This means they now release more carbon than they absorb, accelerating CO2 accumulation. The ongoing demand for agricultural commodities, such as palm oil, soya, and cattle ranching, drives much of this deforestation, particularly in tropical regions like South America and Southeast Asia.
Disruption of Water Cycles
Forests play a significant role in Earth’s water cycle through a process called evapotranspiration. Trees release water vapor into the atmosphere from their leaves. This continuous release of moisture contributes to the formation of clouds and influences local precipitation patterns.
This evapotranspiration process also contributes to local cooling through latent heat transfer. As water evaporates from the leaves, it absorbs heat from the surrounding environment, leading to a cooling effect. When forests are removed, this natural cooling mechanism is lost, resulting in increased local temperatures on the deforested land.
Reduced evapotranspiration in deforested areas can lead to decreased humidity in the atmosphere. This reduction in atmospheric moisture can alter precipitation patterns, potentially leading to less rainfall in deforested regions and even in distant areas downwind. Consequently, deforested areas become more susceptible to droughts. The loss of forest cover disrupts the natural regulation of moisture and temperature, contributing to warmer and drier conditions.
Altering Surface Energy Balance
Forests, with their typically dark and dense canopies, absorb a considerable amount of incoming solar radiation. When these forests are cleared, the exposed land surface changes significantly.
The newly exposed surfaces often have a lighter color compared to the dark forest canopy. This change in surface cover alters the Earth’s albedo, which is its ability to reflect sunlight. Lighter surfaces reflect more sunlight back into space, which can have a localized cooling effect.
Despite this localized albedo effect, the overall impact of forest removal on the Earth’s energy balance contributes to warming. Dense forest canopies provide extensive shade, which keeps the ground and the air beneath the canopy cooler than exposed land. The loss of these properties, combined with the significant carbon emissions and disrupted water cycles from deforestation, results in an overall warming trend.