Deforestation is a primary contributor to climate change, [1] [2] and climate change affects the health of forests. [3] Land use change, especially in the form of deforestation, is the second largest source of carbon dioxide emissions from human activities, after the burning of fossil fuels. [4] [5] Greenhouse gases are emitted from deforestation during the burning of forest biomass and decomposition of remaining plant material and soil carbon. Global models and national greenhouse gas inventories give similar results for deforestation emissions. [5] As of 2019 [update], deforestation is responsible for about 11% of global greenhouse gas emissions. [6] Carbon emissions from tropical deforestation are accelerating. [7] [8]
When forests grow they are a carbon sink and therefore have potential to mitigate the effects of climate change.Some of the effects of climate change, such as more wildfires, [9] invasive species, and more extreme weather events can lead to more forest loss. [10] [11] The relationship between deforestation and climate change is one of a positive (amplifying) climate feedback. [12] The more trees that are removed equals larger effects of climate change which, in turn, results in the loss of more trees. [13]
Forests cover 31% of the land area on Earth. Every year, 75,700 square kilometers (18.7 million acres) of the forest is lost. [14] There was a 12% increase in the loss of primary tropical forests from 2019 to 2020. [15]
Deforestation has many causes and drivers. Examples include agricultural clearcutting, livestock grazing, logging for timber, and wildfires.
Another cause of deforestation is due to the effects of climate change: More wildfires, [18] insect outbreaks, invasive species, and more frequent extreme weather events (such as storms) are factors that increase deforestation. [19]
A study suggests that "tropical, arid and temperate forests are experiencing a significant decline in resilience, probably related to increased water limitations and climate variability" which may shift ecosystems towards critical transitions and ecosystem collapses. [17] By contrast, "boreal forests show divergent local patterns with an average increasing trend in resilience, probably benefiting from warming and CO2 fertilization, which may outweigh the adverse effects of climate change". [17] It has been proposed that a loss of resilience in forests "can be detected from the increased temporal autocorrelation (TAC) in the state of the system, reflecting a decline in recovery rates due to the critical slowing down (CSD) of system processes that occur at thresholds". [17]
23% of tree cover losses result from wildfires and climate change increase their frequency and power. [20] The rising temperatures cause massive wildfires especially in the Boreal forests. One possible effect is the change of the forest composition. [21] Deforestation can also cause forests to become more fire prone through mechanisms such as logging. [22]Several studies since the early 1990s [23] have shown that large-scale deforestation north of 50°N leads to overall net global cooling [24] while tropical deforestation produces substantial warming. Carbon-centric metrics are inadequate because biophysical mechanisms other than CO2 impacts are important, especially the much higher albedo of bare high-latitude ground vis-à-vis intact forest. [23] [25] Irreversible deforestation would result in a permanent rise in the global surface temperature. [26] Moreover, it suggests that standing tropical forests help cool the average global temperature by more than 1 °C or 1.8 °F. [25] [27] Deforestation of tropical forests may risk triggering tipping points in the climate system and of forest ecosystem collapse which would also have effects on climate change. [28] [29] [30] [31]
Deforestation, particularly in large swaths of the Amazon, where nearly 20% of the rainforest has been clear cut, has climactic effects and effects on water sources as well as on the soil. [32] [33] Moreover, the type of land usage after deforestation also produces varied results. When deforested land is converted to pasture land for livestock grazing it has a greater effect on the ecosystem than forest to cropland conversions. [34] Other effect of deforestation in the Amazon rainforest is seen through the greater amount of carbon dioxide emission. The Amazon rainforest absorbs one-fourth of the carbon dioxide emissions on Earth, however, the amount of CO2 absorbed today decreases by 30% than it was in the 1990s due to deforestation. [35]
Modeling studies have concluded that there are two crucial moments that can lead to devastating effects in the Amazon rainforest which are increase in temperature by 4 °C or 7.2 °F and deforestation reaching a level of 40%. [36]
Human activity such as deforestation for livestock grazing and fuel wood has led to forest degradation and over extraction resulting in ecosystem biodiversity loss. Loss and degradation of forest has a direct impact on the Earth's diverse flora and fauna and, therefore, on climate change because they are the best defense against CO2 buildup in the atmosphere. [37] [38] [39] If there is more foliage photosynthesizing more CO2 will be absorbed, thereby balancing the potential temperature increases. [40]
Forests are nature's atmospheric carbon sink; plants take in atmospheric carbon dioxide (a greenhouse gas) and convert the carbon into sugars and plant materials through the process of photosynthesis. [41] The carbon is stored within the trees, vegetation, and soil of the forests. Studies show that "intact forests", in fact, do sequester carbon. [42] Examples of large forests that have a significant impact on the balance of carbon include the Amazonian and the Central African rainforests. [43] However, deforestation disrupts the processes of carbon sequestration and affects localized climates. Additionally, cutting down trees plays a role in a positive feedback loop centered around climate change on a much larger scale, as studies are finding. [42]
When a climate changes, this causes the shift in a species' geographic range in order to maintain the climatic conditions (temperature, humidity) it is accustomed to. Ecological zones will shift by approximately 160 km per 1 degree Celsius. [40] A reduction in the area of any habitat, but particularly in forest habitat along with climatic change, enables species invasion and the possibility of biotic homogenization as stronger invasive species can take over weaker species in a fragile ecosystem. [40] Humans will also be impacted by the loss of biodiversity as food, energy, and other 'ecosystem goods and services' patterns are disrupted. [44]
Burning or cutting down trees reverses the effects of carbon sequestration and releases greenhouse gases (including carbon dioxide) into the atmosphere. [43] Furthermore, deforestation changes the landscape and reflectivity of earth's surface, i.e. decreasing Albedo. This results in an increase in the absorption of light energy from the sun in the form of heat, enhancing global warming. [42]
As a consequence of reduced evapotranspiration, precipitation is also reduced. This implies having a hotter and drier climate, and a longer dry season. [45] [46] This change in climate has drastic ecological and global impacts including increases in severity and frequency of fires, and disruption in the pollination process that will likely spread beyond the area of deforestation. [46] [45]
According to a study published in 2023, tropical deforestation has led to a significant decrease in the amount of observed precipitation. [47] By the year 2100, researchers anticipate that deforestation in the Congo will diminish regional precipitation levels by up to 8-10%. [47]
Statistics have shown that there is a direct correlation between forest fires and deforestation. Statistics regarding the Brazilian Amazon area during the early 2000s have shown that fires and the air pollution that accompanies these fires mirror the patterns of deforestation and "high deforestation rates led to frequent fires". [48]
The Amazon rainforest has recently experienced fires that occurred inside the forest when wildfires tend to occur on the outer edges of the forest. [15] Wetlands have faced an increase in forest fires as well. [15] Due to the change in temperature, the climate around forests have become warm and dry, conditions that allow forest fires to occur. [15]
Under unmitigated climate change, by the end of the century, 21% of the Amazon would be vulnerable to post‐fire grass invasion. In 3% of the Amazon, fire return intervals are already shorter than the time required for grass exclusion by canopy recovery, implying a high risk of irreversible shifts to a fire‐maintained degraded forest grassy state. The south‐eastern region of the Amazon is currently at highest risk of irreversible degradation. [49]
According to a study in tropical peatland forest of Borneo, deforestation also contributes to the increase in fire risk. [50]
Trees
absorb carbon dioxide (CO
2) from the atmosphere through the process of
photosynthesis. Throughout this biochemical process,
chlorophyll in the tree's leaves harnesses sunlight to convert CO
2 and water into
glucose and oxygen.
[51] While glucose serves as a source of energy for the tree, oxygen is released into the atmosphere as a byproduct. Trees store carbon in the form of biomass, encompassing roots, stems, branches, and leaves. Throughout their lifespan, trees continue to sequester carbon, storing atmospheric CO2 long-term.
[52] Sustainable forest management, afforestration, reforestation and proforestation are therefore important contributions to climate change mitigation.
Afforestation is the establishment of a forest in an area where there was no previous tree cover.
Proforestation is the practice of growing an existing
forest intact toward its full ecological potential.
[53] An important consideration in such efforts is that the carbon sink potential of forests will saturate
[54][
need quotation to verify]and forests can turn from sinks to carbon sources [
example needed].
[55]
[56]
IPCC AR6 concluded that “Where carefully and appropriately implemented,
AFOLU mitigation measures are uniquely positioned to deliver substantial co-benefits and help address many of the wider challenges associated with land management. If AFOLU measures are deployed badly then, when taken together with the increasing need to produce sufficient food, feed, fuel and wood, they may exacerbate trade-offs with the conservation of habitats, adaptation, biodiversity and other services.”
[57]
There are four primary ways in which reforestation and reducing deforestation can increase carbon sequestration. First, by increasing the volume of existing forest. Second, by increasing the carbon density of existing forests at a stand and landscape scale. [58] Third, by expanding the use of forest products that will sustainably replace fossil-fuel emissions. Fourth, by reducing carbon emissions that are caused from deforestation and degradation. [59]
The second strategy has to do with selecting species for tree-planting. In theory, planting any kind of tree to produce more forest cover would absorb more carbon dioxide from the atmosphere. However, a genetically modified variant might grow much faster than unmodified specimens. [60]: 93 Some of these cultivars are under development. Such fast-growing trees would be planted for harvest and can absorb carbon dioxide faster than slower-growing trees. [60]: 93 A meta-analysis found that mixed species plantations would increase carbon storage alongside other benefits of diversifying planted forests. [61]
The planting of trees on marginal crop and
pasture lands helps to incorporate carbon from atmospheric CO
2 into
biomass.
[62]
[63] For this carbon sequestration process to succeed the carbon must not return to the atmosphere from biomass burning or rotting when the trees die.
[64] To this end, land allotted to the trees must not be converted to other uses. Alternatively, the wood from them must itself be sequestered, e.g., via
biochar,
bioenergy with carbon capture and storage, landfill or stored by use in construction.
Earth offers enough room to plant an additional 1.2 trillion trees. [65] Planting and protecting them would offset some 10 years of CO2 emissions and sequester 205 billion tons of carbon. [66] This approach is supported by the Trillion Tree Campaign. Restoring all degraded forests world-wide would capture about 205 billion tons of carbon in total, which is[ when?] about two-thirds of all carbon emissions. [67] [68]
Although a bamboo forest stores less total carbon than a mature forest of trees, a bamboo plantation sequesters carbon at a much faster rate than a mature forest or a tree plantation. Therefore, the farming of bamboo timber may have significant carbon sequestration potential. [69]
If all new construction globally utilized 90% wood products, largely via adoption of mass timber in low rise construction, this could sequester 700 million net tons of carbon per year. [70] [71] This is in addition to the elimination of carbon emissions from the displaced construction material such as steel or concrete, which are carbon-intense to produce.
Forests are generally carbon dioxide sinks when they are high in diversity,[ citation needed]density or area. However, they can also be carbon sources if density or area decreases due to deforestation, selective logging, climate change, wildfires or diseases. [72] [73] [74] In 2019 forests took up a third less carbon than they did in the 1990s, due to higher temperatures, droughts and deforestation. The typical tropical forest may become a carbon source by the 2060s. [75]
Life expectancy of forests varies throughout the world, influenced by tree species, site conditions and natural disturbance patterns. In some forests, carbon may be stored for centuries, while in other forests, carbon is released with frequent stand replacing fires. Forests that are harvested prior to stand replacing events allow for the retention of carbon in manufactured forest products such as lumber. [76] However, only a portion of the carbon removed from logged forests ends up as durable goods and buildings. The remainder ends up as sawmill by-products such as pulp, paper and pallets. [77]
The Food and Agriculure Organization (FAO) reported that: "The total carbon stock in forests decreased from 668 gigatonnes in 1990 to 662 gigatonnes in 2020". [78]: 11 The CO2 fertilization effect, on the other hand, was responsible for 47% of the sink, while climate change reduced the sink by 28.6%. [79][ clarification needed] In Canada's boreal forests as much as 80% of the total carbon is stored in the soils as dead organic matter. [80]
Carbon offset programs are planting millions of fast-growing trees per year to reforest tropical lands. [ citation needed] Over their typical 40-year lifetime, one million of these trees can sequester up to one million tons of carbon dioxide. [81] [82]
IPCC AR6 says: “Secondary forest regrowth and restoration of degraded forests and non-forest ecosystems can play a large role in carbon sequestration (high confidence) with high resilience to disturbances and additional benefits such as enhanced biodiversity.” [83] And it says: “Over 420 million ha of forest were lost to deforestation from 1990 to 2020; more than 90% of that loss took place in tropical areas (high confidence), threatening biodiversity, environmental services, livelihoods of forest communities and resilience to climate shocks (high confidence).” [84]
Forests are an important part of the global carbon cycle because trees and plants absorb carbon dioxide through photosynthesis. Therefore, they play an important role in climate change mitigation. [85]: 37 By removing the greenhouse gas carbon dioxide from the air, forests function as terrestrial carbon sinks, meaning they store large amounts of carbon. At any time, forests account for as much as double the amount of carbon in the atmosphere. [86]: 1456 Forests remove around three billion tons of carbon every year. [87][ need quotation to verify]This amounts to about 30% of all anthropogenic carbon dioxide emissions. [88]Therefore, an increase in the overall forest cover around the world would mitigate global warming. [61]
At the beginning of the 21st century, interest in reforestation grew over its potential to mitigate climate change. Even without displacing agriculture and cities, earth can[ clarification needed] sustain almost one billion hectares of new forests. This would remove 25% of carbon dioxide from the atmosphere and reduce its concentration to levels that existed in the early 20th century. A temperature rise of 1.5 degrees would reduce the area suitable for forests by 20% by the year 2050, because some tropical areas will become too hot. [89] The countries that have the most forest-ready land are: Russia, Canada, Brazil, Australia, the United States and China. [90]
Impacts on temperature are affected by the location of the forest. For example, reforestation in boreal or subarctic regions has less impact on climate. This is because it substitutes a high- albedo, snow-dominated region with a lower-albedo forest canopy. By contrast, tropical reforestation projects lead to a positive change such as the formation of clouds. These clouds then reflect the sunlight, lowering temperatures. [86]: 1457
Planting trees in tropical climates with wet seasons has another advantage. In such a setting, trees grow more quickly (fixing more carbon) because they can grow year-round. Trees in tropical climates have, on average, larger, brighter, and more abundant leaves than non-tropical climates. A study of the girth of 70,000 trees across Africa has shown that tropical forests fix more carbon dioxide pollution than previously realized. The research suggested almost one fifth of fossil fuel emissions are absorbed by forests across Africa, Amazonia and Asia. Simon Lewis stated, "Tropical forest trees are absorbing about 18% of the carbon dioxide added to the atmosphere each year from burning fossil fuels, substantially buffering the rate of change." [91]
A 2019 study of the global potential for tree restoration showed that there is space for at least 9 million km2 of new forests worldwide, which is a 25% increase from current conditions. [92] This forested area could store up to 205 gigatons of carbon or 25% of the atmosphere's current carbon pool by reducing CO2 in the atmosphere. [92]
Researchers have found that, in terms of environmental services, it is better to avoid deforestation than to allow for deforestation to subsequently reforest, as the former leads to irreversible effects in terms of biodiversity loss and soil degradation. [93] Furthermore, the probability that legacy carbon will be released from soil is higher in younger boreal forest. [94] Global greenhouse gas emissions caused by damage to tropical rainforests may have been substantially underestimated until around 2019. [95] Additionally, the effects of af- or reforestation will be farther in the future than keeping existing forests intact. [96] It takes much longer − several decades − for the benefits for global warming to manifest to the same carbon sequestration benefits from mature trees in tropical forests and hence from limiting deforestation. [97] Therefore, scientists consider "the protection and recovery of carbon-rich and long-lived ecosystems, especially natural forests" to be "the major climate solution". [98]Possible methods of reforestation include large-scale industrial plantations, the introduction of trees into existing agricultural systems, small-scale plantations by landowners, the establishment of woodlots on communal lands, and the rehabilitation of degraded areas through tree planting or assisted natural regeneration. [99]
Afforestation is the planting of trees where there was no previous tree coverage. There are three different types of afforestation that could have varying effects on the amount of carbon dioxide that is taken from the atmosphere. The three kinds of afforestation are natural regeneration, commercial plantations, and agroforestry. [100] Although afforestation can help reduce the carbon emissions given off as a result of climate change, natural regeneration tends to be the most effective out of the three. [100] Natural regeneration typically concerns a wide variety of vegetation, making natural forest levels so plants can receive sunlight to undergo photosynthesis. Commercial plantations typically result in mass amounts of lumber, which if used for fuel, will release the stored CO2 back into the atmosphere. Agroforestry stores energy based on the size and type of plant, meaning that the effect will vary depending on what is planted. [100]
Wood harvesting and supply have reached around 550 million m3 per year, while the total increasing stock of European forests has more than quadrupled during the previous six decades. It now accounts for around 35 billion m3 of forest biomass. [101] [102] Since the beginning of the 1990s, the amounts of wood and carbon stored in European forests have increased by 50% due to greater forest area and biomass stocks. Every year, European woods adsorb and store around 155 million tonnes CO2 equivalent. This is comparable to 10% of all other sectors' emissions in Europe. [101] [103] [104]
The forestry industry tries to mitigate climate change by boosting carbon storage in growing trees and soils and improving the sustainable supply of renewable raw materials via sustainable forest management. [101] [105]
Forestry projects have faced increasing criticism over their integrity as offset or credit programs. A number of news stories from 2021 to 2023 criticized nature-based carbon offsets, the REDD+ program, and certification organizations. [106] [107] [108] In one case it was estimated that around 90% of rainforest offset credits of the Verified Carbon Standard are likely to be "phantom credits". [109]
Tree planting projects in particular have been problematic. Critics point to a number of concerns. Trees reach maturity over a course of many decades. It is difficult to guarantee how long the forest will last. It may suffer clearing, burning, or mismanagement. [110] [111] Some tree-planting projects introduce fast-growing invasive species. These end up damaging native forests and reducing biodiversity. [112] [113] [114] In response, some certification standards such as the Climate Community and Biodiversity Standard require multiple species plantings. [115] Tree planting in high latitude forests may have a net warming effect on the Earth's climate because tree cover absorbs sunlight thus creating a warming effect that balances out their absorption of carbon dioxide. [116] Tree-planting projects can also cause conflicts with local communities and Indigenous people if the project displaces or otherwise curtails their use of forest resources. [117] [118] [119] For example, Human Rights Watch found that a REDD+ project in Southern Cardamom National Park of Cambodia had driven members of the Chong ethnic group from their indigenous lands. [120]The Bali Action Plan was developed in December 2007 in Bali, Indonesia. [128] [129] It is a direct result of The Kyoto Protocol of December 1997. [130] [39] One of the key elements of The Bali Action Plan involves a concerted effort by the member countries of The Kyoto Protocol to enact and create policy approaches that incentivize emissions reduction caused by deforestation and forest degradation in the developing world. [131] It emphasized the importance of sustainable forest management and conservation practices in mitigating climate change. This coupled with the increased attention to carbon emission stocks as a way to provide additional resource flows to the developing countries. [39]
The Billion Tree Campaign was launched in 2006 by the United Nations Environment Programme (UNEP) as a response to the challenges of global warming, as well as to a wider array of sustainability challenges, from water supply to biodiversity loss. [132] Its initial target was the planting of one billion trees in 2007. Only one year later in 2008, the campaign's objective was raised to 7 billion trees—a target to be met by the climate change conference that was held in Copenhagen, Denmark in December 2009. Three months before the conference, the 7 billion planted trees mark had been surpassed. In December 2011, after more than 12 billion trees had been planted, UNEP formally handed management of the program over to the not-for-profit Plant-for-the-Planet initiative, based in Munich, Germany. [133]
Considered the largest reserve of biological diversity in the world, the Amazon Basin is also the largest Brazilian biome, taking up almost half the nation's territory. The Amazon Basin corresponds to two fifths of South America's territory. Its area of approximately seven million square kilometers covers the largest hydrographic network on the planet, through which runs about one fifth of the fresh water on the world's surface. Deforestation in the Amazon rainforest is a major cause to climate change due to the decreasing number of trees available to capture increasing carbon dioxide levels in the atmosphere. [134]
The Amazon Fund is aimed at raising donations for non-reimbursable investments in efforts to prevent, monitor and combat deforestation, as well as to promote the preservation and sustainable use of forests in the Amazon Biome, under the terms of Decree N.º 6,527, dated August 1, 2008. [135] The Norwegian Government, which is the largest donor to the fund, froze its funding in 2019 over deforestation concerns. Norway has tied the resumption of funding to proof of a reduction in deforestation. [136]
The Amazon Fund supports the following areas: management of public forests and protected areas, environmental control, monitoring and inspection, sustainable forest management, economic activities created with sustainable use of forests, ecological and economic zoning, territorial arrangement and agricultural regulation, preservation and sustainable use of biodiversity, and recovery of deforested areas. Besides those, the Amazon Fund may use up to 20% of its donations to support the development of systems to monitor and control deforestation in other Brazilian biomes and in biomes of other tropical countries. [135]