Forests, especially tropical forests, play an important role in global climate change. Tree biomass stores carbon through photosynthesis, so deforestation contributes to carbon emissions. Tropical forests contain about 25% of the world’s carbon, and other forest regions of the world add another 20% of the world’s carbon. In just the Amazon basin, studies estimate that forests contain 90-140 billion tons of carbon, which could be equivalent to 9-14 decades of human carbon emissions. Previous statements by the IPCCC estimated tropical deforestation and land use change to contribute about 20% of global carbon emissions, although more recent studies have placed this percentage closer to 10%. Nevertheless, carbon emissions from deforestation remain significant, a primary motivation behind the REDD+ mechanisms as an international climate change mitigation program. At the smaller level, forests affect local climate patterns; trees transpire water, so deforestation can reduce rainfall and contribute to desertification. Changes in local climate patterns can have significant impacts on food production, especially in rural tropical areas practicing subsistence agriculture and semi-arid tropical regions such as the Cerrado of Brazil. Studies have found that since 1980, climate change resulted in declines in temperate corn and wheat yields, and mixed effects on soybean and rice yields.
Forests not only affect climate, but climate affects forests. At the global level, increased carbon could potentially benefit forest growth in a “fertilization” scenario, but climate change could also result in a rise in temperatures and increased water stress, causing a decrease in forest growth. Studies in the Amazon basin predicts a “dieback” scenario, where a rise in temperature corresponds with a 10-20% reduction in rainfall, followed by change from forest ecosystems to savanna ecosystems. In this scenario, lower forest cover results in greater carbon emissions, less water retention, further drying, and a pernicious feedback cycle. Forest fires also alter the situation: fires induce drought and further emissions, although smoke facilitates cloud production and reduces surface temperatures. Some estimate the tipping point of this dieback scenario to occur when deforestation passes 40% of the Amazon basin (about double the present level). However, recent studies have found that rainforests may be more resilient to drought and changing climate, and may continue to store carbon longer.
Climate change also affects many threatened species dependent on tropical forests. Globally, temperatures are likely to rise faster in polar regions than in tropical regions, affecting vulnerable species such as polar bears. In the tropics, however, rare species and isolated populations are also threatened, especially ones in sensitive environments such as islands, scrublands and forest canopy. In extreme heat waves in tropical Australia from 2003 to 2006, scientists documented high mortality of flying foxes. Tropical mountains are also extremely vulnerable; in many tropical regions, climate patterns associated with elevation gradients define species distributions. In the tropical Andes and Central America, amphibians are especially vulnerable to changing temperatures and reduced cloud cover. The golden toad from Monteverde, Costa Rica, was the first extinction attributed to climate change, in the early 1990s. Since then, scientists have documented the probable extinction of dozens of species of harlequin frogs, attributed to a synergy of the chytrid fungal disease and climate change.
Many conservation programs address the issues of tropical forests and climate change through mitigation and adaption. The REDD+ mechanism is the primary payment for ecosystem service mechanisms that uses international funding to stem deforestation and prevent carbon emissions. Adaptation programs include agroforestry systems and community forestry which provide forest communities with a diversity of alternatives to ensure economic revenue, food security, and sustainable forest management.
Read more about Climate Change in our tropical focal regions below:
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Harris, et al. (2012). Baseline map of carbon emissions from deforestation in tropical regions. Science, 336(6088), 1573-1576.
Heffernan, O. (2013). Tropical forests unexpectedly resilient to climate change. Nature. doi:10.1038/nature.2013.12570
Kurukulasuriya, P., Rosenthal, S. (2013). Climate Change and Agriculture : A Review of Impacts and Adaptations. World Bank, Washington, DC.
Laurance, W. (2011). The World’s Tropical Forests Are Already Feeling the Heat. Yale Environment 360. Retrieved from: http://e360.yale.edu/feature/the_worlds_tropical_forests_are_already_feeling_the_heat/2397/
Lobell, D. B., Schlenker, W., & Costa-Roberts, J. (2011). Climate trends and global crop production since 1980. Science, 333(6042), 616-620.
Malhi, Y., Roberts, J. T., Betts, R. A., Killeen, T. J., Li, W., & Nobre, C. A. (2008). Climate change, deforestation, and the fate of the Amazon. Science, 319(5860), 169-172.
Nepstad, D. C., Stickler, C. M., Soares-Filho, B., & Merry, F. (2008). Interactions among Amazon land use, forests and climate: prospects for a near-term forest tipping point. Philosophical Transactions of the Royal Society B: Biological Sciences, 363(1498), 1737-1746.
Nobre, C. A., & Borma, L. D. S. (2009). ‘Tipping points’ for the Amazon forest. Current Opinion in Environmental Sustainability, 1(1), 28-36.
Soares-Filho, B. S., et al. (2006). Modelling conservation in the Amazon basin. Nature, 440(7083), 520-523.
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