Deforestation emissions

Extra facts

• Deforestation and land use change (the conversion of forests into farmland) accounts for 2,200 to 6,600 million metric tonnes of carbon dioxide equivalent (MtCO₂e) per year, or 30 to 50 percent of agricultural emissions and about 4 to 14 percent of global emissions (Vermeulen et al. 2012 based on van der Werf et al. 2010 and Blaser and Robledo 2007).
• Since 1850, land use change directly contributed some 35 percent of human-generated CO₂ emissions (Foley et al. 2005).
• Past trends imply that ~10 million km² of land will be cleared by 2050 to meet demand, leading to annual emissions of 3,000 MtCO₂e per year. A future course that spares more land could reduce land clearing to ~2 million km² and GHG emissions to 1,000 MtCO₂e/year per year (Tilman et al. 2011).
• In the 1980s and 1990s, rainforests were the primary source of new agricultural land in the tropics. Future expansion of the global agricultural land base will clear tropical forests and shrubland ecosystems (Gibbs et al. 2010).
• The combined contribution of deforestation and forest degradation emissions to total human-generated CO₂ emissions is about 12 percent (with a range of 6 to 18 percent) (Van der Werf et al. 2009).
• Between 1980 and 2000, more than 55 percent of new agricultural land replaced intact forests; another 28 percent replaced degraded forests. Even with agricultural yield increases and intensification, net agricultural area expansion will probably be needed to meet future demand (Gibbs et al. 2010: 16732).
• Land use activities, primarily the expansion of agricultural land and the extraction of timber, have caused a net loss of ~7 to 11 million km² of forest in the past 300 years (Foley et al. 2005).
• Forests cover about 3952 million hectares of the globe—about 30 percent of the world’s land area. From 2000 to 2005, gross deforestation continued at a rate of 12.9 million hectares per year. Due to afforestation, landscape restoration and the natural expansion of forests, the most recent estimate of net forest loss is 7.3 million hectares per year (IPCC 2007: 544).
• Croplands and pastures have become one of the largest terrestrial biomes on the planet, occupying ~40 percent of the land surface and rivaling forest cover in extent (Foley et al. 2005).
• Between 1963 and 2005, the global area of cropland harvested increased 30 percent from 8.4 million km² to 11.0 million km².
• Managed grazing occupies 25 percent of the global land surface (more than 33 million km²), making it the planet’s single most extensive form of land use (Asner et al. 2004: 262).
• Land use for the livestock sector spans more than 39 million km² (~30% of the world’s surface land area). Of this (FAO 2006), 5 million km² are crops, most of which are intensively managed; 14 million km² are pasture with relatively high productivity; and 20 million km² are extensive pastures with relatively low productivity.
• Some irrigated lands have become heavily salinized, causing a worldwide loss of ~1.5 million hectares of arable land per year and an estimated 11 billion USD in lost production (Foley et al. 2005).
• Soil erosion, reduced fertility or overgrazing impacts up to ~40 percent of global croplands (Foley et al. 2005).
• The main driver of land use change for agriculture was population growth. Now, in most regions, it’s shifting to dietary change (Kastner et al. 2012).
• Cropland would have to be nearly doubled if the projected global population of more than 9 billion people in 2050 were to have North America’s current diet and agricultural technology. Cropland would have to be expanded70 percent to if the global population had Western Europe’s diet and technology (Kastner et al. 2012).

Methods, caveats and issues

Van der Werf et al. (2009: 738) use Intergovernmental Panel on Climate Change (IPCC) methods and updated values, and suggest CO₂ emissions from deforestation and forest degradation (excluding peatland emissions) of about 1.2 petagrams of carbon per year (Pg C yr–1), which is 23 percent less than the value stated in IPCC Working Group I’s 2007 report. As a result, deforestation and forest degradation emissions contribute about 12 percent of total anthropogenic CO₂ emissions.

Van der Werf et al. (2009) assume that rates of forest decline for 2000 to 2005 were almost the same as in the 1990s, based on survey and satellite-based approaches to calculate deforestation area. Carbon emissions from fossil fuel combustion have increased substantially over the same period, making the relative contribution from deforestation and forest degradation even smaller.

The figure for agriculture’s contribution to total deforestation is 75 percent, which was estimated by Blaser and Robledo (2007). However, calculating agriculture’s share of this deforestation is fraught with uncertainties, and is not attempted by the IPCC.

Sources

• Asner GP, Elmore AJ, Olander LP, Martin RE, Harris AT. 2004. Grazing systems, ecosystem response, and global change. Annual Review of Environmental Resources 29:261-299.
• Blaser J, Robledo C. 2007. Analysis on the mitigation potential in the forestry sector. Prepared for the UN Framework for the Convention of Climate Change (UNFCCC) Secretariat. Bern: Intercooperation. (Available from http://unfccc.int/files/cooperation_and_support/financial_mechanism/application/pdf/blaser.pdf)
• [FAO] Food and Agriculture Organization of the United Nations. 2006. Livestock’s Long Shadow. Rome: FAO. (Available from http://www.fao.org/docrep/010/a0701e/a0701e00.HTM)
• Foley, JA, DeFries R, Asner GP, Barford C, Bonan G, Carpenter SR, Chapin FS, Coe MT, Daily GC, Gibbs HK, Helkowski JH, Holloway T, Howard EA, Kucharik CJ, Monfreda C, Patz JA, Prentice IC, Ramankutty N, Snyder PK.2005. Global consequences of land use. Science 309:570-574.
• Gibbs HK, Ruesch AS, Achard F, Clayton MK, Holmgren P et al. 2010. Tropical forests were the primary sources of new agricultural land in the 1980s and 1990s. PNAS  107(38):16732–16737. (Available from www.pnas.org/cgi/doi/10.1073/pnas.0910275107)
• Pachauri RK, Reisinger A., eds. 2007. IPCC fourth assessment report: Climate change 2007.
• Harris et al. (2012) Baseline map of carbon emissions from deforestation in tropical regions, Science 336: 1573-1576.
• Kastner T, Rivas MJI, Koch W, Nonhebel, S. 2012. Global changes in diets and the consequences for land requirements for food. PNAS 109(18):6868–6872. (Available from www.pnas.org/cgi/doi/10.1073/pnas.1117054109)
• [PBL] Planbureau voor de Leefomgeving. 2009. Milieubalans 2009. Bilthoven: Planbureau voor de Leefomgeving. (Available from http://www.pbl.nl/nl/publicaties/2009/milieubalans/)
• Rudel TK, Defries R, Asner GP, Laurance WF. 2009. Changing Drivers of Deforestation and New Opportunities for Conservation, Conservation Biology 23(6):1396–1405.
• Strassburg BBN, Rodrigues ASL, Gusti M, Balmford A, Fritz A, Obersteiner M, Turner RK, Brooks TM. Impacts of incentives to reduce emissions from deforestation on global species extinctions. Nature Climate Change2:350–355.
• Smith P, Martino D, Cai ZC, Gwary D, Janzen H, Kumar P, McCarlg B, Ogleh S, O’Marai F, Ricej C, Scholesk B, Sirotenkol O, Howdenm M, McAllistere T, Pann G, Romanenkovo V, Schneiderp U, Towprayoonq S. 2007. Policy and technological constraints to implementation of greenhouse gas mitigation options in agriculture. Agriculture, Ecosystems & Environment 118:6–28.
• Tilman D, Balzer C, Hill J, Befort BL. 2011. Global food demand and the sustainable intensification of agriculture. PNAS 108(50):20260–20264. (Available from www.pnas.org/cgi/doi/10.1073/pnas.1116437108)
• van der Werf GR, Morton DC, DeFries RS, Olivier JGJ,  Kasibhatla, PS,  Jackson RB, Collatz GJ, Randerson JT. 2009. CO₂ emissions from forest loss. Nature Geoscience 2:738-739.