Re: Is there a correlation between global warming and rainforest destruction?

Dear Tyler,

this is a great question, and one that is the focus of ongoing research. The short answer is that yes, there is a strong link between global warming and the destruction of the world�s remaining tropical forests.

Plant metabolism is highly sensitive to temperature. Plants have an optimum temperature for photosynthesis, at which their enzymes capture solar energy and produce glucose with the highest efficiency. At too-high temperatures, respiration�the process by which plants break down glucose and produce carbon dioxide�may exceed photosynthesis. The optimal temperature ranges of temperate forest plants are fairly well known, but few studies have investigated the optimal temperatures for tropical plants. The evidence that does exist, though, suggests that tropical forest trees may be alarmingly close to exceeding their photosynthetic optimum temperatures already. Long-term, large-scale studies of tree growth in Costa Rica (Clark et al. 2003), South America (Lewis et al. 2004), and Malaysia (Feeley et al. 2007) show that growth is diminished in hotter years. Global warming appears to be affecting tropical forests already.

In addition, tropical forest destruction is contributing to global warming by returning carbon dioxide and other greenhouse gases to the atmosphere. Huge amounts of carbon dioxide are released when tropical forests burn (Melillo et al. 1996, Page et al. 1997). Also, when the forests are destroyed, large amounts of carbon can be lost from the soils (Melillo et al. 1996). Alternate land uses in the tropics�agriculture, cattle farming, tree plantations, human habitation�store very little carbon, compared to tropical forests (Fearnside 1996, Melillo et al. 1996). Livestock also contribute to global warming by producing methane (Kurihara et al. 1999).While this gas is a minor component of the atmosphere, it has a large role in global warming because it is so effective at trapping heat.

One alarming ramification of all this research is that there may be a between tropical forest destruction and global warming. The destruction of the forests leads to further atmospheric warming, which in turn accelerates forest loss... Climate models (complex computer simulations of future climate) have predicted that global warming could lead to the complete destruction of the Amazon forest�the largest contiguous rainforest ecosystem on Earth�by as early as 2080 (Betts et al. 2004, Cox et al. 2004).

As sobering as this prediction sounds, it is important to realize that there is still hope for the Amazon forests. Climate change will be the single most important challenge facing our generation, but if we act now we may be able to stave off the most severe impacts. There are many on-line resources for learning about climate change and how to counteract it. Princeton�s Climate Mitigation Initiative is a good place to start your search.

Literature Cited:

Betts, R.A., Cox, P.M., Collins, M., Harris, P.P., Huntingford, C., and Jones, C.D. 2004. The role of ecosystem-atmosphere interactions in simulated Amazonian precipitation decrease and forest dieback under global climate warming. Theoretical and Applied Climatology 78:157-175.

Cox, P.M., Betts, R.A., Collins, M., Harris, P.P., Huntingford, C., and Jones, C.D. 2004. Amazonian forest dieback under climate-carbon cycle projections for the 21st century. Earth and Environmental Science 78: 137-156.

Fearnside, P.M. 1996. Amazonian deforestation and global warming: carbon stocks in vegetation replacing Brazil�s Amazon forest. Forest Ecology and Management 80:21-34.

Kurihara, M., Magner, T., Hunter, R.A., and McCrabb, G.J. 1999. Methane production and energy partition of cattle in the tropics. British Journal of Nutrition 81: 227-234.

Clark, D.A., Piper, S.C., Keeling, C.D., and Clark, D.B. 2003. Tropical rain forest tree growth and atmospheric carbon dynamics linked to interannual temperature variation during 1984-2000. Proceedings of the National Academy of Sciences 100: 5852-5857.

Feeley, K.J., Wright, S.J., Supardi, M.N.N., Kassim, A.R., and Davies, S.J. 2007. Decelerating growth in tropical forest trees. Ecology Letters 10: 1�9.

Lewis, S.L., Phillips, O.L., Baker, T.R., Lloyd, J., Malhi, Y., Almeida, S., Higuchi, N., Laurance, W.F., Neill, D.A., Silva, J.N.M., Terborgh, J., Lezama, A.T., Martinez, R.V., Brown, S., Chave, J., Kuebler, C., Vargas, P.N., and Vinceti, B. 2004 Concerted changes in tropical forest structure and dynamics: evidence from 50 South American long-term plots. Philosophical Transactions of the Royal Society of London Series B: Biological Sciences 359: 421-436.

Melillo, J.M., Houghton, R.A., Kicklighter, D.W., and McGuire, A.D. 1996.Tropical deforestation and the global carbon budget. Annual Review of Energy and the Environment 21: 293-310.

Page, S.E., Siegert, F., Rieley, J.O., Boehm, H.D., Jaya, A., and Limin, S. 2002. The amount of carbon released from peat and forest fires in Indonesia during 1997. Nature 420: 61-65.