Beyond climate change
The recent fourth assessment report on climate change released by Working Group 1 of the Intergovernmental Panel on Climate Change (IPCC) is a milestone in focusing world attention on the current state of the Earth?s climate. Compared with the previous assessment, the conclusions about the human impact on climate are much firmer. The fact that the climate system is warming is ?unequivocal?. Likelihood estimates are provided for the first time, which hopefully will clearly express the extent to which the peer-reviewed research produced by the climate science community supports conclusions about climate change. Atmospheric carbon dioxide and methane concentrations are far above the envelope of natural variability over the last 650,000 years. The report concludes that ?Most of the observed increase in globally-averaged temperatures in the mid-20th century is very likely [>90%] due to the observed increase in anthropogenic greenhouse gas concentrations.? We humans are having a truly discernable effect on our home planet.
The IPCC report, with its interdisciplinary approach to climate change, is a clear example of how the Earth needs to be considered as a coupled system in order to understand the wider issue of global environmental change. The study of the Earth as a coupled human-environmental system, looking not only at climate but also at changes in the oceans and on land, how those changes affect each other, and the role of humans as a central part of that system is a crucial approach to managing a sustainable planet. This is the approach taken by the International Geosphere-Biosphere Programme (IGBP), one of four global environmental change research programmes sponsored by the International Council for Science (ICSU).
We now know that human activities now match (and often exceed) the natural forces that regulate the Earth System. Roughly half of the world’s ice-free land surface has been altered by human actions. Humans now fix more nitrogen than nature does. Particles emitted by human activities alter the energy balance of the planet, as well as have adverse effects on human health. These may seem to be unrelated issues; however, over the last decades, we have gained a deeper understanding of the degree to which all of these separate issues are linked. The Earth System is a very complex system with myriad feedbacks, and it has and presumably can still exhibit rapid, global-scale responses to changes in environmental conditions.
One example of a potential feedback loop with planetary consequences links deforestation in the Amazon with snow cover in Tibet. Vegetation in the Amazon produces particles, as well as emitting volatile organic compounds (VOCs). These VOCs can oxidize in the atmosphere into compounds that can form or modify existing particles. These particles then form cloud droplets. In the case of the Amazon region (and presumably the tropics in general), changing particle concentrations (and even chemistry) can not only influence how likely clouds are to produce rain, but also the strength of the tropical convective circulation [Kesselmeier, et al., 2002].
Much of the water in the atmosphere over the central Amazon basin is recycled through the vegetation. Thus, the vegetation not only determines the concentration of the aerosol particles in the atmosphere, but also the water vapor concentration – everything needed to make a cloud. Recent research has shown that deforestation and biomass burning (in this case burning vegetation to prepare for the next season’s planting) have caused changes in convection and precipitation over the Amazon basin [Andreae, et al., 2004]. These changes in precipitation complete the feedback loop, since the availability of water influences the amount and kind of VOCs that the vegetation emits [Kesselmeier, et al., 2002].
While at first glance it would appear that this feedback loop would have only a regional effect, the influence of changes in Amazonia in fact can be felt much farther away. Calculations show that deforesting the Amazon could affect surface temperatures as far away as Tibet (J. Foley, personal communication). Large-scale deforestation drastically changes the surface energy balance, leading to a weakening of deep convection. This weakening of convection in the tropics has a number of subsequent effects such as a weakening and northward shift in the Inter-Tropical Convergence Zone (ITCZ), which causes changes in the jet stream that directs the trajectory of mid-latitude weather systems, ultimately influencing weather in Tibet.
Humans are present at both ends of this feedback loop. Deforestation in the Amazon is driven by socioeconomic issues – ones similar to those that powered the European and North American deforestation and land use changes in past centuries. A significant population is dependent on runoff from the mountain areas of the Tibetan region as their primary water source, and decreasing snowfall there will affect water usage in the region. The world is truly a tightly coupled, interacting system.
As illustrated by this one example, global environmental change goes well beyond just climate change. The recently released IPCC report serves to clearly illuminate the need for assembling the “big picture” puzzle in order to support sustainable development on a global scale. IGBP’s international, interdisciplinary research activities aim to do just that.
ReferencesAndreae, M. O., D. Rosenfeld, P. Artaxo, A. A. Costa, G. P. Frank, K. M. Longo, and M. A. F. Silva Dias, 2004: Smoking Rain Clouds over the Amazon. Science, 303, 1337-1342.
Kesselmeier, J., U. Kuhn, S. Rottenberger, T. Biesenthal, A. Wolf, G. Schebeske, M. O. Andreae, P. Ciccioli, E. Brancaleoni, M. Frattoni, S. T. Oliva, M. L. Botelho, C. M. A. Silva, and T. M. Tavares, 2002: Concentrations and species composition of atmospheric volatile organic compounds (VOCs) as observed during the wet and dry season in Rondonia (Amazonia). J. Geophys. Res., 107, 8053.