In science, a process is a series of changes of one or more variables that represent properties or states of an object or a system. Examples of physical, chemical, and biological processes include evaporation, land erosion, oxidation, cell division, germination, dispersion, growth, accumulation, and global warming.

In addition to the processes themselves, the study of the relationship between causes and effects of changes accounts for a major portion of scientific research. There are many ways to classify a process, based on properties of the process itself or the cause-effect relationship behind it. For example, a process can be continuous or discrete, stable or unstable, convergent or divergent, and linear or nonlinear. A process is nonlinear when its effect is not simply proportional to its cause. For example, water evaporation is a nonlinear process, because water being boiled will not vaporize until the temperature reaches the critical threshold of 100œ Celsius, causing a change in water's state from liquid to gas.

The global climate system includes a variety of nonlinear processes that are subject to positive feedbacks, as well as complex interrelations between numerous factors affecting the climate. Such complexity exposes the Earth to a high risk of abrupt climate changes.

A positive feedback loop worth noting is the Arctic permafrost melt, which can speed up the cycle between the accumulation of GHGs in the atmosphere and temperature growth. The greenhouse effect contributes to global warming and higher temperature leads to melting frozen soils in the Artic region. The ice melting can release vast amounts of carbon dioxide (CO2) and methane trapped in the permafrost soils. Estimates show that billions of metric tons of methane--a greenhouse gas twenty-one times more potent than is CO2--can be emitted into the atmosphere and amplify the greenhouse effect (Botterill, 2003).

Another important positive feedback loop is the Arctic albedo change (Axelrod, 2004). The albedo of a surface is the percentage of incident light that it reflects back into space. Since ice masses have high albedos, the ice covering the Arctic Ocean and land surfaces can help the Earth absorb only a small fraction of solar energy. As the Arctic ice melts due to global warming, the uncovered surface assimilates more solar energy and as a consequence intensifies the warming effect.

Besides permafrost melt and the Arctic albedo change, rain-forest decline, water scarcity, land degradation, ocean decline, and persistent toxins have the potential to cause abrupt climate change. Studies of the effects of the nonlinear processes, as well as their interactions with other elements of the climate system, are in progress to resolve uncertainty about abrupt and irreversible climate changes.

References

1. Axelrod, Regina S., David Leonard Downie, and Norman J. Vig, eds. The Global Environment: Institutions, Law, and Policy. 2d ed. Washington, D.C.: CQ Press, 2004.

2. Botterill, Linda C., and Melanie Fisher, eds. Beyond Drought: People, Policy, and Perspectives. Collingwood, Vic.: CSIRO, 2003.

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