Abrupt Climate Change
- It has generally been considered that human-induced climate change will involve a smooth increase in global mean temperature and, similarly, gradual changes in other climate parameters, such as precipitation. The assumption, then, has been that the climate system will continue to function largely as it has since the last ice age, and that any changes will involve perturbations around this relatively steady state.
- Recent geological discoveries and numerous paleoclimate records, however, have now made it evident that major climate changes in the past occurred with remarkable speed. For example, the North Atlantic region warmed by as much as 18ºF (10ºC) within a decade or so during the shift from the last ice age to the current Holocene. Modern civilizations would likely be devastated were such a rapid change to occur.
- According to the National Research Council (NRC) in a 2002 publication “[A]brupt climate changes were especially common when the climate system was being forced to change most rapidly. Thus, greenhouse warming and other human alterations of the earth system may increase the possibility of large, abrupt, and unwelcome regional or global climatic events.”
- However, it is well known that the earth system – including the biological, physical, chemical and human components and their interactions – is highly complex. In this regard, as the NRC pointed out, future abrupt changes are unlikely to be predicted, climate surprises are to be expected and, if they are to occur, adaptation will be difficult. The NRC concludes that “[T]he new paradigm of an abruptly changing climatic system has been well established by research over the last decade, but this new thinking is little known and scarcely appreciated in the wider community of natural and social scientists and policy-makers”.
- Changes in the earth’s climate system are occurring as a result of substantially higher atmospheric concentrations of such natural gases as CO2, methane, water vapor, ozone and nitrous oxide.
- Current atmospheric concentrations of CO2 – the dominant human-influenced greenhouse gas – have not been exceeded during the past 420 000 years and likely haven’t been, according to the Intergovernmental Panel on Climate Change, for the past 20 million years. The main human-related causes of CO2 release are fossil fuel combustion (mainly oil, coal and gas) and deforestation. Atmospheric methane concentration has increased by approximately 150% since the mid-1700s, largely due to livestock production, the decomposition of refuse in landfills, and fossil fuel production and use. Nitrous oxide concentration has increased by 16% since the mid-1700s with the major human-related sources including nitrogen fertilizer use, industrial activities, and livestock production.
- In general, the chances of abrupt changes in the Earth’s climate system – as with any complex system – increases with the extent and speed of the forcing agent (e.g., greenhouse gas increases). It will be extremely difficult, however, to determine what might trigger an abrupt change or how close the climate system is to a dangerous threshold.
- There have been few studies that have attempted to directly analyze the potential impacts of abrupt climatic changes. It is anticipated that in some cases an abrupt change may simply accelerate the effects of gradual change; in other cases the impact may be qualitatively different and more severe.
- The possibility of sudden, dramatic climate shifts, unexpected events (i.e., surprises) such as the collapse of the “conveyor belt” circulation in the North Atlantic Ocean or rapid deglaciation of polar ice sheets, along with high scientific uncertainty, have led many climate scientists – though not all – to strongly advocate for the immediate reduction of greenhouse gas emissions to slow the rate of climate change.
- The U.S. is a signatory to the United Nations Framework Convention on Climate Change (UNFCCC). The Convention, which entered into force in 1994, calls for “stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system.” The UNFCCC did not set out binding, quantitative emission reductions for the signatory countries and so, in 1997, the Kyoto Protocol was adopted to fulfill this need.
- Current U.S. climate policy is geared towards voluntary reductions in greenhouse gas emissions, programs for societal adaptation, and continuing long-term research. Under the proposed voluntary reduction program, U.S. emission rates would continue to increase. The U.S. has also withdrawn from international engagement – such as the Kyoto Protocol – in reducing human interference of the climate system. Present U.S. measures, therefore, have been criticized as running counter to a “no-regrets” or a “precautionary” approach, particularly in light of the potential for rapid or unforeseen climatic changes and the lack of evidence suggesting that changes can be controlled once they have begun to occur.
Higgins, P.A.T.and Vellinga, M. 2004. Ecosystem responses to abrupt climate change: Teleconnections, scale and the hydrological cycle. Climatic Change 64(1-2): 127-142.
National Research Council. 2002. Abrupt Climate Change: Inevitable Surprises. National Academy Press, Washington, DC.
Steffen, W. et al. 2004. Abrupt changes: the Achilles’ heels of the Earth System. Environment 46(3): 8-20. |
