What Constitutes "Dangerous Anthropogenic Interference?"; ENSO Not Linked to Global Warming

What Constitutes "Dangerous Anthropogenic Interference?"

The stated goal of the United Nations Framework Convention on Climate Change it to stabilize greenhouse gas concentrations at levels that avoid dangerous anthropogenic interference with the atmosphere. As President George W. Bush has rightly pointed out, the Kyoto targets "were arbitrary and not based upon science" and "no one can say with any certainty what constitutes a dangerous level of warming, and therefore what level must be avoided."

Brian C. ONeill at the Watson Institute for International Studies and the Center for Environmental Studies at Brown University and Michael Oppenheimer at the Woodrow Wilson School of Public and International Affairs and the Department of Geosciences, Princeton University, attempt to answer that question in a Policy Forum paper in the June 14 issue of Science.

The authors admit that this is a difficult task that must "ultimately involve a mixture of scientific, economic, political, ethical, and cultural considerations, among others. In addition, the links among emissions, greenhouse gas concentrations, climate change, and impacts are uncertain. Furthermore, what might be considered dangerous could change over time."

The Intergovernmental Panel on Climate Change has identified two criteria for defining "dangerous" interference: "warming involving risk to unique and threatened systems and warming engendering a risk of large-scale discontinuities in the climate system."

The authors offer three risks which would fall under these criteria, (1) "Large-scale eradication of coral reef systems," (2) the "disintegration of the Western Antarctic Ice Sheet (WAIS)," and (3) "the weakening or shutdown of the density-driven, large scale circulation of the oceans (thermohaline circulation or THC)."

To prevent severe damage to reef systems, the authors recommend a long-term target of one degree C above 1990 global temperatures. To protect the WAIS would require a limit of two degrees C above 1990 temperatures. And to stop the shutdown of the THC would require a limit of three degrees C warming over the next 100 years.

None of these cases is particularly convincing, however. As noted in a critique of this study by The Center for the Study of Carbon Dioxide and Global Change (www.co2science.org), the evidence shows that coral reefs have been shown to be very resilient in the face of temperature change. Coral reefs have survived several past interglacial periods that experienced warmer temperatures than now. For example, the most recent interglacial was a full three degrees C warmer than the current interglacial, yet coral reefs survived.

Recent studies have cast serious doubt on the likelihood of a collapse of the WAIS or the shutdown of the THC. A June 19 study in Science found that the WAIS is actually thickening. A January 31 study in Nature found that the Antarctic has been cooling since 1966. And another study in the February 21 issue of Nature found that the palaeoclimate data show that abrupt changes to the THC are not characteristic of the current interglacial, but are characteristic of the latest glaciation. In other words, it is unlikely that global warming will cause the THC to shut down.

ENSO Not Linked to Global Warming

With El Nio returning to the southern Pacific, it wont be long before we begin hearing about the ill effects of global warming and its possible link to this large-scale natural weather phenomenon. A study in the February 2002 issue of Paleoceanography shows that there is no connection between global warming and the frequency or strength of El Nio.

Using palaeoclimate data, the researchers reconstructed a record of El Nio activity, the latter 400 years of the record being the most reliable. The data show that El Nio activity "was more frequent after 1980, lower in the 1940-1975 epoch, and again more frequent around the beginning of the 1900s."  It also showed that "the 1860-1880 period was relatively quiescent," while "the 1820-1860 period was also a period of relatively vigorous ENSO [El Nio Southern Oscillation] activity."  Indeed, the 1820-1860 period was "similar to [that] observed in the past two decades."

The study concludes, "As these observations extend at least into the preindustrial period, attribution of the unusually ENSO-rich past few decades may lie in part with natural variability." This is a bit of an understatement given the evidence. It looks like El Nio activity is likely due entirely to natural variability.

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