It’s now or never for greenhouse gas reductions, study’s authors say

What nations do to cut pollution in the short-term can make a world of environmental difference in the long run, says Brian O'Neill of the Watson Institute for International Studies. Waiting until 2020 to take action may be too late.

by Scott J. Turner

Begin to reduce greenhouse gas emissions soon or it might be too late to avoid dangerous climate change, say a Brown author and his Princeton colleague in a policy forum in the June 14 issue of Science. Their scientific analysis responds to calls for well-defined long-term objectives in dealing with climate change.

What nations do to cut pollution in the short-term can make a world of environmental difference in the long run, argue Brian O'Neill of the Watson Institute for International Studies and the Center for Environmental Studies and co-author Michael Oppenheimer, a Princeton geoscientist.

They use scientific evidence to describe what “dangerous” climate change might mean. The principal objective of an international climate change treaty signed in 1992 is to avoid dangerous interference with climate. But the treaty and subsequent agreements, including the Kyoto Protocol, an international framework negotiated in 1997 to stem pollution and global warming, leave “dangerous” undefined.

The authors test the differences between getting started with emissions reductions in 2010 versus in 2020 to meet a long-term goal of 450 parts per million (ppm) for atmospheric carbon dioxide concentration for the year 2100.

Carbon dioxide is a greenhouse gas that comes from burning fossil fuels and destroying forests. The current level is 370 parts per million, and rising. Stabilizing the level of carbon dioxide at 450 ppm is consistent with avoiding several impacts the authors interpret as dangerous interference with the climate. These include disintegration of the West Antarctic Ice Sheet (WAIS) and failure of the density-driven, large-scale circulation of ocean heat called “thermohaline” circulation (THC).

The researchers chose ice sheet melting and ocean circulation shutdown as examples of “large-scale discontinuities” that could occur in the climate system. The also examine major loss of coral reef systems, which represent a unique ecosystem that could be decimated.

O'Neill and Oppenheimer estimate that 450 ppm would lead to a plausible range of warming of 1.2 - 2.3 degrees Celsius over the next 100 years. Their calculations take into account uncertainties in what is known of the climate system. This range of warming would probably, but not certainly, avoid collapse of WAIS, and would likely avoid shutdown of THC.

The potential for WAIS to disintegrate is highly uncertain, but is likely to require an increase of 2 degrees Celsius or more. Complete disintegration, which could take hundreds of years or longer, would result in an increase in sea level of 13 to 20 feet. That would submerge much of the world’s coastlines, including large sections of Manhattan and southern Florida.

A shutdown of the thermohaline ocean current would probably require a 3-degree Celsius increase during this century. The extent of the resulting disruption for societies and ecosystems is uncertain, but “it would be unwise to find out by continuing to pump up levels of greenhouse gases,” said Oppenheimer.

Full protection of coral reefs is probably unfeasible, said the authors. Coral reefs are likely to undergo annual "bleaching" and eventually experience severe damage if the average global temperature increases more than 1 degree Celsius, they said.

Taking into account that scientists don't know exactly how much carbon dioxide plants and oceans absorb from the atmosphere, O'Neill and Oppenheimer conclude that the task of avoiding WAIS collapse and THC shutdown would become considerably harder, if not impossible, by waiting until 2020 to begin cutting greenhouse gas emissions.

“Reductions may become so costly that they would be unfeasible," said O'Neill. “As a result, nations might lose the option of limiting climate change to a relatively low level. To reduce the risk of dangerous impacts, emissions reductions must start sooner rather than later. Implementing the Kyoto Protocol by 2010 keeps options on the table.”

The 2010 scenario in the study assumes that the Kyoto targets are met. The Kyoto Protocol calls for industrialized countries to reduce emissions of heat-trapping gases (defined primarily as carbon dioxide, or CO2) to an average of about 5 percent below 1990 levels. Individual country targets vary, and the overall goal is to be achieved between 2008 and 2012.

“The Bush administration regards large climate changes as inevitable and proposes adaptation as the main response," said Oppenheimer, who holds joint appointments in Princeton's Department of Geosciences and the Woodrow Wilson School of Public and International Affairs. “But some climate changes are so disruptive that avoiding them through emissions reduction is the only sensible alternative. Some have argued that the Kyoto Protocol would have little effect on long-term climate change. But we find that the total emissions reductions it envisions appear to be an important first step toward avoiding dangerous warming.”

The Kyoto Protocol will come into force if nations representing 55 percent of emissions from industrialized countries ratify it. So far ratifications cover 35 percent of those emissions. This includes the European Union and Japan, both of which ratified recently.

Prospects for Kyoto entering into force are good, but are by no means certain, said O’Neill. “Reaching 55 percent depends critically on, among other things, whether Russia decides to ratify. Also, even with Kyoto entering into force, its environmental effect will be substantially weakened without U.S. participation.” Last year, President Bush rejected the protocol. (During the Clinton presidency, the Senate took an informal vote and rejected the protocol by 95-0.)