How warm will it get?

In 2001, delegates from 160 nations dipped their toes into uncharted waters. They completed work on an agreement to trim industrial emissions of gases believed to be warming Earth's climate.

In 2002, the world will see whether the right combination of 55 countries mounts the high dive and takes the plunge to ratify the 1997 Kyoto Protocol - an environmental pact whose provisions reach deeper into the economic machinery of sovereign nations than any before it.

If the protocol enters into force, it could mark a watershed in humanity's relationship with its home. For the first time, countries will have adopted a common set of rules in an attempt to manage a planetary system - global climate.

"Population growth, soil degradation, loss of biodiversity, changes in atmospheric chemistry, these are the major trends" that humans have triggered, changing the character of the landscape, oceans, and atmosphere on time scales far faster than Earth's processes alone typically operate, explains Hartmut Grassl, director of the climate-process research department at the Max Plank Institute for Meteorology in Hamburg, Germany.

Humans have become such a significant force of nature in their own right, Dr. Grassl notes, that humanity no longer can sit back and let nature take its course. The Kyoto Protocol represents "the first step toward Earth-system management," he concludes.

The protocol commits industrial countries to reduce their collective carbon-dioxide emissions by an average of 5 percent below 1990 levels by 2012. Within that average, some countries faced double-digit reductions, while others, such as Russia, have carbon to burn, thanks to the selection of a base year when its economy was in a tailspin.

As 2001 opened, the political landscape for dealing with climate change looked increasingly barren, even as the scientific consensus strengthened that human industrial activity is at least partly responsible for the climate's warming.

Efforts to finish the ground rules for implementing the Kyoto Protocol at a UN-sponsored global climate conference at The Hague in November 2000 collapsed at the last minute when the US and the European Union failed to close the remaining gap between already-narrowed differences on a key provision.

Without ground rules, no industrial nation was willing to ratify the accord. And although the meeting ended in failure, UN officials adjourned it, rather than gaveling it closed. Instead, they eventually scheduled a continuation of the meeting in Bonn for the following July to complete their work.

In the interim, two events in early 2001 galvanized global efforts to pick up the pieces. The Intergovernmental Panel on Climate Change issued a summary of its third five-year report assessing the state of climate-system science. Based on additional research conducted during the preceding half decade, the IPCC's science working group concluded that "most of the observed warming over the last 50 years is likely to have been due to increasing greenhouse gas concentrations."

This marked its strongest statement yet that carbon-dioxide and other emissions from human industrial activity - burning fossil fuels such as coal, oil, and natural gas - were contributing to a 0.6 degree Celsius (1.1 degree Fahrenheit) average increase in global temperatures since the late 19th century.

As if to underscore the temperature trends, the World Meteorological Organization last week issued its preliminary look at weather and climate in 2001. The year looks to be the second warmest on record, after 1998. The WMO noted that while global average surface temperatures have risen at 0.6 degree per century, the rate of increase nearly tripled during the past 25 years, to 1.7 degrees C.

The second prod came in March, when President Bush announced that the US would not take part in further negotiations on the Kyoto Protocol. US negotiators were to jump in only if US interests were jeopardized. The move stunned countries participating in the talks. Ultimately, it caused key countries to reach an agreement. They cleared political logjams in Bonn in July, then completed work on the legal language in Marrakesh, Morocco, last month.

Negotiators and UN officials hope to see the treaty in force by late August 2002, when delegates meet in Johannesburg, South Africa, for a conference that marks the 10th anniversary of the Earth Summit in Rio de Janeiro. The Earth Summit led to the 1992 Framework Convention on Climate Change, which the US ratified, and its Kyoto Protocol.

To take effect, the protocol must be ratified by 55 countries, including enough industrial countries to account for 55 percent of industrial-country emissions.

Without the US, analysts say, the key countries and blocs to watch include Canada, Japan, the European Union, and Russia. If any of these fail to ratify the protocol, it will not reach the 55-55 threshold.

"I think the odds are pretty good" that the Protocol will garner the needed support to take effect, says Eileen Claussen, president of the Pew Center on Global Climate Change in Washington, D.C., and a former assistant secretary of state for oceans and international environmental and scientific affairs.

She notes that the European Union has pledged to ratify the pact. Japanese Prime Minister Kiozumi has indicated Japan will ratify, and a number of Eastern European countries appear set to do likewise.

"The only thing you need for entry into force is Russia," to adopt it she continues. The Russians can be unpredictable, she continues, but they got everything they asked for during the talks in Bonn and Marrakesh. "So I think the odds are that they too will ratify," she says.

Which leaves the US on the outside, looking in - at least under current administration policy. While this state of affairs grates with environmental groups and key Democratic lawmakers in Washington, others see the rest of the industrial world hobbling itself economically.

Ratification would place countries such as Japan and European Union members "at a distinct competitive disadvantage," says Glenn Kelly, executive director of the Washington-based Global Climate Coalition, which draws much of its support from industries related to fossil fuels. The organization backs voluntary approaches to dealing with climate change without imposing targets and timetables.

Ironically, when the US opted out of the protocol process, it may have inadvertently helped cut the cost of compliance for everyone else, notes Henry Jacoby, an economics professor at the Massachusetts Institute of Technology's Sloan School of Management and co-director of the institute's Joint Program of the Science and Policy of Global Change.

He explains that carbon trading is one of the key tools countries can use to meet their targets. This approach allows countries having a tough time meeting targets to buy carbon "credits" or "permits" from countries, such as Russia, whose emissions remain below their targets.

The approach draws on the US's successful sulfur-trading scheme for reducing sulfur -dioxide emissions from power plants.

Like the value of any other commodity, the price of carbon credits depends on demand, as well as on supply. With the world's biggest emitter essentially out of the market, demand for the credits falls.

"If you take the flexibility they agreed to in Marrakesh, assume that all of it is used, and assume Russians sell all their hot air, essentially the market price of carbon is $2 or $3 a ton," Dr. Jacoby says. If Russia and Ukraine act as a cartel and try to milk their carbon credits for as much profit as they can, "then the price of permits rises to about $38 a ton."

Either way, he says, negotiators in effect shifted Kyoto's targets for the first commitment period, which runs from 2008 to 2012, from 5 percent below 1990 levels to about 9 percent above 2000 levels.

"With the US out, you've got an agreement that is machinery in place, but in the first commitment period, it doesn't require very much," he says. "It could be used, however, to tighten down for subsequent commitment periods."

Indeed, several analysts note that with the next major climate meeting scheduled for October in New Delhi, talks are bound to lay the groundwork for rules governing subsequent commitment periods.

If the Bush administration has opted out of Kyoto, it hasn't taken itself out of the international climate-change game altogether. On Dec. 7, representatives from US, Canada, and Mexico met in Toronto for talks that examine the possibility of setting up a carbon emissions-trading scheme among the three countries.

"The meeting raised more questions than answers," says Scott Vaughn, head of economics and trade at the Commission for Environmental Cooperation, established under the North American Free Trade Agreement.

Still, he says, delegates recognized that opportunities exist for establishing a regional carbon-trading scheme. One initial step could be the establishment of a pollutant inventory, which would provide the basic data needed to take any subsequent steps toward establishing a North American carbon market.