On Dec. 27, Interior Secretary Dirk Kempthorne announced a proposal to list the polar bear as a threatened species under the Endangered Species Act because of the loss of its sea ice habitat from global warming.

This proposal marks the first legally binding admission by the Bush administration of the reality of global warming. The significance of the polar-bear decision has not been missed by those who stand to benefit from a continuation of the administration's head-in-the-sand approach to global warming. Once protection for the polar bear is finalized, federal agencies and large greenhouse-gas emitters will be required to ensure that their emissions do not jeopardize the species. And the only way to avoid jeopardizing the polar bear is to reduce emissions.

Predictably, opponents of emissions cuts are doing what they always have done: claim a scientific dispute where none exists and urge that no action be taken until the science is "conclusive." Singing this tired tune, an editorial in The Wall Street Journal last week called the proposal to protect polar bears a "triumph of politics over science," arguing that polar bears are "overly abundant" and that the species cannot be considered threatened until its population has declined further.

The Journal got it wrong in every respect. What is remarkable about the polar-bear decision is that it is a rare case of science actually triumphing over politics, not the other way around. From burying the National Assessment of Climate Change Impacts on the United States to trying to gag top NASA climate scientist James Hansen, the Bush administration systematically has attempted to suppress science on global warming.

However, the "best available science" standard required by the Endangered Species Act forbids political and economic considerations. That was the basis for the strategy of my organization, the Center for Biological Diversity, when, on Feb. 16, 2005, (the same day the Kyoto Protocol entered into force without the participation of the U.S.), we filed a petition requesting protection of the polar bear. The Bush administration could refuse only by denying the science of global warming. So protecting the polar bear was the only decision it could legally make.

Unfortunately for the polar bear, the "best available science" — in fact, the only available science — paints a grim picture. The bear is entirely dependent on sea ice, using it as a platform on which to travel, hunt and give birth. Yet each year, as the Arctic warms, the sea ice shrinks. Polar-bear populations are already suffering from drowning, starvation and lower cub survival. Absent cuts in greenhouse-gas emissions, the summer sea ice, and the polar bear, might disappear entirely in less than 40 years. All this has been documented in peer-reviewed scientific journals.

Notwithstanding the scientific consensus that polar bears are threatened with extinction because of global warming, there always will be fossil-fuel-addicted naysayers misrepresenting reality. Just as the tobacco industry always could find a "scientist" to claim that there was no link between smoking and lung cancer, climate-change deniers such as Sen. James M. Inhofe, R-Okla., always will find polar-bear population numbers and trends that purport to prove that the species is doing fine.

More polar bears are being seen near human settlements in Canada, they say. Therefore, polar-bear populations must be increasing. Wrong. A study by NASA and Canadian Wildlife Service scientists published last September in the journal Arctic demonstrated that more polar bears were indeed being seen on land — not because the species was "overly abundant" but because the bears had nowhere else to go. They should be out on the ice hunting seals, but earlier breakup of sea ice means the bears are stuck on land, where they are more likely to be spotted.

Inhofe and The Wall Street Journal would take no action to protect polar bears until their population has declined significantly. But five of the 19 distinct polar-bear populations are already known to be declining. And given the undisputed trajectory of sea ice retreat, the species must still be considered threatened even if there were not yet any evidence of population decline. If a ship starts taking on water, you don't wait until the first passenger drowns before issuing a mayday; the passengers are clearly "threatened" as soon as the water starts pouring in.

But polar bears are not the first species (nor will they likely be the last) for which we have sought the protections of the Endangered Species Act because of global warming. The first, in 2001, was the Kittlitz's murrelet, a small seabird that feeds at the mouth of tidewater glaciers and whose decline corresponds to the global-warming-induced retreat of those glaciers.

Alas, the eyes of the world did not turn to the plight of the Kittlitz's murrelet, as we had hoped, and the administration quietly refused to protect it, a decision we are challenging in court. In 2004, we filed a petition seeking protection for the staghorn and elkhorn corals, species that have declined by more than 90 percent because of a host of threats, including global warming. The corals were listed as threatened species in May, but with far less fanfare than the polar bear and without an explicit recognition of global warming as a cause of their decline. In November, we petitioned to protect 12 penguin species, including the ice-dependent emperor penguin.

These species are, unfortunately, just the tip of the extinction iceberg. One study estimates that a third of the Earth's creatures will be condemned to extinction by 2050. Polar bears might not be extinct until 2040, but that doesn't mean we have 30 years to do nothing.

Hansen, the NASA climate scientist, repeatedly has warned that merely keeping up the current pace of emissions for 10 more years will irreversibly alter the Earth's climate. If sea levels rise 18 feet or more, a large proportion of the world's human population will be displaced — or worse. Polar bears are not the only species threatened by global warming. Absent political action from the United States and the world, the rest of us might be as well.