This editorial appeared in the St. Louis Post-Dispatch on Friday.

Polar ice sheets are melting faster than anyone predicted. At their seasonal nadir last September, arctic ice floes were 20 percent smaller than the average of the past 25 years.

Two studies published earlier this month suggest that large parts of south Florida, the Gulf Coast and Cape Cod could be inundated by rising sea levels in fewer than 100 years. Although sea levels have been rising since the end of the last ice age, the rate has accelerated since the 1990s.

The new studies come on the heels of other ominous research: A recent NASA report showed that Greenland’s ancient glaciers are melting fast. In January, the Goddard Institute for Space Studies reported that 2005 was the warmest year on record in the Northern Hemisphere.

Since the 1890s, the five warmest years on record are, in order, 2005, 1998, 2002, 2003 and 2004. See a trend?

As if that weren’t enough, the United Nation’s World Meteorological Organization reported late last year that global concentrations of carbon dioxide reached their highest recorded level in 2004. Indeed, between 1994 and 2004, concentrations of carbon dioxide, the most abundant greenhouse gas in the atmosphere, grew by about 20 percent.

That carbon dioxide almost certainly got into the atmosphere from our smokestacks and tailpipes. Jonathan T. Overpeck of the University of Arizona, lead author of one of the new studies, thinks now is the time to do something about it.

“If we don’t like the idea of flooding out New Orleans, major portions of south Florida and many other valued parts of the coastal United States, we will have to commit soon to a major effort to stop most emissions of carbon into the atmosphere,” he said.

As with any science, there is room for disagreement over details and interpretations. But the broad outline of global climate change fueled by human activity gets clearer with each new study.

President Bush conceded last year that global climate change is real. But he has yet to do much about it. Earlier this month, a federal appeals court slapped down the Bush administration’s attempt to allow aging coal-fired power plants to continue spewing carbon dioxide and other pollutants into the air.

The administration tried to impose its rules after it failed to get what it wanted from Congress.

If melting polar ice sheets and glaciers, rising surface temperatures and disappearing permafrost aren’t enough to break the ice and start a serious conversation, it’s hard to imagine what would be.

Midway through his second term, Mr. Bush is said to be increasingly concerned about his place in history. Here’s his chance to do something about it — while there’s still time to act.