IF OUR PATCH of warm winters hasn't provoked some wondering about global warming, then that huge chunk of ice that recently and dramatically broke off Antarctica was certainly cause to sit up and take notice.
This was a staggering geophysical event that unfolded with startling rapidity, over just 35 days. About 650 feet thick and larger than Rhode Island, the disintegrated ice shelf probably was part of the Antarctic Peninsula for 12,000 years.
At minimum, its collapse highlights the daunting scientific, political and economic crosscurrents in the long-running war over the climatic effects of greenhouse gases.
Along with other signs of a warming planet -- such as longer growing seasons and thinning Arctic ice -- it also should ratchet up pressure on the United States to ratify the Kyoto Protocol. One hundred sixty nations have signed on to this plan to cut gas emissions; the Bush administration considers it flawed and favors voluntary efforts.
Don't count on that changing. Just last week, the administration, pushed by auto and energy interests, ousted the respected scientist leading the key United Nations panel on climate change because of his environmentalist leanings.
The only good news here is that, unlike glaciers, ice shelves are floating to begin with -- so the separation of an estimated 720 billion tons of ice will not mean rising seas.
Scientists agree on the immediate cause, a 5-degree temperature increase over the last 50 years in that particular area of the Antarctic, a spike five times greater than anywhere else on Earth. For many, that might suffice to conclude... er... the sky is already falling.
But that's not necessarily so. Antarctica is larger than the United States. Various parts have gone through warming and cooling cycles. Right now, some are getting colder.
At the same time, this wasn't the first large piece of Antarctica to recently fall into the sea; a large portion of the same shelf has disintegrated since 1995. Other Antarctic shelves may be vulnerable.
This shelf disintegrated with truly astounding speed; scientists once thought that process would take decades or centuries. The new worst case: If some of southern Antarctica's shelves were to go, some of the big ice sheets covering the continent could move into the sea with previously unimaginable speed -- spelling worldwide trouble.
But this theory would play out over a century or more. And -- like the broader global warming arguments -- it's a chain of possibilities.
Kyoto Protocol opponents key into such uncertainties. But scientists agree that the Earth is warming, and most trace that to greenhouse gases. The core dispute is over the projected rate of that change.
In the United States, the source of a quarter of the world's greenhouse gases, the political dispute boils down to whether the immediate cost of more efficient energy generation and use -- and perhaps of suffering smaller cars and houses -- is worth staving off the possibility in 100 or more years of a planet perhaps 5 degrees warmer and without an average of 300 feet of oceanfront worldwide.
In that sense, the costs of the controls under the Kyoto Protocol are a down payment on a kind of long-term disaster insurance.
Ardent environmentalists believe the protocol is not enough insurance; some on the other side essentially agree, adding that sufficient steps to forestall warming would decimate our economy, so we'd be better off, say, building seawalls.
With the president and many U.S. voters nervous about anything that might slow economic growth, it seems wise to keep a wary eye on the southernmost continent.