I've been reading Jared Diamond's interesting new book, Collapse, which looks at the ways different societies, past and present, have responded to environmental problems. Some of these societies recognized the trouble in time, changed their practices and thrived. Others carried on like the proverbial ostrich, head in sand, and swiftly collapsed, leaving remnants of once great civilizations behind as precautionary testaments to their fate.

For instance, the Japanese addressed their deforestation problem early and well. Four hundred years ago, they began taking measures to protect and reforest their lands. Today, Japan is 80 percent forested, despite having one of the highest population densities in the developed world. The Easter Islanders, on the other hand, let their deforestation problem get so out of hand that they denuded their entire island. There wasn't even enough wood left to build seaworthy ships with which to escape.

The point of the book is that a moment may come in the life of a society when it must act or face collapse. I worry that our own moment is now -- not so much for deforestation or desertification, overconsumption or biodiversity loss (though these are all urgent problems, too), but for global warming. Here's why I fear this is the problem our civilization could founder on:

Global warming is already well underway. The earth's average surface temperature increased by about 1° F in the 20th century and is projected to increase another 2.5 to 10.4° F in the 21st unless we significantly reduce our global warming gas emissions. Observable changes due to global warming include shrinking glaciers, thawing permafrost, earlier break-up of river and lake ice, sea level rise, lengthening of mid- to high-latitude growing seasons and earlier tree flowering.

The consequences of continued global warming could be highly disruptive -- even catastrophic. Possible effects include the flooding of low-lying islands and coastal areas, increased inland flooding, more heat waves and other extreme weather events, more droughts and wildfires, ecosystem shifts, species die-outs and the spread of disease as disease-bearing insects move to previously inhospitable climes.

Global warming is not easily reversible. Even if we were to cut back on the sources of global warming pollution immediately, the earth's temperature would continue to rise for decades before it stabilized and declined. The process is analogous to what happens during a typical sunny day. The temperature continues to climb into the afternoon, after the sun has reached its zenith, and doesn't drop to its nadir until hours after the sun has set.

Global warming is a worldwide phenomenon. If we are stupid enough to let the problem spin wildly out of control, there won't be new lands to escape to (though some places will be much less affected than others). It's not that I think we'll die out as a species -- just that we'll be thrown back to a more primitive way of living, with all the sickness, struggle and hardship that could entail. The Easter Islanders didn't die out either, but their extraordinary civilization did. By 1722 when the Dutch explorer Jacob Roggeveen found them, they were a small, ragged, hungry population that still had the skills to erect the magnificent multi-ton statues for which they became famous, but no longer had the resources.

Many people throw up their hands at the immensity of the problem, figuring there's nothing they, as individuals, can do. I have the opposite reaction. The immensity is what makes me feel I'd better do something quick. My approach is three-pronged, consisting of:

1) PERSONAL ACTION: I try to keep my family's energy consumption down by buying energy-efficient fixtures and appliances -- and by reducing our reliance on them. (See below for suggestions on how you can do the same.)

2) POLITICAL ACTION: I let elected officials know how I feel about global warming. Mostly, I send email, but I also make calls and write old-fashioned letters, since they count more to some officials.

3) SOCIAL ACTION: I talk the issue up with family, friends and acquaintances. If all of the people concerned about global warming did the same, perhaps we could bring society's recognition of the problem to the "tipping point" where debate would end and action finally begin.

Crucial moments in life and history don't announce themselves, which is why they're so easy to miss. No warning bell rang when the Easter Islanders cut down one tree too many. It's only afterwards, when the damage is done, that the moment finally becomes obvious. By then it's too late to reverse. Let's not let that happen to us.

—Sheryl Eisenberg

ONLINE RESOURCES NRDC Consequences of Global Warming NRDC Global Warming Basics NRDC How to Fight Global Warming DOE Choosing a Fuel-efficient Vehicle DOE & EPA Energy Star UCS Weatherizing NATIONAL GEOGRAPHIC Signs from Earth NPR Interview with Jared Diamond (audio)

Lost civilization. The Easter Islanders carved hundreds of these stone statues, which represent high-ranking ancestors. Most of the statues, called "moai," stood on the coast, not facing out to sea, as you might expect, but inland. The average moai was 10 feet high and weighed 13 tons, but they could be many times taller and heavier. Some of the later ones bore huge stone cylinders on their heads, like hats. The cylinders themselves could weigh up to 12 tons.

Getting hotter. This chart, based on a more detailed one from the Intergovernmental Panel on Climate Change, shows the variation in the earth's surface temperature since 1860. The climb begins around 1910. See the original.

What's a degree here or there? The earth's temperature is projected to rise another 2.5-10.4° F by the end of the century due to global warming. This may not sound like much until you consider that today's average temperature is only 9° warmer than the average during the last Ice Age.

What government needs to do. Though I'm a great believer in the power of personal action, individuals alone can't solve global warming. Industry needs to change the way it does things. But since industry won't change of its own accord, we need government to step in and insist that:

- Power companies clean up their plants and generate a higher percentage of electricity from renewable sources.

- Car and truck makers build cleaner vehicles with higher fuel economy.

- Manufacturers produce efficient appliances that run on less electricity.

Telling your elected officials that this is what you want is one of the most effective things you can do as an individual.