The climate crisis and the need for leadership.

It is now clear that we face a deepening global climate crisis that requires us to act boldly, quickly and wisely. "Global warming" is the name it was given a long time ago. But it should be understood for what it is: a planetary emergency that now threatens human civilization on multiple fronts. Stronger hurricanes and typhoons represent only one of many new dangers as we begin what someone has called "a nature hike through the Book of Revelation."

As I write, my heart is heavy due to the suffering the people of the Gulf Coast have endured. In Florida, Alabama, Mississippi, Louisiana and Texas, and particularly in New Orleans, thousands have experienced losses beyond measure as our nation and the world witnessed scenes many of us thought we would never see in this great country. But unless we act quickly, this suffering will be but a beginning.

The science is extremely clear: Global warming may not affect the frequency of hurricanes, but it makes the average hurricane stronger, magnifying its destructive power. In the years ahead, there will be more storms like Katrina, unless we change course. Indeed, we have had two more Category 5 storms since Katrina - including Wilma, which before landfall was the strongest hurricane ever measured in the Atlantic.

We know that hurricanes are heat engines that thrive on warm water. We know that heat-trapping gases from our industrial society are warming the oceans. We know that, in the past 30 years, the number of Category 4 and 5 hurricanes globally has almost doubled. It's time to connect the dots:

- Last year, the science textbooks had to be rewritten. They used to say, "It's impossible to have a hurricane in the South Atlantic." We had the first one last year, in Brazil. Japan also set an all-time record for typhoons last year: 10. The previous record was seven.

- This summer, more than 200 cities in the United States broke all-time heat records. Reno, Nevada, set a new record with 10 consecutive days above 100 degrees. Tucson, Arizona, tied its all-time record of 39 consecutive days above 100 degrees. New Orleans - and the surrounding waters of the Gulf - also hit an all-time high.

- This summer, parts of India received record rainfall - 37 inches fell in Mumbai in 24 hours, killing more than 1,000 people.

- The new extremes of wind and rain are part of a larger pattern that also includes rapidly melting glaciers worldwide, increasing desertification, a global extinction crisis, the ravaging of ocean fisheries, and a growing range for disease "vectors" like mosquitoes, ticks and many other carriers of viruses and bacteria harmful to people.

All of these are symptoms of a deeper crisis: the "Category 5" collision between our civilization - as we currently pursue it - and the Earth's environment.

Sixty years ago, Winston Churchill wrote about another kind of gathering storm. When Neville Chamberlain tried to wish that threat away with appeasement, Churchill said, "This is only the beginning of the reckoning. This is only the first sip, the first foretaste, of a bitter cup which will be proffered to us year by year - unless by a supreme recovery of moral health and martial vigor, we rise again and take our stand for freedom."

For more than 15 years, the international community has conducted a massive program to assemble the most accurate scientific assessment on global warming. Two thousand scientists, in a hundred countries, have produced the most elaborate, well-organized scientific collaboration in the history of humankind and have reached a consensus as strong as it ever gets in science. As Bill McKibben points out, there is no longer any credible basis to doubt that the Earth's atmosphere is warming because of human activities. There is no longer any credible basis to doubt that we face a string of terrible catastrophes unless we prepare ourselves and deal with the underlying causes of global warming.

Scientists around the world are sounding a clear and urgent warning. Global warming is real, it is already under way and the consequences are totally unacceptable.

Why is this happening? Because the relationship between humankind and the Earth has been utterly transformed. To begin with, we have quadrupled the population of our planet in the past hundred years. And secondly, the power of the technologies now at our disposal vastly magnifies the impact each individual can have on the natural world. Multiply that by six and a half billion people, and then stir into that toxic mixture a mind-set and an attitude that say it's OK to ignore scientific evidence - that we don't have to take responsibility for the future consequences of present actions - and you get this violent and destructive collision between our civilization and the Earth.

There are those who say that we can't solve this problem - that it's too big or too complicated or beyond the capacity of political systems to grasp.

To those who say this problem is too difficult, I say that we have accepted and met such challenges in the past. We declared our liberty, and then won it. We designed a country that respected and safeguarded the freedom of individuals. We abolished slavery. We gave women the right to vote. We took on Jim Crow and segregation. We cured fearsome diseases, landed on the moon, won two wars simultaneously - in the Pacific and in Europe. We brought down communism, we defeated apartheid. We have even solved a global environmental crisis before: the hole in the stratospheric ozone layer.

So there should be no doubt that we can solve this crisis too. We must seize the opportunities presented by renewable energy, by conservation and efficiency, by some of the harder but exceedingly important challenges such as carbon capture and sequestration. The technologies to solve the global-warming problem exist, if we have the determination and wisdom to use them.

But there is no time to wait. In the 1930s, Winston Churchill also wrote of those leaders who refused to acknowledge the clear and present danger: "They go on in strange paradox, decided only to be undecided, resolved to be irresolute, adamant for drift, solid for fluidity, all powerful to be impotent. The era of procrastination, of half-measures, of soothing and baffling expedients, of delays, is coming to a close. In its place, we are entering a period of consequences."

With Hurricane Katrina, the melting of the Arctic ice cap and careless ecological mayhem, we, too, are entering a period of consequences. This is a moral moment. This is not ultimately about any scientific debate or political dialogue. Ultimately it is about who we are as human beings. It is about our capacity to transcend our own limitations.

The men and women honored as warriors and heroes have risen to this new occasion. On the surface, they share little in common: scientists, ministers, students, politicians, activists, lawyers, celebrities, inventors, world leaders. But each of them recognized the threat that climate change poses to the planet - and responded by taking immediate action to stop it. Their stories should inspire and encourage us to see with our hearts, as well as our heads, the unprecedented response that is now called for.

As these heroes demonstrate, we have everything we need to face this urgent challenge. All it takes is political will. And in our democracy, political will is a renewable resource.

ENDS