The danger signals of global warming are all around us -- from the melting snows of Mount Kilimanjaro to the projected increase in ferocity of hurricanes in the Gulf of Mexico. But the biggest red flags are at the North and South poles and in the tropics.

On the tropical mountainsides of Costa Rica, for instance, the golden toad has become extinct, and the harlequin frog has all but disappeared. This is because warmer temperatures have caused the misty clouds that once enshrouded these mountainsides to rise above the forests where the frogs live. The mist has disappeared, leaving the frogs more vulnerable to a killer fungal disease.

Thousands of miles north, in the frozen Arctic, polar bears near the Beaufort Sea have turned to cannibalism to survive. Longer seasons without sea ice, caused by winters that are 4 to 5 degrees warmer than they were 30 years ago, have prevented polar bears from finding their favorite sources of food. If nothing changes, these majestic animals will be extinct by the end of the century.

These are not isolated incidents. Global warming is causing major changes around the world. Coral reefs are dying. Glaciers are melting. Species are disappearing.

What is causing this? The primary culprit is carbon dioxide spewed by coal-fired power plants and automobiles. Automobiles produce nearly 1.5 billion tons of carbon dioxide a year. And coal-burning power plants are the largest U.S. source of carbon dioxide -- producing 2.5 billion tons every year.

Compounding the problem is the fact that carbon dioxide does not dissipate quickly. It stays in the atmosphere for five decades or more. So the carbon dioxide produced in the 1950s, 1960s, 1970s, 1980s and 1990s is still in the atmosphere today. And the carbon dioxide produced today will still be in the atmosphere in 2050 and beyond.

That's why global warming cannot be stopped. But it can be controlled -- if action is taken soon to slow, to stop and to reduce our emissions of greenhouse gases.

But if nothing is done and the Earth warms 5 degrees in the next 50 years, the face of our planet will be changed forever.

If this happens, three out of five species will become extinct by the beginning of the next century. Oceans will rise. Flooding will occur around the world. Hurricanes will be more intense. Malaria will spread. That's according to Tim Flannery, an Australian scientist and author of one of the most interesting and readable books on global warming, ``The Weather Makers.''

Flannery estimates that a 70 percent reduction in carbon dioxide emissions from 1990 levels by the middle of the 21st century is required to stabilize the Earth's climate by the year 2100.

There is no one solution that can achieve this reduction. Rather, there needs to be a commitment on several fronts -- from individuals, from businesses and from state and federal governments to address this challenge.

So what can we do?

Dramatically increase the fuel economy of automobiles. Congress should require that the fuel efficiency of all cars and SUVs increase from 25 to 35 miles per gallon over the next 10 years.

This would save 420 million metric tons of carbon dioxide and save 2.5 million barrels of oil a day by 2025. By coincidence, this is equal to the oil the United States imports today from the Persian Gulf.

Develop a market for alternative fuels in the United States. Fuels -- like E-85, made from ethanol, and biodiesel -- emit less of the greenhouse gases than traditional gasoline. Utilizing these alternative fuels could ultimately lead to an 80 percent reduction of carbon dioxide emissions from automobiles.

Create a national framework for businesses to reduce greenhouse gases. I am working on a mandatory cap and trade system that would involve agriculture and reward farmers for adopting practices that are more environmentally sound. Even with a modest 7.25 percent reduction, it would reduce emissions by 400 million metric tons of carbon dioxide by 2020. This is the equivalent of taking 85 million automobiles off the road.

Promote energy efficiency. This means using energy-efficient light bulbs; encouraging Americans to buy Energy Star air conditioners, refrigerators and boilers; and updating building codes. The Department of Energy says an aggressive program could slash energy use by 20 percent by 2020.

Show leadership on the international level. It is one of my deepest disappointments that the United States hasn't shown leadership in this area. The Kyoto Protocol is certainly not perfect and will expire in 2012. The United States needs to ensure that there is a framework in place for significant reductions after 2012 to prevent catastrophic climate change. The United States should make addressing global warming a top priority and join the European Union and other nations in reducing emissions.

Some doubt whether global warming can be controlled. I believe it can. Already the United Kingdom has brought its emissions to 14 percent of 1990 levels, so steps toward this goal can be achieved.

But there is no silver bullet. We must move quickly to face the dangers head on.