Two American scientists have received a major environmental award, the Tyler Prize, for their work in tracing global warming and chronicling the effects of pollutants on the atmosphere and ice sheets.

Richard Alley of Penn State University has traced climate change through the record left in the ice sheets of Greenland and Antarctica.

Indian American scientist Veerabhadran Ramanathan of the Scripps Institution of Oceanography has studied the effects of pollutants in shifting precipitation patterns. He and his colleagues have shown that so-called brown clouds, caused by carbon and other pollutants, are partly responsible for reducing crop yields in India, while also harming human health.


Both scientists were part of the U.N. Intergovernmental Panel on Climate Change, whose members shared the 2007 Nobel Peace Prize with former U.S. Vice President Al Gore. The two were in Los Angeles to accept this year's Tyler Prize for Environmental Achievement.

They say there is no doubt the earth's climate is warming. The probable results include a dangerous rise in sea levels and coastal flooding, changes in weather patterns, droughts and flooding. The scientists say humans are largely responsible for the changes. Alley says only some details of the process are not yet understood.

"But the broad picture, are we changing the atmosphere in a way that turns up the temperature? Yes. And we have only started. If we find all of the fossil fuels that are out there and we burn them, we can make very, very, very much bigger changes than we have done so far," he said.

Ramanathan studies atmospheric samples in many parts of the world, from the coast of California to the Arabian Sea and the coast of Korea. He sees evidence of climate change in everything he looks at.

"Temperatures are rising, the rainfall is getting more intense, and to me, the most serious of the changes happening now is the dramatic retreat of Arctic sea ice, and the snowpacks in the Sierras here (in California), but more importantly, the whole glacier and snowpack retreat, which is happening in the Himalayan Tibetan region," he said.

He says the Himalayas provide headwaters for major rivers that three-billion Asians depend on.

The main culprit in global warming is carbon dioxide, which is released into the atmosphere by burning fossil fuels. The world's biggest carbon dioxide polluters are China, the United States, Russia and India.

The scientists say that cutting major greenhouse gases is a crucial long-term task, but a pollutant called black carbon can be reduced more quickly. It is produced by burning diesel fuel, and in the developing world, by burning firewood and other fuels for cooking.

Ramanathan says filters can reduce diesel pollution and a switch to alternative fuels can cut emissions in places like Asia.

"If you look at India and China, cooking with coal and firewood and cow dung is about two-thirds of the source of black carbon. And we know how to cook without them. There are better ways to cook. So it is giving people who are, what is considered, the bottom of the pyramid in terms of the economic scale access to a better source of energy," he said.

He says the change could buy us time, providing a 10- to 30-year buffer for development of technology to make serious reductions in emissions of carbon dioxide and other so-called greenhouse gases.

The scientist sees some hopeful signs. He notes that four U.S. senators - three Democrats and a Republican - have introduced legislation directing the Environmental Protection Agency to study the impact of black carbon and find ways to reduce it.

Alley says the long-term effort of controlling carbon dioxide by adopting clean energy sources and reducing greenhouse gases is just as important. There are projections that show without aggressive action, the earth's mean temperature will rise two or three degrees Celsius, and maybe higher, depending how much fossil fuel we burn in coming years.

He says the solution will be expensive, but that the costs will be much higher if we do nothing.

"If you say that the cost of solving the problem is something like one percent of the world economy per year, we as humans have done way bigger things. We call them world wars, and we have invested a lot of money in things that did not seem terribly forward-going sometimes. But we have not gotten together, shaken hands, signed on the dotted line, and agreed to do things that were that big," he said.

He says this is a pivotal time, and a healthy future for the earth requires cooperation and decisive action.