Twelve years ago in Kyoto, the world was poised to act on a climate treaty but looked for a clear signal from the United States. Now, with the Copenhagen talks set to begin, the outcome once again hinges on what the U.S. is prepared to do.

On the eve of the Copenhagen conference, a group of scientists has issued an update on the 2007 report of the Intergovernmental Panel on Climate Change. Their conclusions? Ice at both poles is melting faster than predicted, the claims of recent global cooling are wrong, and world leaders must act fast if steep temperature rises are to be avoided.

For months, hopes that a climate treaty would be signed at the upcoming Copenhagen conference have been raised, then dashed, then raised again. Now, with prospects waning that a binding accord on reducing greenhouse gas emissions can be reached this year, ten environmental leaders and climate experts outline for Yale Environment 360 what they believe can still be accomplished at Copenhagen.

Even as the climate science becomes more definitive, polls show that public concern in the United States about global warming has been declining. What will it take to rally Americans behind the need to take strong action on cutting carbon emissions?

Over the last century, the intensive use of chemical fertilizers has saturated the Earth’s soils and waters with nitrogen. Now scientists are warning that we must move quickly to revolutionize agricultural systems and greatly reduce the amount of nitrogen we put into the planet's ecosystems.

With skepticism growing about the chances of reaching a climate agreement next month in Copenhagen, Rajendra Pachauri, chairman of the Intergovernmental Panel on Climate Change, says he is “cautiously optimistic” that a treaty can still be signed. But in an interview with Yale Environment 360, Pachauri says the global community may have to move ahead without any commitment from the United States.

As the world warms, how different societies fare in dealing with rising seas and changing weather patterns will have as much to do with political, social, and economic factors as with a changing climate.

Green rankings in the U.S. don’t tell the full story about the places where the human footprint is lightest. If you really want the best environmental model, you need to look at the nation’s biggest — and greenest — metropolis: New York City.

Interfering with the Earth’s climate system to counteract global warming is a controversial concept. But in an interview with Yale Environment 360, climate scientist Ken Caldeira talks about why he believes the world needs to better understand which geoengineering schemes might work and which are fantasy — or worse.

Amid a growing call for reducing atmospheric concentrations of CO2 to 350 parts per million, a group of economists maintains that striving to meet that target is a smart investment — and the best insurance policy humanity could buy.

As humans increasingly encroach on forested lands and as temperatures rise, the transmission of disease from animals and insects to people is growing. Now a new field, known as “conservation medicine,” is exploring how ecosystem disturbance and changing interactions between wildlife and humans can lead to the spread of new pathogens.

In her long career as an oceanographer, Sylvia Earle has witnessed the damage that humanity has done to the Earth’s oceans. But in an interview with Yale Environment 360, she says there's still time to pull the seas back from the brink.

Of the various geoengineering schemes being proposed to cool an overheated planet, one approach — extracting carbon dioxide from the atmosphere using “artificial trees” — may have the most potential. But both questions and big hurdles remain before this emerging technology could be widely deployed.

As the international community focuses on climate change as the great challenge of our era, it is ignoring another looming problem — the global crisis in land use. With agricultural practices already causing massive ecological impact, the world must now find new ways to feed its burgeoning population and launch a "Greener" Revolution.

It has been more than 30 years since a groundbreaking book predicted that if growth continued unchecked, the Earth’s ecological systems would be overwhelmed within a century. The latest study from an international team of scientists should serve as an eleventh-hour warning that cannot be ignored.

The average American produces three times the amount of CO2 emissions as a person in France. A U.S. journalist now living in Europe explains how she learned to love her clothesline and sweating in summer.

The Earth has nine biophysical thresholds beyond which it cannot be pushed without disastrous consequences, the authors of a new paper in the journal Nature report. Ominously, these scientists say, we have already moved past three of these tipping points.

By the end of the century, New York’s climate could resemble that of present-day Raleigh, North Carolina and its harbor could easily rise by two feet or more. Faced with this prospect, the city is among the first urban centers to begin changing the way it builds its infrastructure — and the way it thinks about its future.

If a cap-and-trade bill passes Congress this year, it may include weak emissions targets and will likely need to be strengthened in the years to come. One way to guide future policy: create a Global Climate Change Index that could be used to track global warming’s impacts.

China is on its way to becoming the world’s largest producer of renewable energy, yet it remains one of the most polluted countries on earth. A year after the Beijing Olympics, economic and political forces are combining to make China simultaneously a leader in alternative energy — and in dirty water and air.

John Holdren, the president’s top science adviser, is playing a key role in shaping the Obama administration’s strategy to combat global warming. In an interview with Yale Environment 360, Holdren discusses the prospects for achieving key breakthroughs on climate change, both in Congress and at upcoming talks in Copenhagen.