Lawyers from top environmental groups in the U.S. are considering such new legal strategies as broad-based class-action lawsuits to force the U.S. and corporations to reduce greenhouse gas emissions. Whether in federal courts or international tribunals, the lawyers would sue on behalf of people or whole countries suffering from the effects of global warming. For example, the lawyers might represent the nine-island nation of Tuvalu, which is home to 10,000 people. Scientists say that Tuvalu could disappear within 50 years because of rising sea levels caused by warmer temperatures. Overall, the U.N. estimates the cost of global warming at more than $300 billion a year.