A global economic slump may hurt efforts to fight global warming.

This week, representatives from 190 countries are meeting in Poland to talk about the problem of global climate change. Scientists say that human-caused pollution is affecting Earth's climate, and one result is global warming -- the slow rise in Earth's average temperatures. Experts say global warming is causing damage around the world, and we'll learn more about this in a moment.

For several years, the United Nations, or U.N., has been working to get all the world's nations to sign an agreement to lower their emissions of the pollution that causes global warming. This involves using less energy, and investing in cleaner forms of energy, such as the wind farm shown here. Ten years ago, most advanced countries in the world except the United States signed an agreement to reduce the pollution that causes global warming. The United States didn't participate because the agreement didn't require developing countries like China and India to cut their pollution. China, India, and the United States are among the leading polluters in the world. Do you think the United States should have signed the treaty?

Now the U.N. is trying to create a new treaty to limit the pollution of all countries. But they have a new problem to deal with now -- the global economic slump. Countries have less money to invest in clean energy programs. How else might the economic crisis affect efforts to cut down on pollution and energy use?