The levels of carbon dioxide and methane in the atmosphere are increasing, and they contribute to global warming, a rise in the average temperature of the Earth. Scientists agree that this is happening because systematic reviews of thousands of peer-reviewed studies support it, although in such a complex situation some evidence is still uncertain or incomplete.
Global warming has several biological consequences. Ice melts and sea levels rise, so low-lying areas are flooded and organisms lose their habitats.
Higher temperatures also cause changes in the distribution of species, because some organisms move to cooler places where they can survive. Animals that travel long distances each year may change their migration patterns.