On February 16, the Kyoto Protocol to the United Nations Framework Convention on Climate Change will take effect. Negotiated in 1997 and ratified by more than 100 nations (although not the United States), the agreement is a coordinated effort to limit emissions of carbon dioxide and other greenhouse gases blamed for climate change. Nations that ratified the protocol commit to reducing emissions below 1990 levels by the period of 2008–2012, with higher-polluting nations facing more ambitious targets. The protocol also sets up a system of emissions trading to help nations meet their targets. The protocol raises a number of important science and policy issues. These include the potential impacts of our changing climate, the extent to which the protocol will minimize climate change, and how emissions of greenhouse gases can be tracked. NCAR researchers are on the forefront of climate change research. By using some of the world’s most powerful supercomputers and analyzing worldwide data, they estimate how natural factors and human-induced changes to the atmosphere are affecting our climate, as well as how agreements such as Kyoto may affect global warming. They also are important contributors to the Intergovernmental Panel on Climate Change (IPCC), which provides assessments of climate science for policy makers worldwide.