Human activity, such as the burning of fossil fuels to power our homes and businesses and changes to the land caused by the rise of modern cities and expanded agriculture, undoubtedly affect the global environment. It is the extent of that effect and how it relates to changes in the modern climate which is the subject of current scientific debate. […] Many of the temperature data and computer models used to predict climate change are themselves as uncertain as are our understanding of important interactions in the natural climate.