Global warming, the gradual heating of Earth’s surface,oceans and atmosphere, is caused by human activity, primarily the burning offossil fuels. Certain gases in the atmosphere trap heat act just like the glassin a greenhouse. As the greenhouse gases build up in the atmosphere the Earthgets hotter. This process is leading to a rapid climate change. Already, globalwarming is having a measurable effect on the planet. Ice is melting in bothpolar ice caps and mountain glaciers. Lakes around the world, including LakeSuperior, are warming rapidly. Animals are changing migration patterns. One ofthe most immediate and obvious effects of global warming is the increase intemperatures around the world. Extreme weather is another effect of globalwarming. While experiencing some of the hottest summers on record, much of theUnited States has also been experiencing colder-than-normal winters. Over thepast 50 years, the average global temperature has increased at the fastest ratein recorded history.
