Is global warming real?

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Is global warming real?

Image: NASA

Over the past two decades, the global average surface temperature has increased noticeably. This observed warming trend indicates a significant global change and is consistent with other observed changes on our planet:

  • There is a widespread retreat of non-polar glaciers.
  • Arctic sea-ice has thinned by 40 percent in recent decades in late summer to early autumn, and decreased in extent by about 15 percent since the 1950s in spring and summer.
  • Northern Hemisphere snow cover has decreased in area by 10 percent since the 1960s.
  • Global mean sea level has increased at an average annual rate of 1 to 2 mm during the 20th Century, due to melting ice and water expanding as it warms.
  • The growing season has lengthened by about one to four days per decade during the last 40 years in the Northern Hemisphere, especially at higher latitudes.
  • The duration of ice cover on lakes has decreased by about two weeks over the 20th century in mid- and high latitudes of the Northern Hemisphere.

Is this temperature change a natural fluctuation in our climate, or is it a result of human activities during the last 200 years or so? The vast majority of Earth scientists agree that human activity in this has made a significant contribution to the observed increase in average global temperatures.

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.