Climate Change Over the last four million years there have been at least 30 “Ice Ages” - glacial periods lasting 90,000 years or more. They were separated by relatively short interglacial period, each about 10,000 to 15,000 years long.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Temperature/900,000 yrs ago Figure 9.11a 9-11 Source: Data from National Climate Data Center/NESDIS/NOAA, 1998.

About 110,000 years ago, an interglacial period ended and a new ice age began. Planetary ice caps expanded, oceans fell, and ice sheets advanced. In North America this was known as the Laurentide glaciation, which reached its maximum extension approximately 18,000 years ago.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Temperature/10,000 yrs ago Figure 9.11b 9-12

Ice sheets reached as far south as London, England and St. Louis, Missouri. Some continental ice sheets became as thick as 3km (~1.9 miles)

Then about 15,000 years ago a warming period began marking the end of the ice age and the beginning of the current interglacial period.

In the last thousand years, there was a Medieval Warm period between about 1000CE and 1450CE. Following this was a “Little Ice Age” when temperatures fell, glaciers advanced once again, and winters were severe. The Little Ice Age ended about 1900 and a new warming trend began.

Settlement of North America - 18,000 years ago

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Temperature/1,000 yrs ago Figure 9.11c 9-13 Start of Industrial Revolution

Ice Cores At the Vostok station in Antarctica, scientists are obtaining ice core samples down to ice depths exceeding 3600 m. (Courtesy Claude Lorius, LLGE)

For the past 100 years temperatures have been directly measured at over 2,000 meteorological stations around the world

IPCC In 1988 the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP) formed an Intergovernmental Panel on Climate Change (IPCC). The panel analyzed the available data and came to the consensus that worldwide average temperatures have significantly increased over the past century.

Three conclusions 1.Over very long periods of time, global temperatures have varied greatly, rising as much as 8°C between glacial and interglacial periods

Three conclusions 2.During the past 118 years, average global temperatures have tended to increase and are continuing to increase.

Three conclusions 3.On average, the earth’s atmosphere is warmer now than at any other time in the last 1,000 years. Furthermore, the rate of atmospheric warming is greater now than at any earlier time during the past 1,000 years.

Why ? Some people argue that because the average global temperature during the Medieval Warm period was approximately 1°C (~1.8°F) than those recorded during , the current temperature increase of 0.8°C (~1.4°F) is “natural” and not due to human influence at all.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Climate change (earth's orbit) Figure 9.12a 9-15

However 1.The current global warming trend appears to have started at the time of the Industrial Revolution 2.Analyses show that pre-industrial CO2 levels were about 280ppmv and that they have risen by 1998 to 365 ppmv, an increase of ~30% 3.Carbon dioxide levels are at their highest level in 160,000 years

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Global warming and CO 2 Figure Source: Data from Dave Keeling and Tim Whorf, Scripps Institute of Oceanography.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Greenhouse diagram Figure

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Carbon dioxide emissions Figure Source: Data from World Resources , World Resources Institute.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Greenhouse gases 9-20

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Climate changes and species Figure Source: Data from Margaret Davis and Catherine Zabriskie in Global Warming and Biological Diversity, ed. by Peters and Lovejoy, 1991, Yale University Press.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Greenhouse precipitation Figure

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Temperature/120 yrs ago Figure 9.11d 9-14