Past History

Indirect methods (proxy measures) indicate that Earth's average temperature has varied many times as much as 10°C in concert with changes in atmospheric concentrations of greenhouse gases.

A drill that extracts cores from trees to study tree rings.

Hannes Globe

Proxy Measures

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  • The Past Million Years Featured Article The Past Million Years The Past Million Years

    Climate researchers have reliable temperature records from weather stations dating back to about 1850. To study variations in climate that pre-date the advent of weather... More »

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Climate Last Updated on 2014-10-01 10:48:54 Climate is the typical pattern of conditions of the earth’s atmosphere over a given region, as defined by factors such as temperature, air pressure. humidity, precipitation, sunlight, cloudiness, and winds. The World Meteorological Organization defines climate as "the statistical description in terms of the mean and variability of relevant quantities over a period of time," where an appropriate period is typically at least thirty years. Climate can be assessed at different, overlapping geographic regions. For example, Earth is thought to have a climate that is distinct from that of other planets, while different regions of Earth are also thought to have distinct climate types. Climate is often described as the "average" conditions; however, since daily and seasonal variability (including extremes) are critical determinants, using the term... More »
Coral bleaching Last Updated on 2014-05-12 12:51:51 Coral bleaching is the reduction of intracellular endosymbionts in living coral reefs either via loss or expulsion of algal pigmentation. The symbiotic relationship between coral and zooxanthellae is directly related to coral bleaching. When this relationship fails, and the zooxanthellae do not receive required inputs from the coral or vice-versa, the zooxanthellae will pale and turn white or be expelled into the water. The resultant decline in coral health from bleaching is deleterious to the coral ecosystem. Chief drivers for coral bleaching are freshwater dilution, change in pH, marine water pollution, increase in sunlight or alteration of seawater temperature. Particularly widespread water pollution is in the form of marine sedimentation from excessive runoff and discharge of untreated sewage. In addition to these abiotic causes of coral bleaching, the phenomenon of overfishing... More »
Ice Cores and History of Climate Change Last Updated on 2011-02-02 00:00:00 Ice Cores Yield Rich History of Climate Change Research project completes drilling for the year, reaching two miles below West Antarctic Ice Sheet In late January 2011, in Antarctica, a research team investigating the last 100,000 years of Earth's climate history reached an important milestone completing the main ice core to a depth of 3,331 meters (10,928 feet) at West Antarctic Ice Sheet Divide (WAIS). The project will be completed over the next two years with some additional coring and borehole logging to obtain additional information and samples of the ice for the study of the climate record contained in the core. As part of the project, begun six years ago, the team, has been drilling deep into the ice at the WAIS Divide site and recovering and analyzing ice cores for clues about how changes in the concentration of greenhouse gases in the atmosphere have... More »
Earth's Hot Past: Prologue to Future Climate? Last Updated on 2011-01-14 00:00:00 Earth's Hot Past: Prologue to Future Climate? Study of Earth's deep past leads to look into the future The magnitude of climate change during Earth's deep past suggests that future temperatures may eventually rise far more than projected if society continues its pace of emitting greenhouse gases, a new analysis concludes. The study, by National Center for Atmospheric Research (NCAR) scientist Jeffrey Kiehl, will appear as a "Perspectives" article in this week's issue of the journal Science. View a video interview with Jeff Kiehl of UCAR. The work was funded by the National Science Foundation (NSF), NCAR's sponsor. Building on recent research, the study examines the relationship between global temperatures and high levels of carbon dioxide in the atmosphere tens of millions of years ago. It warns that, if carbon dioxide... More »
The Past Million Years Last Updated on 2010-12-19 00:00:00 Climate researchers have reliable temperature records from weather stations dating back to about 1850. To study variations in climate that pre-date the advent of weather stations, climatologists rely on reconstructions based on a variety of proxy and direct measurements.   Reconstruction of global temperature changes based on 695 boreholes in the Northern Hemisphere. Blue-shaded area indicates the range of values for various reconstructions. After Pollack and Smerdon 2004.   The historical temperature record based on ice core proxy measures indicates that Earth’s climate during the past million years has been punctuated with about 8 cycles of relatively long, colder periods (glacials) interrupted by relatively short, warmer periods (interglacials). Each of nine interglacial periods correlates with higher concentrations of the greenhouse gases CH4,... More »