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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



  • 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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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 »
Lecture: Stephen Schneider Climate Change Mitigation and Adaptation Video Last Updated on 2010-10-07 00:00:00 This video is of a lecture that Stephen Schneider presented a number of times. It covers climate change from a risk perspective, discussing the underlying science, uncertainties, and implications of different possible decisions. Here is it captured with many (although not all) of his graphics. It is a well organized, evenly presented lecture that carefully differentiates questions of "what we know" from "what we should do." It presents data and modelling at a level appropriate for undergraduates. More »
Fossil Last Updated on 2010-09-27 00:00:00   A fossil is the preserved remain of a lifeform that lived in prehistoric times. Most commonly fossils are mineralized parts or a whole organism which is no longer alive. In other cases the fossil may contain actual remains of the dead organism; in particular, DNA may be preserved over long periods of time under the right conditions, since DNA is fundamentally an inanimate molecule. While the most familiar fossils are those derived from animals and plants including such exotic species as dinosaurs and woolly mammoths, there are also fossils from ancient bacteria. There are several methods of fossil formation including re-crystallization, permineralization, compression, molding and entombment. Examination of fossils was the earliest technique of palaeoentology, the study of ancient lifeforms, and it continues as the companion of molecular biology, to be key in the... More »