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Future Forecasts: Looking at the Past...Predicting the Future

Graph of Vostok and other measures of CO2

The Chinese philosopher Confucius some 26 centuries ago proclaimed "study the past to divine the future." From the paleo perspective that looks at climate and environmental systems over thousands and millions of years, climate change is normal and part of the Earth's natural variability related to interactions among the atmosphere, ocean, and land, as well as changes in the amount of solar radiation reaching the earth.

There is evidence to suggest the Earth's temperature has been significantly hotter than it is today. During the mid Cretaceous Period about 100 million years ago, the mean temperature may have been as high as 21 degrees Celsius as compared to about 15 C today. The planet has also experienced colder temperatures, not only during the Ice Ages of the past several million years, but also during the end of the Carboniferous and beginning of the Permian periods about 300-260 million years ago.

Photo of dinosaurs from Smithsonian InstituteThe largest
abrupt climate event of the last 100 million years ago likely occurred when a meteor hit the region of Yucatan, causing mass extinctions about 65 million years ago including the extinctions of the dinosaurs, allowing mammals to become dominant. About 55 million years ago, a warm spell led to significant global warming, with palm trees in Alaska and crocodiles in the Arctic.

Around 25 million years ago, the Antarctic ice shelf began to form, and some 20 million years back, major modern mountain ranges such as the the Cordilleras, the Andes, and the Himalayan range were formed, with mammals becoming dominant.

Massive terrestrial ice sheets throughout the Northern Hemisphere indicate cold conditions during the last glacial maximum (21,000 years ago). Warm climate, vegetation, dinosaurs, and corals living at high latitudes during the mid-Cretaceous (120-90 million years ago) indicate globally warm conditions. (See Beyond for more.)

More recently during the Little Ice Age (AD 1450 -1890) historic and instrumental record, predominately around the North Atlantic, indicate colder than modern temperatures.

Based on past climate patterns and current understanding of how orbital dynamics of the Earth such as precession, eccentricity and variations in Earth axial tilt influence glacial and interglacial cycles, it would be expected that Earth's climate would be heading back into an Ice Age within the next few thousand years. But evidence now indicates that much of the climate system is in fact heating up.

The paleoclimate record also shows that climate doesn't necessarily change slowly over hundreds or thousands of years. In some cases, major increases or decreases in precipitation and/or temperature can occur in periods less than a decade. Since the end of the last Age there have been at least four abrupt changes, including the "Younger Dryas" event dated by ice cores to between 12,800 and 11,500 years B.P., which chilled and dried out much of the northern hemisphere. The study of abrupt change in climate is currently one of the hottest areas of climate research. There are few theories and no models that address how such large changes can occur in such short periods of time.

Is it possible that such abrupt climate changes will occur in the future? The short answer is, yes... and that the change may not necessarily be warming. Some scientists warn that it is possible that global warming caused by increased greenhouse gases in the atmosphere could actually produce an abrupt cooling in some parts of the world-- such as Europe or North America-- by shutting down the Gulf Stream. As oceanographer Jochem Marotzke has stated "We are in a state now where the more we know, the more it becomes clear how little we really understand about the (climate) system." (See Marotzke, 2000)

Predicting the Future

Additional Resources and References

Graph of carbon dioxide levels from NOAA Paleoclimatology Program. Image of dinosaurs from Smithsonian online.



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