Paleoclimatology

"The farther backward you can look, the farther forward you are likely to see."

 -Winston Churchill

In order to understand and predict climate change in the future we must determine the natural variability of Earth's climate system.  This is accomplished by studying the historical, or paleo-, climate record.  Paleoclimate data is also necessary for validating numerical models used to elucidate important climate processes and feedbacks and to predict future climate change.  MIT is at the forefront of climate change studies, both experimental and theoretical.  

Earth's climate changes on inter-annual to billion-year timescales.  Solar radiation receipts at the Earth's surface are modulated by volcanic eruptions and natural solar variability on inter-annual to decadal timescales.  Climate change occurs in response to changing ocean circulation patterns  (Fig. Conveyor) on decadal-to-century timescales.  Periodic changes in Earth's tilt and its orbit around the sun modulate incoming solar radiation on 10⁴-10⁵-yr timescales.  Such changes in radiation receipts can cause the buildup and decay of ice sheets whose reflectivity acts as a positive feedback on climate--more ice reflects more sunlight back to space, which leads to more cooling and more ice.  Fluctuations in greenhouse gas concentrations, such as those observed in the Vostok, Antarctica CO2 record, also change on 10²-10⁴-yr timescales, modulating the amount of outgoing reflected radiation that is trapped and retained to heat the Earth's surface.  On 10⁷-10⁸-yr timescales plate tectonics cause mountains to be built (orogeny) and continents to be placed at polar latitudes, where ice can build up; or at equatorial latitudes where the rate of weathering reactions that consume carbon dioxide, may be greater.  On the longest timescales (10⁹ yr) substantial changes in solar luminosity occur, with an increase of ~30% occurring over the last ~4 byr.

Fig. Conveyor:  The large-scale thermohaline circulation of the ocean is driven by the sinking of cold, salty water in the far North Atlantic and around Antarctica.  The return flow of warm surface water to the North Atlantic transports heat to the region, resulting in a substantially warmer climate on the eastern, relative to the western side of the basin.  (Just compare the climate of London, England to St. John's, Newfoundland which are at comparable latitudes.)