Cores of glacial ice drilled from the Greenland glacier reveal a record of sharp worldwide environmental fluctuations going back more than 100,000 years. Greenland retains the largest remaining remnant of the Pleistocene Ice Sheet that covered two-thirds of North America (including parts of Long Island) as recently as 18,000 years ago.
Ice crystals in glacial layers formed from summer snows are different from those formed from winter snows, which enables pairs of annual layers to represent years of time. The ice core layers contain excellent evidence of dozens of former climate shifts. Oxygen isotopes in the layers indicate the air temperatures at the time the snows fall. Snowfall from 'warmer' (but still below freezing) air contains higher ratios of oxygen-18, whereas low oxygen-18 amounts signify the snow fell from colder air. While the Greenland air temperatures are quite cold today, they were almost 40 F lower during the coldest parts of the Ice Age.
Snowfall (and global precipitation in general as measured by other means) was proportional to air temperature; with higher temperatures correlated with higher precipitation amounts. Ice layer sequences formed during colder Pleistocene periods are thinner than ice layers formed in 'warm' Ice Age times. The colder layers also contain more dust with larger particle sizes. This is due to fast winds during colder periods (when vegetation and precipitation were scarce) being able to blow larger and drier dust particles around the earth.
During warmer (and correspondingly wetter) interglacial segments, less and smaller dust particles were available to fall on glaciers because they were protected from wind erosion by extensive vegetation. Larger desert areas, typical of the Pleistocene's coldest periods, provided more and larger dust grains for faster winds to carry and deposit on glaciers. The dust minerals in different ice layers can be traced to specific rock areas from which they were eroded, enabling Ice Age wind patterns to be worked out.
In addition, trapped air bubbles in the ice provide information about the changing gaseous composition of the Pleistocene atmosphere. CO2 (carbon dioxide) and methane Greenhouse gasses were respectively 50 percent and 75 percent more abundant during warmer glacial periods than during cooler ones. This implies an important role for natural Greenhouse gasses with respect to Pleistocene global warmings. The CO2 amount in the Pleistocene atmosphere was 160 ppm (parts per million). After the ice age ended, the natural amount in the 1700s before the industrial revolution was roughly 275 ppm. Scientists are concerned that doubling this amount to 550 ppm would trigger a premature and disastrous global warming that we are not prepared for. Because of human activities, CO2 is now 360 ppm and is still increasing.
Glacial ice cores show similar climate shifts as deep ocean sediment cores deposited over the last 100,000 years. But the glaciers show sharper details of the sudden, short-term, global climate swings from warm to cold or vice-versa. These lasted about 1,000 years each and shifted in as little as a few years.
Deep-sea sediment core analysis of microscopic shells of Pleistocene temperature-sensitive planktonic (floating) protozoans called forams which inhabited surface waters when they were alive, commenced 50 years ago. This provided the first substantial evidence of dozens of environmentally disruptive ice age climate changes that our human ancestors had to contend with.
Modern humans are no more able to deal with global warming's 420-foot sea-level rise, than with global cooling's return of the ice-sheet glaciers. Will leaders of the world's nations reach effective agreement on preventing global warming which is beginning to accelerate? Can we curtail the Greenhouse gasses? Is anybody ready for more efficient road vehicles, fuel conservation, and preservation of woodlands and rain forests?
(In 1956, Julian Kane published results of a seven-year study on deep-sea submarine cores containing millions of microscopic shells that revealed Pleistocene sea surface temperatures. His 42-year-old research paper was one of the first to use microfossils to analyze ice-age climate shifts. It included graphs of ice age temperature changes similar to graphs of glacial core data from Greenland and Antarctica and of ocean sediment isotope data just published in the February 1998 Scientific American) .