Can Global Climate Change Abruptly?

How fast will climate change in the future? How fast has climate changed in the past? Did climate change happen simultaneously around the world? Scientists from many countries are investigating such questions by studying the remains of plants in lakes and bogs. Seeds, needles, pollen and other plant parts are very well-preserved in lake muds because of the lack of oxygen in these sediments. By analyzing this detritus, layer by layer from bottom to top, the history of vegetation and climate can be extracted.

From analysis of these sediments, we now know that since the last ice age (21000 years ago), the climate has experienced at least one major climatic reversal to cold conditions, called the "Younger Dryas" for an arctic-alpine plant "Dryas" which populated Europe during the cold conditions. The flip to cold conditions is clearly seen in records throughout Greenlands and in Europe, and it occurred suddenly, within a decade.

Dorothy Peteet (NASA/GISS) has shown through field and laboratory work in New Jersey and Connecticut that the climate also flipped rapidly in southern New England, where a warm mixed boreal-hardwood forest was replaced suddenly by a cold boreal forest. Furthermore, her work on Kodiak Island, Aslaska, reveals that the climate there also reversed rapidly, and a lush coastal environment changed to a cold, dry tundra for almost a thousand years. Do other continents reveal this change? According to Peteet, the localities marked in the accompanying world map show evidence of this change. Future work will continue to pinpoint the geographic distribution, precise timing, and magnitude of the Younger Dryas. The final goal is to understand why this dramatic change happened in order to better understand our climate system.

References:

• Peteet, D. 1995. Global Younger Dryas? Quaternary Intl. 28, 93-104.