Climate Number: 120 Meters (394 feet)
For about the past two million years, Earth’s climate system has been characterized by glacial cycles that last between 80,000 to 120,000 years. These cycles have long periods when the Earth cools and ice sheets build up to their maximums, followed by relatively short warming periods when the ice retreats and then “interglacial periods” like the climate we inhabit today. Glacial maximums are characterized by Northern Hemisphere ice sheets extending from the Arctic all the way down to the Ohio River and central Europe, low carbon dioxide (CO2) concentrations (about 180 parts per million) and sea levels about 120 meters lower than today. Sea levels were lower because the water that is in the oceans today was in ice back then. From 20,000 to 7,000 years ago, Earth “deglaciated” and by about 5,000 BCE all that was left of the Northern Hemisphere ice sheet was a small remnant on Canada’s Baffin Island. Carbon dioxide levels by that point had risen to about 280 parts per million, where they remained until the early 19th century, and sea-levels and coastlines were about where they are today.
For Comparison: Twenty-thousand (20,000) years ago, when sea levels were 120 meters lower than today, the Bering Strait was dry land that served as a bridge for the ancestors of today’s Native Americans, who crossed the strait on foot around 15,000 years ago and settled North America. Indochina (Vietnam, Thailand, Cambodia, Laos) was connected by land to the Indonesian Islands of Sumatra, Java and Borneo. Much of the Florida coastline today was hundreds of miles inland back then. The black line in the image below (Image Courtesy of Exploring the Submerged New World 2009 Expedition NOAA-OER) marks the location of the Florida coastline 20,000 years ago.
Seasons: Winter, Spring, Summer, Fall
Source: Denton, GH et al. “The Last Glacial Termination.” Science 328 (2010): 1652-1655.
