Paleoclimates

Paleoclimate - a climate that existed sometime in the past, as recently as a few centuries or as long as billions of years ago. For example, the world was warmer in the Mesozoic Era.

Continental Ice Sheets Presently, Earth is in an interglacial interval: a period of warmer climate following a colder, glacial period. Earth today has two continental ice sheets, one covering most of Greenland and one covering most of Antarctica.

Continental Glaciers The last retreat of continental glaciers occurred between about 20,000 and 8000 years ago. Without written records, Paleoclimatologists must use a variety of methods to infer past climate.

Glacial Retreat

Inter-Glacial Recession

Inferring Paleoclimate Many kinds of evidence give us an indirect record of past temperature. These are called climate proxies. Something that represents something indirectly is called a proxy (none are perfect).

Proxy - Fossil Pollen Pollen - tiny particles produced in flowers to make seeds. Blown into lakes or bogs and preserved in sediments. Pollen from spruce trees infers cold climates.

Ah-chooo! Pollen

Proxy - Ice Cores Scientists study ice cores drilled deep into glaciers for inferring paleoclimates.

Glaciers and Ice Core Dust Glaciers consist of snow that accumulates and is gradually compressed into ice. The annual layers can be detected and studied through the slight changes in dust content. Dust

Proxy - Air bubbles Bubbles of air trapped in ice contain samples of the atmosphere from the time when the snow fell. Oxygen in the atmosphere is in two forms of isotopes. They are 18O (heavier and in higher proportion from warmer climate), and 16O. Paleoclimatologists can also measure 1H and 2H.

Air Bubbles in Ice CO2 in the glacier depends on the amount in the air at that time, which can be correlated to global temperature. Warmer times show higher levels of CO2 than in colder times. This can give a more accurate proxy because CO2 is uniformly distributed in the global atmosphere.

Methane, Deuterium, Carbon Dioxide Cyclic or not?

Proxy - Dust In colder climates the wind is stronger, eroding more dust, and deposits it in small quantities over larger areas of the Earth.

Proxy - Deep Sea Sediments Sand sized shells of a kind of single celled animal called Foraminifera accumulate in layers of ocean bottom sediment. During warm climates, the shells spiral in one direction, and in cold climates, the opposite direction. Also, the shells contain calcium carbonate, which contains oxygen that can be studied. foraminifera

Proxy - Glacial Land Forms and Sediments Glaciers leave recognizable evidence in the geological record. Glacial land forms are common in North America. Glaciers erode the rock beneath and carry the sediment and deposit it to form distinctive landforms. (Here in Colorado) Glacial till

Glacial Sediment Fine glacial sediment is picked up by the wind and deposited over large areas as a sediment called loess. These layers reveal several intervals of glaciation during the Pleistocene Epoch. Glaciers also leave evidence in the ocean. When they break off into ice bergs which melt, the glacial sediment rains down to the ocean bottom, where it is easily recognized. Glacial sediment from ocean floor Loess blowing off

Proxy - Tree Rings Paleoclimate is also recorded in the annual growth rings in trees. Trees grow more in warm years than in cold years. A drawback is that few tree species live long enough to provide a very far look. Bristlecone pines and Sequoias which are both long lived, are most often used.

Ranger Rick Dating Sequoia Tree Rings for two fashionable attractive young ladies from the past