 The study of past climates prior to the instrument record.

 Scientists use indirect evidence (data) during past time periods to determine the climate at that time period.

 These climate imprints are referred to as

proxies

.

 It may help us to understand natural climate changes.

 The study of past climates may give us information into future climate scenarios.

Warm Cold Warm

Satellites Ancient Proxy Records Historical Proxy Records Instrument Record

 The instrument record extends back about 150 years (~1860).

 Since that time Earth’s temperature has increased 0.7 ° C (1.3 ° F).

 In the past, climates were sometimes much colder than today.  At other times they were much warmer than today.

Pollen Stable Isotopes Tree Rings Examples of Climate Proxies Sediment Cores Ice Cores Coral Reefs

 Weather and climate observations can be found in ships logs, farmers’ diaries, newspaper accounts, and other written records.

 Sediment cores can be taken from lakes, the shallow ocean, or the deep ocean.

 In some cases the thickness of these layers can be used to infer past climate.

 In other cases, these layers are composed of organic material that can be analyzed for other climate proxies.

 Pollen grains are well preserved in lake and ocean sediment.

 The analysis of each of these sediment layers provides information on the vegetation present at that time.

 Scientists can infer past climates (warm or cold) based on the distribution and changes in plant species.

 The most common element used in climate studies is oxygen.

 ◦ ◦ ◦ The isotopes of oxygen are: O 18 (rare) O 17 O 16 (common)  The ratio of O 18 to O 16 is affected by temperature and can be used as a climate proxy.

 Corals are composed of calcium carbonate.

 This carbonate contains isotopes of oxygen that can be used to determine the water temperature when and where the corals grew.

   As snow and ice accumulate in polar glaciers a paleoclimate record accumulates of the environmental conditions of the time of formation.

Ice cores can analyzed using stable isotope approaches for water or air bubbles within the ice as a record of past atmospheric gas concentrations.

 Tree growth is influenced by climate. These patterns can be seen in tree ring width and isotopic composition.

 Trees generally produce one ring each year.

 Trees ring records can extend back to the last 1000 years.

All of these examples used individually or together can help piece together the past climate of a particular time period or region.