Paleoclimate Proxies A proxy is a natural data set that mimics an environmental change, e.g. increased tree ring width and increased temperature and moisture

What is Paleoclimatology? 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. Proxies help scientists to extend the climate record longer than the instrument record which is shown as temperature anomalies in the figure above. The instrument record only extends back to about 1880. After that scientists need to use proxies to determine what the climate was like during past time periods. The instrument record includes temperature and satellite data.

Why Study Past Climates? It may help us to understand natural climate changes. The study of past climates may give us information into future climate scenarios. Warm Cold

Why Study Climate? The picture in this slide represent the current climate regions on a global scale. 1. Earth’s climate is always changing. 2. Severe droughts or large storms can have a large monetary effect on a region. 3. Studying climate helps us to understand the effect that humans are having on the current scenario.

How do scientists study climate? Satellites Historical Proxy Records Ancient Proxy Records 1. measurements have been used to reconstruct global atmospheric temperatures since 1979. 2. Temperature Records have been recorded by two different groups since ~1860. This is the National Climate Data Center and the Climate Research Unit. 3. Jakobshavn Glacier Retreat 2001-2003. The advance and retreat of certain glaciers has been recorded each year for a very long time. 4. Proxies can be used to study climates older than the extent of the temperature record. Instrument Record

Climate History 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.

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

Historical Records Weather and climate observations can be found in ships logs, farmers’ diaries, newspaper accounts, and other written records. Historical documents contain information about climate change. Historical data can yield both qualitative and quantitative data about past climate. This picture is just one example…..Grape harvest dates were used to reconstruct summer temperatures.

Sediment Cores 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. Annual sediment layers can be dated and analyzed for other climate proxies like calcite containing material and pollen These cores can be dated based on the theory of superposition. Sediment cores are typically removed by drilling and contain layers like the picture shown to the right.

Pollen 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. All flowering plants produce pollen. Pollen grains have distinct shapes that can be used to identify which plant they came from. Changes in the type of vegetation over a long time period can help scientists to determine whether a certain time period was warm or cold. Pollen analysis is often performed with radio carbon dating so that years can be assigned to the data set. Plants have adapted to live in various conditions throughout evolutionary history. Some plants prefer to grow in colder regions, while others have adapted to survive in warmer regions. Changes in the type of vegetation (pollen) can help us to understand how climate has changed in the past.

Stable Isotopes The most common element used in climate studies is oxygen. The isotopes of oxygen are: O18 (rare) O17 O16 (common) The ratio of O18 to O16 is affected by temperature and can be used as a climate proxy. An isotope is a natural occurring variation in an element (same atomic number, number of protons) but with a different atomic mass (protons plus neutrons). Some isotopes are stable (e.g. Oxygen) some are radiogenic (e.g. Uranium) and some have both stable and radiogenic isotopes (e.g. carbon 12 and carbon 14 respectively). The ratios of isotopic oxygen are also differentially affected by global patterns and regional topography as moisture is transported. Areas of lower humidity cause the preferential loss of 18O water in the form of vapor and precipitation. Furthermore, evaporated 16O water returns preferentially to the atmospheric system as it evaporates and 18O remains in liquid form or is incorporated into the body water of plants and animals.

Coral Reefs 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. The picture on the left shows two scuba divers taking a core from a coral reef. The picture on the right shows pieces of coral. Like trees, corals have annual layers. These layers contain oxygen from the water during the time when that coral was growing.

Ice Cores 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 Rings 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. In most cases a good year (warm and wet) is indicated by a thicker tree ring. A stressful growing season is indicated by a thinner tree ring.

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