Reconstructing Climate History through Ice Core Proxies Natasha Paterson Econ 331 April 7 th, 2010

Introduction Plan for the presentation: Proxies Ice Cores: What They Are Ice Cores: What They Tell Us Calibrating the δ 18 O Record with Temperature Leads and Lags in the System Does CO 2 Cause Temperature Change

Proxies What is a climate proxy? Why use proxies? Measuring interaction between climate variables Examples of proxies include: -Deap sea and continental sediments -Tree rings -Ice cores

Ice Cores – What Are They? The proxy that provides the most direct, detailed and complete measure of past climate change

Ice Cores – What Can They Tell Us? What can they tell us about past climate conditions? Atmospheric chemistry and circulation Temperature Precipitation Solar variability Volcanic activity Greenhouse gases

Ice Cores – Advantages –What are their advantages over other proxies? High resolution Long time span (several glacial cycles) Precise dating

Ice Cores – Key Findings Last interglacial period centered around 130,000 years ago with temperatures slightly higher than today. The last glacial-interglacial transition began 18,000 years ago and ended 10,000 years ago. Strong correlation between CO 2, CH 4 and temperature. Greenland (GISP2) and Antarctic (Vostok) climate records covering the last glacial-interglacial cycle. Upper part shows close correlation between GISP2 and Vostok d18O of O 2 in air in these ice cores. Lower part shows close correlation between dD and d 18 O (proxies for temperature) of the ice. Modified from Bender et al. (1994).

The central Greenland d 18 O history for the most recent 40,000 years. The smooth curve results when this history is filtered to mimic the thermal averaging in the ice sheet. All temperature histories that give this same curve when filtered are indistinguishable to borehole thermometry. The right axis shows the calibrated temperature scale. Reprinted figure with permission from Cuffey et al., Science, 270, ©1995, American Association for the Advancement of Science. Calibrating the δ 18 O Record with Temperature

What is isotopic fractionation? Isotopic fractionation occurs : - when sea water evaporates into clouds - in the clouds as the water vapor precipitates Fractionation is a temperature dependant relationship If we attribute the signal solely to temperature change, ignoring salinity and ice volume change, a δ 18 O change of 0.22% = 1 o Celsius of cooling.

Calibrating the δ 18 O Record with Temperature Comparison of stable isotope (d 18 O) ratios in the GISP2 core, 10 Be in the Dye 3 core, and 14 C residual in tree rings with sunspot number (bold lines). All time-series were filtered using an identical year bandpass filter. Taken from Stuiver et al. (1995).

Leads and Lags in the System

CO 2 and CH 4 either amplify or de-amplify the system. CO 2 and CH 4 lag the processional and obliquity cycles, but tend to lead the 100,000 year eccentricity cycle.

Does CO2 Cause Temperature Change? The data supports a strong correlation between changes in atmospheric CO 2 and temperature. Changes in the Milankovitch cycle cause changes in temperature: - Solubility of CO 2 in water falls as the southern ocean warms. - CO 2 released from the ocean spreads throughout the atmosphere, causing additional warming. CO 2 both causes and is caused by increases in temperature.