Reconstructing Climate History through Ice Core

Proxies

Natasha Paterson

Econ 331

April 7th, 2010

Introduction

Plan for the presentation:

• Proxies

• Ice Cores: What They Are

• Ice Cores: What They Tell Us

• Calibrating the δ18O Record with Temperature

• Leads and Lags in the System

• Does CO2 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

• CO2, CH4 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 O2 in air in these ice cores. Lower part shows close correlation between dD and d18O (proxies for temperature)

of the ice. Modified from Bender et al. (1994).

The central Greenland d18O 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, 455-458. ©1995, American Association for the Advancement of Science.

Calibrating the δ18O Record with Temperature

Calibrating the δ18O 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 δ18O change of

0.22% = 1o Celsius of cooling.

Calibrating the δ18O Record with Temperature

Comparison of stable isotope (d18O) ratios in the GISP2 core, 10Be in the Dye 3 core, and 14C residual in tree rings with sunspot number (bold lines). All time-series were filtered using an identical 10-12 year bandpass filter. Taken from Stuiver et al. (1995).

Leads and Lags in the System

Leads and Lags in the System

• CO2 and CH4 either amplify or de-amplify the system.

• CO2 and CH4 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 CO2 and temperature.

• Changes in the Milankovitch cycle cause changes in temperature:

- Solubility of CO2 in water falls as the southern ocean warms.

- CO2 released from the ocean spreads throughout the atmosphere, causing additional warming.

• CO2 both causes and is caused by increases in temperature.