How ice records climate change over millions of years - The Climate Question, BBC World Service

Key Concepts

• Ice Cores: Cylindrical ice samples drilled from ice sheets and glaciers, containing trapped air bubbles and other materials that provide a historical record of Earth’s climate and atmospheric composition.
• Paleoclimatology: The study of past climates.
• Glacial Cycles: Recurring periods of glacial advance and retreat over geological timescales.
• Greenhouse Gases: Gases in the atmosphere (e.g., carbon dioxide, methane) that trap heat and contribute to the greenhouse effect.
• Isotopes: Variants of chemical elements with different numbers of neutrons, used to trace climate changes.
• Tephra: Volcanic ash deposited in ice cores, providing a dating marker.
• Cosmogenic Nuclides: Rare isotopes produced by cosmic ray interactions, used to reconstruct past solar activity.
• Firn: Partially compacted snow that is transitioning into glacial ice.
• Beyond EPICA – Oldest Ice project: An international research project aiming to retrieve and analyze the oldest continuous ice core record.

The Science of Ice Cores: Unlocking Earth’s Climate History

Introduction & Initial Observations

The discussion begins with a lighthearted anecdote about the “scientific salt test” – researchers tasting ice core offcuts to gauge proximity to the bottom of an ice shelf. This illustrates the practical, sometimes unconventional, methods employed in ice core research. The core focus of the program is understanding how ice cores provide evidence of climate change, going beyond recent observational data (air temperatures, sea levels) to reconstruct past climates. The program features Dr. Liz Thomas (British Antarctic Survey) and Lonnie Thompson (Ohio State University), both leading experts in the field.

Logistical Challenges of Ice Core Retrieval

Retrieving ice cores is a complex logistical undertaking. Both Dr. Thomas and Professor Thompson detail the challenges of working in remote, extreme environments.

• Antarctica (Dr. Thomas): Cores are flown from drilling sites to a station, then shipped to the UK, a process taking up to six months. The primary challenge is the extreme cold and wind. The British Antarctic Survey benefits from a dedicated logistics team.
• High Altitudes (Professor Thompson): Work in the Himalayas involves using yaks to transport ice cores down from high altitudes (above 23,000 feet) to freezer trucks. This requires collaboration with local Tibetan communities and skilled whistlers to manage the yaks, which behave much like cats – independent and requiring persuasion. Professor Thompson recounts a story of using an ice cream shop to temporarily store cores while a truck was repaired in the Gobi Desert.
• Lower Latitudes (Professor Thompson): Expeditions to locations like Guliya involve navigating challenging terrain and ensuring the ice remains frozen during transport.

These anecdotes highlight the dedication and resourcefulness required to obtain these valuable climate records.

What Ice Cores Reveal: A Multi-Proxy Record

Ice cores are described as “the best recorder of the past on this planet” due to their ability to capture a wide range of climate-related information.

• Air Bubbles: Trapped air bubbles provide a direct sample of the atmosphere at the time the snow fell, allowing scientists to measure past concentrations of greenhouse gases like carbon dioxide and methane. The bubbles “fizz and pop” when the ice melts due to pressure.
• Isotopes: Variations in the ratios of isotopes (e.g., oxygen and hydrogen) within the ice reveal past temperatures.
• Volcanic Ash (Tephra): Layers of volcanic ash act as time markers, helping to date the ice core.
• Cosmogenic Nuclides: These isotopes, produced by cosmic ray interactions, provide a record of past solar activity.
• Black Carbon: Soot deposited in the ice indicates past fire activity.
• Microbes (Bacteria & Viruses): Ice cores can also preserve ancient microbes, offering insights into their response to past climate changes.

Professor Thompson emphasizes that ice cores record not only climate itself but also the forcings of climate – the factors that cause it to change.

Ice Cores vs. Other Paleoclimate Proxies

Professor Thompson argues that ice cores are superior to other paleoclimate proxies (fossilized pollen, tree rings, seashells) because they are a physical record, not a biological one. Living organisms can adapt to changing conditions, potentially altering the signal. Ice, however, is a direct, unaltered snapshot of the past atmosphere and climate. However, he acknowledges the importance of integrating data from all available proxies to create a comprehensive picture.

The Importance of Preserving Ice Cores

A critical concern raised is the preservation of existing ice cores. Professor Thompson notes that four cores in their archive come from glaciers that no longer exist. Increasing temperatures are causing glaciers to melt, potentially compromising the integrity of the climate record. He stresses the need to preserve existing cores for future analysis with more advanced technologies. Dr. Thomas also notes melt layers are appearing even in Antarctic ice cores.

The Beyond EPICA Project & Extending the Climate Record

Dr. Thomas discusses the ongoing Beyond EPICA – Oldest Ice project, which aims to retrieve and analyze the oldest continuous ice core record. The project has already extended the record back to approximately 1.5 million years, nearly doubling the previous record of 800,000 years.

• Shifting Glacial Cycles: Analysis of the older ice suggests that glacial cycles may have been different before 1 million years ago – shorter and less extreme. This could have implications for understanding future sea level rise and climate stability.
• Potential Analog for the Future: The conditions prior to 1 million years ago, with smaller ice sheets and potentially higher greenhouse gas concentrations, may offer an analogue for the future climate.

Data Integration & Climate Modeling

The data obtained from ice cores is crucial for refining climate models. Professor Thompson explains that understanding both natural climate forcings and anthropogenic impacts is essential for accurate predictions. The more data available from the past, the more refined and reliable climate models become, narrowing the range of uncertainty in future projections.

Conclusion

The program concludes by emphasizing the importance of ice core research for understanding Earth’s climate history and predicting future climate change. The challenges of obtaining and preserving these records are significant, but the insights they provide are invaluable. The ongoing Beyond EPICA project promises to further extend our understanding of past climate variability and inform our response to the current climate crisis. The final message is a call to action – to preserve these vital archives of the past for future generations.