. Extreme Climates

Irish Geoscience Research Meeting (Fri 27th Feb – Sun 1st March)

• Volunteers needed for:
    - Evening Reception
    - Registration desk
    - Roving microphones

• Benefits for volunteers:
    - Free lunch & refreshments
    - Attendance to keynote lectures:
      - "Correlates of extinction"
      - "Geology of Mars"

BL1009 Lecture 10: Extreme Climates

Key Quote from Mayhew (2011)

• “The Earth system is expected to enter a state which has not been seen for millions of years.”

Introduction to Palaeoclimate

• Topics Covered:
    - Long-term trends in climate
    - Carbon sinks in geological history
    - Case Studies:
      - Case Study 1: Snowball Earth
      - Case Study 2: Carboniferous Ice Age
      - Case Study 3: End-Permian Hyperthermal
    - Lecture Summary

Definition of Climate

• Climate is defined as weather over a long-term period, which encompasses more than just temperature.

Components of Climate

• Atmospheric Contents Influencing Climate:
    - Greenhouse gases
    - Aerosols (e.g., SO2)
    - Water vapour

• Influencing Factors:
    - Precipitation rates
    - Circulation patterns leading to heat transfer

Deep-Time Climate Forcing Agents

• Milankovitch Cycles: Cycles relating to Earth's orbital changes which affect climate over long timescales.

Climate Variability Through Geological Time

• Sea Surface Temperatures Over Time: Reflects a global climate that is in constant flux.

• Classification of Earth's Climate History:
    - Icehouse Climate (25% of Earth history)
    - Greenhouse Climate (75% of Earth history)
    - Examples:
      - Greenhouse Antarctica (90 Ma)
      - Icehouse Antarctica (present day)

Phanerozoic Average Global Temperature Trends

• Key Data:
    - CO₂ (ppm) vs Antarctic Temperature change (°C)

• Historical CO₂ Levels Comparison:
    - 50 Ma: 1600 ppm, temperature 24°C
    - 34 Ma: 900 ppm, formation of Antarctic ice sheet
    - 16 Ma: 480 ppm (higher than today)

The Hockey Stick Model of Climate Change

• Graphical Representation of Temperature Change:
    - Shows change in global surface temperature, with both reconstructed and observed data from year 1 to 2020.
    - Notable periods include Medieval Warm Period and the Little Ice Age.

• Key Realization:
    - Current warming is unprecedented in over 2000 years and represents the warmest period in more than 100,000 years.

Palaeoclimatology Overview

• Key Focus Areas:
    - Are we living in unusual climatic times?
    - Providing environmental context for evolution.
    - Documenting extreme global conditions that lack modern analogues.
    - The only empirical source of data for global climate change includes various methods documenting CO₂ levels highest in 2 million years.

Data Sources for Atmospheric CO₂ and Climate

• Analyzed Data Sources:
    - Ice core bubbles
    - Soil and sediment chemistry
    - Anatomy of fossil plant leaves

• Historical CO₂ Levels Compared:
    - 50 Ma: 1600 ppm, temperature 24°C
    - 34 Ma: 900 ppm, formation of Antarctic ice sheet
    - 16 Ma: 480 ppm (much higher than current levels)

Case Study 1: Snowball Earth

• Conditions:
    - Global temperatures ranging from -25°C to -12°C.
    - CO₂ concentrations approximately 200 ppm.
    - High rates of weathering and low rates of volcanism.
    - Ice formation occurred within tens of years, ice at sea level at 0° latitude.
    - Ice caps forming at 33° latitude, leading to a runaway ice albedo cooling effect.

Evidence for Snowball Earth

• Three Major Late Pre-Cambrian Glaciations:
    - Sturtian (720 Ma): 39 localities
    - Marinoan (645 Ma): 48 localities
    - Gaskiers (580 Ma): Evidence of glacial dropstones

Palaeomagnetic Data Supporting Snowball Earth Hypothesis

• Angle of inclination of magnetic mineral crystals informs palaeolatitude placements.

• Evidence extracted from sedimentary strata, with data showing paleolatitudes in Australian locations from the Marinoan period (~635 Ma).

Banded Iron Formations (BIFs) Evidence

• Occurred during anoxic ocean conditions—ice sealed off oceans from interacting with the atmosphere.

• Hydrothermal vents contributed to increased oceanic iron levels, which were not consumed due to absence of dissolved oxygen reactions.

Aftermath of Snowball Earth

• Cap Carbonates:
    - Deposits of carbonate rocks found immediately over glacial diamictites, indicating ocean supersaturation with carbonate ions.
    - Extremely abrupt transitions from icehouse conditions, indicating major transgressions.
    - These cap carbonates found even beneath the diamictites signify extreme climatic fluctuations.

• Characteristics:
    - Tubestone stromatolites indicating rapid precipitation of CaCO₃.
    - Crystalline arrangements showing aragonite crystal fans of 10 cm in size.

Case Study 2: Carboniferous Ice Age (340 – 255 Ma)

• Global Temperature:
    - Average temperature around 12°C with CO₂ levels below 100 ppm.
    - Repeated short-lived severe glacial events were common due to high rates of weathering and carbon burial.

• Efficient Carbon Sink:
    - Peat represented the most effective carbon sink on Earth leading to coal formation.

• Conditions for Peat Formation:
    - High productivity of plants with low biological consumption and low sedimentation rates.
    - Ideal conditions include wetlands, abundant plant life, and low elevation.

Carboniferous Ice Age: Peatlands and CO₂ Drawdown

• Tropical Peatlands:
    - Dominated the Earth's surface with high prevalence during this era.
    - Longest glacial intervals observed in the Phanerozoic.
    - Variscan orogeny event exposed ultramafic rocks leading to increased chemical weathering and CO₂ drawdown.

Sea Level Fluctuations During Carboniferous Ice Age

• Fluctuations greater than 100 m were correlated across thousands of kilometers in Pangean palaeotropics.

• Modulated by variations in Earth's axial tilt (obliquity).

End Permian Hyperthermal (252 Ma)

• Extreme Climate Conditions:
    - Global temperatures exceeding 60°C with very high CO₂ levels above 2500 ppm.
    - Events likely triggered global wildfires shifting carbon sinks to sources.

Large Igneous Provinces (LIPs)

• Formation and Effects:
    - Characterized by extensive lava flows that injected massive volumes of SO₂ and CO₂ into the stratosphere, contributing to climate changes.
    - Triggered widespread heating of the atmosphere and oceans, disrupting global circulation patterns.

Responses to the End Permian Hyperthermal

• Effects of the Siberian Traps LIP:
    - Increased atmospheric CO₂ levels by 8 times with sea surface temperatures rising to 32°C.
    - Triggered melting of methane clathrates, decreasing circulation and leading to severe environmental effects.
    - Resulted in acid rain and damage to the ozone layer, driving habitat conditions into catastrophic realms.

Redox Chemistry Changes During End Permian Hyperthermal

• Analysis of δ238U indicated a drastic increase in anoxic conditions by approximately a factor of 100 (0.2 - 20% of the seafloor).

• Significant oscillations between sulfidic and oxic states over 5 million years negatively impacted the ecosystem.

Environmental Impacts on Terrestrial Ecosystems

• Effects on Flora:
    - Death of forests leading to the loss of terrestrial carbon sinks.
    - A rise in water tables caused widespread flooding, leading to a runaway greenhouse effect.
    - Long biological recovery times estimated at 10 to 15 million years.

The Grand Challenge: Climate Response

• Human Relevance:
    - Current human conditions differ significantly from ancient crises; modern cognition allows us to predict, mitigate, and adapt.

Solutions Drawn from the Fossil Record

• Recommendations to manage present and future climate issues:
    - Preventing fires in wetlands to protect carbon sinks.
    - Keeping waterways clean to avoid toxic conditions with high nutrients and temperature.
    - Converting carbon sources back to sinks, emphasizing the role of peatlands in carbon storage.