ch 12 hazards

Env & Geol Hazards Chapter 12: Human Impact in the Holocene

Goldilocks Hypothesis

  • Definition: The hypothesis states that Earth is hospitable because it sits at the "right" distance from the sun.

    • Not too hot → Venus: 460°C

    • Not too cold → Mars: -60°C

    • Just right → Earth: 15°C

Recent Environmental Changes

  • 2016 Wildfires: Seven of the last ten years have been recorded as the hottest.

Modern Climate Trends

Hurricanes 2017

  • Notable Event: First time three category 4 storms (Harvey, Irma, Maria) make landfall in the United States.

Global Temperature Records

  • 2024: Warmest year in NOAA’s 140-year series.

  • 2023: Second warmest year.

  • 2000-2024: Out of 20 hottest years on record, 19 have occurred.

  • Recent Warm Years: The seven warmest years have all occurred since 2010.

  • Data Source: Can download data from NOAA: NOAA Global Time Series

Instrumental Temperature Records

  • Worldwide Instrumental Temperature Record: Last 150 years.

  • Before 1850: Use temperature proxies for data.

  • Cooling Period: From the 1940s to the 1970s observed only in the Northern Hemisphere.

  • Impact of Industrialization: Primarily affects the Northern Hemisphere.

  • Average Global Temperature Increase: Increased by 1.1°C (1.9°F) since 1880, with most warming since 1975 occurring at a rate of roughly 0.15 to 0.20°C per decade.

Evidence of Temperature Changes

  • Glacier Bay National Park in Alaska: Comparisons taken in September 2022 and September 1979 show dramatic changes.

Understanding Global Climate Change

Hottest Planets in the Solar System

  • Mercury: 36 million miles from the sun - 801°F (427°C) to -279°F (-173°C).

  • Venus: 67 million miles from the sun - 870°F (465°C).

  • Earth: 93 million miles from the sun - Range from 90°F (32°C) to -30°F (-34°C).

Greenhouse Gases

  • Key Greenhouse Gases: { ext{CO}}2 (carbon dioxide) and { ext{CH}}4 (methane).

Discovering the Greenhouse Effect

Historical Contributions to Understanding

  • Joseph Fourier (1824): Discovered that Earth’s atmosphere traps heat coming in.

  • John Tyndall (1850s): Discovered that { ext{N}}2 (nitrogen) and { ext{O}}2 (oxygen) do not contribute to heat trapping capabilities. Water vapor and { ext{CO}}_2 absorb Earth's radiant heat.

  • Svante Arrhenius (1896): Calculated the warming power of CO2 and predicted warming from increased human activities.

Mechanism of Greenhouse Effect

  • Explanation: Water, carbon dioxide, and methane absorb infrared radiation in the atmosphere, which is then reradiated to warm the lower atmosphere.

  • Carbon Cycle Dynamics:

    • Natural emissions, human emissions, storage.

Carbon Pathways

Sinks and Sources

  • Carbon Pathways – Sinks:

    • Subduction zones

    • Incorporation into terrestrial biomass:

    • Chemical equation: 6{ ext{CO}}2 + 6{ ext{H}}2{ ext{O}} + ext{sun}
      ightarrow { ext{C}}6{ ext{H}}{12}{ ext{O}}6 + 6{ ext{O}}2

    • Deposition of plant material without decomposition (e.g., swamps, bogs).

  • Carbon Pathways – Sources:

    • Oceans

    • Volcanism

    • Biomass burning/deforestation/decomposition:

    • Chemical equation: { ext{C}}6{ ext{H}}{12}{ ext{O}}6 + 6{ ext{O}}2
      ightarrow 6{ ext{CO}}2 + 6{ ext{H}}2{ ext{O}}

    • Methane Sources: Produced by rice paddies, intestines of ruminants, and termites.

    • Methane from melting permafrost.

Natural Causes of Climate Change

Factors Influencing Climatic Shifts

  • Long Term Factors (millions of years):

    • Position of continents/plate tectonics

    • Uplift of land surfaces

    • Formation of coal and oil

    • Evolution of life forms

    • Volcanism

  • Albedo Effects:

    • Ocean water at the equator has an albedo of 0.03 to 0.1 (contributes to a warm planet).

    • Ocean water at high latitudes has an albedo of 0.1 to 0.25 (contributes to a cold planet).

Snowball Earth Concept

  • Definition: Period when glaciers extended to the equator, and Earth became encased in ice.

  • Runaway Albedo Effect: Snow reflected the sun’s heat back to space, acting as a positive feedback loop.

  • Sea Floor Spreading Rate:

    • Cretaceous period (145 – 66 my) saw increased spreading leading to more CO2 emissions.

Long Term Climate Change Influences

Uplift of Land Surfaces

  • Weathering Process: Exposes land to weathering and chemical weathering absorbs CO2, particularly in silicates and limestone, which also affects atmospheric circulation.

Formation of Coal and Oil

  • Late Paleozoic Era: Formation of large areas of coal that removed CO2 from the atmosphere, possibly leading to global cooling.

Evolution and Extinction of Life Forms

  • Modern Stromatolites: Found in Shark Bay, Australia; significant for understanding ancient climates.

  • Fossil Stromatolites: Found in places like Central Texas from the Cambrian (approximately 500 million years ago).

  • Volcanic Eruptions: Contribute to long-term warming due to CO2 influx (e.g., Palisades sill formed by the breakup of Pangea).

Short Term Climate Change Factors

Milankovitch Cycles

  • Definition: Long-term climate variations due to Earth's orbital changes over thousands of years.

Surface Albedo Effect

  • Definition: Albedo measures reflectivity; ranging from 0 (absorbs all solar radiation) to 1 (reflects all).

  • Current Average Albedo: Approximately 0.3, with variations influencing temperatures (higher albedo = colder, lower albedo = warmer).

Volcanism

  • Example: Mount Tambora eruption (April 10-11, 1815)

    • Resulted in the “Year Without Summer” (1816), where global temperatures lowered by 0.3°C (0.54°F) leading to significant agricultural failures and famine in the Northern Hemisphere.

Solar Irradiance

  • 11-Year Solar Cycle: Variations in solar irradiance measured by satellites since 1979 and associated with solar magnetic storms.

Ocean Circulation Dynamics

  • Influences on Climate: Details concerning solar radiation and heat balance related to ocean currents are critical for understanding climate variations.

Studying Past Climate Variations

Use of Proxies

  • Definition: Geologic and biologic indicators of temperature and precipitation preserved in the geologic record.

  • Keeling Curve (1958-2009): Direct measurement of atmospheric gases showing a perfect correlation with CO2 levels.

  • Oxygen Isotope Ratios: Used as a temperature proxy for climate reconstructions over the last 900,000 years.

  • Sources for Climate Records: Ice cores, sediment samples, and various biotic indicators such as foraminifera and their shells, which use 18O/16O isotope ratios to indicate past temperatures.

Culture Experiments

  • Understanding Past Climates: Experiments using foraminifera and oxygen isotopes provide a continuous record of ocean conditions.

Current Carbon Dioxide Levels

  • Current Levels: Atmospheric carbon dioxide levels have increased to approximately 422 ext{ ppm} from about 275 ext{ ppm} prior to the Industrial Revolution.

Rate of Change Calculations

  • Historical Rate from Last Ice Age to Pre-Industrial Period:

    • 180 ext{ centuries} to go from 180 ext{ ppm} to 275 ext{ ppm} results in a rate of approximately 0.528 ext{ ppm/century}.

  • Rate of Change since Industrial Revolution (~1750):

    • Current increase to 422 ext{ ppm} implies a change of 147 ext{ ppm} over 2.74 ext{ centuries}, leading to a rapid rate of approximately 53.6 ext{ ppm/century}, which is roughly 102 times the natural rate.

    • Recent increases observed up to 200 times the natural rate according to NOAA.

Broader Implications of Climate Change

Impact on Coral Reefs

  • Nancy Knowlton: Marine biology professor noted the catastrophic collapse of coral reefs over the past three decades, with about half of the reefs dying as of 2015.

  • Coral Bleaching Trigger: Occurs above 85°F with thermal expansion of seawater causing sea levels to rise approximately 3.6 ext{ mm/year} from 2006 to 2015.

Consequences of Rising Temperatures

  • Polar Ice Melting:

    • Arctic amplification leads to significant loss of Arctic sea ice, with over 2 million square kilometers lost in the last decade.

    • Lower albedo from loss of ice enhances global warming.

    • Projected rise in sea level potentially reaching 80 ext{ meters} due to thermal expansion and ice melt.

Summary and Reviews

  • Importance of CO2: Critical greenhouse gas regulating planetary temperature, enabling habitability. The average temperature without CO2 would be around -18°C.

  • Geologic Factors: Include weathering processes, continental positions, and volcanism, all influencing climate across vast time scales.

  • Proxies for Understanding Past Climate: Utilized various geological indicators, including oxygen isotopes and fossil records, to reconstruct historical climates.