Climate and Climate Change Notes

Chapter 21: Climate and Climate Change

21.1 - Global Climate

  • Global climate is generally stable over centuries, influencing farming, tourism, and other aspects of life.
  • However, this stability is only relative to short geological periods.
  • A simplified global climate model would assume:
    • A uniform surface.
    • No tilt in Earth's axis.
    • No Earth rotation.
  • The three-cell model explains global climate patterns.
  • Equatorial regions experience the highest temperatures.
    • Warm air rises, creating low pressure zones.
    • Air moves north and south from the equator.
    • At approximately 30° latitude in both hemispheres, high-altitude air descends, resulting in calm, high-pressure areas known as the horse latitudes.
  • Descending air at the horse latitudes is affected by the Coriolis effect:
    • Air moving back toward the equator forms trade winds.
    • Air moving poleward creates prevailing westerlies.
  • Persistent high pressure exists at the poles due to descending cold air.
    • Air flowing away from the poles forms polar easterlies.
  • Convergence of westerlies and polar easterlies creates a low-pressure boundary zone called a polar front, characterized by precipitation favorable for agriculture (30°-60° latitude).
  • Jet streams develop at these cell boundaries.

21.2 - Climate Types

  • Major climate types are classified based on temperature and precipitation, with consideration for seasonal variations.
  • Plant life can visually indicate climate types (e.g., cacti in deserts).
  • A biome is a community of plants in a specific climate.
  • The Köppen Climate Classification is widely used by climatologists.
    • It includes 6 major types (A, B, C, D, E, and H) with subtypes.
    • Details are represented on a climograph, showing average annual temperature and precipitation over the course of a year, with latitude and longitude of the recording station.
  • Type A - Humid Tropical:
    • Consistent low pressure near the equator leads to high year-round rainfall (approximately 400 cm/year), supporting tropical rainforests.
    • Dense canopy formed by tall, thin trees.
    • Minimal sunlight reaches the surface (as little as 0.1%).
    • Variations:
      • Tropical monsoon (rice-growing regions in India and Southeast Asia).
      • Tropical savanna (large grasslands, Africa, lacking forests).
  • Type B - Arid:
    • Characterized by dry zones.
      • Semiarid regions receive 25-35 cm of precipitation per year, predominantly grassland steppes like those in central Asia.
      • Deserts receive less than 25 cm/year, with sparse vegetation.
    • Often located along high-pressure zones at 30° latitude.
    • Can be hot or frigid (arctic deserts).
  • Type C - Humid Mesothermal:
    • Found in midlatitudes with distinct winter and summer seasons and ample moisture.
    • Mild winters with occasional snow that doesn't persist; average temperature in the coldest month is above -3°C (27°F).
    • Subclimates:
      • Humid subtropical (southeastern U.S.): Hot and humid summers, occasional snow in winter.
      • Mediterranean (west coasts between 30°-40°, California): Dry summers, rainy winters, moderate temperatures.
      • Marine west coast (north of Mediterranean zones, Portland, OR): Ocean-influenced, abundant precipitation, little temperature variation.
        • Temperate rainforests grow with rainfall > 100 cm/yr.
  • Type D - Humid Microthermal:
    • Continental interiors at midlatitude with severe winters and hot summers (like the U.S.).
    • Humid continental climates with large temperature swings.
    • Coniferous forests (wetter) or grasslands (dryer).
    • Subarctic regions support the taiga biome, with forests adapted to extreme winters.
  • Type E - Polar:
    • Harsh and long winters; temperatures above freezing only briefly in summer.
    • Supports the tundra biome with low-lying mosses, grasses, and bushes, but no trees.
    • Ice cap subclimate where no vegetation can survive.
  • Type H - Highlands:
    • Determined by elevation, found at latitudes worldwide.
    • Temperature varies with altitude, ranging from about -18°C (0°F) to 10°C (50°F).
    • Precipitation tends to decrease with altitude; windward sides of mountains usually receive more precipitation than leeward sides.
  • Urban Heat Island Effect:
    • Major cities exhibit measurably different climates from surrounding rural areas.
    • Temperature variance can be up to 6°C.
    • Factors include absorption and reradiation of heat by stone, concrete, and asphalt; limited surface water for heat transfer; heat release from fuel burning; wind blockage; and air pollution creating a local greenhouse effect.
    • Urban areas experience:
      • 5 to 10% more precipitation and cloudiness.
      • 100% more fog in winter and 30% more in summer.
      • 2% lower relative humidity in winter and 8% lower in summer.
      • 15 to 20% less total radiation and 5 to 15% less direct sunshine.
      • 0.5 to 1.0°C higher annual mean temperature and 1.0 to 3.0°C higher winter minimum temperature.
      • 20 to 30% lower annual mean wind speed and 10 to 20% lower extreme gusts.
      • 5 to 20% higher frequency of calm winds.

21.3 - Historical Climate Change

  • Understanding historical climate change is crucial for studying current climate dynamics.
  • Climate change is now a specifically human issue due to population size, settlement patterns, and reliance on agriculture.
  • The planet has experienced a cooling trend over the past 5 million years.
  • Global temperatures have varied significantly over the last 800,000 years, with only two periods (Holsteinian and Eemian) warmer than today.
  • Data since 1880 indicates rapid warming, particularly in the last 40 years.
  • Evidence of past climates is gathered through:
    • Relatively recent evidence:
      • Tree rings: Growth patterns reflect temperature and moisture conditions.
      • Plant pollen: Preserved in lakes and bogs, indicating past vegetation and climate.
        • Example: Spruce replaced by pines in Minnesota 10,500 years ago, suggesting a warmer climate than present.
    • Older evidence:
      • Oxygen isotopes: Ratio of O-16 and O-18 in ice cores reveals past water temperatures, reflecting atmospheric conditions.
        • Ice cores from Antarctica provide data up to 800,000 years ago.
      • Carbon-14 dating: Radioactive decay in preserved organic matter can date samples back approximately 50,000 years.
    • Much older evidence:
      • Plankton species ratios in ocean sediment reflect surface temperature.
      • Oxygen isotopes in shells, teeth, bones, and exoskeletons.
      • Oxygen isotopes in soil minerals.
      • Fossilized life forms (e.g., cacti, ferns) indicate past climate conditions.
      • Sedimentary deposits (e.g., tillite from glacial debris, carbonate rocks indicating CO2 levels).
  • Earth's atmospheric temperature is determined by:
    • Energy input from the Sun.
    • Energy reflected (albedo).
    • Energy absorbed by the surface and atmosphere (greenhouse effect).
    • Feedback loops and threshold effects in the bio-, atmo-, and geospheres.
    • The Sun produced only 70% of its current energy at the beginning of Earth's life, balanced by abundant greenhouse gases.
  • Climate change factors:
    • Tectonic activity, outgassing, heat absorption rates, erosion, and bolide impacts.
    • Slight changes in Earth’s axial tilt and orbit shape.

21.4 - Climate Change Today

  • Carbon cycle is affected by increase by human activity.
  • Industry releases major greenhouse gases:
    • CO2 from burning fuels and logging.
    • Methane from industrial processes.
    • CFCs (chlorofluorocarbons) - usage halted.
    • Nitrogen oxides from fertilizer and chemical syntheses.
  • Summary of human impact data:
    • Humans release greenhouse gases.
    • Concentrations of greenhouse gases have increased since the Industrial Revolution.
    • These gases trap heat.
    • The atmosphere has warmed nearly 1.5°C over the past 130 years, including 0.8°C in the last 50 years.
    • The top five hottest years on record have occurred since 2014.
    • There is a consensus among scientists that humans are driving this warming.
  • Climate change modeling is complex, influenced by human greenhouse gas emissions.
  • Inputs and outputs from the carbon cycle can occur anywhere.
  • Even if emissions stopped today, global average temperature will continue to rise for decades.

21.5 - Consequences of Climate Change

  • Climate change impacts are mixed, with potential benefits like extended frost-free periods in northern latitudes, but negatives outweigh positives.
  • Weather patterns:
    • Increased evaporation, net loss of soil moisture and groundwater.
    • Reduced resources, increased need for irrigation.
    • Potential decrease in global food production.
    • Less water in long-term storage, less available overall.
    • More frequent extreme weather events (floods, tropical storms).
  • Ecosystems:
    • Tree death and increased wildfires.
    • Conversion of forests to savannas.
    • Increased survival of plant and animal pathogens.
    • Potential extinction of species unable to adapt.
  • Sea-Level Rise:
    • Thermal expansion of warmer water and melting of polar ice sheets.
    • Expected rise of 20 cm in the next century.
    • Significant effects on the east coast of the U.S., west coast of Africa, Netherlands, Bangladesh, and Pacific islands.
    • Melting of Greenland's ice sheet could raise sea levels by approximately 7 meters (21 feet).
    • Melting of the ice sheet from the west side of Antarctica could contribute to sea-level rise by 8 meters (26 feet).
  • Ocean Acidification:
    • Increased carbonic acid due to higher atmospheric CO2 levels, impacting marine ecosystems.
  • Economic Impacts:
    • Vulnerability of agriculture and tourism.
    • Lower crop yields, coastal areas underwater.
    • Significant expenditures on protective measures in countries like Holland, England, and Italy.
    • A 1-meter rise would flood 17% of the land area of Bangladesh.
    • Erosion along coastlines reduces protective wetlands.
  • Ice Melt / Albedo:
    • Melting occurs above 0°C threshold.
    • High albedo of ice sheets reflects sunlight, cooling the Earth; melting reduces albedo, warming the atmosphere (feedback loop).
  • Photosynthesis / Decomposition:
    • Reduced nutrients and soil moisture limit plant growth, reducing CO2 uptake via photosynthesis.
    • Increased decomposition rates release more CO2 into the atmosphere (feedback loop).
  • Release of Methane:
    • Methane is 20 times more effective at trapping heat than CO2.
    • Large methane deposits in permafrost and ocean sediments.
    • Microbes producing methane thrive in warmer, carbon-rich environments.
    • Theory: A rapid methane release may have caused a 100,000-year hot spell approximately 55 million years ago.
  • Mitigating the Effects of Climate Change:
    • Urgent threat.
    • The UN established the Intergovernmental Panel on Climate Change (IPCC) in 1988.
    • The IPCC’s 2nd report in 1995 led to the Kyoto Protocol, which had limited success and expired in 2012.
    • The Paris Agreement (2015) set a goal for maximum increase in global temperature.
    • Countries pledged to reduce greenhouse gas emissions and meet every 5 years.
    • The 2018 United Nations Environment Programme Emissions Gap Report compared current efforts with those required to limit the global temperature increase to 1.5°C compared to preindustrial levels.
    • Emissions standards by 2030 must be 55% lower than those proposed in 2017.
    • Carbon capture techniques are being developed to reduce emissions and remove excess CO2.