Unit 1: Climate Change- Climate Change and the Carbon Cycle

Introduction

  • Climate change is a critical and complex topic, driven largely by increased carbon dioxide levels.
  • The lecture aims to provide essential information, acknowledging the limited time available for such a significant issue.

The Carbon Cycle

  • The carbon cycle is closely linked to climate change due to the impact of carbon dioxide levels on the atmosphere.
  • Review the carbon cycle through the provided link in the post-lecture assignment if needed.
  • The carbon cycle itself won't be directly tested, but understanding it is beneficial.

Early Life and Oxygen

  • Early Earth (3.7 billion years ago) had an anaerobic atmosphere, where oxygen was toxic to existing organisms (oxygen toxicity).
  • Example: Coral Reefs:
    • Coral polyps host algae (zooxanthellae) in a mutualistic relationship.
    • Algae photosynthesize, slowly releasing oxygen that coral polyps use.
    • Climate change warms oceans, increasing algal blooms due to fertilizer runoff.
    • Warmer temperatures cause algae to photosynthesize faster, producing excess oxygen.
    • Excess oxygen leads to coral bleaching, where coral polyps eject algae and eventually die due to lack of carbohydrates.

Evolution of Photosynthesis

  • Around 2.8 billion years ago, organisms evolved to use CO2 and produce O2 as waste.
  • This was detrimental to anaerobic organisms, described as the "most severe pollution episode" by ecologist Walker in 1986.

Atmospheric Composition

  • Current atmospheric composition:
    • 78% Nitrogen
    • 20% Oxygen
    • 0.93% Argon
    • 0.03% Carbon Dioxide
    • Trace amounts of Ozone (O3)

The Natural Greenhouse Effect

  • The atmosphere functions like a blanket, trapping heat and keeping the Earth warm.
  • The Earth's surface is warmed by direct sunlight and heat radiating from the atmosphere.
  • The greenhouse effect is beneficial, maintaining an average temperature of 15 degrees Celsius instead of -18 degrees Celsius.
  • Climate change results from disrupting the natural greenhouse effect.
  • Global warming refers to the increase in the planet's temperature, but scientists now use the term climate change to account for increased variability in weather patterns.

Carbon Reservoirs

  • Carbon reservoirs are sources that exchange carbon with other parts of the globe.

  • Examples:

    • Atmosphere: An active reservoir where CO2 cycles in and out regularly.

    • Terrestrial Ecosystems: Plants act as carbon sinks, but overall, these ecosystems are reservoirs due to respiration and decomposition.

    • Oceans: Surface layers exchange CO2 with the atmosphere actively, while deeper layers are relatively inactive carbon storage areas.

    • Sediments: Accumulation of carbon-based molecules, including fossil fuels.

      • Fossil fuels are becoming an active reservoir due to human extraction and combustion.

Earth's Energy Budget

  • Incoming solar radiation: 100%.
  • 30% is reflected away by the atmosphere, clouds, and Earth's surface.
  • 70% is absorbed by oceans, land, atmosphere, and clouds, then radiated back into space.

Climate Change and the Atmosphere

  • Climate change is primarily impacting the atmosphere's ability to retain heat.
  • Increased greenhouse gases (CO2, methane) enhance the atmosphere's heat-trapping capacity.
  • The atmosphere has shifted from being a regular blanket to an electric blanket,radiating heat back to the surface.

Temperature Increases Observation

  • Since the late 19th century, the average global temperature has increased by nearly 2 degrees Fahrenheit.
  • Most of the increase has occurred in the last 35 years.
  • 18 of the 19 warmest years on record have been since 2000.
  • Oceans have absorbed much of the heat, with ocean temperatures increasing by almost a half-degree since 1970.

Greenhouse Gases

  • Greenhouse gases trap heat by absorbing energy and re-emitting it back into the environment.
  • Common greenhouse gases include:
    • Water Vapor (H2O)
    • Carbon Dioxide (CO2)
    • Methane (CH4)
    • Ozone (O3)
    • Nitrous Oxide (N2O)
    • Chlorofluorocarbons (CFCs)
  • CFCs, once widely used, have been phased out due to their ozone-depleting effects but persist in the atmosphere for 75-100 years.

Ozone Depletion vs. Climate Change

  • Ozone depletion and climate change are distinct issues.
  • Ozone depletion does not cause global warming.
  • Ozone is a greenhouse gas, and its decrease would slightly cool the Earth.
  • The ozone hole is a localized area of ozone thinning, allowing more UV radiation to penetrate, but it doesn't cause overall warming.

CO2 and Temperature Correlation

  • Analysis of ice cores reveals a strong correlation between CO2 concentrations and temperature over the past 160,000-200,000 years.
  • Increased CO2 levels correlate with increased temperatures, and vice versa.
  • The data indicates a link, though not necessarily a direct cause-and-effect relationship in the past, but with the evidence we have now it is clear that CO2CO_2 causes temperature increase

Current CO2 Levels

  • CO2 levels have increased dramatically since the early 1700s.
  • Current CO2 concentrations are the highest in the last 160,000-200,000 years.

Causes of Increased CO2 Levels

  • Multiple correlations point to human activities as the primary cause of increased CO2 levels.
  • Increased industrial activity.
  • Continuous CO2 increase interrupted only by human events (wars, economic depressions).
  • Decline in radioactive carbon in the atmosphere (the Suess effect).

Historical CO2 Trends

  • For approximately 500,000 years, CO2 levels remained below 300 parts per million (ppm).
  • Around 1950, CO2 levels surpassed 300 ppm and have been increasing rapidly ever since.
  • Current CO2 levels exceed 400 ppm.
  • The rate of increase is about ten times greater than any previous period.

Correlations: Industrial Revolution

  • The industrial revolution, starting in the early 1800s, led to increased burning of fossil fuels (coal, gasoline, oil).
  • This resulted in a dramatic increase in atmospheric CO2.
  • Decreases in CO2 emissions during World War I, World War II, and the Great Depression indicate the impact of industrial activity on CO2 levels.
  • The COVID-19 pandemic may result in a temporary dip in CO2 levels due to reduced driving and industrial activity.

The Suess Effect

  • Carbon-12 and carbon-14 occur naturally in the atmosphere.
  • Carbon-14 is radioactive with a half-life of approximately 5,700 years.
  • Fossil fuels contain little or no carbon-14, as it has decayed over millions of years.
  • Burning fossil fuels releases carbon-12 into the atmosphere, diluting carbon-14 concentrations.
  • The Suess effect refers to the decrease in the ratio of carbon-14 to carbon-12 in the atmosphere due to fossil fuel combustion.

Consequences of Temperature Increase

  • The planet's temperature is increasing at an unprecedented rate.
  • The temperature increase in the past 50 years is equivalent to that since the last ice age (10,000 years ago), but occurring 10-40 times faster.
  • Rapid temperature changes may exceed the ability of organisms to adapt and evolve.
  • Soil quality and food production are at risk as optimal crop-growing regions shift.

Observed Climate Change Effects

  • Global weather patterns are changing, with more extreme weather events.
  • Record-warm temperatures are increasing in the winter and summer.
  • Severe storms and rainstorms are becoming more frequent.
  • Ecosystems are being disrupted due to species' intolerance of changes.
  • Ice sheets and glaciers are melting, causing ocean currents disruption and sea-level rise.

Sea Level Changes

  • Sea levels have risen approximately 10 inches in the past 150 years.
  • Since 2000, sea levels have increased by about 40 millimeters (4 centimeters).
  • Sea-level rise is due to:
    • Melting glaciers and ice sheets.
    • Thermal expansion of warming oceans.
  • Even small increases in sea level can lead to coastal flooding during storms.

Conclusions

  • CO2 concentrations have varied over the past 560,000 years, paralleling global temperature changes.
  • Increased CO2 leads to increased temperatures.
  • Current CO2 levels are the highest ever measured and are strongly influenced by burning fossil fuels.

Future Temperature Predictions

  • Models from the 1990s predicted a temperature increase of 1.5 to 5.5 degrees Celsius by the end of the 21st century.
  • Revised models now predict an increase of 3.5 to 7 degrees Celsius by 2100 if current trends continue.
  • Potential for massive die-offs of populations if significant temperature changes occur by 2050.

Call for Action

  • Changes are needed now to mitigate climate change.

  • Solutions will be discussed later in the semester.

  • Acknowledges the slow pace of change and human resistance but emphasizes the potential for future solutions. #Unit 1 Conclusion

  • This concludes the Unit 1 lecture material.

  • The post-lecture assignment focuses on balancing energy sources for global energy demands.