CU 2

Past, Present, and Future Climate

Overview

  • The document discusses various aspects of climate change, including astronomical factors, Earth's surface and atmosphere, sources of carbon dioxide (CO₂), temperature records, and implications for the future.

Accomplishments

  • The accomplishments in understanding climate are outlined in the chapters of the document:

    1. Astronomical factors

    2. Earth’s surface and atmosphere

    3. Source of CO₂

    4. Temperature records

    5. Past, present, and future climate studies

    6. Modeling the climate

Climate Change Measurements

  • Global Average Temperature:

    • Comparison to pre-industrial temperatures:

    • 1975 Broecker paper indicated an increase of +1.33°C compared to pre-industrial temperatures.

    • In 2023: +1.44°C

    • In 2024: +1.55°C

  • Historical temperature data points illustrate the increase in global temperatures over the decades from 1940 to 2020:

    • +1.0°C (2020)

    • +0.5°C (2010)

Energy Balance

Energy In

  • Incoming Solar Radiation: 342 W/m²

    • Reflected Solar Radiation: 107 W/m²

    • Reflected by clouds, aerosols, and atmospheric gases: 77 W/m²

    • Reflected by the surface: 30 W/m²

  • Heat provided to the system:

    • Absorbed by the surface via radiation: 390 W/m²

Energy Out

  • Outgoing Longwave Radiation: 235 W/m²

    • The breakdown includes:

    • Emitted by atmosphere/clouds: 165 W/m²

    • Absorbed by greenhouse gases: 67 W/m²

    • Heat absorbed and radiated by the surface: 324 W/m²

Temperature Over Long Time Scales

Climate Records

  • Types of climate records include:

    • Instrumental measurements

    • Written historical records

    • Tree rings (dendrochronology)

    • Ice cores

    • Ocean floor sediments

    • Fossils and rocks

  • Timescale of records:

    • Instrumental: <150 years

    • Written records: ~2500 years

    • Tree Rings: 13,910 years

    • Ice cores: 800,000 years

    • Ocean floor sediments: 50 million years

    • Fossils and rocks: 4.4 billion years

Dendrochronology (Tree Rings)

  • A method to read past climate conditions based on tree growth patterns:

    • Innermost ring: The oldest

    • Outermost ring: Current year's growth

    • Ring thickness correlates with yearly growth conditions.

  • Example: Bristlecone Pines are over 5000 years old and provide vital information about past climates.

Temperature Records from Vikings

  • The study of Viking settlements in Greenland and Canada provides historical temperature records:

    • Medieval Warm Period: 985 - 1410 AD was warmer than the current climate.

    • Migration patterns illustrated by temperature data from thermometers and tree rings.

Impacts of Greenhouse Gas Emissions

  • Atmospheric CO₂ concentrations have risen rapidly since 1800:

    • CO₂ concentrations over recent decades have shown significant increase:

    • Fact: CO₂ levels and temperature have a strong correlation over time.

Climate Modeling

Energy Balance and Feedback

  • The relationship of Energy In = Energy Out forms the basis of climate modeling.

  • Feedback loops complicate climate prediction:

    • Positive Feedback: Amplifies the effect (e.g., Arctic ice melt increasing solar absorption).

    • Negative Feedback: Suppresses the effect (e.g., increased evaporation leads to cloud formation and reflects sunlight).

  • The climate system is evaluated based on numerous feedback pathways affecting temperature, precipitation, and solar energy absorption.

Predictions Scenarios

Future Projections

  • Models predict significant warming due to human activities.

    • Predicted average temperature changes for varying scenarios (A1B, B1, A2) illustrate expected warming trends up through 2100.

Observed Climate Changes and Their Effects

  • Ice Melt and Sea Level Rise:

    • Observations indicate accelerated ice flow rates, and potential sea levels could rise significantly if ice caps melt.

    • Arctic sea ice losses change global reflectivity and temperature patterns.

  • Wildfires: Examples include:

    • Increased fire risks in Siberia and the boreal regions due to higher temperatures and drier conditions.

Economic and Social Aspects

  • Global greenhouse gas emissions vary by sector:

    • Electricity and heat production: 25%

    • Industry: 21%

    • Transportation: 14%

  • The need for rapid emission reductions is emphasized to meet international climate targets such as the Paris Agreement.

Conclusions

  • Urgent action is needed to address climate change and the influence of human activity on the planet's climate.

  • The continuous rise in emissions and CO₂ levels necessitates efforts toward sustainability and a significant shift in energy use patterns.