CU 1

Climate Change Overview

  • Introduction

    • Discussion on climate change and global warming.

    • Reference to the historical context of climate science with Wally Broecker’s pivotal paper from 1975.

Historical Context

  • Wally Broecker (1931-2019)

    • National Medal of Science laureate.

    • Authored the 1975 paper in Science titled "Climatic Change: Are we on the brink of pronounced global warming?"

    • Significant points made in the paper:

    • Average global temperature from 1965-1975 was equal to long-term averages.

    • Mean global temperature in 1975 was +0.02 °C.

    • Mentioned future risks: "the exponential rise in the atmospheric carbon dioxide content will tend to become a significant factor and by early in the next century will have driven the mean planetary temperature beyond the limits experienced during the last 1000 years."

The Concept of Global Warming

  • Definitions

    • Global Warming: A gradual increase in the average temperature of Earth's atmosphere and its oceans.

    • Climate Change: Refers to long-term shifts in temperature and weather patterns, particularly due to human activities.

  • Broader context from Frank Luntz (2001):

    • Noted political strategies concerning public perception of climate science.

    • Notable quote: "The scientific debate is closing [against us] but is not yet closed…"

    • Suggested framing of the issue:

    • Shift from "global warming" to "climate change" due to public perception of scientific consensus.

    • Emotional storytelling can be more compelling than factual representations of data.

Differentiating Effects of Weather and Climate

  • Weather vs. Climate

    • Weather:

    • Short-term changes in atmospheric conditions (minutes to years).

    • Examples include storms, droughts, and cold snaps.

    • Climate:

    • Long-term patterns (decades to millennia).

    • Historical periods like Ice Ages and the Medieval Warm Period.

Factors Determining Earth's Temperature

  • Key Determinants

    • Sun’s Energy Output

    • Distance to Earth

    • Tilt of Earth’s Axis

    • Reflectivity of Earth (Albedo)

    • Cloud Cover

    • Ice Cover

    • Vegetation

    • Aerosols

    • Atmospheric Composition:

    • Water vapor

    • Carbon dioxide (CO₂)

    • Methane (CH₄)

    • Nitrous oxides (N₂O)

    • Chlorofluorocarbons (CFCs)

Astronomical Factors Affecting Climate

  • Sun's Energy Output

    • Core Fact: Average solar energy output is approximately 3.839 imes 10^{26} Watts.

    • Variations happen due to solar phenomena like sunspots.

  • Sunspot Cycle:

    • Typically a variation of about 0.1% in solar output over an 11-year cycle.

Observational Data

  • Sunspot Numbers through the Years

    • Data shows declining numbers with peaks affecting solar activity.

    • Example Observations:

    • In 2019, for 87 days (24%), there were no sunspots (average = 3.6).

    • In 2020, for 192 out of 366 days (52%), there were no sunspots (average = 8.5).

  • Energy Contributions From Other Sources:

    • Moonlight: 0.22 TW

    • Tides: 3.3 TW

    • Radioactivity: 15-41 TW

    • Infalling Matter: <0.01 TW

    • Total energy received from solar power is around 174,400 TW.

Changes in Earth's Orbit and Tilt

  • Earth’s Orbit and Axis Tilt

    • Earth is approximately 1.495978707 imes 10^{8} km from the sun (~93,000,000 miles).

    • Orbital variance:

    • The Earth's orbit is elliptical and changes over time, affecting climate cycles known as Milankovic Cycles.

    • Seasons result from axial tilt affecting sunlight distribution throughout the year.

Climate Cycle Changes

  • Milankovic Cycles:

    • Precession: approximately 23,000 years

    • Axial Tilt: approximately 41,000 years

    • Eccentricity: approximately 100,000 years

    • These cycles exhibit significant long-term climatic changes, impacting Earth’s climate system.

Recent Climate Trends

  • Recent Temperature Increases:

    • Annual temperature increases observed are rising above historical averages.

    • The increase factors include amplified greenhouse gas effects.

  • Example Data:

    • 2023 recorded all 365 days over 1 °C above pre-industrial levels

    • Continuous increase in global average temperature observed, correlating to anthropogenic factors.

Ice Melt and Sea-Level Rise

  • Associated risks of global warming such as accelerated ice melt in polar regions leading to a rise in sea levels and changing global weather patterns.

Conclusion

  • Climate change reflects an unprecedented challenge driven primarily by human actions, particularly fossil fuel consumption and deforestation, leading to higher concentrations of greenhouse gases.

  • Immediate action is needed to mitigate impacts and future changes in climatic systems, emphasizing renewable energy sources and sustainable practices.