Anthropogenic Climate Change

Anthropogenic Climate Change

Global Warming

Lesson Goals

  • Understand how climate has changed, and its drivers, over the past 1000 years.

  • Recognize how humans are impacting global temperature.

  • Understand how emissions are changing.

  • Explain overview of how climate is changing due to increased temperatures (more details in future classes).

Climate Change Over the Past 1000 Years

  • Overall Cooling from 1000 Years Ago to 1850

    • Medieval Warm Period (1000-1300)

    • Less evidence found in regions like eastern Canada, Greenland, Iceland, and Northern Europe.

    • Small cooling from the Medieval Warm Period to Little Ice Age (~1400-1900).

    • Noted as a regional phenomenon, not global.

    • Since the 1800s, there has been unprecedented warming!

Drivers of Climate Change from 1000-1850

  • Potential Factors Influencing Climate Change

    • Orbital forcing

    • Solar Variability

    • Volcanic Activity

    • Greenhouse Gases

CO₂ Concentrations over Time

  • CO₂ (parts per million, ppm) data shows fluctuations, with numbers as follows:

    • Approximate values from the graph:

    • 284 ppm in early periods

    • Spiking during various historical events

Population and Emissions

  • Catastrophic Population Losses

    • European and Mediterranean regions faced significant declines in population percentage.

    • China experienced significant population reductions between 1000 to 1500.

Current Climate Conditions

  • Average Global Temperature

    • Current rise of 1.1°C above the 1850-1900 average, as reported by IPCC (2023).

    • Noted small cooling period from 1940 to 1970, potentially attributed to increased aerosol emissions following WWII industrialization.

Changes in Global Average Temperatures (1918 vs 2018)

  • Color-coded temperature maps where:

    • Dark Blue: Areas cooler than average.

    • Dark Red: Areas warmer than average.

  • Surface temperatures have accelerated over the past 50 years compared to any other time in the last 2000 years.

Drivers of Warming

  • Scientific Consensus on Anthropogenic Climate Change

    • Climate models suggest that only about 25% of warming in the 20th century is due to natural variability (e.g., solar irradiance changes).

    • Observation of atmospheric carbon isotopes indicates trends of CO₂ levels.

    • Noting that higher levels of the atmosphere are reportedly cooling.

    • Thermodynamic feedbacks play a significant role, but most warming correlates with predicted increases in anthropogenic greenhouse gases (GHGs).

IPCC Contributors to Climate Change (2023)

  • Human-Caused Temperature Increase (1850-1900 to 2010-2019)

    • Estimated range of temperature increase: 0.8°C to 1.3°C

    • Best estimate indicates a rise of approximately 1.07°C.

    • Contribution breakdown:

    • Well-mixed greenhouse gases raised temperatures by 1.0°C to 2.0°C.

    • Other human factors (primarily aerosols) cooled by 0.0°C to 0.8°C.

    • Natural solar and volcanic drivers shifted global temperature minimally by –0.1°C to +0.1°C.

    • Internal variability’s impact ranged from –0.2°C to +0.2°C.

Effects of Greenhouse Gases on Climate

  • Mechanism of Energy Absorption by CO₂

    • CO₂ molecules absorb energy from infrared (IR) radiation, leading to molecular vibrations.

    • Emission of infrared photons occurs after vibrations cease.

Human Contributions to Warming

  • Key anthropogenic gases identified:

    • Carbon Dioxide (CO₂)

    • Methane (CH₄)

    • Equivalence: 1 molecule of methane ≈ 28-60 molecules of CO₂.

    • Chlorofluorocarbons (CFCs)

    • Soot

    • Sulfate aerosols

Water Vapor Feedback Effect

  • Positive Feedback Loop

    • Increased carbon dioxide in the atmosphere raises temperatures, leading to higher water evaporation.

    • Water vapor acts as a greenhouse gas, enhancing atmospheric warming further as its concentration increases.

US Greenhouse Gas Emissions

  • Net GHG Emissions from Human Activities

    • Decreased by 13% from 2005 to 2019.

    • Approximately 42% of cumulative emissions occurred between 1990 to 2019.

    • Atmospheric levels in 2019:

    • CO₂: 410 ppm, the highest in at least 2 million years.

    • Methane: 1866 ppb, highest in at least 800,000 years.

    • Nitrous Oxide: 332 ppb, also a record high.

Impacts of Climate Change

Global Temperature Changes

  • Increased variability in regional temperatures.

  • Higher latitudes experiencing average increases of 2.5°C, which is double the global average.

  • Notable phenomena includes the 'cold blob' in the North Atlantic tied to Gulf Stream weakening and strong local winds.

Heat Waves

  • Definition: A heat wave consists of a daily maximum temperature exceeding the average maximum by 5 °C (9 °F) for over five consecutive days, referencing the normal period from 1961 to 1990.

  • Increased frequency and severity documented:

    • Summer 2003 in Western Europe resulted in 30,000 deaths, noted as the hottest in 500 years.

    • 2010 summer in Russia resulted in 15,000 to 55,000 deaths due to excessive heat.

    • Summer 2022 saw multiple heatwaves in Europe, with temperatures reaching 40°C (104°F) in the UK and 47°C (116°F) in Portugal, contributing to 53,000 excess deaths in July.

Changes in Global Annual Precipitation

  • Atmospheric Water Vapor (AWV) Control

    • Temperature directly influences AWV.

    • Changes in precipitation patterns reflect alterations in temperature affecting AWV across the globe.

    • Increased instances of extreme single-day precipitation have been noted, leading to flash floods.

Changes in Precipitation for the USA

  • Diagram representing rainfall change across the US from 1900 to 2000 shows:

    • Midwest experiencing wetter conditions while SW regions have become increasingly dry, especially in the last decade.

Long-term Temperature Records

  • Global surface temperatures previously sustained at or above 2.5°C occurred over 3 million years ago.

  • 2011-2020 showcased a temperature that was approximately 1.1°C warmer than the 1850-1900 benchmarks.

Projected Climate Impacts

  • Changes concerning global warming levels (GWL):

    • GWL above 1850-1900 see projections of annual hottest-day temperature changes up to 1.5-2 times in specific regions.

    • Projected decreases in annual mean total column soil moisture, following precipitation projections but influenced by evapotranspiration.

    • Increases in annual wettest-day precipitation across nearly all continental regions, even where mean soil moisture is expected to decline.

Arctic Sea Ice and Snow Cover Trends

  • Declines in Arctic sea ice area recorded since satellite monitoring started.

    • 2015 marked the lowest maximum areal extent compared to the 1979-2014 average.

  • Snow cover decreasing since the mid-1980s, which adversely affects:

    1. Reflecting solar radiation, which keeps high latitudes cool.

    2. Serving as a major water source for agricultural areas and rivers.

    3. Protecting vegetation during harsh winters.

Sea Level Change Relationship

  • Close monitoring of combined land and ocean surface temperatures relative to sea level changes.

  • Historical data collection methods for ocean temperatures revealed early trends.

Contribution of Melting Ice to Sea Level Rise

  • Between 1993 and 2018, components contributing to sea level rises were:

    • Thermal expansion of oceans: 42%

    • Melting temperate glaciers: 21%

    • Greenland ice melt: 15%

    • Antarctica ice melt: 8%

Future Projections and Implications

  • Even with stabilization of GHG concentrations, warming will continue.

    • By 2050, an estimated temperature increase of approximately 2.2°C is expected (intermediate estimate).

    • Anticipated decreases in snow cover and sea ice.

    • Expect to see more frequent heat waves and increased drought likelihood in the Mid-West USA.

  • Warmer climates forecasted to lower the Earth system's ability to absorb CO₂, thereby reinforcing the greenhouse effect.

  • Potential for the North Atlantic conveyor belt to start slowing by 2100.

Impact of Climate Change on Hurricanes

  • Evidence remains mixed regarding the detection of anthropogenic signals in tropical cyclone records.

  • Research suggests a 3-5% increase in wind speed for each °C increase in tropical sea surface temperatures.

  • While individual tropical cyclones cannot be solely attributed to climate change, societal impacts have risen due to increased coastal populations and infrastructure.

  • Tropical cyclone wind speed monitoring faced alterations over the decades, complicating trend accuracy determinations.

Future Climate Uncertainties

  • Need for extensive research into radiative forcing and feedback mechanisms.

  • Limited understanding of localized changes in rainfall and atmospheric pressure.

  • Occurrence of extreme events linked to global warming requires further refinement.

  • The role of oceans in climate change dynamics remains insufficiently understood, particularly their effects on glaciers.

Recap of Lesson Goals

  • Understand how climate has changed, and its drivers, over the past 1000 years.

  • Recognize how humans are impacting global temperature.

  • Understand how emissions are changing.

  • **Explain overview of how climate is changing due to increased temperatures (more details in future classes).