☁️Meteorology Unit 15 – Climate Change: Impacts on Weather Patterns

Key Climate Change Concepts

• Greenhouse effect traps heat in Earth's atmosphere due to gases like carbon dioxide (CO2) and methane (CH4)
• Anthropogenic activities, primarily fossil fuel combustion, have increased atmospheric CO2 levels from pre-industrial levels of ~280 ppm to current levels exceeding 410 ppm
• Positive feedback loops amplify warming, such as melting Arctic sea ice reducing albedo and increasing heat absorption
• Negative feedback loops mitigate warming, like increased plant growth absorbing more CO2
  • However, the net effect of feedbacks is positive, amplifying warming
• Climate sensitivity quantifies the temperature change in response to a doubling of atmospheric CO2 concentration
  • Estimated to be between 1.5°C and 4.5°C, with a likely range of 2°C to 3°C
• Tipping points are thresholds beyond which abrupt, irreversible changes occur, such as the collapse of the West Antarctic Ice Sheet or the shutdown of the Atlantic Meridional Overturning Circulation (AMOC)
• Radiative forcing measures the difference between incoming and outgoing energy in Earth's atmosphere, with positive values indicating warming

Atmospheric Composition Changes

• Burning fossil fuels releases CO2, the primary greenhouse gas driving climate change, into the atmosphere
• Deforestation reduces carbon sinks, as forests absorb CO2 through photosynthesis
• Agriculture contributes to rising methane levels through livestock farming (cattle) and rice cultivation
• Nitrous oxide (N2O) concentrations are increasing due to fertilizer use and industrial processes
• Chlorofluorocarbons (CFCs), while regulated by the Montreal Protocol, are potent greenhouse gases that also deplete the ozone layer
• Atmospheric water vapor content is increasing as a result of warming, further amplifying the greenhouse effect
  • Water vapor is a potent greenhouse gas, but its atmospheric concentration is controlled by temperature rather than direct emissions
• Aerosols, such as sulfates from volcanic eruptions or industrial pollution, can have a cooling effect by reflecting sunlight

Global Temperature Trends

• Global average surface temperatures have risen by approximately 1.1°C since pre-industrial times
• The past five years (2016-2020) have been the warmest on record since 1850
• The rate of warming has accelerated in recent decades, with the most rapid warming occurring in the Arctic region
• Warming is not uniform across the globe, with land areas warming faster than oceans and high latitudes warming more than the tropics
• The upper ocean (top 700 meters) has absorbed about 90% of the excess heat trapped by greenhouse gases
• Satellite measurements show a cooling trend in the upper atmosphere (stratosphere), consistent with the enhanced greenhouse effect
• Paleoclimate records (ice cores, tree rings) indicate that current warming is unprecedented in at least the past 2,000 years

Alterations in Precipitation Patterns

• Warmer air can hold more moisture (about 7% more per degree Celsius of warming), leading to increased evaporation and precipitation
• Wet regions (tropics, high latitudes) are generally becoming wetter, while dry regions (subtropics) are becoming drier, following the "rich get richer" principle
• The intensity of heavy precipitation events is increasing, as warmer air can release more moisture when it does rain
  • This can lead to more frequent and severe flooding
• Snowfall is declining in many regions as more precipitation falls as rain instead of snow
• Monsoon patterns are shifting, with some regions (South Asia) experiencing more intense monsoon rains and others (East Asia) seeing a weakening of monsoon circulation
• Droughts are becoming more frequent and severe in some regions (Mediterranean, Southwest US) due to reduced precipitation and increased evaporation
• Changes in precipitation patterns can have significant impacts on agriculture, water resources, and ecosystems

Extreme Weather Events

• Heatwaves are becoming more frequent, intense, and prolonged as global temperatures rise
  • The European heatwave of 2003 and the Russian heatwave of 2010 caused tens of thousands of excess deaths
• Hurricanes and tropical cyclones are likely becoming more intense (higher wind speeds and more precipitation) due to warmer ocean temperatures, although changes in frequency are less certain
• Wildfires are increasing in frequency and severity in many regions (California, Australia) due to a combination of heat, drought, and land management practices
• Heavy precipitation events can trigger landslides and mudslides, particularly in deforested or mountainous areas
• Storm surges are becoming more damaging as sea levels rise, increasing the risk of coastal flooding during hurricanes and typhoons
• Compound events, such as simultaneous heatwaves and droughts, can have amplified impacts on human health and ecosystems
• Attribution studies indicate that many recent extreme weather events were made more likely or more severe by human-induced climate change

Ocean-Atmosphere Interactions

• Oceans absorb over 90% of the excess heat trapped by greenhouse gases, leading to ocean warming and thermal expansion
• Warmer oceans provide more energy for hurricanes and typhoons, potentially increasing their intensity
• Rising ocean temperatures are causing coral bleaching and the loss of coral reefs, which support immense biodiversity
• Melting land ice (glaciers, ice sheets) and thermal expansion are causing sea level rise, which amplifies coastal flooding and erosion
  • Global mean sea level has risen by about 21-24 centimeters since 1880
• Ocean acidification is occurring as oceans absorb excess CO2, lowering the pH and making it harder for calcifying organisms (corals, shellfish) to build their skeletons
• Changes in ocean circulation, such as a weakening of the Atlantic Meridional Overturning Circulation (AMOC), can affect regional climates and weather patterns
• The El Niño-Southern Oscillation (ENSO) influences global weather patterns, and some studies suggest that climate change may make extreme El Niño and La Niña events more frequent

Regional Climate Shifts

• The Arctic is warming 2-3 times faster than the global average, leading to rapid sea ice loss and permafrost thaw
  • This has impacts on Arctic ecosystems, infrastructure, and Indigenous communities
• The Sahel region of Africa has experienced a greening trend in recent decades due to increased rainfall, likely related to changes in Atlantic Ocean temperatures
• The Mediterranean region is becoming hotter and drier, with increased risk of heatwaves, droughts, and wildfires
• The American Southwest is experiencing a "megadrought" that has been ongoing since 2000, exacerbated by climate change
• Monsoon patterns are shifting, with some regions (South Asia) seeing more intense rainfall and others (East Asia) experiencing a weakening of the monsoon circulation
• Tropical rainforests, such as the Amazon, are facing increased risks of drought, fire, and deforestation, which can further amplify climate change by releasing stored carbon
• Mountain glaciers are retreating worldwide, affecting water resources for downstream communities and ecosystems

Modeling and Predicting Future Weather Patterns

• Climate models, based on physical principles and observations, are the primary tools for projecting future climate change
  • They simulate the complex interactions between the atmosphere, oceans, land surface, and ice
• Models are constantly improving in resolution and complexity, incorporating more detailed processes and feedbacks
• Ensemble modeling involves running multiple simulations with slightly different initial conditions or model physics to capture the range of possible outcomes
• Downscaling techniques are used to translate coarse global model outputs into higher-resolution regional projections
  • This is important for assessing local impacts and informing adaptation strategies
• Scenarios, such as the Representative Concentration Pathways (RCPs), are used to explore different possible futures based on assumptions about greenhouse gas emissions and socioeconomic development
• Uncertainty in projections arises from natural variability, model differences, and future emissions pathways
  • However, the direction and general magnitude of warming are robust across models and scenarios
• Improving predictions of regional climate change and extreme weather events is an active area of research, crucial for informing risk assessments and resilience planning