🌦️Atmospheric Science Unit 16 – Climate Change: Ecosystem & Society Impacts

Key Climate Change Concepts

• Greenhouse effect traps heat in Earth's atmosphere due to gases like carbon dioxide (CO2) and methane (CH4)
• Global warming refers to the long-term trend of rising average global temperatures
• Climate change encompasses broader shifts in weather patterns, precipitation, and extreme events beyond just temperature increases
• Anthropogenic climate change is caused by human activities releasing greenhouse gases (burning fossil fuels, deforestation)
• Climate sensitivity measures how much global temperatures rise in response to a doubling of atmospheric CO2 concentrations
  • Equilibrium climate sensitivity (ECS) ranges from 1.5°C to 4.5°C based on current models
  • Transient climate response (TCR) is lower than ECS due to ocean heat uptake delaying warming
• Radiative forcing quantifies the change in Earth's energy balance due to factors like greenhouse gases, aerosols, and land use changes (measured in watts per square meter)
• Carbon cycle describes the exchange of carbon between the atmosphere, oceans, land, and biosphere
  • Human emissions have disturbed the natural carbon cycle, leading to rising atmospheric CO2 levels

Ecosystem Impacts

• Rising temperatures alter species' geographic ranges, causing shifts towards the poles and higher elevations
• Phenology, the timing of seasonal events like plant flowering and animal migration, is changing in response to earlier spring onset
• Ocean acidification occurs as the ocean absorbs excess atmospheric CO2, lowering pH and impacting marine life (coral reefs, shellfish)
• Coral bleaching results from prolonged exposure to high water temperatures, causing corals to expel their symbiotic algae
• Increased wildfire frequency and intensity due to hotter, drier conditions in many regions
• Invasive species can expand their ranges and outcompete native species as climate zones shift
• Biodiversity loss accelerates as species struggle to adapt to rapidly changing conditions and face habitat fragmentation
• Ecosystem services, like pollination, water filtration, and carbon sequestration, are disrupted by climate change impacts on biodiversity

Societal Impacts

• Sea level rise threatens coastal communities and infrastructure through increased flooding, erosion, and saltwater intrusion into aquifers
• Extreme weather events (hurricanes, heatwaves, droughts) become more frequent and intense, causing damage to property and loss of life
• Agricultural yields are affected by changing temperature and precipitation patterns, as well as increased pest and disease pressure
  • Some regions may see improved yields for certain crops, while others face significant declines
• Water scarcity intensifies in drought-prone areas, straining resources for drinking, irrigation, and hydropower
• Human health is impacted by heat stress, air pollution, and the spread of vector-borne diseases (malaria, dengue fever) into new areas
• Climate refugees are forced to migrate due to sea level rise, drought, or other climate-related factors, potentially leading to social and political instability
• Economic costs of climate change include direct damages from extreme events, adaptation measures, and lost productivity
  • Developing countries are often the most vulnerable and least able to adapt

Climate Change Drivers

• Burning of fossil fuels (coal, oil, natural gas) for energy releases CO2 into the atmosphere
• Deforestation removes carbon sinks and releases stored carbon, contributing to atmospheric CO2 levels
  • Agriculture, particularly livestock and rice cultivation, produces methane emissions
• Industrial processes, such as cement production and refrigerant use, release greenhouse gases
• Urbanization creates heat islands and alters local climate through changes in land use and energy consumption
• Population growth and rising living standards drive increased energy demand and resource consumption
• Positive feedback loops amplify climate change, such as melting Arctic sea ice reducing Earth's albedo and absorbing more solar radiation
• Natural climate variability (El Niño, volcanic eruptions) can temporarily mask or exacerbate human-caused warming trends

Feedback Loops and Tipping Points

• Positive feedback loops amplify climate change by reinforcing warming or other effects
  • Examples include melting permafrost releasing methane, and declining Arctic sea ice reducing Earth's albedo
• Negative feedback loops counteract climate change, such as increased plant growth absorbing more CO2
• Tipping points are thresholds beyond which abrupt or irreversible changes occur in the climate system
  • Examples include the collapse of the West Antarctic Ice Sheet or the shutdown of the Atlantic Meridional Overturning Circulation (AMOC)
• Tipping elements are components of the Earth system susceptible to tipping points, such as the Amazon rainforest or the Greenland ice sheet
• Cascading effects can occur when one tipping point triggers others, leading to a domino-like sequence of changes
• Hysteresis refers to the difficulty in reversing changes once a tipping point has been crossed, even if the original forcing is removed
• Identifying and anticipating tipping points is crucial for assessing climate risks and guiding mitigation and adaptation efforts

Mitigation Strategies

• Reducing greenhouse gas emissions is the primary goal of mitigation, aiming to limit future warming
• Transitioning to renewable energy sources (solar, wind, hydro) reduces reliance on fossil fuels
• Improving energy efficiency in buildings, transportation, and industry helps reduce energy demand and emissions
• Carbon pricing, through taxes or cap-and-trade systems, creates economic incentives to reduce emissions
• Afforestation and reforestation increase carbon sequestration by creating new forests or restoring degraded ones
• Sustainable land management practices, like reduced tillage and cover cropping, can increase soil carbon storage
• Lifestyle changes, such as reducing meat consumption and using public transportation, can lower individual carbon footprints
• International cooperation and agreements, like the Paris Agreement, set global targets and coordinate mitigation efforts

Adaptation Measures

• Adaptation involves adjusting to the impacts of climate change that are already occurring or expected to occur
• Coastal protection measures, like seawalls and beach nourishment, help protect against sea level rise and storm surges
• Drought-resistant crops and improved irrigation techniques can maintain agricultural productivity in water-stressed regions
• Urban planning and green infrastructure (green roofs, permeable pavements) mitigate heat island effects and manage stormwater
• Early warning systems for extreme weather events allow for better preparation and emergency response
• Resilient infrastructure, designed to withstand more frequent and intense weather events, reduces damage and disruption
• Ecosystem-based adaptation, like mangrove restoration, provides natural buffers against climate impacts while supporting biodiversity
• Public health measures, such as heat wave response plans and disease surveillance, help protect vulnerable populations
• Adaptation finance and technology transfer support developing countries in building resilience to climate change

Future Projections and Uncertainties

• Climate models project a range of future warming scenarios based on different greenhouse gas emission pathways (Representative Concentration Pathways, or RCPs)
  • RCP2.6 represents a stringent mitigation scenario, while RCP8.5 represents a high-emission "business as usual" scenario
• Global mean surface temperature is projected to rise by 1.5°C to 4°C by 2100, depending on the emission scenario
• Sea level rise projections range from 0.3 to 1.0 meters by 2100, with the possibility of multi-meter rise over longer timescales if ice sheets destabilize
• Precipitation patterns are expected to change, with wet regions generally becoming wetter and dry regions becoming drier (the "rich get richer" effect)
• Extreme weather events, like heatwaves, droughts, and heavy rainfall, are projected to become more frequent and intense
• Uncertainties in climate projections arise from factors like natural climate variability, incomplete understanding of climate processes, and future human behavior and technology development
• Tipping points and feedback loops add to the uncertainty, as they can lead to abrupt and irreversible changes not captured by gradual projections
• Decision-making under uncertainty requires considering a range of possible futures and prioritizing robust adaptation and mitigation strategies