🌱Intro to Environmental Systems Unit 7 – Climate Change: Causes and Consequences

What's Climate Change Anyway?

• Climate change refers to long-term shifts in global or regional climate patterns
• Includes changes in temperature, precipitation, wind patterns, and other measures of climate that occur over several decades or longer
• Caused by a variety of factors, both natural and anthropogenic (human-induced)
• Currently, the term is most often used to describe the rapid warming and related changes observed in Earth's climate system since the mid-20th century
• Primarily attributed to increasing atmospheric concentrations of greenhouse gases, particularly carbon dioxide (CO2), due to human activities
• Has far-reaching impacts on natural systems, human societies, and the global economy
• Poses significant challenges for ecosystems, agriculture, water resources, public health, and infrastructure

The Science Behind It

• Earth's climate system is driven by energy from the sun and the greenhouse effect
• Greenhouse gases (GHGs) in the atmosphere, such as CO2, methane (CH4), and water vapor, absorb and re-emit infrared radiation, trapping heat
• Increasing GHG concentrations enhance the greenhouse effect, leading to global warming
• Climate sensitivity describes how much the Earth's surface temperature rises 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 4°C
• Positive feedback loops can amplify climate change
  • Examples include melting Arctic sea ice (reduced albedo) and thawing permafrost (releasing stored GHGs)
• Negative feedback loops can dampen climate change, such as increased plant growth absorbing more CO2
• Climate models, based on physical principles and observations, simulate the complex interactions within the Earth system to project future climate changes

Human Activities Driving Climate Change

• Burning fossil fuels (coal, oil, and natural gas) for energy releases CO2 into the atmosphere
• Deforestation and land-use changes reduce carbon sinks and contribute to GHG emissions
• Agriculture, particularly livestock production, emits methane and nitrous oxide (N2O)
• Industrial processes, such as cement production and chemical manufacturing, release GHGs
• Transportation, including cars, trucks, ships, and planes, relies heavily on fossil fuels
• Urbanization and the built environment contribute to the urban heat island effect and energy consumption
• Waste management, including landfills and wastewater treatment, produces methane emissions
• Population growth and increasing consumption drive energy demand and resource use

Natural Climate Drivers

• Variations in Earth's orbit (Milankovitch cycles) cause long-term changes in the amount and distribution of solar energy reaching the planet
• Solar variability, such as the 11-year sunspot cycle, affects the amount of energy received from the sun
• Volcanic eruptions can cool the Earth by injecting sulfate aerosols into the stratosphere, reflecting sunlight
  • Example: The 1991 eruption of Mount Pinatubo in the Philippines cooled global temperatures by ~0.5°C for several years
• Internal climate variability, such as the El Niño-Southern Oscillation (ENSO), can influence regional temperatures and precipitation patterns
• Plate tectonics and continental drift affect the distribution of land and ocean, influencing global climate patterns over millions of years
• Changes in ocean circulation, such as the Atlantic Meridional Overturning Circulation (AMOC), can affect heat transport and regional climates
• Feedbacks within the Earth system, such as the ice-albedo feedback and the water vapor feedback, can amplify or dampen climate changes

Observed Changes in the Earth System

• Global average surface temperature has increased by ~1.1°C since pre-industrial times (1850-1900)
• Warming is not uniform, with greater temperature increases observed in the Arctic and over land
• Sea levels have risen by ~21-24 cm since 1880, due to thermal expansion of water and melting of glaciers and ice sheets
• Arctic sea ice extent and thickness have declined significantly, with summer minimum extent decreasing by ~13% per decade since 1979
• Glaciers and ice sheets, such as those in Greenland and Antarctica, are losing mass at an accelerating rate
• Ocean acidification is occurring as the oceans absorb excess CO2, reducing the pH of seawater
• Changes in precipitation patterns, with some regions experiencing more frequent and intense droughts or floods
• Shifts in the timing and distribution of seasonal events, such as spring leaf unfolding and animal migrations

Future Projections and Scenarios

• Climate models project continued warming under all emission scenarios, with the magnitude depending on future GHG emissions and climate sensitivity
• The Paris Agreement aims to limit global warming to well below 2°C, and preferably to 1.5°C, compared to pre-industrial levels
  • Achieving these targets requires substantial and sustained reductions in GHG emissions
• Representative Concentration Pathways (RCPs) describe different 21st century pathways of GHG emissions and atmospheric concentrations
  • RCP2.6 assumes aggressive emission reductions, RCP4.5 and RCP6.0 are intermediate scenarios, and RCP8.5 represents a high-emission "business-as-usual" scenario
• Sea levels are projected to rise by 0.43-0.84 m by 2100 relative to 1986-2005, depending on the emission scenario
• Extreme weather events, such as heatwaves, droughts, and heavy precipitation, are expected to become more frequent and intense in many regions
• Changes in the cryosphere, including further reductions in Arctic sea ice, permafrost thaw, and glacier mass loss, are projected to continue
• Ocean acidification and deoxygenation are expected to intensify, with negative impacts on marine ecosystems

Environmental Impacts

• Ecosystems and biodiversity are threatened by changing climatic conditions, habitat loss, and ocean acidification
• Species' ranges are shifting poleward and to higher elevations, with some unable to keep pace with the rate of change
• Increased risk of extinction for many species, particularly those with limited ability to adapt or migrate
• Coral reefs are experiencing more frequent and severe bleaching events due to warming oceans and ocean acidification
• Changes in the timing of seasonal events (phenology) can disrupt species interactions and ecosystem functioning
• Wildfires are becoming more frequent and intense in some regions, such as the western United States and Australia
• Coastal ecosystems, such as mangroves and salt marshes, are threatened by sea-level rise and storm surges
• Invasive species may expand their ranges and compete with native species as climatic barriers shift

Socioeconomic Consequences

• Agriculture and food security are affected by changes in temperature, precipitation, and extreme events
  • Crop yields may increase in some regions but decrease in others, with a net negative impact on global food production
• Water resources are impacted by changes in precipitation patterns, glacier melt, and sea-level rise
  • Increased risk of water scarcity, particularly in regions dependent on snowmelt or glacial runoff
• Human health is threatened by extreme heat, air pollution, water-borne diseases, and the spread of vector-borne diseases (malaria)
• Infrastructure, including buildings, roads, and energy systems, is vulnerable to extreme weather events and sea-level rise
• Economic impacts include costs of adaptation and damage to property and infrastructure
  • Estimated global annual economic losses from climate change could reach 1-5% of GDP by 2100
• Climate change can exacerbate existing social inequalities and disproportionately affect vulnerable populations (low-income communities, indigenous peoples)
• Climate-related migration and displacement may increase as some regions become uninhabitable due to sea-level rise, drought, or other factors

Mitigation Strategies

• Reducing GHG emissions is crucial for limiting the magnitude of future climate change
• Transitioning to renewable energy sources, such as solar, wind, and hydropower, can reduce reliance on fossil fuels
• Improving energy efficiency in buildings, transportation, and industry can reduce energy demand and associated emissions
• Implementing carbon pricing mechanisms, such as carbon taxes or cap-and-trade systems, can create incentives for emission reductions
• Promoting sustainable land management practices, such as reforestation and soil carbon sequestration, can enhance natural carbon sinks
• Developing and deploying low-carbon technologies, such as electric vehicles and carbon capture and storage (CCS), can help decarbonize various sectors
• Encouraging sustainable consumption and production patterns, including reducing waste and promoting circular economy principles
• Fostering international cooperation and support for developing countries to enable a global transition to a low-carbon future

Adaptation Measures

• Adaptation involves adjusting to the impacts of climate change that are already occurring or are expected to occur in the future
• Developing early warning systems and emergency response plans can help communities prepare for and respond to extreme weather events
• Improving infrastructure resilience, such as building sea walls or upgrading drainage systems, can reduce vulnerability to sea-level rise and flooding
• Implementing water management strategies, such as water conservation, efficiency measures, and diversifying water sources, can help address water scarcity
• Adapting agricultural practices, such as using drought-resistant crops or implementing precision irrigation, can help farmers cope with changing conditions
• Protecting and restoring ecosystems, such as wetlands and forests, can provide natural buffers against climate impacts and support biodiversity
• Promoting sustainable urban planning and design, such as green infrastructure and urban greening, can reduce the urban heat island effect and improve livability
• Strengthening public health systems and disease surveillance can help prevent and respond to climate-related health risks

Climate Policy and Agreements

• The United Nations Framework Convention on Climate Change (UNFCCC) provides a global platform for addressing climate change
  • Adopted in 1992, with near-universal membership (197 parties)
• The Kyoto Protocol, adopted in 1997, set legally binding emission reduction targets for developed countries
  • First commitment period (2008-2012) achieved limited success, with some countries not meeting their targets
• The Paris Agreement, adopted in 2015, aims to strengthen the global response to climate change
  • Commits parties to holding the increase in global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the increase to 1.5°C
  • Requires all parties to submit Nationally Determined Contributions (NDCs) outlining their emission reduction targets and actions
• National and sub-national policies, such as renewable energy targets, energy efficiency standards, and carbon pricing, are being implemented to support climate goals
• Non-state actors, including businesses, cities, and civil society organizations, are playing an increasingly important role in climate action

Challenges and Controversies

• The global nature of climate change requires collective action, but differing national interests and priorities can hinder progress
• Equity and fairness concerns arise, as developed countries have historically contributed the most to GHG emissions, while developing countries are often the most vulnerable to impacts
• Climate change denial and misinformation campaigns, often funded by fossil fuel interests, can undermine public understanding and support for action
• Technological and economic challenges, such as the intermittency of renewable energy sources and the costs of transitioning to a low-carbon economy, need to be addressed
• Potential unintended consequences of climate policies, such as impacts on energy access and affordability for low-income households, require careful consideration
• Geoengineering proposals, such as solar radiation management or large-scale carbon dioxide removal, raise ethical and governance concerns
• Balancing climate action with other sustainable development goals, such as poverty eradication and energy access, can present trade-offs and synergies that need to be navigated