🌱Intro to Environmental Systems Unit 7 – Climate Change: Causes and Consequences
Climate change is a long-term shift in global weather patterns, primarily caused by human activities like burning fossil fuels and deforestation. It's leading to rising temperatures, sea levels, and extreme weather events, posing significant challenges for ecosystems and human societies worldwide.
The science behind climate change involves the greenhouse effect, where gases like CO2 trap heat in the atmosphere. Human activities are increasing these gases, amplifying the effect. Natural factors like solar variability and volcanic eruptions also play a role, but human influence is now dominant.
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