8.4 Climate change

Climate change is primarily driven by human activities that increase greenhouse gas concentrations in the atmosphere. The burning of fossil fuels, deforestation, and industrial processes are major contributors. These activities trap heat, causing global temperatures to rise.

Evidence for climate change is overwhelming, with rising temperatures, melting ice, and extreme weather events. The impacts are far-reaching, affecting human health, food security, water resources, and ecosystems. Mitigation and adaptation strategies are crucial to address this global challenge.

Causes of climate change

• Climate change is primarily driven by human activities that increase greenhouse gas concentrations in the atmosphere, leading to a warming planet
• The burning of fossil fuels (coal, oil, natural gas) for energy releases carbon dioxide (CO2), a potent greenhouse gas that traps heat
• Other significant greenhouse gases include methane (CH4) from agriculture and landfills, nitrous oxide (N2O) from fertilizers, and fluorinated gases from industrial processes

Greenhouse gas emissions

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• Greenhouse gases absorb and emit infrared radiation, trapping heat in the Earth's atmosphere and causing the greenhouse effect
• CO2 is the most significant greenhouse gas, with atmospheric concentrations increasing from pre-industrial levels of 280 ppm to over 410 ppm today
• Methane has a shorter atmospheric lifetime than CO2 but a much higher global warming potential (28-36 times that of CO2 over 100 years)
• Nitrous oxide and fluorinated gases (HFCs, PFCs, SF6) are potent greenhouse gases with long atmospheric lifetimes
• Emissions from electricity generation, transportation, industry, and buildings are the main sources of greenhouse gases

Deforestation and land use

• Deforestation, the clearing of forests for agriculture, logging, or development, reduces the Earth's natural carbon sinks that absorb CO2
• Land use changes, such as the conversion of grasslands to croplands or the draining of wetlands, can release stored carbon and reduce the land's capacity to sequester CO2
• Agriculture contributes to greenhouse gas emissions through methane from livestock, nitrous oxide from fertilizers, and CO2 from soil disturbance and machinery
• Urbanization and the expansion of built environments can increase the urban heat island effect and reduce the land's ability to regulate temperature and store carbon

Feedback loops and tipping points

• Climate feedback loops amplify or diminish the effects of climate change, leading to accelerated warming or cooling
• Positive feedback loops, such as the melting of Arctic sea ice that exposes darker ocean waters and increases heat absorption, can accelerate warming
• Negative feedback loops, such as increased plant growth that absorbs more CO2, can mitigate warming but are often overwhelmed by positive feedbacks
• Tipping points are thresholds beyond which the climate system undergoes irreversible changes, such as the collapse of the West Antarctic Ice Sheet or the dieback of the Amazon rainforest
• Crossing tipping points can lead to abrupt and catastrophic changes in the Earth's climate, with far-reaching consequences for ecosystems and human societies

Evidence for climate change

• The scientific evidence for climate change is overwhelming, with multiple lines of evidence from observations, experiments, and models
• The Earth's climate has warmed by approximately 1.1°C since the pre-industrial era, with the last decade being the warmest on record
• The impacts of climate change are already being observed across the globe, from rising sea levels to more frequent and intense extreme weather events

Rising global temperatures

• Global average surface temperatures have risen by 0.8°C to 1.2°C since the late 19th century, with the rate of warming accelerating in recent decades
• The 20 warmest years on record have all occurred since 1998, with 2016 and 2020 being the warmest years ever recorded
• Warming is not uniform across the planet, with the Arctic experiencing warming at twice the global average rate (Arctic amplification)
• Rising temperatures are causing more frequent and intense heatwaves, droughts, and wildfires, with significant impacts on human health and ecosystems

Melting ice and rising sea levels

• Rising temperatures are causing the melting of glaciers, ice sheets, and sea ice, leading to rising global sea levels
• Arctic sea ice extent has declined by approximately 13% per decade since 1979, with the summer minimum extent reaching record lows in recent years
• The Greenland and Antarctic ice sheets are losing mass at an accelerating rate, contributing to sea level rise and potentially triggering irreversible ice sheet collapse
• Global average sea level has risen by about 21-24 cm since 1880, with the rate of rise accelerating to about 3.6 mm per year
• Rising sea levels are increasing coastal flooding, erosion, and saltwater intrusion, threatening low-lying islands, coastal communities, and infrastructure

Extreme weather events

• Climate change is increasing the frequency, intensity, and duration of extreme weather events, such as heatwaves, droughts, floods, and hurricanes
• Warmer temperatures are leading to more frequent and severe heatwaves, with record-breaking temperatures observed in many parts of the world
• Changing precipitation patterns are causing more intense and prolonged droughts in some regions (Australia, California) and more frequent and severe flooding in others (South Asia, Europe)
• Warmer ocean temperatures are fueling more powerful hurricanes and typhoons, with increased wind speeds, rainfall, and storm surges
• Extreme weather events are causing significant economic losses, infrastructure damage, and loss of life, disproportionately affecting vulnerable populations

Shifting ecosystems and species

• Climate change is altering the distribution, composition, and functioning of ecosystems, with significant impacts on biodiversity and ecosystem services
• Warmer temperatures are causing species to shift their ranges poleward and to higher elevations, leading to changes in community composition and interactions
• Phenological mismatches, such as the earlier arrival of spring and the asynchrony between plants and pollinators, are disrupting ecological relationships and food webs
• Ocean acidification, caused by the absorption of CO2 by the oceans, is impacting marine ecosystems, particularly coral reefs and shellfish populations
• Climate change is increasing the risk of species extinctions, particularly for species with narrow ranges, limited dispersal abilities, or specialized habitat requirements

Impacts of climate change

• The impacts of climate change are far-reaching and diverse, affecting human societies, economies, and the natural world
• The severity and distribution of impacts depend on the magnitude and rate of warming, as well as the vulnerability and adaptive capacity of affected systems and populations
• Climate change is a threat multiplier, exacerbating existing risks and creating new challenges for sustainable development and human well-being

Human health and well-being

• Climate change poses significant risks to human health, both directly through exposure to extreme weather events and indirectly through changes in air quality, water availability, and the spread of infectious diseases
• Heatwaves can cause heat stress, heat exhaustion, and heatstroke, particularly among vulnerable populations such as the elderly, children, and outdoor workers
• Air pollution, exacerbated by climate change, can increase the risk of respiratory and cardiovascular diseases, as well as premature mortality
• Changes in precipitation and water availability can impact water quality and sanitation, increasing the risk of waterborne diseases (cholera, dysentery)
• Climate change can expand the range and seasonality of vector-borne diseases, such as malaria, dengue fever, and Zika virus, by altering the distribution and abundance of disease vectors (mosquitoes, ticks)

Food security and agriculture

• Climate change is affecting food security and agricultural production, with significant implications for rural livelihoods, nutrition, and global food prices
• Rising temperatures, changing precipitation patterns, and increased frequency of extreme weather events can reduce crop yields, lower livestock productivity, and damage agricultural infrastructure
• Droughts can lead to crop failures, reduced water availability for irrigation, and increased risk of wildfires, threatening food production and rural incomes
• Floods can destroy crops, erode topsoil, and contaminate water sources, reducing agricultural productivity and food safety
• Climate change can alter the distribution and abundance of agricultural pests and diseases, as well as the effectiveness of pest control measures
• Ocean acidification and warming can impact marine fisheries, reducing the availability and quality of seafood and threatening the livelihoods of coastal communities

Water resources and droughts

• Climate change is altering the global water cycle, affecting the availability, quality, and distribution of water resources
• Changing precipitation patterns, with more frequent and intense droughts in some regions and more heavy rainfall events in others, can impact water supply and demand
• Droughts can reduce surface water and groundwater availability, leading to water scarcity, reduced crop yields, and increased risk of wildfires
• Reduced snowpack and earlier spring melting can alter the timing and amount of water available for irrigation, hydropower generation, and ecosystem services
• Rising sea levels can lead to saltwater intrusion into coastal aquifers, reducing the quality and availability of freshwater resources
• Competition for limited water resources can increase the risk of water conflicts and exacerbate existing social and economic inequalities

Economic costs and instability

• Climate change is imposing significant economic costs on societies, through direct damages from extreme weather events, reduced productivity, and the need for adaptation and mitigation measures
• Extreme weather events, such as hurricanes, floods, and wildfires, can cause billions of dollars in damages to infrastructure, property, and agricultural production
• Rising temperatures can reduce labor productivity, particularly in sectors such as agriculture, construction, and manufacturing, leading to economic losses
• The need for adaptation measures, such as building sea walls, upgrading infrastructure, and developing drought-resistant crops, can impose significant costs on governments and businesses
• The transition to a low-carbon economy, while necessary to mitigate climate change, can also entail economic costs and disruptive changes in employment and energy systems
• Climate change can exacerbate existing economic inequalities, both within and between countries, as the poorest and most vulnerable populations are often the most exposed and least able to adapt to climate impacts

Climate change mitigation

• Climate change mitigation refers to actions and strategies aimed at reducing greenhouse gas emissions and enhancing carbon sinks to limit the magnitude and rate of future climate change
• Mitigation efforts are crucial to avoid the most severe impacts of climate change and to achieve the goals of the Paris Agreement, which aims to keep global temperature rise well below 2°C above pre-industrial levels
• Mitigation measures span a range of sectors, including energy, transportation, industry, agriculture, and land use, and involve technological, behavioral, and policy changes

Renewable energy transition

• Transitioning from fossil fuels to renewable energy sources, such as solar, wind, hydro, and geothermal power, is a key strategy for reducing greenhouse gas emissions from the energy sector
• Renewable energy technologies have become increasingly cost-competitive with fossil fuels, with falling prices and improved efficiency driving rapid growth in deployment
• The expansion of renewable energy can also provide co-benefits, such as improved energy security, reduced air pollution, and job creation in the clean energy sector
• Policies such as renewable energy targets, feed-in tariffs, and tax incentives can accelerate the deployment of renewable energy and create a supportive environment for investment
• The integration of renewable energy into electricity grids requires investments in energy storage, smart grid technologies, and demand-side management to ensure system stability and reliability

Carbon pricing and markets

• Carbon pricing, through carbon taxes or emissions trading systems (ETS), is a market-based approach to reducing greenhouse gas emissions by putting a price on carbon
• Carbon taxes impose a fixed price on each unit of carbon dioxide emitted, providing a clear economic incentive for businesses and consumers to reduce their emissions
• Emissions trading systems, also known as cap-and-trade, set a cap on total emissions and allow companies to trade emission allowances, creating a market for carbon and encouraging cost-effective emission reductions
• Carbon pricing can generate revenue that can be used to support low-carbon investments, compensate affected communities, or reduce other taxes (revenue neutrality)
• The effectiveness of carbon pricing depends on the level of the price, the coverage of emission sources, and the use of revenue, as well as the political acceptability and distributional impacts of the policy

Energy efficiency and conservation

• Improving energy efficiency, through technological improvements and behavioral changes, can significantly reduce energy consumption and greenhouse gas emissions
• Energy efficiency measures, such as building insulation, efficient appliances, and LED lighting, can reduce energy demand and costs for households and businesses
• Energy conservation, through changes in behavior and lifestyle (e.g., reducing energy waste, using public transportation), can also contribute to emission reductions
• Policies such as energy efficiency standards, building codes, and labeling schemes can drive improvements in energy efficiency and create markets for efficient products and services
• Energy efficiency and conservation measures often have short payback periods and can provide multiple benefits, such as reduced energy bills, improved energy security, and increased comfort and productivity

Sustainable transportation solutions

• The transportation sector is a significant contributor to greenhouse gas emissions, particularly through the burning of fossil fuels in vehicles
• Sustainable transportation solutions aim to reduce emissions by shifting to low-carbon modes of transport, improving vehicle efficiency, and reducing travel demand
• The electrification of transportation, through the adoption of electric vehicles (EVs) powered by renewable energy, can significantly reduce emissions from passenger cars and light trucks
• Public transportation systems, such as buses and trains, can provide low-carbon mobility options and reduce traffic congestion and air pollution in cities
• Active transportation, such as walking and cycling, can reduce emissions while providing health benefits and improving urban livability
• Sustainable urban planning, through compact development, mixed land use, and transit-oriented development, can reduce travel demand and enable low-carbon transportation options

Climate change adaptation

• Climate change adaptation refers to actions and strategies aimed at reducing the vulnerability and increasing the resilience of human and natural systems to the impacts of climate change
• Adaptation measures are necessary to cope with the unavoidable impacts of climate change that are already occurring and to prepare for future risks and opportunities
• Adaptation efforts span a range of sectors, including agriculture, water resources, coastal management, public health, and infrastructure, and involve technological, institutional, and behavioral changes

Resilient infrastructure and cities

• Building resilient infrastructure, such as roads, bridges, and buildings, can reduce the vulnerability of communities to climate impacts and ensure the continuity of essential services during extreme weather events
• Resilient infrastructure design incorporates measures such as elevated structures, permeable surfaces, and green infrastructure (e.g., green roofs, rain gardens) to manage flooding, heat stress, and other climate risks
• Resilient cities integrate climate adaptation into urban planning, land use, and building codes, and develop strategies for managing risks such as sea-level rise, urban heat islands, and water scarcity
• Nature-based solutions, such as urban green spaces, wetlands, and coastal ecosystems, can provide multiple benefits for climate adaptation, such as flood control, heat mitigation, and biodiversity conservation
• Community-based adaptation, through participatory planning and local knowledge, can empower communities to identify and address their specific vulnerabilities and adaptation needs

Ecosystem-based adaptation strategies

• Ecosystem-based adaptation (EbA) involves the conservation, sustainable management, and restoration of ecosystems to provide services that help people adapt to climate change
• EbA measures, such as mangrove restoration, wetland protection, and agroforestry, can provide multiple benefits for adaptation, such as coastal protection, water regulation, and food security
• Healthy ecosystems can buffer communities from climate impacts, such as floods, droughts, and heatwaves, and provide essential services such as water purification, pollination, and carbon sequestration
• EbA can be cost-effective compared to engineered solutions and can provide co-benefits for biodiversity conservation, poverty alleviation, and sustainable development
• The effectiveness of EbA depends on the context-specific vulnerabilities and capacities of communities and ecosystems, as well as the integration of EbA into broader adaptation and development strategies

Disaster risk reduction measures

• Disaster risk reduction (DRR) measures aim to reduce the damage caused by natural hazards, such as floods, droughts, and cyclones, and to build the resilience of communities to withstand and recover from disasters
• DRR measures include early warning systems, emergency preparedness and response plans, risk assessment and mapping, and land-use planning to avoid development in high-risk areas
• Nature-based solutions, such as wetland restoration and reforestation, can reduce disaster risks by regulating water flows, stabilizing slopes, and absorbing storm surges
• Structural measures, such as flood barriers, sea walls, and earthquake-resistant buildings, can protect communities and infrastructure from disaster impacts
• Community-based DRR, through participatory risk assessment, capacity building, and local action, can empower communities to reduce their own risks and vulnerabilities

Climate-resilient agriculture practices

• Climate-resilient agriculture practices aim to increase the productivity, sustainability, and resilience of agricultural systems to climate change impacts, such as droughts, floods, and temperature extremes
• Climate-smart agriculture (CSA) practices, such as conservation tillage, crop diversification, and integrated pest management, can improve soil health, water efficiency, and crop yields while reducing greenhouse gas emissions
• Agroecological practices, such as agroforestry, intercropping, and organic farming, can enhance the resilience of agricultural systems by promoting biodiversity, soil fertility, and water conservation
• Improved water management practices, such as drip irrigation, rainwater harvesting, and water-saving technologies, can increase water use efficiency and reduce the vulnerability of crops to water stress
• Climate information services, such as seasonal forecasts and early warning systems, can help farmers make informed decisions about planting, harvesting, and managing risks
• Capacity building and extension services can support farmers in adopting climate-resilient practices and accessing markets and financial services

Climate justice and equity

• Climate justice and equity refer to the fair and equitable distribution of the benefits and burdens of climate change and climate action, both within and between countries and generations
• Climate change is a deeply moral and ethical issue, as it disproportionately affects the poorest and most vulnerable populations who have contributed the least to the problem
• Climate justice seeks to address the historical responsibility of developed countries for greenhouse gas emissions and to ensure that the costs and benefits of climate action are shared fairly among all countries and communities

Disproportionate impacts on vulnerable populations

• Climate change impacts, such as sea-level rise, droughts, and extreme weather events, disproportionately affect vulnerable populations, such as low-income communities, women, children, and indigenous peoples
• These populations often have limited resources and capacities to adapt to climate impacts and are more dependent on climate-sensitive sectors such as agriculture and fisheries for their livelihoods