Climate change represents one of the most significant challenges facing humanity in the 21st century. This report provides a comprehensive assessment of the current scientific understanding of climate change, its projected impacts on Earth's environmental systems and human societies over the next century, and the strategies available for adaptation and mitigation.
The scientific evidence is unequivocal that human activities, primarily through greenhouse gas emissions, have warmed the planet by approximately 1.1°C since pre-industrial times. Without immediate, rapid, and large-scale reductions in greenhouse gas emissions, global warming is projected to reach between 1.5°C and 4.4°C by 2100, depending on emission scenarios.
The environmental impacts of this warming are already observable and will intensify throughout the century, affecting biodiversity, ocean systems, freshwater resources, and agricultural productivity. These environmental changes will cascade into profound societal and economic impacts, including threats to human health, displacement of populations, economic losses, and potential conflicts over increasingly scarce resources.
However, this report also highlights that humanity has the knowledge, technology, and capacity to substantially reduce emissions and adapt to unavoidable impacts. A portfolio of mitigation strategies—including renewable energy transition, carbon capture technologies, and sustainable land management—combined with targeted adaptation measures can limit the worst impacts of climate change. The choices made in this decade will be crucial in determining the climate trajectory for the rest of this century and beyond.
The report concludes that addressing climate change requires urgent, ambitious, and coordinated action across all sectors of society. While the challenges are substantial, there are many feasible and effective options available that can create a more sustainable and resilient future for both human societies and Earth's ecosystems.
Climate change is the defining challenge of our time, with far-reaching implications for current and future generations. The Earth's climate has always varied naturally over long time periods, but the rate and magnitude of current changes are unprecedented in human history. Scientific evidence has established beyond reasonable doubt that human activities—primarily the burning of fossil fuels and land-use changes—are the dominant cause of the observed warming since the mid-20th century.
This report aims to provide a comprehensive assessment of how climate change is projected to impact Earth's systems and human societies over the next century. It draws on the latest scientific research, including the authoritative assessments of the Intergovernmental Panel on Climate Change (IPCC), to present a detailed picture of potential futures under different emission scenarios.
The report is structured to first establish the scientific basis of climate change projections, then examine the cascading impacts on environmental systems, followed by an analysis of how these environmental changes will affect human societies. Finally, it explores the range of strategies available to both reduce emissions (mitigation) and adjust to unavoidable changes (adaptation).
Throughout this report, we emphasize that while climate change presents enormous challenges, it also offers opportunities for transformative change toward more sustainable and equitable societies. The severity of future impacts depends significantly on the choices made today and in the coming decades. By understanding the potential consequences of different pathways, decision-makers at all levels—from international bodies to national governments, businesses, communities, and individuals—can make informed choices that shape a more resilient future.
The Intergovernmental Panel on Climate Change (IPCC) has provided the most comprehensive and authoritative assessment of climate change science. According to the IPCC's sixth assessment report (AR6), human influence on the climate system is now an established fact. The report states in the clearest and most evidenced detail yet how humans are responsible for the 1.1°C of temperature rise seen since the start of the industrial era.
The scientific consensus is unequivocal that this warming is caused by greenhouse gas emissions from human activities, primarily the burning of fossil fuels and land-use changes. The current rate of warming is unprecedented in human history, with each of the last four decades being successively warmer than any decade that preceded it since 1850.
The IPCC AR6 synthesis report provides clear projections for future warming based on different emission scenarios:
Crucially, the report notes that policies in place by the end of 2021 (the cut-off date for evidence cited in the assessment) would likely see temperatures exceed 1.5°C this century and reach around 3.2°C by 2100. This projection highlights the significant gap between current policies and the actions needed to meet the Paris Agreement goals.
The IPCC has narrowed the range of uncertainty in these projections compared to previous assessments, due to improved understanding of climate sensitivity and better observational data of recorded warming to date.
Sea level rise is one of the most significant and long-lasting consequences of climate change. According to the IPCC:
Climate models project robust differences in regional climate characteristics between present-day and global warming of 1.5°C, and between 1.5°C and 2°C. These differences include:
Specific projections include:
The IPCC reports identify several potential tipping points in the climate system that could lead to abrupt and irreversible changes:
Climate change has already altered marine, terrestrial, and freshwater ecosystems all around the world with very high confidence. According to the IPCC's Sixth Assessment Report (AR6), climate change has caused local species losses, increases in disease, and mass mortality events of plants and animals.
Local population extinctions caused by climate change have been widespread among plants and animals, detected in 47% of 976 species examined and associated with increases in the hottest yearly temperatures. The risk of species extinction increases with warming in all climate change projections for native species studied in biodiversity hotspots, being about 10 times greater for endemic species from 1.5°C to 3°C above pre-industrial levels.
For endemic species, extinction risk due to climate change is more common than for other native species:
At warming levels beyond 2°C by 2100, risks of extirpation, extinction, and ecosystem collapse escalate rapidly. The observed rate of range shifts since the 1950s is estimated to be 51.5 ± 33.3 km per decade and 29.0 ± 15.5 km per decade for organisms in the epipelagic and seafloor ecosystems, respectively.
Climate change has already altered terrestrial, freshwater and ocean ecosystems at global scale, with multiple impacts evident at regional and local scales where there is sufficient literature to make an assessment. Impacts are evident on ecosystem structure, species geographic ranges, and timing of seasonal life cycles (phenology).
Approximately 4% of the global terrestrial land area is projected to undergo a transformation of ecosystems from one type to another at 1°C of global warming, compared with 13% at 2°C. This indicates that the area at risk is projected to be approximately 50% lower at 1.5°C compared to 2°C.
Several ecosystems are particularly vulnerable to climate change:
The ocean has warmed unabated since 2005, continuing the clear multi-decadal ocean warming trends documented in the IPCC Fifth Assessment Report. The warming trend is further confirmed by the improved ocean temperature measurements over the last decade.
The ocean is continuing to acidify in response to ongoing ocean carbon uptake. The open ocean surface water pH is observed to be declining by a very likely range of 0.017-0.027 pH units per decade since the late 1980s across individual time series observations longer than 15 years.
The anthropogenic pH signal is very likely to have emerged for three-quarters of the near-surface open ocean prior to 1950, and it is very likely that over 95% of the near surface open ocean has already been affected. These changes in pH have reduced the stability of mineral forms of calcium carbonate due to a lowering of carbonate ion concentrations, most notably in the upwelling and high-latitude regions of the ocean.
There is a growing consensus that the open ocean is losing oxygen overall with a very likely loss of 0.5-3.3% between 1970-2010 from the ocean surface to 1000 m. Globally, the oxygen loss due to warming is reinforced by other processes associated with ocean physics and biogeochemistry, which cause the majority of the observed oxygen decline.
The oxygen minimum zones (OMZs) are expanding by a very likely range of 3-8%, most notably in the tropical oceans, but there is substantial decadal variability that affects the attribution of the overall oxygen declines to human activity in tropical regions.
In response to ocean warming and increased stratification, open ocean nutrient cycles are being perturbed and there is high confidence that this is having a regionally variable impact on primary producers. The upper ocean is very likely to have been stratifying since 1970. Observed warming and high-latitude freshening are making the surface ocean less dense over time relative to the deeper ocean and inhibiting the exchange between surface and deep waters.
Multiple datasets and models show that the rate of ocean uptake of atmospheric CO2 has continued to strengthen in the recent two decades in response to the increasing concentration of CO2 in the atmosphere. The very likely range for ocean uptake is between 20-30% of total anthropogenic emissions in the recent two decades.
Climate change is altering the water cycle in complex ways. Impacts include changes in precipitation patterns, increasing intensity of rainfall, accelerated melting of glaciers, and changes in river flows and groundwater recharge.
Climate models project robust differences in regional climate characteristics between present-day and global warming of 1.5°C, and between 1.5°C and 2°C. These differences include increases in mean precipitation in several high-latitude regions, increases in heavy precipitation in several regions, and probability of drought and precipitation deficits in some regions.
High Mountain areas are experiencing pronounced warming, leading to the retreat of glaciers and changes in snow cover. This affects the quantity and seasonality of water resources in regions dependent on meltwater, with implications for agriculture, hydropower, and ecosystems.
Freshwater ecosystems are particularly vulnerable to climate change impacts. Changes in water temperature, flow regimes, and water quality affect aquatic species and ecosystem functions. Warming rivers and lakes lead to shifts in species composition and can facilitate the spread of invasive species and waterborne diseases.
Climate change is affecting forests and other terrestrial ecosystems through changes in temperature, precipitation patterns, and the frequency and intensity of extreme events such as droughts, wildfires, and storms.
Rising temperatures and changes in precipitation patterns are causing shifts in forest composition and structure. Some regions are experiencing forest dieback due to drought stress, pest outbreaks, and increased fire frequency. Tree mortality has increased in many areas, and the geographic ranges of many tree species are shifting toward higher elevations and latitudes.
Climate change is increasing wildfire risk in many regions through longer fire seasons, more frequent heatwaves, and more intense droughts. This leads to greater burned areas, carbon emissions, and threats to biodiversity and human settlements.
Terrestrial ecosystems currently act as a carbon sink, absorbing about 29% of annual anthropogenic CO2 emissions. However, the capacity of these sinks may diminish with continued warming, potentially accelerating the rate of climate change. Some ecosystems, such as permafrost regions, may switch from being carbon sinks to carbon sources as warming continues.
Polar regions are experiencing some of the most rapid and severe climate changes on Earth, with profound implications for global climate systems.
There is high confidence that the probability of a sea ice-free Arctic Ocean during summer is substantially lower at global warming of 1.5°C when compared to 2°C. With 1.5°C of global warming, one sea ice-free Arctic summer is projected per century. This likelihood is increased to at least one per decade with 2°C global warming.
The Greenland and Antarctic ice sheets are losing mass at an accelerating rate. This contributes to sea level rise and may affect ocean circulation patterns. Marine ice sheet instability in Antarctica and/or irreversible loss of the Greenland ice sheet could result in multi-metre rise in sea level over hundreds to thousands of years. These instabilities could be triggered at around 1.5°C to 2°C of global warming.
Permafrost regions are thawing, releasing stored carbon and methane into the atmosphere and creating a positive feedback loop that amplifies warming. Limiting global warming to 1.5°C rather than 2°C is projected to prevent the thawing over centuries of a permafrost area in the range of 1.5 to 2.5 million km².
Climate change affects agricultural productivity through changes in temperature, precipitation, extreme weather events, and the geographic ranges of crop pests and diseases.
Climate change is already affecting crop yields in many regions. Increases in global temperature are projected to further reduce yields of major crops like wheat, rice, and maize in most regions, although some high-latitude regions may experience yield increases in the short term. The stability of food supply is projected to decrease as the magnitude and frequency of extreme weather events increase.
Livestock production is affected by heat stress, changes in water availability, and changes in the quality and quantity of feed. Higher temperatures reduce animal productivity and increase disease susceptibility.
Ocean warming and acidification are affecting marine fisheries and aquaculture. Changes in water temperature alter the distribution and abundance of fish species, while acidification affects shellfish and other calcifying organisms. Marine heatwaves, including well-documented events along the west coast of North America (2013–2016) and east coast of Australia (2015–2016, 2016–2017 and 2020), drive abrupt shifts in community composition that may persist for years, with associated biodiversity loss and collapse of regional fisheries and aquaculture.
Climate change has adversely affected physical health of people globally (very high confidence) and mental health of people in the assessed regions (very high confidence). According to the IPCC AR6 Working Group II report, climate change impacts on health are mediated through natural and human systems, including economic and social conditions and disruptions.
Climate change has adversely affected physical health of people globally with very high confidence. The impacts include:
Mental health impacts are expected to arise from exposure to extreme weather events, displacement, migration, famine, malnutrition, degradation or destruction of health and social care systems, and climate-related economic and social losses and anxiety and distress associated with worry about climate change.
Climate change and related extreme events will significantly increase ill health and premature deaths from the near- to long-term. An excess of 250,000 deaths per year by 2050 attributable to climate change is projected due to heat, undernutrition, malaria and diarrheal disease, with more than half of this excess mortality projected for Africa (compared to a 1961-1991 baseline period for a mid-range emissions scenario).
With proactive, timely and effective adaptation, many risks for human health and well-being could be reduced and some potentially avoided. Early warning systems based on targeted climate services can be effective for disaster risk reduction, social protection programmes, and managing risks to health and food systems.
Climate change is increasingly driving migration and displacement, with significant implications for human security and well-being.
Since 2008, an average of more than 20 million people per year have been displaced by extreme weather events, many of which were exacerbated by climate change, according to the IPCC. Climate-related migration is already underway in areas like Pacific islands, sub-Saharan Africa, and South Asia.
The IPCC report highlights several projections for displacement and migration due to climate change:
Climate change effects on migration are not uniform or consistent across regions:
The IPCC has suggested that migration could provide a way for some people to escape the worst impacts of climate change. Migration is often a last resort, with people doing all they can to stay where they are. This means people are willing to try a lot of different strategies to deal with the effects of warming, even in precarious places like islands facing rising sea levels.
Climate change is already having significant economic impacts and these are projected to increase substantially in the coming decades.
Economic impacts attributable to climate change are increasingly affecting people's livelihoods and causing economic and societal impacts across national boundaries. Climate-driven impacts on ocean and coastal ecosystems and their services have cascading and compounding effects that propagate through socio-economic systems.
Risks to global aggregated economic growth due to climate change impacts are projected to be lower at 1.5°C than at 2°C by the end of this century. The economic damages from climate change will increase with global warming level.
According to the IPCC, developing countries alone will need $127 billion per year by 2030 and $295 billion per year by 2050 to adapt to climate change. This represents a significant financial burden, particularly for countries with limited resources.
Climate change affects various economic sectors differently:
Climate change poses significant risks to infrastructure systems and urban areas, affecting millions of people worldwide.
Critical infrastructure including energy, water, sanitation, transportation, and telecommunication systems are vulnerable to climate change impacts. Extreme events like floods, heatwaves, and storms can damage or destroy infrastructure, disrupt services, and require costly repairs or replacements.
Urban areas are particularly vulnerable to heat-related impacts due to the urban heat island effect, which amplifies temperature increases. This affects human health, energy demand for cooling, and urban ecosystems.
Sea level rise poses particular challenges for coastal cities and infrastructure. Many major urban centers are located in low-lying coastal areas and face increasing risks of flooding, erosion, and saltwater intrusion into freshwater supplies.
Considering climate change impacts and risks in the design and planning of urban and rural settlements and infrastructure is critical for resilience and enhancing human well-being. Heat Health Action Plans that include early warning and response systems are effective adaptation options for extreme heat.
Climate change can exacerbate existing tensions and contribute to instability and conflict, though the relationship is complex and context-specific.
The IPCC notes that climate change can indirectly increase risks of violent conflicts through pathways such as:
Areas with high exposure to climate hazards, high vulnerability, and low adaptive capacity face the greatest security risks. This includes regions already experiencing conflict, political instability, or economic challenges.
Climate change can create compound risks when it interacts with other stressors like poverty, inequality, and weak governance. These compound risks can overwhelm adaptive capacity and increase the likelihood of conflict.
While climate change presents security challenges, addressing it can also create opportunities for cooperation and peace-building. Collaborative approaches to managing shared resources like transboundary water systems can build trust and reduce conflict potential.
Climate change disproportionately affects vulnerable populations, exacerbating existing inequalities and creating new ones.
Approximately 3.3 to 3.6 billion people live in contexts that are highly vulnerable to climate change. Vulnerability is influenced by factors including:
Climate change impacts are not distributed equally:
The IPCC recognizes that those who have contributed least to climate change are often the most affected by its impacts. This raises important questions of climate justice and equity in both mitigation and adaptation efforts.
Climate change intensifies existing vulnerability and inequality, with adverse impacts on the most vulnerable groups. These impacts can create feedback loops that further entrench disadvantage and limit adaptive capacity.
Climate change threatens cultural heritage sites, practices, and knowledge systems around the world, with particular impacts on indigenous communities.
Physical cultural heritage sites face risks from:
Climate change also affects intangible cultural heritage, including:
Indigenous knowledge systems offer valuable insights for climate adaptation but are themselves threatened by rapid environmental change. The IPCC recognizes the importance of integrating indigenous knowledge with scientific approaches to enhance climate resilience.
For many communities, especially indigenous peoples, climate impacts on cultural heritage represent not just material loss but profound damage to identity, well-being, and social cohesion.
International cooperation is essential for addressing climate change effectively. The IPCC has assessed various international agreements and policies aimed at reducing greenhouse gas emissions and enhancing climate resilience.
The Paris Agreement, adopted in 2015, is the most significant international climate agreement to date. Its central aim is to strengthen the global response to climate change by:
The Paris Agreement operates through nationally determined contributions (NDCs), which are climate action plans submitted by each country outlining their efforts to reduce emissions and adapt to climate change impacts.
Beyond the Paris Agreement, other important international frameworks include:
According to the IPCC, current policies in place by the end of 2021 would likely see temperatures exceed 1.5°C this century and reach around 3.2°C by 2100. This highlights the significant gap between current commitments and the actions needed to meet the Paris Agreement goals.
The IPCC emphasizes that enhanced international cooperation is essential for achieving ambitious climate goals, particularly in areas such as finance, technology transfer, and capacity building to support developing countries.
The transition to renewable energy is a cornerstone of climate change mitigation. The IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation provides a comprehensive assessment of the potential role of renewable energy in reducing greenhouse gas emissions.
Renewable energy sources currently supply approximately 20% of global energy consumption, with the largest contribution coming from traditional biomass. However, modern renewables (including hydropower, wind, solar, geothermal, and modern bioenergy) are growing rapidly.
The IPCC finds that the technical potential of renewable energy technologies exceeds global energy demand, suggesting that renewable energy could theoretically meet all global energy needs. However, the practical deployment depends on various factors including costs, policies, and integration challenges.
The IPCC assesses several key renewable energy technologies:
The integration of high shares of variable renewable energy (particularly wind and solar) presents challenges for existing electricity systems. The IPCC identifies several strategies to address these challenges:
The IPCC outlines various pathways for transitioning to renewable energy systems, emphasizing that no single approach will be sufficient. Successful transitions will likely involve a portfolio of renewable technologies tailored to specific regional conditions and integrated with energy efficiency measures.
Carbon capture and storage (CCS) technologies are increasingly recognized as essential components of comprehensive climate change mitigation strategies, particularly for hard-to-abate sectors.
Once captured, CO₂ can be stored through various methods:
BECCS combines bioenergy use with carbon capture and storage, potentially resulting in negative emissions (removing CO₂ from the atmosphere). The IPCC notes that many pathways to limiting warming to 1.5°C rely heavily on BECCS, though there are concerns about its large-scale deployment related to land use, food security, and biodiversity.
While CCS technologies are technically proven, their deployment remains limited due to:
The IPCC emphasizes that CCS is likely to be most important for industries with process emissions that are difficult to eliminate otherwise, such as cement and steel production.
Urban areas, where the majority of the global population lives, face significant climate risks but also offer opportunities for effective adaptation.
As urban areas are particularly vulnerable to heat-related impacts due to the urban heat island effect, adaptation strategies include:
To address increased flood risks from extreme precipitation and sea level rise, urban adaptation measures include:
Strategies to enhance urban water security in the face of changing precipitation patterns include:
Climate-resilient urban infrastructure incorporates:
Effective urban adaptation requires:
Agriculture is particularly vulnerable to climate change but also offers significant opportunities for adaptation.
Adaptation strategies for crop production include:
For livestock systems, adaptation measures include:
Practices that enhance soil health and land management include:
Financial and institutional mechanisms to support agricultural adaptation include:
Water resources are highly vulnerable to climate change, necessitating comprehensive adaptation strategies.
The IPCC emphasizes integrated water resources management (IWRM) as a framework for addressing climate impacts on water. Key elements include:
Strategies to enhance water supply include:
Approaches to manage water demand include:
Specific strategies for extreme water events include:
Economic instruments play a crucial role in both mitigation and adaptation efforts.
Carbon pricing mechanisms aim to incorporate the social cost of carbon emissions into economic decision-making:
The IPCC notes that carbon pricing is most effective when prices are sufficiently high and when combined with other policies addressing market failures and distributional concerns.
Financial incentives to promote low-carbon technologies and practices include:
Scaling up climate finance requires:
The IPCC emphasizes the importance of ensuring that climate policies do not exacerbate existing inequalities:
Climate change represents one of the most significant challenges facing humanity in the 21st century. The scientific evidence is unequivocal that human activities have warmed the planet by approximately 1.1°C since pre-industrial times, with observable impacts already affecting ecosystems and human societies worldwide. Without immediate, rapid, and large-scale reductions in greenhouse gas emissions, global warming is projected to reach between 1.5°C and 4.4°C by 2100, depending on emission scenarios.
The environmental impacts of this warming are already observable and will intensify throughout the century, affecting biodiversity, ocean systems, freshwater resources, and agricultural productivity. These environmental changes will cascade into profound societal and economic impacts, including threats to human health, displacement of populations, economic losses, and potential conflicts over increasingly scarce resources.
However, this report also highlights that humanity has the knowledge, technology, and capacity to substantially reduce emissions and adapt to unavoidable impacts. A portfolio of mitigation strategies—including renewable energy transition, carbon capture technologies, and sustainable land management—combined with targeted adaptation measures can limit the worst impacts of climate change.
Based on the comprehensive assessment presented in this report, we offer the following recommendations for addressing climate change in the coming century:
The choices made in this decade will be crucial in determining the climate trajectory for the rest of this century and beyond. While the challenges are substantial, there are many feasible and effective options available that can create a more sustainable and resilient future for both human societies and Earth's ecosystems. By acting decisively now, we can limit the severity of climate change impacts and build a more equitable and sustainable world for future generations.
This report draws on the latest scientific research on climate change, with particular reliance on the authoritative assessments of the Intergovernmental Panel on Climate Change (IPCC). Key references include:
Additional references from peer-reviewed scientific literature, international organizations, and government reports have been incorporated throughout the report to provide the most current and comprehensive assessment of climate change impacts and responses.