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The IPCC uses a very specific language when it comes to expressing the degree of uncertainty or agreement for each statement in the fifth assessment report. For an overview of the specific meaning of each qualifier, you can read the relevant section in our summary of the Working Group I report.
Evidence of climate-change impacts is strongest and most comprehensive for natural systems. Some climate change impacts have also been observed on human systems. Farmers have seen more negative impacts than positive ones on the yield of their crops (high confidence).
Changing precipitation or melting snow and ice are altering hydrological systems and in turn affecting water resources. As a consequence, there have been observed impacts, for instance the change in geographic range of many terrestrial, freshwater, and marine species. Many species have also changed their seasonal activities, migration patterns, abundances, and interactions with other species in response to ongoing climate change (high confidence).
Climate change has caused significant ecosystem shifts and species extinctions during the past millions of years (high confidence)., At present the world-wide burden of diseases and health problems from climate change is relatively small compared with the effects from other stressors, although it is not well quantified. Local changes in temperature and rainfall have altered the distribution of some water-borne illnesses and disease vectors (medium confidence).
Differences in vulnerability arising from non-climatic factors, uneven development processes (very high confidence) or violent conflicts, also shape the risks from climate change that each population is exposed to.
The impacts of climate extremes that have already been observed on ecosystems, food production, water supply, infrastructure and settlements, morbidity and mortality, and mental health and human well-being. show that societies are not properly prepared for the current variability in climate, and this is especially true for people living in poverty (high confidence).
Throughout history, people and societies have adjusted to climate, climate variability, and extremes, with varying degrees of success. Adaptation is becoming more and more a part of planning processes, although the implementation of responses is still limited (high confidence). The responses that are implemented are usually engineered or technological in nature, and are often integrated within existing programs such as disaster risk management and water management. Most assessments of adaptation have been restricted to impacts, vulnerability, and adaptation planning, with very few assessing the process of implementing the adaptation solutions, and the effect that those actions have (medium evidence, high agreement). Climate-change adaptation is an iterative risk management process with multiplefeedbacks. The mitigation choices (such CO2 emissions reductions) that are being taken right now and in the near future will have an impact on the effect of climate change throughout the 21st century and beyond (high confidence). Governments at various levels worldwide are starting to develop adaptation plans and policies and to integrate climate-change considerations into broader development plans. Expert judgment is used to integrate evidence into evaluations of risks. Future risks related to climate change vary substantially between the different emission and development scenarios that are being considered, and the importance of climate change varies also between the different sector of human activity, between regions, and when considering different time scales (high confidence). Scenarios are useful tools for characterizing possible future socioeconomic pathways, climate change and its risks, and policy implications.
uncertainties about future vulnerability, exposure, and responses of interlinked human and natural systems are large (high confidence). International dimensions such as trade and relations among states are also important for understanding the risks of climate change at regional scales.
Eight categories of key risks were identified with high confidence, spanning differents sectors and regions.
| (1) Flooding, storms and sea-level rise in low-lying coastal zones and islands | 5) Food insecurity and breakdown of food production chains |
| (2) Inland flooding in large urban zones. | (6) Insufficient access to drinking water and lack of irrigation water affecting agriculture |
| (3) Breakdown of infrastructure networks due to extreme weather events | (7) Loss of marine and coastal ecosystems, their biodiversity and the services they provide |
| (4) Mortality and morbidity during periods of extreme heat | (8) Loss of terrestrial and inland water ecosystems, their biodiversity and the services they provide. |
Many key risks constitute particular challenges for the least developed countries and vulnerable communities, given their limited ability to cope. From this assessment, five integrative reasons for concern (RFCs) provide a framework for summarizing key risks across sectors and regions. These are: (1) unique and threatened systems, (2) extreme weather events , (3) unevenly distributed risks, (4) global aggregate impacts and (5) large-scale singular events due to abrupt and extreme events. They provide one starting point for evaluating dangerous anthropogenic interference with the climate system.
The precise levels of climate change that would trigger tipping points (thresholds for abrupt and irreversible change) remain uncertain, but the risk associated with crossing a large number of such tipping points in the earth system or in interlinked human and natural systems increases with rising temperature (medium confidence). Reducing climate change can reduce the scale of adaptation that might be required, but under all assessed scenarios for adaptation and mitigation, some risk from adverse impacts remains (very high confidence).
Within this century, the magnitude and rate of climate change associated with medium- to high-emission scenarios pose a high risk of abrupt and irreversible regional-scale change in the composition, structure, and function of terrestrial and freshwater ecosystems, including wetlands (medium confidence). If such changes were to happen in the boreal-tundra Arctic system, where methane currently trapped in the permanently frozen ground could be released, (medium confidence) and the Amazon forest, where there could a chance in the amount of carbon dioxide captured by the trees (low confidence), it could lead to substantial impact on climate through a feedback mechanism.
Many global risks of climate change are concentrated in urban areas (medium confidence), for people, assets, economies, and ecosystems (very high confidence). Risks are amplified for those lacking essential infrastructure and services or living in poor-quality housing and exposed areas. In rural areas, impacts are expected, through impacts on water availability and supply, to have an effect on food security and agricultural incomes, and lead to shifts in production areas of food and non-food crops across the world (high confidence). These impacts in rural areas are expected to disproportionately affect the welfare of the poor, such as female-headed households and those with limited access to land, modern agricultural inputs, infrastructure, and education.
| Potential cause | Main consequences |
| sea-level rise projected throughout the 21st century and beyond | coastal systems and low-lying areas will increasingly experience adverse impacts such as submergence, coastal flooding, and coastal erosion (very high confidence). |
| Global marine-species redistribution and marine-biodiversity reduction in sensitive regions | Will challenge the sustained provision of fisheries productivity and other ecosystem services (high confidence). |
| the progressive expansion of oxygen minimum zones and anoxic “dead zones” | is projected to further constrain fish habitat |
| Ocean acidification | poses substantial risks to marine ecosystems, especially polar ecosystems and coral reefs, associated with impacts on the physiology, behavior, and population dynamics of individual species from phytoplankton to animals (medium to high confidence). |
| Simultaneous drivers, such as warming and ocean acidification. | can lead to interactive, complex, and amplified impacts for species and ecosystems |
| Local temperature increases of 2°C or more above late-20th-century levels) in tropical and temperate regions | negatively impact production of the major crops (wheat, rice, and maize |
The IPCC uses a very specific language when it comes to expressing the degree of uncertainty or agreement for each statement in the fifth assessment report. For an overview of the specific meaning of each qualifier, you can read the relevant section in our summary of the Working Group I report.
For most economic sectors, the impacts of other drivers such as changes in population, age structure, income, technology, relative prices, lifestyle, regulation, and governance are projected to be large relative to the impacts of climate change (medium evidence, high agreement). Climate change is projected to reduce energy demand for heating and increase energy demand for cooling in the residential and commercial sectors (robust evidence, high agreement). Climate change is projected to affect energy sources and technologies differently, depending on resources (e.g., water flow, wind, insolation), technological processes (e.g., cooling), or locations (e.g., coastal regions, floodplains).
The incomplete estimates of global annual economic losses for additional temperature increases of ~2°C are between 0.2 and 2.0% of income(medium evidence, medium agreement). Losses are more likely than not to be greaterthan this range (limited evidence, high agreement).
The associated slow down economic growth will make poverty reduction more difficult, further erode food security, and prolong existing and create new poverty traps, the latter particularly in urban areas and emerging hotspots of hunger (medium confidence). Climate-change impacts are expected to exacerbate poverty in most developing countries and create new poverty pockets in countries with increasing inequality, in both developed and developing countries.
Until mid-century, projected climate change will impact human health mainly by exacerbating health problems that already exist (very high confidence). Throughout the 21st century, climate change is expected to lead to increases in ill-health in many regions and especially in developing countries with low income, as compared to a baseline without climate change (high confidence). Globally, over the 21st century, the magnitude and severity of negative impacts are projected to increasingly outweigh positive impacts (high confidence).
In terms of international security, populations can migrate in response to extreme weather events or to longer-term climate variability and change, and also it can be an effective adaptation strategy. Climate change can indirectly increase risks of violent conflicts in the form of civil war and inter-group violence by amplifying well-documented drivers of these conflicts such as poverty and economic shocks (medium confidence) and influence national security policies (medium evidence, medium agreement).
Managing the risks of climate change involves adaptation and mitigation decisions that have implications for future generations, economies, and environments. Adaptation and mitigation should be considered together rather than as separate responses. Coordination between levels, from individuals to governments can enhance the effect of adaptation and minitagion actions. (high confidence). A first step towards adaptation to future climate change is reducing vulnerability and exposure to present climate variability (high confidence). There are strategies and actions that can increase resilience to a range of different paths that the climate could take, while helping to improve human health, livelihoods, social and economic well-being, and environmental quality. However, many constraints such as limited financial and human resources, different perceptions of risks; competing values; absence of key adaptation leaders and advocates; and limited tools to monitor the effectiveness of adaptation can interact to impede adaptation planning and implementation (high confidence). Poor planning, overemphasizing short-term outcomes, or failing to sufficiently anticipate consequences can result in maladaptation (medium evidence, high agreement).
Increasing efforts to mitigate and adapt to climate change imply an increasing complexity of interactions, particularly at the intersection of water resources, energy, land use, and biodiversity, but tools to understand and manage these interactions remain limited.
Resilience is the capacity of social, economic, and environmental systems to cope with a disturbance, to respond or reorganize in ways that maintain their essential function, identity, and structure, while also maintaining the capacity for adaptation, learning, and transformation.
Prospects for climate-resilience are related closelsy to what the world accomplishes in terms of sustainable development with climate-change mitigation (high confidence). Transformations in economic, social, technological, and political decisions and actions can enable climate-resilient pathways (high confidence). At national level, a transformation is considered most effective when it reflects a country’s own visions and approaches to achieving sustainable development in accordance with their national circumstances and priorities. Transformations towards sustainability are considered to benefit from iterative learning, deliberative processes, and innovation.
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