Climate change impacts research

Scientific research into climate change adaptation generally starts with analyses of the likely effects of climate change on people, ecosystems, and the environment. These impacts cover its effects on lives, livelihoods, health and well-being, ecosystems and species, economic, social and cultural assets, and infrastructure.^{[11] : 2235} Impacts may include changed agricultural yields, increased floods, and droughts or coral reef bleaching. Analysis of such impacts is an important step in understanding current and future adaptation needs and options.

As of 2022, the level of warming is 1.2°C (2.2°F) above levels before the industrial revolution. It is on track to increase to 2.5 to 2.9°C (4.5 to 5.2°F) by the end of the century.^[12] This is causing a variety of secondary effects.

Many negative effects of climate change involve changes in extremes or the way conditions vary rather than changes in average conditions.^[14] For example, the average sea level in a port might not be as important as the height of water during a storm surge. That is because a storm surge can cause flooding. The average rainfall in an area might not be as important as how frequent and severe droughts and extreme precipitation events become.^[15]

Disaster risks, response and preparedness

Climate change contributes to disaster risk. So experts sometimes see climate change adaptation as one of many processes within disaster risk reduction.^[16] In turn, disaster risk reduction is part of the broader consideration of sustainable development. Climate change adaptation and disaster risk reduction have similar goals (to reduce potential impacts of hazards and increase the resilience of people at risk). They use similar concepts and are informed by similar sources and studies.^[17]

Disasters are often triggered by natural hazards. A natural event such as a fire or flood is not of itself a disaster: it's only when it affects people or is caused by them that is counts as a disaster. It is argued that natural disasters are always linked to human action or inaction or rooted in anthropogenic processes. Disasters, economic loss, and the underlying vulnerabilities that drive risk are increasing. Global risks like climate change are having major impacts everywhere.^[18] Scientists forecast climate change will increase the frequency and severity of extreme weather events and disasters. So adaptation may include measures to increase preparedness and relevant disaster response capacities.

Policy aims

The Paris Agreement of 2015 requires countries to keep global temperature rise this century to less than 2°C above pre-industrial levels, and to pursue efforts to limit the temperature increase to 1.5°C.^[19] Even if greenhouse gas emissions are stopped relatively soon, global warming and its effects will last many years. This is due to the inertia of the climate system. So both carbon neutrality ("net zero") and adaptation are necessary.^[20]

The Global Goal on Adaptation was also established under the Paris Agreement. The specific targets and indicators for the Global Goal are in development as of 2023. It will support the long-term adaptation goals of the governments that are parties to the agreement. It also aims to fund support for the most vulnerable countries’ adaptation needs in the context of the 1.5/2°C goal. It has three core components. These are reducing vulnerability to climate change, enhancing adaptive capacity, and strengthening resilience.^[21]

Reduce risk factors: vulnerability and exposure

Adaptation can help decrease climate risk by addressing three interacting risk factors. These are hazards, vulnerability, and exposure. It is not possible to directly reduce hazards. This is because hazards are affected by current and future changes in climate. Instead, adaptation addresses the risks of climate impacts that arise from the way climate-related hazards interact with the exposure and vulnerability of human and ecological systems.^{[8]: 145–146} Exposure refers to the presence of people, livelihoods, ecosystems and other assets in places that could suffer negative effects.^[1] It is possible to reduce exposure by retreating from areas with high climate risks, such as floodplains. Improving systems for early warnings and evacuations are other ways to reduce exposure.^[22]: 88 The IPCC defines climate change vulnerability as "the propensity or predisposition to be adversely affected" by climate change.^[1] It can apply to humans but also to natural systems. Human and ecosystem vulnerability are interdependent.^[7]: 12 According to the IPCC, climate change vulnerability encompasses a variety of concepts and elements, including sensitivity or susceptibility to harm and lack of capacity to cope and adapt.^[7]: 5 Sensitivity to climate change could be reduced by for example increasing the storage capacity of a reservoir, or planting crops that are more resistant to climate variability.^[23] It is also possible to reduce vulnerability in towns and cities with green garden spaces. These can reduce heat stress and food insecurity for low-income neighbourhoods.^[24]: 800

Ecosystem-based adaptation is one way to reduce vulnerability to climate hazards. For instance, mangroves can dampen storm energy. So they can help prevent flooding. In this way, protection of the mangrove ecosystem can be a form of adaptation. Insurance and livelihood diversification increase resilience and decrease vulnerability. Other ways to decrease vulnerability include strengthening social protection and building infrastructure more resistant to hazards.^[22]

Increase adaptive capacity

Adaptive capacity in the context of climate change covers human, natural, or managed systems. It looks at how they respond to both climate variability and extremes. It covers the ability of a system to adjust to climate change to moderate potential damages, to take advantage of opportunities, or to cope with consequences.^[1] Adaptive capacity is not the same as adaptation itself.^[25] Adaptive capacity is the ability to reduce the likelihood of negative impacts of climate-related hazards.^[26] It does this through the ability to design and implement effective adaptation strategies, or to react to evolving hazards and stresses. Societies that can respond to change quickly and successfully have a high adaptive capacity.^[27] Conversely, high adaptive capacity does not necessarily lead to successful adaptation action. It does not necessarily succeed in goals of equity and enhancing well-being.^[8]: 164 For example, adaptive capacity in Western Europe is generally considered to be high. Experts have documented the risks of warmer winters increasing the range of livestock diseases. But many parts of Europe were still badly affected by outbreaks of bluetongue virus in livestock in 2007.^[28]

In general, adaptation capacity differs between high and low-income countries.^[29] By some indices such as ND-GAIN, high-income countries tend to have higher adaptive capacity. However, there is strong variation within countries.^[8]: 164

The determinants of adaptive capacity include:^{[30]: 895–897}

• Economic resources: Wealthier nations are better able to bear the costs of adaptation to climate change than poorer ones.
• Technology: Lack of technology can impede adaptation.
• Information and skills: Information and trained personnel are necessary to assess and implement successful adaptation options.
• Social infrastructure
• Institutions: Nations with well-developed social institutions are likely to have greater adaptive capacity than those with less effective institutions. These are typically developing nations and economies in transition.
• Equity: Some believe that adaptive capacity is greater where there are government institutions and arrangements in place that allow equitable access to resources.

Adaptive capacity is closely linked to social and economic development.^[31] In general higher levels of development mean higher adaptive capacity. However, some development locks people into certain patterns or behaviours. And the most developed areas may have low adaptation capacity to new types of natural hazards that they have not previously experienced.

Measures to promote sustainable development often overlap with those for adaptive capacity. Both types of activity can reduce climate risk while also yielding development benefits.^[32] These activities can include: Improving access to resources, reducing poverty, lowering inequities of resources and wealth among groups, improving education and information, improving infrastructure, improving institutional capacity and efficiency, and promoting local indigenous practices, knowledge, and experiences.^[30]: 899

Strengthening resilience

The IPCC considers climate resilience to be “the capacity of social, economic and ecosystems to cope with a hazardous event or trend or disturbance”. It includes the abilities to reorganise and learn.^[7]: 7 This definition is similar to that of climate change adaptation. However resilience involves a more systematic approach to absorbing change. It involves using those changes to become more efficient. The idea is that people can intervene to reorganise the system when disturbance creates an opportunity to do so.^[8]: 174 They could guide the reorganisation in more desirable directions such as social or development goals.^[33]

Implemented adaptation most often builds upon resilience as a way of bouncing back to recover after a disturbance. Experts consider it to be incremental rather than transformational.^{[8]: 130, 134} On the other hand, climate resilience-focused projects can be activities to promote and support transformational adaptation. This is because transformational adaptation is connected with implementation at scale and ideally at the system-level.^{[8]: 72 [34]: 26}

Strengthening resilience is therefore important for maintaining a capacity for transformation. Transformations, and the processes of transition, cover the major systems and sectors at scale. These are energy, land and ecosystems, urban and infrastructure, and industrial and societal.^[8]: 125 Transformations may fail if they do not integrate social justice, consider power differences and political inclusion, and if they do not deliver improvements in incomes and wellbeing for everyone.^[8]: 171

Climate resilient development is a closely related area of work and research topic that has recently emerged. It describes situations in which adaptation, mitigation and development solutions are pursued together. It is able to benefit from synergies from among the actions and reduce trade-offs.^[8]: 172

Co-benefits with mitigation

Strategies to limit climate change are complementary to efforts to adapt to it.^[8]: 128 Limiting warming, by reducing greenhouse gas emissions and removing them from the atmosphere, is also known as climate change mitigation.

There are some synergies or co-benefits between adaptation and mitigation. Synergies include the benefits of public transport for both mitigation and adaptation. Public transport has lower greenhouse gas emissions per kilometer travelled than cars. A good public transport network also increases resilience in case of disasters. This is because evacuation and emergency access becomes easier. Reduced air pollution from public transport improves health. This in turn may lead to improved economic resilience, as healthy workers perform better.^[35]

Infrastructural and technological options

Wetland restoration in Australia

Checking contours in Monterey County strawberry fields, United States

Terraces, conservation tillage and conservation buffers save soil and improve water quality on this farm in Woodbury County in northwest Iowa, United States.

Institutional options

Launching the Coastal City Adaptation Project in Quelimane, Mozambique

Coastal City Adaptation Project, in Quelimane city, Mozambique. It will improve Quelimane's preparation for events like floods, erosion, sea level rise and other weather and climate related events.

Institutional responses include zoning regulations, new building codes, new insurance schemes, and coordination mechanisms.^[45]

Policies are important tools to integrate issues of climate change adaptation.^[46] At the national level, adaptation strategies appear in National Adaptation Plans (NAPS) and National Adaptation Programmes of Action (NAPA). They also occur in national climate change policies and strategies.^[47] These are at different levels of development in different countries and in cities. This is discussed further in the section below on "implementation".

Cities, states, and provinces often have considerable responsibility in land use planning, public health, and disaster management. Institutional adaptation actions occur more frequently in cities than in other sectors.^[2]: 2434 Some have begun to adapt to threats intensified by climate change, such as flooding, bushfires, heatwaves, and rising sea levels.^[48][49][50]

Behavioural and cultural options

Individuals and households play a central role in adaptation. There are many examples particularly in the global south. Behavioural adaptation is a change in the strategies, practices and actions that help to reduce risk. These can include protecting homes from flooding, protecting crops from drought, and adopting different income-earning activities. Behavioural change is the most common form of adaptation.^[2]: 2433

Migration and managed retreat

See also: Climate migration, Effects of climate change § Displacement and migration, and Managed retreat

The Government of Kiribati is addressing the threats of climate change to Kiribati, under the Kiribati Adaptation Program. Island nations in the Pacific are particularly vulnerable to sea level rise.

Migration counts as behavioural climate adaptation for some, although others refer to it as a climate response rather: The IPCC Sixth Assessment Report states: "Some responses, such as migration, relocation and resettlement may or may not be considered to be adaptation".^[62]: 27

Many factors influence migration decisions. It is difficult to say how much climate change influences migration.^[45]: 2428 The environment is one of many factors. Economic, demographic or political factors are often important in migration decisions. Climate change is an indirect or less important cause.^{[63]: 1079–1080}

Seasonal migration or mobility includes traditional strategies such as pastoralism or seeking seasonal employment in urban centres. These are normally voluntary and economically motivated. Weather fluctuations and extremes can influence migration.^[45]: 2428 Weather variability is an important contributor to declines in agricultural incomes and employment. Climate change has made these impacts more likely. As a result migration has increased, particularly rural to urban movement.^[45]: 2428

Measures to increase adaptive capacity, such as social protection and promoting women's empowerment, can help people with little power in migration decisions.^[7]: 25 Sometimes people are unwilling or unable to migrate. In such cases it may be necessary for the government to intervene to keep people safe.^{[63]: 1079–1081} This is also referred to as managed retreat.

Nature-based options

Main articles: Ecosystem-based adaptation and Nature-based solutions

Mangroves protect coastlines against erosion (Cape Coral, Florida, United States)

Nature-based solutions (NBS) work with nature and ecosystems to provide benefits to both societies and overall biodiversity. In the context of climate change, they provide adaptation and mitigation options that benefit and support wild species and habitats. In doing this they often contribute to other sustainable development goals.^[64]: 303

Nature-based solutions is an overarching term that includes actions known as ecosystem-based adaptation. However NBS is not restricted to climate change, and often also refers to climate change mitigation. So it is a less specific term.^[64]: 284 Both approaches require benefits to people and nature to be delivered simultaneously.

Flooding

Flood protection for town of Ybbs along the river Donau

Flooding can occur in cities or towns as urban flooding. It can also take place by the sea as coastal flooding. Sea level rise can make coastal flooding worse. In some areas there are also risks of glacial lake outburst floods.

There are many adaptation options for flooding:^[66]

• Installing better flood defences such as flood barriers, sea walls and increased pumping capacity^[67]
• Installing devices to prevent seawater from backflowing into storm drains^[68]
• Rainwater storage to deal with increased run-off from rainfall. This includes reducing paved areas or changing to water-permeable pavements, adding water-buffering vegetation, adding underground storage tanks, and subsidizing household rain barrels^[69][70]
• Raising pumps at wastewater treatment plants^[68]
• Buying out homeowners in flood-prone areas^[71]
• Raising street level to prevent flooding^[67]
• Using and protecting mangroves^[72]
• Glacial lakes in danger of outburst flooding can have their moraines replaced with concrete dams to provide protection. This may also provide hydroelectric power^[73]

More frequent drenching rains may make it necessary to increase the capacity of stormwater systems. This separates stormwater from blackwater, so that overflows in peak periods do not contaminate rivers. One example is the SMART Tunnel in Kuala Lumpur.

New York City produced a comprehensive report for its Rebuilding and Resiliency initiative after Hurricane Sandy. It includes making buildings less prone to flooding. It also aims to make specific problems encountered during and after the storm less likely to recur. These include weeks-long fuel shortages even in unaffected areas due to legal and transportation problems, flooded health care facilities, insurance premium increases, damage to electricity and steam generation and distribution networks, and flooding of subway and roadway tunnels.^[74]

Sea level rise

Heat waves

Green roof

A 2020 study projects that regions inhabited by one third of the human population could become as hot as the hottest parts of the Sahara within 50 years. This will happen without a change in patterns of population growth and without migration, unless there is a sharp reduction in greenhouse gas emissions to limit warming to 1.5 °C. The most affected regions have little adaptive capacity as of 2020.^[85][86][87]

Cities are particularly affected by heat waves due to the urban heat island effect. Climate change does not cause urban heat islands. But it leads to more frequent and more intense heat waves which in turn amplify the urban heat island effect in cities.^[88]: 993 Compact, dense urban development may increase the urban heat island effect. This results in higher temperatures and increased exposure.^[89]

Tree cover and green space can reduce heat in cities. They act as sources of shade and promote evaporative cooling.^[90] Other options include green roofs, passive daytime radiative cooling applications, and the use of lighter-coloured surfaces and less absorptive building materials in urban areas. These reflect more sunlight and absorb less heat.^[91][92][93] It may be necessary to change city trees to more heat-tolerant varieties.^[69][94]

Methods for adapting to increased heat include:

• The use and development of air conditioning and cooling systems. Adding air conditioning can make schools^[69] and workplaces cooler. But it results in additional greenhouse gas emissions unless it uses renewable energy.
• Solar-energy passive cooling systems for houses and/or refrigeration.

Changed rainfall patterns in agriculture

Cclimate change is altering global rainfall patterns. This affects agriculture.^[95] Rainfed agriculture accounts for 80% of global agriculture.^[96] Many of the 852 million poor people in the world live in parts of Asia and Africa that depend on rainfall to cultivate food crops. Climate change will modify rainfall, evaporation, runoff, and soil moisture storage. Extended drought can cause the failure of small and marginal farms. This results in increased economic, political and social disruption.

Water availability strongly influences all kinds of agriculture. Changes in total seasonal precipitation or its pattern of variability are both important. Moisture stress during flowering, pollination, and grain-filling harms most crops. It is particularly harmful to corn, soybeans, and wheat. Increased evaporation from the soil and accelerated transpiration in the plants themselves will cause moisture stress.

There are many adaptation options. One is to develop crop varieties with greater drought tolerance^[97] and another is to build local rainwater storage. Using small planting basins to harvest water in Zimbabwe has boosted maize yields. This happens whether rainfall is abundant or scarce. And in Niger they have led to three or fourfold increases in millet yields.^[98]

Climate change can threaten food security and water security. It is possible to adapt food systems to improve food security and prevent negative impacts from climate change in the future.^[99]

Drought and desertification

Reforestation activities in Praslin, Seychelles

Reforestation is one way to stop desertification fueled by climate change and non-sustainable land use. One of the most important projects is the Great Green Wall that aims to stop the southward expansion of the Sahara desert. By 2018 only 15% of it had been carried out. But there are already many positive effects. These include the restoration of over 12 million acres (5 million hectares) of degraded land in Nigeria; the planting of roughly 30 million acres of drought-resistant trees across Senegal; and the restoration of 37 million acres of land in Ethiopia. Tree maintenance led to the refilling of groundwater wells with drinking water, additional food supplies for rural towns, and new sources of work and income for villagers.^{[101][102][103]}

Ecosystems and their services

The main risks to ecosystems from climate change are biodiversity loss, ecosystem structure change, increased tree mortality, increased wildfire, and ecosystem carbon losses. These risks are linked. Loss of species can increase the risks to ecosystem health.^[64]: 279 Wildfire is an increasing risk for people as well as to ecosystems in many parts of the world.^[64]: 290 Wildfires and increased pest infestations due to climate change caused much of the recent tree mortality in North America.^{[64] : 280}

Risks to seas and coastal areas include coral bleaching linked with ocean warming. This can change the composition of ecosystems. Coral bleaching and mortality also increase the risks of flooding on nearby shorelines and islands. Ocean acidification attributed to climate change drives change in coral reefs and other ecosystems such as rocky shores and kelp forests.^[105]: 142

Ecosystems can respond to climatic and other environmental pressures in different ways. Individual organisms can respond through growth, movement and other developmental processes. Species and populations can relocate or genetically adapt. Human interventions can make ecosystems more resilient and help species adapt. Examples are protecting larger areas of semi-natural habitat and creating links between parts of the landscape to help species move.^[64]: 283

Ecosystem-based adaptation actions provide benefits for both ecosystems and humans. They include restoring coastal and river systems to reduce flood risk and improve water quality, creating more green areas in cities to reduce temperatures, and reinstating natural fire regimes to reduce risk of severe wildfires. There are many ways to reduce the risk of disease outbreaks. They include building surveillance systems of pathogens affecting humans, wildlife and farm animals.^{[64]: 288, 295}

Health

Climate change-related risks to health include direct risks from extreme weather such as cold waves, storms, or prolonged high temperatures. There are also indirect risks such as mental health impacts of undernutrition or displacement caused by extreme weather.^[63]: 1076 Similarly there are mental health risks from loss of access to green spaces, reduced air quality, or from anxiety about climate change.^{[63]: 1076, 1078} There are further risks from changes in conditions for transmission of infectious diseases. Malaria and dengue are particularly climate-sensitive.^[63]: 1062

There are several approaches to adapt to new or increased infectious disease risks. These include vector control through improved housing and better sanitation conditions through WASH services. It could also include insecticide-treated bed nets and indoor spraying. For food-borne diseases it includes food processing and storage.^[63]: 1107

Adaptation options for heat include expanding access to air conditioning and establishing heat action plans that include early warning systems for heatwaves. Other options are passive cooling systems to include shading and ventilation. These could be part of improved building and urban design and planning, green infrastructure or public cooling centres.^{[63]: 1108–1109}

Adaptation options to respond to mental health impacts include increasing funding and access to mental healthcare, incorporating mental health into climate resilience and disaster risk planning, and improving post-disaster support.^[63]: 1112 Mental health also benefits from broader activities such as design of healthy natural spaces, education and cultural activities. It is also closely related to food security and nutrition.

Cities

Rising temperatures and heatwaves are key risks for cities. With warmer temperatures the urban heat island effect is likely to get worse. Population growth and land use change will influence human health and productivity risks in cities.^[51]: 993 Urban flooding is another key risk. This is especially the case in coastal settlements where flood risks are exacerbated by sea-level rise and storm surges. A further set of risks arises from reduced water availability. When supply cannot meet demand from expanding settlements, urban residents become exposed to water insecurity and climate impacts. This is especially so during periods of lower rainfall. These key risks differ greatly between cities, and between different groups of people in the same city.^[51]: 993

Adaptation options for cities include flood control measures within and outside properties and urban drainage projects. Other examples are nature-based solutions such as bioswales or other vegetated infrastructure and restoration and/or protection of mangroves along coastlines. Vegetation corridors, greenspace, wetlands and other green infrastructure can also reduce heat risks. Building designs such as installing air conditioning, ‘cool roofs’ with high-reflectance materials or solar chimneys can also help. Several institutional adaptations are particularly important for cities, for example legislation of building codes, zoning and land use measures.^[51]: 952

Many cities have integrated city-wide adaptation strategies or plans that bring together social and economic activities, civil authorities and infrastructure services. Such actions are more effective if they are implemented in partnership with local communities, national governments, research institutions, and the private and third sector.^[51]: 994

Water

Climate change is affecting the overall and seasonal availability of water across regions. Climate change is projected to increase the variability of rain. There will be impacts on water quality as well as quantity. Floods can wash pollutants into water bodies and damage water infrastructure. In many places, particularly in the tropics and sub-tropics, there are longer dry spells and droughts, sometimes over consecutive years. These have contributed to drier soil conditions, lower groundwater tables and reduced or changed flows of rivers. There are risks to ecosystems, and across many water-using sectors of the economy.^[110]: 660 Agriculture is likely to be affected by changes in water availability, putting food security at risk. Irrigation has often contributed to groundwater depletion and changes in the water cycle. It can sometimes make a drought worse.^{[111]: 1157}

Some of the most popular adaptations in agriculture include choosing less water-intensive crops or drought and flood-resistant varieties. They include shifting the timing of sowing and harvesting according to the start of the rainy season. There are other technological options available for saving water.^[110]: 584 Water is used for hydroelectric generation, for cooling of power plants, and in other industries such as mining. Adapting hydroelectric plant designs and control systems to operate with less water or diversifying in energy generation with other renewables are effective options.^[110]: 626

Livelihoods and communities

Climate change affects livelihoods and living conditions in significant ways. These include access to natural resources and ecosystems, land and other assets.  Access to basic infrastructure services such as water and sanitation, electricity, roads, telecommunications is another aspect of vulnerability of communities and livelihoods to climate change.^{[112]: 1119}

The biggest livelihood-related risks stem from losses of agricultural yields, impacts on human health and food security, destruction of homes, and loss of income. There are also risks to fish and livestock that livelihoods depend on.^{[112] : 1178} Some communities and livelihoods also face risks of irreversible losses and challenges to development, as well as more complex disaster risks.^{[112]: 1214}

The consequences of climate change are the most severe for the poorest populations. These are disproportionately more exposed to hazards such as temperature extremes and droughts. They usually have fewer resources and assets and less access to funding, support and political influence. There are other forms of disadvantage due to discrimination, gender inequalities and through lack of access to resources This includes people with disabilities or minority groups.^{[112]: 1251}

Across livelihoods sectors for households and communities the most common adaptation responses are engineered and technological options. These include traditional infrastructure to protect a specific land use, ecosystem approaches such as watershed restoration or climate-smart agriculture technologies. Adaptation requires public and private investment in various natural assets. It also requires institutions that prioritize the needs of communities, including the poorest.^{[112]: 1253}

International impacts and cascading risk

International climate risks are climate risks that cross national borders. Sometimes the impacts of climate change in one country or region can have further consequences for people in other countries. Risks can spread from one country to a neighbouring country, or from one country to distant regions. Risks can also cascade and have knock-on effects elsewhere, across multiple borders and sectors. For example, an impact of the floods in Thailand in 2011 was disruption to manufacturing supply chains affecting the automotive sector and electronics industry in Japan, Europe and the USA.^{[113]: 2441–2444 [114]}

Options for adapting are less developed. They include developing resilient infrastructure in the originating country, increasing storage facilities to allow more buffer in the recipient country, or diversifying and re-routing trade.^{[113]: 2441–2444}

Economic costs

The economic costs of adaptation to climate change will depend on how much the climate changes. Higher levels of warming lead to considerably higher costs. Globally, adaptation is likely to cost tens or hundreds of billions of dollars annually for the next several decades. The IPCC's most recent summary states that adaptation will cost $15 to 411 billion per year for climate change impacts to 2030. Most estimates are well above $100 billion."^{[115]: Cross-Chapter Box FINANCE} Because these costs are much higher than the finance available, there is an adaptation gap. This is especially pressing in developing countries.^{[115]: SPM C1.2} This gap is widening^{[116][115]: ch 17}and forms a major barrier to adaptation.^[117] This widening has become apparent because the overwhelming majority of global tracked climate finance goes to mitigation. Only a small proportion goes on adaptation.^[62]

More regional estimates are also available. For example, the Asian Development Bank has a series of studies on the Economics of Climate Change in the Asia-Pacific region.^[118] These studies provide cost analysis of both adaptation and mitigation measures. The WEAP (Water Evaluation And Planning system) assists water resources researchers and planners in assessing impacts of and adaptations to climate change. The United Nations Development Programme's Climate Change Adaptation Portal includes studies on climate change adaptation in Africa, Europe and Central Asia, and Asia and the Pacific.^[119]

Cost benefit analysis

As of 2007 there was still a lack of comprehensive, global cost and benefit estimates for adaptation.^[120]: 719 Since then, an extensive research literature has emerged. Studies generally focus on adaptation in developing countries or within a sector. For many adaptation options in specific contexts, the investment will be lower than the avoided damages. But global estimates have considerable uncertainty.^{[121]: ch 15 [115]: Cross-Chapter Box FINANCE}

International finance

The United Nations Framework Convention on Climate Change incorporates a financial mechanism to developing country parties to support them with adaptation.^[122] This is in Article 11 of the convention. Until 2009, three funds existed under the UNFCCC financial mechanism. The Global Environmental Facility administers the Special Climate Change Fund (SCCF)^[123] and the Least Developed Countries Fund (LDCF).^[124] The Adaptation Fund resulted from negotiations during COP15 and COP16 in 2009 and 2010. It has its own Secretariat. Initially, when the Kyoto Protocol was in operation, the Adaptation Fund was financed by a 2% levy on the Clean Development Mechanism (CDM).

At the 2009 Copenhagen Summit, nations committed to the goal of sending $100 billion per year to developing countries for climate change mitigation and adaptation by 2020.^[125] The Green Climate Fund was created in 2010 as one of the channels for mobilizing this climate finance. The 2015 Paris conference, COP21, clarified that the $100 billion per year should involve a balanced split between mitigation and adaptation. As of December 2020, the promised $100 billion per year had not been fully delivered. Most developing country finance was still targeted towards mitigation. Adaptation received only 21% of the public finance provided in 2020.^{[126][127][128]}

Global adaptation financing from multilateral development banks exceeded €19 billion in 2021. This implies a rising trend in the financing of adaptation.^[129][130] Multilateral banks made a commitment to increase adaptation financing in a joint declaration on climate change at COP27.^[131] This particularly targets low-income nations, small island developing states, and underprivileged people. The European Investment Bank has said that it will raise the share it contributes to 75% for projects focusing on climate adaptation.^[129][132] The bank usually contributes up to 50% to a project it participates in.

Also in 2022, nations agreed on a proposal to establish a loss and damage fund to support communities in averting, minimizing, and addressing damages and risks where adaptation is not enough or comes too late.^[133]: 63

Additionality

A key feature of international adaptation finance is the concept of additionality. This reflects the linkages between adaptation finance and other levels of development aid.^[134] Many developed countries already provide international aid assistance to developing countries. This addresses challenges such as poverty, malnutrition, food insecurity,^[135] availability of drinking water, indebtedness, illiteracy, unemployment, local resource conflicts, and lower technological development. Climate change threatens to exacerbate or stall progress on fixing some of these problems, and creates new ones. Additionality refers to the extra costs of adaptation to avoid existing aid being redirected.

The four main definitions of additionality are:^[134]

1. Climate finance classified as aid, but additional to the Millennium Development Goals;
2. Increase on previous year's Official Development Assistance (ODA) spent on climate change mitigation;
3. Rising ODA levels that include climate change finance but where it is limited to a specified percentage; and
4. Increase in climate finance not connected to ODA.

A criticism of additionality is that it encourages business as usual. This is because it does not account for the future risks of climate change. Some advocates have proposed integrating climate change adaptation into poverty reduction programs.^[136]

From 2010 to 2020, Denmark increased its global warming adaptation aid by one third, from 0.09% of GDP to 0.12% of GDP. But this did not involve additional funds. Instead, the aid was taken from other foreign assistance funds. Politiken wrote: "Climate assistance is taken from the poorest."^[137]

Differing time scales

Adaptation can occur in anticipation of change or be a response to those changes.^[138] For example, artificial snow-making in the European Alps responds to current climate trends. The construction of the Confederation Bridge in Canada at a higher elevation takes into account the effect of future sea-level rise on ship clearance under the bridge.^[139]

Effective adaptive policy can be difficult to implement because policymakers are rewarded more for enacting short-term change, rather than long-term planning.^[140] Since the impacts of climate change are generally not seen in the short term, policymakers have less incentive to act. Furthermore, climate change is occurring on a global scale. This requires a global framework for adapting to and combating climate change.^[141] The vast majority of climate change adaptation and mitigation policies are being implemented on a more local scale. This is because different regions must adapt differently. National and global policies are often more challenging to enact.^[142]

Maladaptation

Much adaptation takes place in relation to short-term climate variability. But this may cause maladaptation to longer-term climate trends. The expansion of irrigation in Egypt into the Western Sinai desert after a period of higher river flows is maladaptation given the longer-term projections of drying in the region.^[143] Adaptations at one scale can have impacts at another by reducing the adaptive capacity of other people or organizations. This is often the case when broad assessments of the costs and benefits of adaptation are examined at smaller scales. An adaptation may benefit some people, but have a negative effect on others.^[138] Development interventions to increase adaptive capacity have tended not to result in increased power or agency for local people.^[144] Agency is a central factor in all other aspects of adaptive capacity and so planners need to pay more attention to this factor.

Limits to adaptation

People have always adapted to climate change. Some community coping strategies already exist. Examples include changing sowing times or adopting new water-saving techniques.^[143] Traditional knowledge and coping strategies must be maintained and strengthened. If not there is a risk of weakening adaptive capacity as local knowledge of the environment is lost. Strengthening these local techniques and building upon them also makes the adoption of adaptation strategies more likely. This is because it creates more community ownership and involvement in the process.^[139] In many cases this will not be enough to adapt to new conditions. These may be outside the range of those previously experienced, and new techniques will be necessary.^[27]

The incremental adaptations become insufficient as the vulnerabilities and risks of climate change increase. This creates a need for transformational adaptations which are much larger and costlier.^[145] Current development efforts increasingly focus on community-based climate change adaptation. They seek to enhance local knowledge, participation and ownership of adaptation strategies.^[146]

The IPCC Sixth Assessment Report in 2022 put considerable emphasis on adaptation limits.^[7]: 26 It makes a distinction between soft and hard adaptation limits. The report stated that some human and natural systems already reached "soft adaptation limits" including human systems in Australia, Small Islands, America, Africa and Europe and some natural systems reach even the "hard adaptation limits" like part of corals, wetland, rainforests, ecosystems in polar and mountain regions. If the temperature rise will reach 1.5 °C (2.7 °F) additional ecosystems and human systems will reach hard adaptation limits, including regions depending on glaciers and snow water and small islands. At 2 °C (3.6 °F) temperature rise, soft limits will be reached by many staple crops in many areas while at 3 °C (5.4 °F) hard limits will be reached by parts of Europe.^[7]: 26

Incentivizing private investment in adaptation

Climate change adaptation is a much more complex investment area than mitigation. This is mainly because of the lack of a well-defined income stream or business case with an attractive return on investment on projects. There are several specific challenges for private investment:^[147][148]

• Adaptation is often needed in non-market sectors or is focused on public goods that benefit many. So there is a shortage of projects that are attractive to the private sector;
• There is a mismatch between the timing of investments needed in the short term and the benefits that may occur in the medium or long term. Future returns are less attractive to investors than short-term returns;
• There is a lack of information about investment opportunities. This especially concerns uncertainties associated with future impacts and benefits. These are key considerations when returns may accrue over longer timeframes;
• There are gaps in human resources and capacities to design adaptation projects and understand financial implications of legal, economic and regulatory frameworks.

However, there is considerable innovation in this area. This is increasing the potential for private sector finance to play a larger role in closing the adaptation finance gap.^[6] Economists state that climate adaptation initiatives should be an urgent priority for business investment.^[149][150]

Trade-offs with mitigation

Trade-offs between adaptation and mitigation may occur when climate-relevant actions point in different directions. For instance, compact urban development may lead to reduced greenhouse gas emissions from transport and building. On the other hand, it may increase the urban heat island effect, leading to higher temperatures and increasing exposure, making adaptation more challenging.^[151]

By country and city

National governments typically have the key role in setting policies, planning, coordinating and distributing finance for climate adaptation. They are  also accountable to the international community through international agreements.^[153] Many countries document their adaptation plans in their NDCs submitted under the Paris Agreement and/or national adaptation plans. Developing countries can receive support with international funding to help them develop their national adaptation plans.^[154]

As of 2020, 72% of countries had a high level adaptation instrument – such as a plan, policy or strategy. Relatively few had progressed to the tangible implementation of projects: at least not to significantly reduce the climate risk their populations are exposed to.^[6]

Countries have also made progress in developing plans for subnational government authorities. These include county/provincial level, sectors and city plans. In 2020, around 21% of countries had sub-national plans and 58% had sectoral plans.^[6]

As of 2022, there is better integration of adaptation priorities into other national plans and planning systems. Planning is also more inclusive. This means that climate laws and policies increasingly reference different groups such as persons with disabilities, children, young people and future generations.^[155]

Many cities have integrated city-wide adaptation strategies or plans that bring together their social and economic activities, civil authorities and infrastructure services.^[51]: 994   A survey of 812 global cities found that 93% reported they are at risk from climate change, 43% did not have an adaptation plan in 2021, and 41% of cities had not carried out a climate risk and vulnerability assessment.^[156]

Global goals

Sustainable Development Goal 13 aims to strengthen countries' resilience and adaptive capacities to climate-related issues.^[157] This adjustment includes many areas such as infrastructure,^[158] agriculture^[159] and education. The Paris Agreement includes several provisions for adaptation. It seeks to promote the idea of global responsibility, improve communication via the adaptation component of the Nationally Determined Contributions, and includes an agreement that developed countries should provide some financial support and technology transfer to promote adaptation in more vulnerable countries.^[160]

The United Nations estimates Africa would need yearly funding of $1.3 trillion to achieve the Sustainable Development Goals in the region, considering population growth. The International Monetary Fund also estimates that $50 billion may be needed only to cover the expenses of climate adaptation.^{[161][162][163]}