Editing IPCC:AR6/WGII/Cross-Chapter-Paper-5 (section)

== Executive Summary ==

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Mountains are highly significant regions in the context of climate change and sustainable development. They lie at the intersection of accelerated warming and large populations that depend directly or indirectly on them. They are regions of high biological and cultural diversity and provide vital goods and services to people living in and around mountain regions and in downstream areas. Building on the IPCC’s Fifth Assessment Report (AR5), Chapter 2, ‘High Mountain Areas’, of the Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) ( [[#Hock--2019|Hock et al., 2019]] ), and the IPCC Working Group I contribution to AR6 ( [[#IPCC--2021|IPCC, 2021]] ), this Cross-Chapter Paper (CCP) assesses new evidence on observed and projected climate change impacts in mountain regions, their associated key risks and adaptation measures.

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===== Observed changes, their impacts and adaptation responses in mountains =====

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'''Climate change impacts in mountains and their attribution to human influence have increased in recent decades with observable and serious consequences for people and ecosystems in many mountain regions (''' '''''high confidence''''' [[#footnote-001|1]] ''').''' Observed changes include increasing temperatures, changing seasonal weather patterns, reductions in snow cover extent and duration at low elevation, loss of glacier mass, increased permafrost thaw and an increase in the number and size of glacier lakes ( ''high confidence'' ). {CCP5.2.7, Figure CCP5.4, SROCC Chapter 2, WGI Section 9.5}

'''The spatial distributions of many plant species have shifted to higher elevations in recent decades, consistent with rising temperatures across most mountain regions (''' '''''high confidence''''' ''').''' Around two-thirds of treeline ecotones have also shifted upwards in recent decades, though these shifts are not ubiquitous and slower than expected based on rising temperatures ( ''high confidence'' ). Impacts on biological communities and animal species are also increasingly being reported, with species of lower elevations increasing in mountain regions, creating more homogeneous vegetation and increasing risks to mountain-top species ( ''medium confidence'' ). {CCP5.2.1; 2.4}

'''Climate and cryosphere change have negatively impacted the water cycle in mountains, including variable timing of glacier melt and snowmelt stream discharge (''' '''''high confidence''''' '''). These changes have variable impacts on water availability for people and economies, contributing to increasing tensions or conflicts over water resources, especially in seasonally dry regions (''' '''''medium confidence''''' ''').''' Mountains are an essential source of freshwater for large and growing populations; the number of people largely or fully dependent on water from mountains has increased worldwide from approximately 0.6 billion in the 1960s to approximately 2 billion in the past decade, and globally two-thirds of irrigated agriculture depends on essential runoff contributions from mountains. {CCP5.2.2; Figure CCP5.2; SROCC Chapter 2; 4.2.2.3; 4.4.4.1}

'''Climate-change-driven changes in precipitation, river flow regimes and landslides affect the production and use of energy in mountain regions, in particular hydropower (''' '''''high confidence''''' ''').''' Billions of USD in investment and assets of energy production are exposed to changing mountain hazards. The combined effects of climate change, hydropower development and other human interventions have exacerbated water security problems and social injustice ( ''medium confidence'' ). {CCP5.2.2, SROCC Chapter 2}

'''Observed climate-driven impacts on mountain ecosystem services, agriculture and pastoralism are largely negative in most mountain regions (''' '''''medium confidence''''' ''').''' Agriculture has been negatively affected through increased exposure to hazards such as droughts and floods, changes in the onset of seasons, the timing and availability of water, increasing pests and decreasing pollinator diversity, which in turn have negatively influenced overall food production, dietary diversity and the nutritional value of food ( ''medium confidence'' ). Negative climate impacts on pastoralism, such as drought-induced degradation of rangelands and pastures, have affected livestock productivity and the livelihood of pastoralists, while other non-climatic factors, such as land use change and management, also play a role ( ''medium confidence'' ). {CCP5.2.3; CCP5.2.5; Table CCP5.2; SROCC Section 2.3.1.3.2; SROCC Section 2.3.7}

'''While contributing to poverty reduction in some mountain regions, there is''' '''''limited evidence''''' '''of adaptations effectively contributing to the remediation of underlying social determinants of vulnerability, such as gender and ethnicity (''' '''''medium confidence''''' ''').''' Exposure and vulnerability exacerbate the negative effects of climate impacts on livelihoods and intertwine with power imbalances and gender and other inequalities ( ''medium confidence'' ). {CCP5.2.7; CCP5.3.2.2 }

'''Observed changes in seasonality (timing and extent) are negatively affecting mountain winter tourism and recrea''' '''t''' '''ion (''' '''''high confidence''''' ''') and variably affect tourism and recreation activities in other seasons (''' '''''medium confidence''''' ''').''' For winter activities such as skiing, diminishing snow at lower elevations has challenged operating conditions ( ''medium confidence'' ), increasing the demand for and dependence on snow management measures such as snow-making ( ''high confidence'' ). Climate-induced hazards are negatively affecting some climbing, mountaineering and hiking routes ( ''medium confidence'' ). In some regions, options to change routes or shift seasons to reduce hazard exposure have been employed as adaptation strategies, with variable outcomes ( ''medium confidence).'' In some cases, higher temperatures and extreme heat conditions at lower elevations have made some mountain destinations more appealing, increasing the potential for summer visitation demand ( ''medium confidence'' ). {CCP5.2.5; Table CCP5.2; SROCC Section 2.3.5}

'''Climate-related hazards, such as flash floods and landslides, have contributed to an increase in disasters affecting a growing number of people in mountain regions and areas further downstream (''' '''''high confidence''''' ''').''' As a result, the number of disasters has increased; however, there is ''limited evidence'' that this is due to changes in the underlying hazard processes, pointing mainly to increasing levels of exposure ( ''medium confidence'' ). {CCP5.2.6; CCP5.2.7; CCP5.3.2.1 } .

'''Adaptation responses to climate-driven impacts in mountain regions vary significantly in terms of goals and priorities, scope, depth and speed of implementation, governance and modes of decision-making and the extent of financial and other resources to implement them (''' '''''high confidence''''' ''').''' Observed adaptation responses in mountains are largely incremental and mainly focus on early warning systems and the diversification of livelihood strategies in smallholder agriculture, pastoralism and tourism. However, there is ''limited evidence'' of the feasibility and long-term effectiveness of these measures in addressing climate-related impacts and related losses and damages, including in cities and settlements experiencing changing demographics. {CCP5.2.4; CCP5.2.7.2 }

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===== Projected impacts, key risks and limits to adaptation in mountains =====

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'''Increasing temperatures will continue to induce changes in mountain regions throughout the 21st century, with expected negative consequences for mountain cryosphere, biodiversity, ecosystem services and human well-being (''' '''''very high confidence''''' ''').''' Many low-elevation and small glaciers around the world will lose most of their total mass at a 1.5°C global warming level (GWL) ( ''high confidence'' ). A large majority of endemic mountain species will be at risk of extinction; regions heavily relying on glacier melt and snowmelt for irrigation will face erratic water supply and increased food insecurity, whereas agriculture in some regions might see positive changes. Damages and losses from water-related hazards such as floods and landslides are projected to increase considerably between 1.5°C and 3°C GWL. {CCP5.3.1}

'''Projected changes in hazards, such as floods and landslides, as well as changes in the water cycle, will lead to severe risk consequences for people, infrastructure and the economy in many mountain regions (''' '''''high confidence''''' ''').''' These risks will be more pervasive and increase more rapidly in south and central Asia and northwestern South America. However, nearly all mountain regions will face at least moderate and some regions even high risks at around 2°C GWL ( ''medium confidence'' ). {CCP5.3.2.1, CCP5.3.2.2 }

'''There is an increasing risk of local and global species extinctions where species are not able to move to higher elevations or other cooler locations (''' '''''high confidence''''' '''), with risks from extreme events such as wildfire potentially exacerbating those risks (''' '''''medium confidence''''' ''').''' The topographic variation in mountains, such as elevation or aspect, may mean that some species will be able to survive in cooler microclimates. Mountain regions may act as refugia for some species from lower elevations if they can move into them. This may enable some species to persist in a region, though it may pose a threat to cold-adapted species, including endemics, which may be outcompeted ( ''high confidence'' ); invasive non-native species may become an increasing problem in some places. {CCP5.3.2.3, Box CCP5.1; CCP1.2.2.1; 2.6.6; 16.6.3.1}

'''Climate change is projected to lead to profound changes and irreversible losses in mountain regions with negative consequences for ways of life and cultural identity (''' '''''medium confidence''''' ''').''' Intangible losses and loss of cultural values will become increasingly more widespread in mountain regions, mainly driven by a decline in snow and ice and an increase in intangible harm to people from hazards ( ''medium confidence'' ). However, there is ''limited evidence'' on the magnitude of the consequences. {CCP5.3.2.4; 16.5.2.1; 16.5.2.3.7}

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===== Options for future adaptation and climate-resilient sustainable development in mountains =====

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'''The current pace, depth and scope of adaptation are insufficient to address future risks in mountain regions, particularly at higher warming levels (''' '''''high confidence''''' ''').''' While the incremental nature of most implemented adaptations will not be sufficient to reduce severe risk consequences, options exist which offer practical and timely prospects to address risks before limits to adaptation are reached or exceeded. Reducing climate risks will depend on addressing the root causes of vulnerability, which include poverty, marginalisation and inequitable gender dynamics ( ''high confidence'' ). {CCP5.4.1, Figure CCP5.7: CCP5.4.2, Cross-Chapter Box DEEP in Chapter 17; Cross-Chapter Box LOSS in Chapter 17; 17.3, 17.6}

'''Adaptation decision-making processes that engage with and incorporate people’s concerns and values and address multiple risks are more robust than those with a narrow focus on single risks (''' '''''medium confidence''''' ''').''' Risk management strategies that better integrate the adaptation needs of all affected sectors, account for different risk perceptions and build on multiple and diverse knowledge systems, including Indigenous knowledge and local knowledge, are important enabling conditions to reduce risk severity ( ''medium confidence'' ). {CCP5.2.6, CCP5.4.2; 17.3; 17.4; Cross-Chapter Box PROGRESS in Chapter 17; Cross-Chapter Box DEEP in Chapter 17}

'''Regional cooperation and transboundary governance in mountain regions, supported by multi-scale knowledge networks and monitoring programmes, enable long-term adaptation actions where risks transcend boundaries and jurisdictions (''' '''''medium confidence''''' ''').''' Collectively, they show potential to form an important component of the adaptation solution space in mountains. There are increasing calls for more ambitious climate action in mountains, providing impetus for stronger cooperation within and across mountain regions and downstream areas ( ''medium confidence'' ). {CCP5.4.2; CCP5.4.3 }

'''With warming above 1.5°C, the need for adaptation to address key risks in mountains becomes increasingly urgent (''' '''''high confidence''''' ''').''' Pathways and system transitions that strengthen climate-resilient sustainable mountain development are starting to receive attention, but current levels of resourcing are substantially insufficient to support timely action. {CCP5.4.2; CCP5.4.3; CCP5.5; 18.1; 18.2}

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