Editing IPCC:AR6/WGII/Chapter-2 (section)

=== 2.1.1 Overview ===

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We provide assessments of observed and projected impacts of climate change across species, biomes (vegetation types), ecosystems and ecosystem services, highlighting the processes that are emerging on a global scale. Where sufficient evidence exists, differences in biological responses across regions, taxonomic groups or types of ecosystems are presented, particularly when such differences provide meaningful insights into current or potential future autonomous or human-mediated adaptations. Human interventions that might build the resilience of ecosystems and minimise the negative impacts of climate change on biodiversity and ecosystem functioning are assessed. Such interventions include adaptation strategies and programmes to support biodiversity conservation and Ecosystem-based Adaptation (EbA). The assessments were done in the context of the Convention on Biological Diversity (CBD) and sustainable development goals (SDGs), whose contributions to climate resilient development (CRD) pathways are assessed. This chapter highlights both the successes and failures of adaptation attempts and considers potential synergies and conflicts with land-based climate change mitigation. Knowledge gaps and sources of uncertainty are included to encourage additional research.

The Working Group II Summary for Policymakers of the AR5 stated that ‘many terrestrial and freshwater species have shifted their geographic ranges, seasonal activities, migration patterns, abundances, and species interactions in response to ongoing climate change’ ( [[#IPCC--2014d|IPCC, 2014d]] ). Based on long-term observed changes across the regions, it was estimated that approximately 20–30% of plant and animal species are at risk of extinction when global mean temperatures rise 2–3°C above pre-industrial levels ( [[#Fischlin--2007|Fischlin et al., 2007]] ). In addition, the WGII AR5 Synthesis Report ( [[#IPCC--2014e|IPCC, 2014e]] ) broadly suggested that autonomous adaptation by ecosystems and wild species might occur, and proposed human-assisted adaptations to minimise negative climate change impacts.

Risk assessments for species, communities, key ecosystems and their services were based on the risk assessment framework introduced in the IPCC AR5 ( [[#IPCC--2014b|IPCC, 2014b]] ). Assessments of observed changes in biological systems emphasise detecting and attributing the impacts of climate change on ecological and evolutionary processes, particularly freshwater ecosystems, and ecosystem processes such as wildfires, that were superficially assessed in previous reports. Where appropriate, assessment of interactions between climate change and other human activities is provided.

Land use and land cover change (LULCC) as well as the unsustainable exploitation of resources in terrestrial and freshwater systems continue to be major factors contributing to the loss of natural ecosystems and biodiversity ( ''high confidence'' ). Fertiliser input, pollution of waterways, dam construction and the extraction of freshwater for irrigation put additional pressure on biodiversity and alter ecosystem function ( [[#Shin--2019|Shin et al., 2019]] ). Likewise, for biodiversity, invasive alien species have been identified as a major threat, especially in freshwater systems, on islands and in coastal regions ( ''high confidence'' ) ( [[#IPBES--2018b|IPBES, 2018b]] ; [[#IPBES--2018e|IPBES, 2018e]] ; [[#IPBES--2018c|IPBES, 2018c]] ; [[#IPBES--2018d|IPBES, 2018d]] ; [[#IPBES--2019|IPBES, 2019]] ). Climate change and CO 2 are expected to become increasingly important as drivers of change over the coming decades ( [[#Ciais--2013|Ciais et al., 2013]] ; [[#Settele--2014|Settele et al., 2014]] ; [[#IPBES--2019|IPBES, 2019]] ; [[#IPCC--2019c|IPCC, 2019c]] ).

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