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

== 2.7 Reducing Scientific Uncertainties to Inform Policy and Management Decisions ==

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Research since the AR5 ( [[#Settele--2014|Settele et al., 2014]] ) has increased the understanding of climate change impacts and vulnerability in ecosystems. Evidence gaps remain and geographic coverage of research is uneven. This section assesses gaps in ecosystem science where research is necessary for environmental policies and the management of natural resources, including under the UNFCCC and the CBD.

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=== 2.7.1 Observed Impacts ===

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Detection and attribution efforts have increased since AR5, but there are some key impacts of high societal importance that would benefit from more detailed and sophisticated attribution studies. For example, while it is clear that diseases have altered considerably in both wild animals and humans in some areas ( ''high'' confidence in detection), there are many regions that are under-studied, and few regions that provide robust assessments of the role of climate change, particularly with respect to human infectious diseases. While wildfire has been robustly linked to climate change in some regions, there are still a lack of attribution studies in some regions that have experienced large burns recently, and only one fire impact—the increase of the area burned by wildfire in western North America in the period 1984–2017 ( [[#2.4.4.2.1|Section 2.4.4.2.1]] ) —has been formally attributed to anthropogenic climate change. Global changes in soil and freshwater ecosystem carbon over time remain uncertainties in global carbon stocks and changes ( [[#2.4.4.4|Section 2.4.4.4]] ); due to the physical inability to conduct repeat-monitoring and the lack of remote sensing to scale up point measurements, no global methods can yet produce repeating spatial estimates of soil carbon stock changes.

Despite the growing understanding of the importance of ecosystem services, this assessment found limited research on the observed impacts of climate change for 14 of 18 ecosystem services (Table 2.1).

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=== 2.7.2 Projected Risks ===

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A challenge for future projections that continues from previous IPCC reports is accurately characterising and quantifying the interactions of climate change vs. other, non-climate factors that cause ecological change, including LULCC (particularly deforestation, agricultural expansion, and urbanisation) and air and water pollution. Interactions can be particularly complex for invasive species, pests, pathogens and human infectious diseases. Modelling of risks at the species level requires comprehensive databases of the physiological, life-history, and reproduction of individual species, and modeling the impact of changes in species’ compositions requires a mechanistic understanding of functional traits relevant to ecosystem integrity, functioning and resilience to climate change. Taxa that particularly lack this basis for model projections include fungi and bacteria. For numerous plant and animal species, research into genotypic and phenotypic diversity as a source of ecosystem resilience would inform projections of risk.

Soil plays a vital role in ecosystem function, is the habitat of a large number of species and is a large carbon store which is currently a major source of GHG emissions; it is therefore a priority for climate change research ( [[#Hashimoto--2015|Hashimoto et al., 2015]] ). Major uncertainties remain in our understanding of soil functions. ESMs predict that soil respiration will increase with rising temperatures ( [[#Friedlingstein--2014|Friedlingstein et al., 2014]] ). However, there is evidence of acclimation post-increase ( [[#Carey--2016|Carey et al., 2016]] ) as the opposite response of decrease in respiration with warming ( [[#Li--2013|Li et al., 2013]] ; [[#Reynolds--2015|Reynolds et al., 2015]] ). Long-term, large-scale field observations combined with a better conceptual understanding of the factors governing soil process responses to climate change are needed. A better understanding of plant–water relations is also necessary, including the response of plant transpiration to increased CO 2 , climate warming and changes in soil moisture and groundwater elevation.

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=== 2.7.3 Adaptation and Climate Resilient Development ===

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There are significant evidence gaps in developing adaptation, both for biodiversity conservation and EbA. In particular, while many adaptation measures have been proposed and implementation is starting, there are very few evaluations of success in the scientific literature ( [[#Morecroft--2019|Morecroft et al., 2019]] ; [[#Prober--2019|Prober et al., 2019]] ). As detailed in [[#2.6.2|Section 2.6.2]] , there is a strong body of literature on conceptual approaches to climate change adaptation for biodiversity but very little empirical testing of which approaches actually work best. Going forward, it is important to put in place good monitoring and evaluation of adaptation strategies. For EbA, there are good examples of measuring changes in response to new adaptation measures, but these remain relatively rare globally.

Human factors which promote or hinder adaptation are important as well as the technical issues. Only a few studies incorporate climate change and ecosystem services in integrated decision-making, and even fewer aim to identify solutions robust to uncertainty ( [[#Runting--2017|Runting et al., 2017]] ).

Over the last decades, losses due to natural disasters including those from events related to extreme weather have strongly increased ( [[#Mechler--2015|Mechler and Bouwer, 2015]] ). There is a need for better assessment of global adaptation costs, funding and investment ( [[#Micale--2018|Micale et al., 2018]] ). Potential synergies between international finance for disaster risk management (DRM) and adaptation have not yet been fully realised. Research has almost exclusively focused on normalising losses for changes in exposure, but not for vulnerability, which is a major gap, given the dynamic nature of vulnerability ( [[#Mechler--2015|Mechler and Bouwer, 2015]] ).

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