Climate driven threshold effects in the natural environment

The second CCRA (CCRA2) was published in 2017 and was supported by a comprehensive Evidence Report from the Adaptation Sub-Committee (ASC). Defra and the devolved administrations are in the process of drafting updated national adaptation programmes in response to the risks and opportunities set out in the report.

The third CCRA will be published by the government in January 2022, and Defra have asked the ASC to produce an accompanying Evidence Report by summer 2021.To inform this Evidence Report the ASC are commissioning six research projects, funded by Defra, the devolved administrations and the research councils (NERC, ESRC and EPSRC). The ASC has been engaging with relevant stakeholders (e.g. researchers, funders, academies) with a view of addressing key evidence gaps from the CCRA2 report on a variety of timescales. The scientific literature is also being reviewed to identify work that may already exist in these areas.

A key knowledge gap identified in applying the urgency framework in CCRA2 related to the fact that many current studies of future risk provide linear projections of change, when there is a high probability that some changes will be non-linear. The natural environment (in both rural and urban areas) is particularly vulnerable to crossing thresholds that can potentially result in non-linear changes to the stock of natural capital (e.g. soil, water, certain species) and following this, the delivery of ecosystem goods and services (e.g. food, water regulation, cooling). For instance, as resilience is reduced or lost, the buffering the natural environment provides against climate hazards can also reach a point where it is sharply reduced.

Examples of thresholds in the natural environment might include: - the extent of sea level rise that would render agricultural production of high value crops in coastal zones economically unviable, through the intrusion of saline water into soils and aquifers, thereby forcing land managers to consider the need for land use change - drought levels at which green infrastructure loses its cooling and water regulation capacity due to drying out and hardening of surfaces.

The crossing of thresholds can result in irreversible changes to the natural environment, with major implications for human well-being. Through identifying and analysing the effect of crossing such thresholds, and prioritising those which have the most impact on societal health and well-being, and economic stability, this project will help us better assess the nature of the risk (step 1 in the urgency method) the effectiveness of current adaptation strategies to manage the risks (step 2 in the urgency method), and what the effects of further potential adaptations might be (step 3 in the urgency method).

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