1. Introduction

The aim of this document is to provide practical and relevant advice to national plant protection organizations (NPPOs) and regional plant protection organizations (RPPOs) on how to strengthen both national and regional phytosanitary systems to better assess and manage the pest risk that is a consequence of climate change.

The document also provides technical advice on incorporating climate-change considerations into regular phytosanitary activities. The advice has been developed by reviewing relevant literature and considering how it applies to the role of NPPOs.

Detailed factsheets about the impacts of climate change on plant pests are provided by several organizations, including the Food and Agriculture Organization of the United Nations (FAO), the Centre for Agriculture and Bioscience International (CABI), the Standards and Trade Development Facility and the Intergovernmental Panel on Climate Change (IPCC), among others. In addition, a video is provided by FAO (FAO, n.d.):
www.youtube.com/watch?v=xaK7CWtcNh4

Why is climate important for determining pest risk?

Climate change and extreme events can have significant impacts on pests by influencing their distribution and life cycle and hence their pest status and the associated level of pest risk.

Climate has a direct effect on invertebrate pests by influencing their rate of reproduction, development, survival, longevity and dispersal. Climate can also have an indirect influence on insect pests by its effect on plant hosts, natural enemies and competitors. With some exceptions, insects are ectothermic, meaning that they rely on external heat sources and sinks to regulate their body temperature. Small changes in temperature can have dramatic effects on the rate of biochemical reactions in insects, pathogens and vectors (Prakash et al., 2014). Therefore, any changes to the climate in a particular location or a period of extreme weather can have major impacts on insect pests.

Climatic factors are one of the three elements of the conceptual plant-disease triangle that explains the likely impact of plant pathogens. For an infection to take place, specific conditions must align: a susceptible host, a plant pathogen and an environment conducive to the pathogen’s proliferation. An example of this can be seen in the case of Xylella fastidiosa, which is a vector-transmitted bacterial plant pathogen of which some subspecies affect grapevines, Prunus, olives and a range of other plants. It is native to the Americas but has spread to parts of southern Europe as a result of host-plant availability and a conducive environment for its spread and establishment. The distribution of X. fastidiosa has been shown to be limited by cold conditions in the winter and, in the case of grapevines, temperatures above 37 °C have also been shown to limit its distribution (Godefroid, 2019).

All plants, including plants as pests, are also directly affected by climatic factors such as temperature, precipitation, humidity, radiation and carbon dioxide levels. These climatic factors affect the ability of plants to grow, establish, resist infection and spread. Although responses are variable and complex, in many cases anticipated climate changes are expected to favour plants as pests (Clements, DiTommaso and Hyvönen, 2014).

Trade offers a way to resolve challenges such as regional food shortages that result from climate-change impacts (Liu et al., 2014). However, climate-change impacts on pests and pest vectors also threaten the international trading system, as international trade provides a pathway for pests and pest vectors to spread into new areas of the world. Pest pressure resulting from increasing pest abundance may pose a challenge, as existing phytosanitary measures may not be sufficient to mitigate the risk of pests entering new environments. To reduce the potential negative impacts of international trade, it is therefore imperative to strengthen phytosanitary measures in response to climate change (Hulme, 2021).

Since pest and plant distribution, pest epidemiology and pest impacts may change considerably as a result of climate change, robust surveillance and monitoring systems are vital at national, regional and international levels. Knowledge about the potential changes in pest life cycles, epidemiology and pathogenicity that may be induced by climate change is essential when undertaking pest risk assessments to determine how to manage pest risk effectively and economically. Greater attention needs to be paid to phytosanitary issues in general policy considerations on climate change. It is essential that phytosanitary policies and strategies are adequately reflected in the work of the IPCC. Political influence, resourcing, and funding for phytosanitary needs at a national, regional and international level will only be available when phytosanitary issues are recognized as an important component of the climate-change debate.

Recent and projected changes in climate

It is unequivocal that human activities have resulted in a warming of the atmosphere, ocean and land over recent decades (IPCC, 2021). Widespread and rapid changes in the whole climate system have been observed, and the scale of some changes are unprecedented over thousands of years. By the 2010s, global surface temperature had risen by 1.1 °C above pre-industrial temperatures. Extreme weather and climate events, including heat waves, droughts, heavy precipitation and tropical cyclones have become more frequent and severe, and these have led to some irreversible impacts on ecosystems and people as natural and human systems are pushed beyond their ability to adapt (IPCC, 2022a).

Figure 1: Increase in global surface temperature change relative to the period 1850–1990.

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NOTES: Notes: Scenarios range from very low greenhouse-gas emissions (SSP1-1.9) to very high (SSP5-8.5).
For a description of the scenarios, see IPCC (2022). SSP, socioeconomic pathway.
SOURCE: IPCC (Intergovernmental Panel on Climate Change). 2022. Summary for policymakers. H.-O. Pörtner, D.C. Roberts, E.S. Poloczanska, K. Mintenbeck, M. Tignor, A. Alegría, M. Craig et al., eds. In: H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig et al., eds. Climate change 2022 – Impacts, adaptation and vulnerability, pp. 3–33. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK and New York, USA, Cambridge University Press. 3056 pp. doi.org/10.1017/9781009325844.001

Recent increases in temperature are projected to continue in the near term, then diverge on trajectories that are dependent on future emissions, as characterized by the IPCC shared socioeconomic pathways (SSPs: see Box 1). The trajectory of projected future change in climate is modelled under different assumptions of future emissions of greenhouse gases. In Figure 1, the scenarios range from projections of very low emissions (SSP1-1.9) to the highest emission scenario of SSP5-8.5. The actual rate of emissions that will occur in the future is dependent on the degree to which countries are able to reduce emissions and when they make these changes. Under the two lowest emission scenarios, temperature is projected to stabilize by the middle of this century and start to decline before the end of the century. Under the medium- and high-emission scenarios, temperature is projected to carry on increasing to 2100 and beyond. However, the shaded areas around the SSP-2.6 and SSP-7.0 projections illustrate the very likely range of possible outcomes under each scenario. By 2100, the range in projected temperature increase is about 1.4–2.3 °C and 3.0–5.0 °C for SSP1-2.6 and SSP3-7.0, respectively, from an 1850–1900 baseline. Thus, there is still considerable uncertainty about potential changes in temperature by the end of the century, even with the same emissions scenario.

The volume of precipitation has also been changing and is projected to change further. The IPCC synthesis report (IPCC, 2023) shows how soil moisture is projected to change under different temperature-increase scenarios from 1.5 to 4 °C. Under all scenarios, northern and western parts of South America, central America and the central area of North America, southern Africa, the Mediterranean region and central east Asia are projected to get dryer. Northern Canada, tropical areas of Africa, the Arabian Peninsula, central and northern Asia and much of India are projected to get wetter.

In addition to trends in average conditions (climate change), the frequency and severity of extreme climatic events have also been increasing in response to human-induced emissions of greenhouse gases (IPCC, 2021).

Box 1 · Representative concentration pathways (RCPs) and shared socioeconomic pathways (SSPs).

Representative concentration pathways (RCPs) and shared socioeconomic pathways (SSPs) are scenarios that have been developed to help understand the outcomes of different levels of greenhouse gas concentrations.

RCPs are scenarios based on a measure of the level of radiative force (the difference between incoming and outgoing energy). They describe the amount of the sun’s energy that is trapped by earth, measured in watts per square metre. Four scenarios have been developed: 2.6, 4.5, 6.0 and 8.5 (W/m2), where RCP 2.6 represents a pathway in which greenhouse gas emissions are strongly reduced, while RCP 8.5 is a pathway in which greenhouse gas emissions continue to grow. SSPs, on the other hand, broadly outline the socioeconomic conditions that lead to different levels of greenhouse gas emissions. Five SSPs have been described, ranging from SSP 1 (a world of sustainable growth and equality) to SSP 5 (a world of rapid and unconstrained growth in economic output and energy use). While SSPs elaborate five different world socioeconomic scenarios, RCPs describe the outcomes in terms of energy trapped for four different scenarios. RCPs were used in the IPCC Fifth Assessment Report (IPCC, 2014) and the SSPs in the Sixth Assessment Report (IPCC, 2022a).

Source: Authors’ own elaboration.

Temperature fluctuations and extremes have increased around the globe, based on observations since 1950. Furthermore, heavy rainfall events are likely to have increased over many land areas, although complex interactions between hydrology, climate and human management make it difficult to assess if climate change is affecting the character of droughts and floods over recent decades. Warming in tropical oceans is likely to have resulted in the increase in intensity and frequency of tropical storms over the last 40 years (IPCC, 2021).