Introduction

Effects of climate change on agriculture, forestry and ecosystems

The focus of this review is to assess the potential effects of climate change on plant pests and hence on plant health. A plant pest, hereafter referred to as a “pest”, is any species, strain or biotype of plant, animal or pathogenic agent injurious to plants or plant products, as per the definition in the International Standard for Phytosanitary Measures No. 5 (ISPM 5) adopted by the Commission on Phytosanitary Measures of the International Plant Protection Convention (IPPC).

Climate change is defined as an increase in combined surface-air and sea-surface temperatures, averaged over the globe, over a 30-year period. Warming is expressed relative to the period 1850–1900, which is used as an approximation of pre-industrial temperatures. Warming from pre-industrial levels compared to the decade 2006–2015 has been assessed to be 0.87 °C. Since 2000, the estimated level of human-induced warming has been equal to the level of observed warming, with a likely range of ±20 percent accounting for uncertainty due to contributions from solar and volcanic activity over the historical period (IPCC, 2018). Climate models project robust differences in regional climate characteristics between the present day and global warming of 1.5 °C and between 1.5 and 2.0 °C. Such differences include increases in mean temperature in most land and ocean regions, hot extremes in most inhabited areas, heavy precipitation in several regions, and the probability of drought and precipitation deficits in some regions (IPCC, 2018).

Climate change continues to present challenges to life and livelihoods globally (Altizer et al., 2013; IPCC, 2018). Changes observed include increased global land and ocean temperatures (Figure 1), loss of ice sheets and snow cover, rising sea levels, increased ocean acidification, more frequent warm extremes, more variable rainfall patterns and more frequent heavy-precipitation events and droughts (Figure 2). These changes have been attributed to increased emissions of anthropogenic greenhouse gases since the pre-industrial era, due to intensification of agricultural and industrial activities, combustion of fossil fuels, and changes in land use (Figures 3 and 4). Chemical analysis of ice and sediments indicates that atmospheric concentrations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) have been at unprecedented levels for at least the last 800 000 years.

Figure 1

Source: IPCC (2013).

The original, full legend for Figure 1 as published in IPCC (2013) is as follows:

Figure SPM.8 | Maps of CMIP5 multi-model mean results for the scenarios RCP2.6 and RCP8.5 in 2081–2100 of (a) annual mean surface temperature change, (b) average percent change in annual mean precipitation, (c) Northern Hemisphere September sea ice extent, and (d) change in ocean surface pH. Changes in panels (a), (b) and (d) are shown relative to 1986–2005. The number of CMIP5 models used to calculate the multi-model mean is indicated in the upper right corner of each panel. For panels (a) and (b), hatching indicates regions where the multi-model mean is small compared to natural internal variability (i.e., less than one standard deviation of natural internal variability in 20-year means). Stippling indicates regions where the multi-model mean is large compared to natural internal variability (i.e., greater than two standard deviations of natural internal variability in 20-year means) and where at least 90% of models agree on the sign of change (see Box 12.1). In panel (c), the lines are the modelled means for 1986−2005; the filled areas are for the end of the century. The CMIP5 multi-model mean is given in white colour, the projected mean sea ice extent of a subset of models (number of models given in brackets) that most closely reproduce the climatological mean state and 1979 to 2012 trend of the Arctic sea ice extent is given in light blue colour. For further technical details see the Technical Summary Supplementary Material. {Figures 6.28, 12.11, 12.22, and 12.29; Figures TS.15, TS.16, TS.17, and TS.20}

For more information, please consult the original source (IPCC, 2013). Reproduced with the kind permission of the Intergovernmental Panel on Climate Change.

Figure 2

Source: IPCC (2013).

The original full legend for Figure 2 as published in IPCC (2013) is as follows:

Figure SPM.2 | Maps of observed precipitation change from 1901 to 2010 and from 1951 to 2010 (trends in annual accumulation calculated using the same criteria as in Figure SPM.1) from one data set. For further technical details see the Technical Summary Supplementary Material. {TS TFE.1, Figure 2; Figure 2.29}

For more information, please consult the original source (IPCC, 2013). Reproduced with the kind permission of the Intergovernmental Panel on Climate Change.

Figure 3

Source: IPCC (2013).

The original full legend for Figure 3 as published in IPCC (2013) is as follows:

Figure SPM.10 | Global mean surface temperature increase as a function of cumulative total global CO2 emissions from various lines of evidence. Multimodel results from a hierarchy of climate-carbon cycle models for each RCP until 2100 are shown with coloured lines and decadal means (dots). Some decadal means are labeled for clarity (e.g., 2050 indicating the decade 2040−2049). Model results over the historical period (1860 to 2010) are indicated in black. The coloured plume illustrates the multi-model spread over the four RCP scenarios and fades with the decreasing number of available models in RCP8.5. The multi-model mean and range simulated by CMIP5 models, forced by a CO2 increase of 1% per year (1% yr–1 CO2 simulations), is given by the thin black line and grey area. For a specific amount of cumulative CO2 emissions, the 1% per year CO2 simulations exhibit lower warming than those driven by RCPs, which include additional non-CO2 forcings. Temperature values are given relative to the 1861−1880 base period, emissions relative to 1870. Decadal averages are connected by straight lines. For further technical details see the Technical Summary Supplementary Material. {Figure 12.45; TS TFE.8, Figure 1}

For more information, please consult the original source (IPCC, 2013). Reproduced with the kind permission of the Intergovernmental Panel on Climate Change.

Figure 4

Source: IPCC (2013).

The original, full legend for Figure 4 as published in IPCC (2013) is as follows:

Figure SPM.5 | Radiative forcing estimates in 2011 relative to 1750 and aggregated uncertainties for the main drivers of climate change. Values are global average radiative forcing (RF14), partitioned according to the emitted compounds or processes that result in a combination of drivers. The best estimates of the net radiative forcing are shown as black diamonds with corresponding uncertainty intervals; the numerical values are provided on the right of the figure, together with the confidence level in the net forcing (VH – very high, H – high, M – medium, L – low, VL – very low). Albedo forcing due to black carbon on snow and ice is included in the black carbon aerosol bar. Small forcings due to contrails (0.05 W m^–2, including contrail induced cirrus), and HFCs, PFCs and SF6 (total 0.03 W m^–2) are not shown. Concentration-based RFs for gases can be obtained by summing the like-coloured bars. Volcanic forcing is not included as its episodic nature makes is difficult to compare to other forcing mechanisms. Total anthropogenic radiative forcing is provided for three different years relative to 1750. For further technical details, including uncertainty ranges associated with individual components and processes, see the Technical Summary Supplementary Material. {8.5; Figures 8.14–8.18; Figures TS.6 and TS.7}

For more information, please consult the original source (IPCC, 2013). Reproduced with the kind permission of the Intergovernmental Panel on Climate Change.

Their effects, together with those of other anthropogenic drivers such as deforestation, are the dominant cause of the observed warming since the mid-twentieth century (IPCC, 2014a, 2014b, 2018; Wuebbles and Hayhoe, 2002). Importantly, global climate change, especially global warming, is likely to continue. According to the Intergovernmental Panel on Climate Change (IPCC) Special Report on Global Warming of 1.5 °C, global warming is likely to reach a 1.5 °C increase between 2030 and 2052 compared to pre-industrial levels if the warming continues to increase at the current pace (IPCC, 2018).¹

Climate-related risks are higher for global warming of 1.5 °C compared to the current risks,² but the risks are significantly more severe if the global warming reaches 2 °C. Risks depend on the degree and pace of warming, geographical location, levels of regional and local development and vulnerability, and realized adaptation and mitigation activities (IPCC, 2018).

Climate-change impacts are already emerging for natural and human systems, including changes in water quantity and quality, and shifts in geographical ranges, seasonal activities, migration patterns, species abundance and interactions for many terrestrial, freshwater and marine species (IPCC, 2014a, 2019a, 2019b), with more negative than positive impacts on the yields of most crops (Porter et al., 2019). There is evidence that climate change is affecting biological systems at multiple scales, from genes to ecosystems (Garrett et al., 2006; Sutherst et al., 2011). According to Scheffers et al. (2016), anthropogenic climate change has impaired 82 percent of 94 core ecological processes recognized by biologists, from genetic diversity to ecosystem function.

Furthermore, already existing risks such as reduced freshwater availability will be amplified, and new ones will arise during and beyond the twenty-first century. Future impacts will include increased extinction risk. For example, most plant species cannot naturally change their geographical range quickly enough to keep pace with the rate of climate change, and marine organisms will be exposed to lower oxygen levels and greater acidification, to which they might not be able to adapt. Further climate change may also threaten food security through impacts on food crops and plant-based animal feed. For wheat, rice and maize, the worst impacts are expected in the tropics and subtropics, with climate change projected to negatively impact production where local temperature increases by 2 °C or more above late twentieth-century levels, although some individual locations may benefit from this change, especially at higher latitudes and altitudes. Global food and fibre production, plant protection and plant biosecurity, which include all strategies to assess and manage the risks posed by infectious diseases, quarantine regulated pests, invasive alien species and living modified organisms in natural and managed ecosystems, will also be adversely impacted (Gregory et al., 2009; Stack, Fletcher and Gullino, 2013).

The aim of this report is to provide information on (i) what has happened in the last decades; (ii) what is expected to happen in the coming decades as a result of climate change; and (iii) what we can do in order to mitigate the impacts of, and adapt to, changing climates locally, regionally and globally.

It is beyond the scope of this report either to address the causes of climate change or to provide a comprehensive summary of all results published during the past 30 years. Instead, many examples of publications are cited for further, in-depth reading.