Editing IPCC:AR6/SR15/Chapter-3 (section)

=== 3.4.3 Terrestrial and Wetland Ecosystems ===

<div id="section-3-4-3-1"></div>

<span id="biome-shifts"></span>
==== 3.4.3.1 Biome shifts ====

<div id="section-3-4-3-1-block-1"></div>

Latitudinal and elevational shifts of biomes (major ecosystem types) in boreal, temperate and tropical regions have been detected (Settele et al., 2014) <sup>[[#fn:r448|448]]</sup> and new studies confirm these changes (e.g., shrub encroachment on tundra; Larsen et al., 2014) <sup>[[#fn:r449|449]]</sup> . Attribution studies indicate that anthropogenic climate change has made a greater contribution to these changes than any other factor ( ''medium confidence'' ) (Settele et al., 2014) <sup>[[#fn:r450|450]]</sup> .

An ensemble of seven Dynamic Vegetation Models driven by projected climates from 19 alternative general circulation models (GCMs) (Warszawski et al., 2013) <sup>[[#fn:r451|451]]</sup> shows 13% (range 8–20%) of biomes transforming at 2°C of global warming, but only 4% (range 2–7%) doing so at 1°C, suggesting that about 6.5% may be transformed at 1.5°C; these estimates indicate a doubling of the areal extent of biome shifts between 1.5°C and 2°C of warming ( ''medium confidence'' ) (Figure 3.16a). A study using the single ecosystem model LPJmL (Gerten et al., 2013) <sup>[[#fn:r452|452]]</sup> illustrated that biome shifts in the Arctic, Tibet, Himalayas, southern Africa and Australia would be avoided by constraining warming to 1.5°C compared with 2°C (Figure 3.16b). Seddon et al. (2016) <sup>[[#fn:r453|453]]</sup> quantitatively identified ecologically sensitive regions to climate change in most of the continents from tundra to tropical rainforest. Biome transformation may in some cases be associated with novel climates and ecological communities (Prober et al., 2012) <sup>[[#fn:r454|454]]</sup> .

<div id="section-3-4-3-1-block-2"></div>

<span id="figure-3.16a"></span>
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'''Figure 3.16a'''

<span id="a-fraction-of-global-natural-vegetation-including-managed-forests-at-risk-of-severe-ecosystem-change-as-a-function-of-global-mean-temperature-change-for-all-ecosystems-models-global-climate-change-models-and-representative-concentration-pathways-rcps."></span>
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'''(a) Fraction of global natural vegetation (including managed forests) at risk of severe ecosystem change as a function of global mean temperature change for all ecosystems, models, global climate change models and Representative Concentration Pathways (RCPs).'''
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[[File:fef2728679f8329baa7d71882cc054c0 Figure-3.16a-1024x736.jpg]]

The colours represent the different ecosystem models, which are also horizontally separated for clarity. Results are collated in unit-degree bins, where the temperature for a given year is the average over a 30-year window centred on that year. The boxes span the 25th and 75th percentiles across the entire ensemble. The short, horizontal stripes represent individual (annual) data points, the curves connect the mean value per ecosystem model in each bin. The solid (dashed) curves are for models with (without) dynamic vegetation composition changes. Source: (Warszawski et al., 2013) <sup>[[#fn:r455|455]]</sup>

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<span id="figure-3.16b"></span>
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'''Figure 3.16b'''

<span id="b-threshold-level-of-global-temperature-anomaly-above-pre-industrial-levels-that-leads-to-significant-local-changes-in-terrestrial-ecosystems."></span>
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'''(b) Threshold level of global temperature anomaly above pre-industrial levels that leads to significant local changes in terrestrial ecosystems.'''
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[[File:0d97820d01076b5b32d68d0c7864863f figure-3.16b-1024x512.jpg]]

Regions with severe (coloured) or moderate (greyish) ecosystem transformation; delineation refers to the 90 biogeographic regions. All values denote changes found in &gt;50% of the simulations. Source: (Gerten et al., 2013) <sup>[[#fn:r456|456]]</sup> . Regions coloured in dark red are projected to undergo severe transformation under a global warming of 1.5°C while those coloured in light red do so at 2°C; other colours are used when there is no severe transformation unless global warming exceeds 2°C.

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<div id="section-3-4-3-2"></div>

<span id="changes-in-phenology"></span>
==== 3.4.3.2 Changes in phenology ====

<div id="section-3-4-3-2-block-1"></div>

Advancement in spring phenology of 2.8 ± 0.35 days per decade has been observed in plants and animals in recent decades in most Northern Hemisphere ecosystems (between 30°N and 72°N), and these shifts have been attributed to changes in climate ( ''high confidence'' ) (Settele et al., 2014) <sup>[[#fn:r457|457]]</sup> . The rates of change are particularly high in the Arctic zone owing to the stronger local warming (Oberbauer et al., 2013) <sup>[[#fn:r458|458]]</sup> , whereas phenology in tropical forests appears to be more responsive to moisture stress (Zhou et al., 2014) <sup>[[#fn:r459|459]]</sup> . While a full review cannot be included here, trends consistent with this earlier finding continue to be detected, including in the flowering times of plants (Parmesan and Hanley, 2015) <sup>[[#fn:r460|460]]</sup> , in the dates of egg laying and migration in birds (newly reported in China; Wu and Shi, 2016) <sup>[[#fn:r461|461]]</sup> , in the emergence dates of butterflies (Roy et al., 2015) <sup>[[#fn:r462|462]]</sup> , and in the seasonal greening-up of vegetation as detected by satellites (i.e., in the normalized difference vegetation index, NDVI; Piao et al., 2015) <sup>[[#fn:r463|463]]</sup> .

The potential for decoupling species–species interactions owing to differing phenological responses to climate change is well established (Settele et al., 2014) <sup>[[#fn:r464|464]]</sup> , for example for plants and their insect pollinators (Willmer, 2012; Scaven and Rafferty, 2013) <sup>[[#fn:r465|465]]</sup> . Mid-century projections of plant and animal phenophases in the UK clearly indicate that the timing of phenological events could change more for primary consumers (6.2 days earlier on average) than for higher trophic levels (2.5–2.9 days earlier on average) (Thackeray et al., 2016) <sup>[[#fn:r466|466]]</sup> . This indicates the potential for phenological mismatch and associated risks for ecosystem functionality in the future under global warming of 2.1°C–2.7°C above pre-industrial levels. Further, differing responses could alter community structure in temperate forests (Roberts et al., 2015) <sup>[[#fn:r467|467]]</sup> . Specifically, temperate forest phenology is projected to advance by 14.3 days in the near term (2010–2039) and 24.6 days in the medium term (2040–2069), so as a first approximation the difference between 2°C and 1.5°C of global warming is about 10 days (Roberts et al., 2015) <sup>[[#fn:r468|468]]</sup> . This phenological plasticity is not always adaptive and must be interpreted cautiously (Duputié et al., 2015) <sup>[[#fn:r469|469]]</sup> , and considered in the context of accompanying changes in climate variability (e.g., increased risk of frost damage for plants or earlier emergence of insects resulting in mortality during cold spells). Another adaptive response of some plants is range expansion with increased vigour and altered herbivore resistance in their new range, analogous to invasive plants (Macel et al., 2017) <sup>[[#fn:r470|470]]</sup> .

In summary, limiting warming to 1.5°C compared with 2°C may avoid advance in spring phenology ( ''high confidence'' ) by perhaps a few days ( ''medium confidence'' ) and hence decrease the risks of loss of ecosystem functionality due to phenological mismatch between trophic levels, and also of maladaptation coming from the sensitivity of many species to increased climate variability. Nevertheless, this difference between 1.5°C and 2°C of warming might be limited for plants that are able to expand their range.

<div id="section-3-4-3-3"></div>

<span id="changes-in-species-range-abundance-and-extinction"></span>
==== 3.4.3.3 Changes in species range, abundance and extinction ====

<div id="section-3-4-3-3-block-1"></div>

AR5 (Settele et al., 2014) <sup>[[#fn:r471|471]]</sup> concluded that the geographical ranges of many terrestrial and freshwater plant and animal species have moved over the last several decades in response to warming: approximately 17 km poleward and 11 m up in altitude per decade. Recent trends confirm this finding; for example, the spatial and interspecific variance in bird populations in Europe and North America since 1980 were found to be well predicted by trends in climate suitability (Stephens et al., 2016) <sup>[[#fn:r472|472]]</sup> . Further, a recent meta-analysis of 27 studies concerning a total of 976 species (Wiens, 2016) <sup>[[#fn:r473|473]]</sup> found that 47% of local extinctions (extirpations) reported across the globe during the 20th century could be attributed to climate change, with significantly more extinctions occurring in tropical regions, in freshwater habitats and for animals. IUCN (2018) <sup>[[#fn:r474|474]]</sup> lists 305 terrestrial animal and plant species from Pacific Island developing nations as being threatened by climate change and severe weather. Owing to lags in the responses of some species to climate change, shifts in insect pollinator ranges may result in novel assemblages with unknown implications for biodiversity and ecosystem function (Rafferty, 2017) <sup>[[#fn:r475|475]]</sup> .

Warren et al. (2013) <sup>[[#fn:r476|476]]</sup> simulated climatically determined geographic range loss under 2°C and 4°C of global warming for 50,000 plant and animal species, accounting for uncertainty in climate projections and for the potential ability of species to disperse naturally in an attempt to track their geographically shifting climate envelope. This earlier study has now been updated and expanded to incorporate 105,501 species, including 19,848 insects, and new findings indicate that warming of 2°C by 2100 would lead to projected bioclimatic range losses of &gt;50% in 18% (6–35%) of the 19,848 insects species, 8% (4–16%) of the 12,429 vertebrate species, and 16% (9–28%) of the 73,224 plant species studied (Warren et al., 2018a) <sup>[[#fn:r477|477]]</sup> . At 1.5°C of warming, these values fall to 6% (1–18%) of the insects, 4% (2–9%) of the vertebrates and 8% (4–15%) of the plants studied. Hence, the number of insect species projected to lose over half of their geographic range is reduced by two-thirds when warming is limited to 1.5°C compared with 2°C, while the number of vertebrate and plant species projected to lose over half of their geographic range is halved (Warren et al., 2018a) <sup>[[#fn:r478|478]]</sup> ( ''medium confidence'' ). These findings are consistent with estimates made from an earlier study suggesting that range losses at 1.5°C were significantly lower for plants than those at 2°C of warming (Smith et al., 2018) <sup>[[#fn:r479|479]]</sup> . It should be noted that at 1.5°C of warming, and if species’ ability to disperse naturally to track their preferred climate geographically is inhibited by natural or anthropogenic obstacles, there would still remain 10% of the amphibians, 8% of the reptiles, 6% of the mammals, 5% of the birds, 10% of the insects and 8% of the plants which are projected to lose over half their range, while species on average lose 20–27% of their range (Warren et al., 2018a) <sup>[[#fn:r480|480]]</sup> . Given that bird and mammal species can disperse more easily than amphibians and reptiles, a small proportion can expand their range as climate changes, but even at 1.5°C of warming the total range loss integrated over all birds and mammals greatly exceeds the integrated range gain (Warren et al., 2018a) <sup>[[#fn:r481|481]]</sup> .

A number of caveats are noted for studies projecting changes to climatic range. This approach, for example, does not incorporate the effects of extreme weather events and the role of interactions between species. As well, trophic interactions may locally counteract the range expansion of species towards higher altitudes (Bråthen et al., 2018) <sup>[[#fn:r482|482]]</sup> . There is also the potential for highly invasive species to become established in new areas as the climate changes (Murphy and Romanuk, 2014) <sup>[[#fn:r483|483]]</sup> , but there is no literature that quantifies this possibility for 1.5°C of global warming.

Pecl et al. (2017) <sup>[[#fn:r484|484]]</sup> summarized at the global level the consequences of climate-change-induced species redistribution for economic development, livelihoods, food security, human health and culture. These authors concluded that even if anthropogenic greenhouse gas emissions stopped today, the effort for human systems to adapt to the most crucial effects of climate-driven species redistribution will be far-reaching and extensive. For example, key insect crop pollinator families (Apidae, Syrphidae and Calliphoridae; i.e., bees, hoverflies and blowflies) are projected to retain significantly greater geographic ranges under 1.5°C of global warming compared with 2°C (Warren et al., 2018a) <sup>[[#fn:r485|485]]</sup> . In some cases, when species (such as pest and disease species) move into areas which have become climatically suitable they may become invasive or harmful to human or natural systems (Settele et al., 2014) <sup>[[#fn:r486|486]]</sup> . Some studies are beginning to locate ‘refugial’ areas where the climate remains suitable in the future for most of the species currently present. For example, Smith et al., (2018) <sup>[[#fn:r487|487]]</sup> estimated that 5.5–14% more of the globe’s terrestrial land area could act as climatic refugia for plants under 1.5°C of warming compared to 2°C.

There is no literature that directly estimates the proportion of species at increased risk of global (as opposed to local) commitment to extinction as a result of climate change, as this is inherently difficult to quantify. However, it is possible to compare the proportions of species at risk of very high range loss; for example, a discernibly smaller number of terrestrial species are projected to lose over 90% of their range at 1.5°C of global warming compared with 2°C (Figure 2 in Warren et al., 2018a) <sup>[[#fn:r488|488]]</sup> . A link between very high levels of range loss and greatly increased extinction risk may be inferred (Urban, 2015) <sup>[[#fn:r489|489]]</sup> . Hence, limiting global warming to 1.5°C compared with 2°C would be expected to reduce both range losses and associated extinction risks in terrestrial species ( ''high confidence'' ).

<div id="section-3-4-3-4"></div>

<span id="changes-in-ecosystem-function-biomass-and-carbon-stocks"></span>
==== 3.4.3.4 Changes in ecosystem function, biomass and carbon stocks ====

<div id="section-3-4-3-4-block-1"></div>

Working Group II of AR5 (Settele et al., 2014) <sup>[[#fn:r490|490]]</sup> concluded that there is ''high confidence'' that net terrestrial ecosystem productivity at the global scale has increased relative to the pre-industrial era and that rising CO <sub>2</sub> concentrations are contributing to this trend through stimulation of photosynthesis. There is, however, no clear and consistent signal of a climate change contribution. In northern latitudes, the change in productivity has a lower velocity than the warming, possibly because of a lack of resource and vegetation acclimation mechanisms (M. Huang et al., 2017) <sup>[[#fn:r491|491]]</sup> . Biomass and soil carbon stocks in terrestrial ecosystems are currently increasing ( ''high confidence'' ), but they are vulnerable to loss of carbon to the atmosphere as a result of projected increases in the intensity of storms, wildfires, land degradation and pest outbreaks (Settele et al., 2014; Seidl et al., 2017) <sup>[[#fn:r492|492]]</sup> . These losses are expected to contribute to a decrease in the terrestrial carbon sink. Anderegg et al. (2015) <sup>[[#fn:r493|493]]</sup> demonstrated that total ecosystem respiration at the global scale has increased in response to increases in night-time temperature (1 PgC yr <sup>–1</sup> °C <sup>–1</sup> , ''P'' =0.02).

The increase in total ecosystem respiration in spring and autumn, associated with higher temperatures, may convert boreal forests from carbon sinks to carbon sources (Hadden and Grelle, 2016) <sup>[[#fn:r494|494]]</sup> . In boreal peatlands, for example, increased temperature may diminish carbon storage and compromise the stability of the peat (Dieleman et al., 2016) <sup>[[#fn:r495|495]]</sup> . In addition, J. Yang et al. (2015) <sup>[[#fn:r496|496]]</sup> showed that fires reduce the carbon sink of global terrestrial ecosystems by 0.57 PgC yr <sup>–1</sup> in ecosystems with large carbon stores, such as peatlands and tropical forests. Consequently, for adaptation purposes, it is necessary to enhance carbon sinks, especially in forests which are prime regulators within the water, energy and carbon cycles (Ellison et al., 2017) <sup>[[#fn:r497|497]]</sup> . Soil can also be a key compartment for substantial carbon sequestration (Lal, 2014; Minasny et al., 2017) <sup>[[#fn:r498|498]]</sup> , depending on the net biome productivity and the soil quality (Bispo et al., 2017) <sup>[[#fn:r499|499]]</sup> .

AR5 assessed that large uncertainty remains regarding the land carbon cycle behaviour of the future (Ciais et al., 2013) <sup>[[#fn:r500|500]]</sup> , with most, but not all, CMIP5 models simulating continued terrestrial carbon uptake under all four RCP scenarios (Jones et al., 2013) <sup>[[#fn:r501|501]]</sup> . Disagreement between models outweighs differences between scenarios even up to the year 2100 (Hewitt et al., 2016; Lovenduski and Bonan, 2017) <sup>[[#fn:r502|502]]</sup> . Increased atmospheric CO <sub>2</sub> concentrations are expected to drive further increases in the land carbon sink (Ciais et al., 2013; Schimel et al., 2015) <sup>[[#fn:r503|503]]</sup> , which could persist for centuries (Pugh et al., 2016) <sup>[[#fn:r504|504]]</sup> . Nitrogen, phosphorus and other nutrients will limit the terrestrial carbon cycle response to both elevated CO <sub>2</sub> and altered climate (Goll et al., 2012; Yang et al., 2014; Wieder et al., 2015; Zaehle et al., 2015; Ellsworth et al., 2017) <sup>[[#fn:r505|505]]</sup> . Climate change may accelerate plant uptake of carbon (Gang et al., 2015) <sup>[[#fn:r506|506]]</sup> but also increase the rate of decomposition (Todd-Brown et al., 2014; Koven et al., 2015; Crowther et al., 2016) <sup>[[#fn:r507|507]]</sup> . Ahlström et al. (2012) <sup>[[#fn:r508|508]]</sup> found a net loss of carbon in extra-tropical regions and the largest spread across model results in the tropics. The projected net effect of climate change is to reduce the carbon sink expected under CO <sub>2</sub> increase alone (Settele et al., 2014) <sup>[[#fn:r509|509]]</sup> . Friend et al. (2014) <sup>[[#fn:r510|510]]</sup> found substantial uptake of carbon by vegetation under future scenarios when considering the effects of both climate change and elevated CO <sub>2</sub> .

There is limited published literature examining modelled land carbon changes specifically under 1.5°C of warming, but existing CMIP5 models and published data are used in this report to draw some conclusions. For systems with significant inertia, such as vegetation or soil carbon stores, changes in carbon storage will depend on the rate of change of forcing and thus depend on the choice of scenario (Jones et al., 2009; Ciais et al., 2013; Sihi et al., 2017) <sup>[[#fn:r511|511]]</sup> . To avoid legacy effects of the choice of scenario, this report focuses on the response of gross primary productivity (GPP) – the rate of photosynthetic carbon uptake – by the models, rather than by changes in their carbon store.

Figure 3.17 shows different responses of the terrestrial carbon cycle to climate change in different regions. The models show a consistent response of increased GPP in temperate latitudes of approximately 2 GtC yr <sup>–1 °</sup> C <sup>–1</sup> . Similarly, Gang et al. (2015) <sup>[[#fn:r512|512]]</sup> projected a robust increase in the net primary productivity (NPP) of temperate forests. However, Ahlström et al. (2012) <sup>[[#fn:r513|513]]</sup> showed that this effect could be offset or reversed by increases in decomposition. Globally, most models project that GPP will increase or remain approximately unchanged (Hashimoto et al., 2013) <sup>[[#fn:r514|514]]</sup> . This projection is supported by findings by Sakalli et al. (2017) <sup>[[#fn:r515|515]]</sup> for Europe using Euro-CORDEX regional models under a 2°C global warming for the period 2034–2063, which indicated that storage will increase by 5% in soil and by 20% in vegetation. However, using the same models Jacob et al. (2018) <sup>[[#fn:r516|516]]</sup> showed that limiting warming to 1.5°C instead of 2°C avoids an increase in ecosystem vulnerability (compared to a no-climate change scenario) of 40–50%.

At the global level, linear scaling is acceptable for net primary production, biomass burning and surface runoff, and impacts on terrestrial carbon storage are projected to be greater at 2°C than at 1.5°C (Tanaka et al., 2017) <sup>[[#fn:r517|517]]</sup> . If global CO <sub>2</sub> concentrations and temperatures stabilize, or peak and decline, then both land and ocean carbon sinks – which are primarily driven by the continued increase in atmospheric CO <sub>2</sub> – will also decline and may even become carbon sources (Jones et al., 2016) <sup>[[#fn:r518|518]]</sup> . Consequently, if a given amount of anthropogenic CO <sub>2</sub> is removed from the atmosphere, an equivalent amount of land and ocean anthropogenic CO <sub>2</sub> will be released to the atmosphere (Cao and Caldeira, 2010) <sup>[[#fn:r519|519]]</sup> .

In conclusion ''',''' ecosystem respiration is expected to increase with increasing temperature, thus reducing soil carbon storage. Soil carbon storage is expected to be larger if global warming is restricted to 1.5°C, although some of the associated changes will be countered by enhanced gross primary production due to elevated CO <sub>2</sub> concentrations (i.e., the ‘fertilization effect’) and higher temperatures, especially at mid-and high latitudes ( ''medium confidence'' ).

<div id="section-3-4-3-4-block-2"></div>

<span id="figure-3.17"></span>
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'''Figure 3.17'''

<span id="the-response-of-terrestrial-productivity-gross-primary-productivity-gpp-to-climate-change-globally-top-left-and-for-three-latitudinal-regions-30s30n-3060n-and-6090n."></span>
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'''The response of terrestrial productivity (gross primary productivity, GPP) to climate change, globally (top left) and for three latitudinal regions: 30°S–30°N; 30–60°N and 60–90°N.'''
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[[File:eed1efa6770815d3006b426ffc7e5322 figure-3.17-1024x755.jpg]]

Data come from the Coupled Model Intercomparison Project Phase 5 (CMIP5) archive (http://cmip-pcmdi.llnl.gov/cmip5/). Seven Earth System Models were used: Norwegian Earth System Model (NorESM-ME, yellow); Community Earth System Model (CESM, red); Institute Pierre Simon Laplace (IPLS)-CM5-LR (dark blue); Geophysical Fluid Dynamics Laboratory (GFDL, pale blue); Max Plank Institute-Earth System Model (MPI-ESM, pink); Hadley Centre New Global Environmental Model 2-Earth System (HadGEM2-ES, orange); and Canadian Earth System Model 2 (CanESM2, green). Differences in GPP between model simulations with (‘1pctCO <sub>2</sub> ’) and without (‘esmfixclim1’) the effects of climate change are shown. Data are plotted against the global mean temperature increase above pre-industrial levels from simulations with a 1% per year increase in CO <sub>2</sub> (‘1pctCO <sub>2</sub> ’).

Original Creation for this Report using CMIP5

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<div id="section-3-4-3-5"></div>

<span id="regional-and-ecosystem-specific-risks"></span>
==== 3.4.3.5 Regional and ecosystem-specific risks ====

<div id="section-3-4-3-5-block-1"></div>

A large number of threatened systems, including mountain ecosystems, highly biodiverse tropical wet and dry forests, deserts, freshwater systems and dune systems, were assessed in AR5. These include Mediterranean areas in Europe, Siberian, tropical and desert ecosystems in Asia, Australian rainforests, the Fynbos and succulent Karoo areas of South Africa, and wetlands in Ethiopia, Malawi, Zambia and Zimbabwe. In all these systems, it has been shown that impacts accrue with greater warming, and thus impacts at 2°C are expected to be greater than those at 1.5°C ( ''medium confidence'' ).

The High Arctic region, with tundra-dominated landscapes, has warmed more than the global average over the last century (Section 3.3; Settele et al., 2014) <sup>[[#fn:r520|520]]</sup> . The Arctic tundra biome is experiencing increasing fire disturbance and permafrost degradation (Bring et al., 2016; DeBeer et al., 2016; Jiang et al., 2016; Yang et al., 2016) <sup>[[#fn:r521|521]]</sup> . Both of these processes facilitate the establishment of woody species in tundra areas. Arctic terrestrial ecosystems are being disrupted by delays in winter onset and mild winters associated with global warming ( ''high confidence'' ) (Cooper, 2014) <sup>[[#fn:r522|522]]</sup> . Observational constraints suggest that stabilization at 1.5°C of warming would avoid the thawing of approximately 1.5 to 2.5 million km <sup>2</sup> of permafrost ( ''medium confidence'' ) compared with stabilization at 2°C (Chadburn et al., 2017) <sup>[[#fn:r523|523]]</sup> , but the time scale for release of thawed carbon as CO <sub>2</sub> or CH <sub>4</sub> should be many centuries (Burke et al., 2017) <sup>[[#fn:r524|524]]</sup> . In northern Eurasia, the growing season length is projected to increase by about 3–12 days at 1.5°C and 6–16 days at 2°C of warming ( ''medium confidence'' ) (Zhou et al., 2018) <sup>[[#fn:r525|525]]</sup> . Aalto et al. (2017) <sup>[[#fn:r526|526]]</sup> predicted a 72% reduction in cryogenic land surface processes in northern Europe for RCP2.6 in 2040–2069 (corresponding to a global warming of approximately 1.6°C), with only slightly larger losses for RCP4.5 (2°C of global warming).

Projected impacts on forests as climate change occurs include increases in the intensity of storms, wildfires and pest outbreaks (Settele et al., 2014) <sup>[[#fn:r527|527]]</sup> , potentially leading to forest dieback ( ''medium confidence'' ). Warmer and drier conditions in particular facilitate fire, drought and insect disturbances, while warmer and wetter conditions increase disturbances from wind and pathogens (Seidl et al., 2017) <sup>[[#fn:r528|528]]</sup> . Particularly vulnerable regions are Central and South America, Mediterranean Basin, South Africa, South Australia where the drought risk will increase (see Figure 3.12). Including disturbances in simulations may influence productivity changes in European forests in response to climate change (Reyer et al., 2017b) <sup>[[#fn:r529|529]]</sup> . There is additional evidence for the attribution of increased forest fire frequency in North America to anthropogenic climate change during 1984–2015, via the mechanism of increasing fuel aridity almost doubling the western USA forest fire area compared to what would have been expected in the absence of climate change (Abatzoglou and Williams, 2016) <sup>[[#fn:r530|530]]</sup> . This projection is in line with expected fire risks, which indicate that fire frequency could increase over 37.8% of the global land area during 2010–2039 (Moritz et al., 2012) <sup>[[#fn:r531|531]]</sup> , corresponding to a global warming level of approximately 1.2°C, compared with over 61.9% of the global land area in 2070–2099, corresponding to a warming of approximately 3.5°C <sup>[[#fn:9|9]]</sup> .The values in Table 26-1 in a recent paper by Romero-Lankao et al. (2014) <sup>[[#fn:r532|532]]</sup> also indicate significantly lower wildfire risks in North America for near-term warming (2030–2040, considered a proxy for 1.5°C of warming) than at 2°C ( ''high confidence'' ).

The Amazon tropical forest has been shown to be close to its climatic limits (Hutyra et al., 2005) <sup>[[#fn:r533|533]]</sup> , but this threshold may move under elevated CO <sub>2</sub> (Good et al., 2011) <sup>[[#fn:r534|534]]</sup> . Future changes in rainfall, especially dry season length, will determine responses of the Amazon forest (Good et al., 2013) <sup>[[#fn:r535|535]]</sup> . The forest may be especially vulnerable to combined pressure from multiple stressors, namely changes in climate and continued anthropogenic disturbance (Borma et al., 2013; Nobre et al., 2016) <sup>[[#fn:r536|536]]</sup> . Modelling (Huntingford et al., 2013) <sup>[[#fn:r537|537]]</sup> and observational constraints (Cox et al., 2013) <sup>[[#fn:r538|538]]</sup> suggest that large-scale forest dieback is less ''likely'' than suggested under early coupled modelling studies (Cox et al., 2000; Jones et al., 2009) <sup>[[#fn:r539|539]]</sup> . Nobre et al. (2016) <sup>[[#fn:r540|540]]</sup> estimated a climatic threshold of 4°C of warming and a deforestation threshold of 40%.

In many places around the world, the savanna boundary is moving into former grasslands. Woody encroachment, including increased tree cover and biomass, has increased over the past century, owing to changes in land management, rising CO <sub>2</sub> levels, and climate variability and change (often in combination) (Settele et al., 2014) <sup>[[#fn:r541|541]]</sup> . For plant species in the Mediterranean region, shifts in phenology, range contraction and health decline have been observed with precipitation decreases and temperature increases ( ''medium confidence'' ) (Settele et al., 2014) <sup>[[#fn:r542|542]]</sup> . Recent studies using independent complementary approaches have shown that there is a regional-scale threshold in the Mediterranean region between 1.5°C and 2°C of warming (Guiot and Cramer, 2016; Schleussner et al., 2016b) <sup>[[#fn:r543|543]]</sup> . Further, Guiot and Cramer (2016) <sup>[[#fn:r544|544]]</sup> concluded that biome shifts unprecedented in the last 10,000 years can only be avoided if global warming is constrained to 1.5°C ( ''medium confidence'' ) – whilst 2°C of warming will result in a decrease of 12–15% of the Mediterranean biome area. The Fynbos biome in southwestern South Africa is vulnerable to the increasing impact of fires under increasing temperatures and drier winters. It is projected to lose about 20%, 45% and 80% of its current suitable climate area under 1°C, 2°C and 3°C of global warming, respectively, compared to 1961–1990 ( ''high confidence'' ) (Engelbrecht and Engelbrecht, 2016) <sup>[[#fn:r545|545]]</sup> . In Australia, an increase in the density of trees and shrubs at the expense of grassland species is occurring across all major ecosystems and is projected to be amplified (NCCARF, 2013) <sup>[[#fn:r546|546]]</sup> . Regarding Central America, Lyra et al. (2017) <sup>[[#fn:r547|547]]</sup> showed that the tropical rainforest biomass would be reduced by about 40% under global warming of 3°C, with considerable replacement by savanna and grassland. With a global warming of close to 1.5°C in 2050, a biomass decrease of 20% is projected for tropical rainforests of Central America (Lyra et al., 2017) <sup>[[#fn:r548|548]]</sup> . If a linear response is assumed, this decrease may reach 30% ( ''medium confidence'' ).

Freshwater ecosystems are considered to be among the most threatened on the planet (Settele et al., 2014) <sup>[[#fn:r549|549]]</sup> . Although peatlands cover only about 3% of the land surface, they hold one-third of the world’s soil carbon stock (400 to 600 Pg) (Settele et al., 2014) <sup>[[#fn:r550|550]]</sup> . When drained, this carbon is released to the atmosphere. At least 15% of peatlands have drained, mostly in Europe and South east Asia, and are responsible for 5% of human derived CO <sub>2</sub> emissions (Green and Page, 2017) <sup>[[#fn:r551|551]]</sup> . Moreover, in the Congo basin (Dargie et al., 2017) <sup>[[#fn:r552|552]]</sup> and in the Amazonian basin (Draper et al., 2014) <sup>[[#fn:r553|553]]</sup> , the peatlands store the equivalent carbon as that of a tropical forest. However, stored carbon is vulnerable to land-use change and future risk of drought, for example in northeast Brazil ( ''high confidence'' ) (Figure 3.12, Section 3.3.4.2). At the global scale, these peatlands are undergoing rapid major transformations through drainage and burning in preparation for oil palm and other crops or through unintentional burning (Magrin et al., 2014) <sup>[[#fn:r554|554]]</sup> . Wetland salinization, a widespread threat to the structure and ecological functioning of inland and coastal wetlands, is occurring at a high rate and large geographic scale (Section 3.3.6; Herbert et al., 2015) <sup>[[#fn:r555|555]]</sup> . Settele et al. (2014) <sup>[[#fn:r556|556]]</sup> found that rising water temperatures are projected to lead to shifts in freshwater species distributions and worsen water quality. Some of these ecosystems respond non-linearly to changes in temperature. For example, Johnson and Poiani (2016) <sup>[[#fn:r557|557]]</sup> found that the wetland function of the Prairie Pothole region in North America is projected to decline at temperatures beyond a local warming of 2°C–3°C above present-day values (1°C local warming, corresponding to 0.6°C of global warming). If the ratio of local to global warming remains similar for these small levels of warming, this would indicate a global temperature threshold of 1.2°C–1.8°C of warming. Hence, constraining global warming to approximately 1.5°C would maintain the functioning of prairie pothole ecosystems in terms of their productivity and biodiversity, although a 20% increase of precipitation could offset 2°C of global warming ( ''high confidence'' ) (Johnson and Poiani, 2016) <sup>[[#fn:r558|558]]</sup> .

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<span id="summary-of-implications-for-ecosystem-services"></span>
==== 3.4.3.6 Summary of implications for ecosystem services ====

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In summary, constraining global warming to 1.5°C rather than 2°C has strong benefits for terrestrial and wetland ecosystems and their services ( ''high confidence'' ). These benefits include avoidance or reduction of changes such as biome transformations, species range losses, increased extinction risks (all ''high confidence'' ) and changes in phenology ( ''high confidence'' ), together with projected increases in extreme weather events which are not yet factored into these analyses (Section 3.3). All of these changes contribute to disruption of ecosystem functioning and loss of cultural, provisioning and regulating services provided by these ecosystems to humans. Examples of such services include soil conservation (avoidance of desertification), flood control, water and air purification, pollination, nutrient cycling, sources of food, and recreation.

<span id="ocean-ecosystems"></span>