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

==== 3.4.3.1 Biome shifts ====

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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> .

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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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'''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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