Editing IPCC:AR6/SRCCL/Chapter-5 (section)

==== 5.2.2.4 Impacts on pollinators ====

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Pollinators play a key role on food security globally (Garibaldi et al. 2016 <sup>[[#fn:r338|338]]</sup> ). Pollinator-dependent crops contribute up to 35% of global crop production volume and are important contributors to healthy human diets and nutrition (IPBES 2016 <sup>[[#fn:r339|339]]</sup> ). On a global basis, some 1500 crops require pollination (typically by insects, birds and bats) (Klein et al. 2007 <sup>[[#fn:r340|340]]</sup> ). Their importance to nutritional security is therefore perhaps under-rated by valuation methodologies, which, nonetheless, include estimates of the global value of pollination services at over 225 billion USD2010 (Hanley et al. 2015 <sup>[[#fn:r341|341]]</sup> ). As with other ecosystem processes affected by climate change (e.g., changes in pests and diseases), how complex systems respond is highly context dependent. Thus, predicting the effects of climate on pollination services is difficult (Tylianakis et al. 2008 <sup>[[#fn:r342|342]]</sup> ; Schweiger et al. 2010 <sup>[[#fn:r343|343]]</sup> ) and uncertain, although there is ''limited evidence'' that impacts are occurring already (Section 5.2.2.4), and ''medium evidence'' that there will be an effect.

Pollination services arise from a mutualistic interaction between an animal and a plant – which can be disrupted by climate’s impacts on one or the other or both (Memmott et al. 2007 <sup>[[#fn:r344|344]]</sup> ). Disruption can occur through changes in species’ ranges or by changes in timing of growth stages (Settele et al. 2016 <sup>[[#fn:r345|345]]</sup> ). For example, if plant development responds to different cues (e.g., day length) from insects (e.g., temperature), the emergence of insects may not match the flowering times of the plants, causing a reduction in pollination. Climate change will affect pollinator ranges depending on species, life-history, dispersal ability and location. Warren et al. (2018) <sup>[[#fn:r346|346]]</sup> estimate that under a 3.2°C warming scenario, the existing range of about 49% of insects will be reduced by half by 2100, suggesting either significant range changes (if dispersal occurs) or extinctions (if it does not). However, in principle, ecosystem changes caused by invasions, in some cases, could compensate for the decoupling generated between native pollinators and pollinated species (Schweiger et al. 2010 <sup>[[#fn:r347|347]]</sup> ).

Other impacts include changes in distribution and virulence of pathogens affecting pollinators, such as the fungus ''Nosema cerana,'' which can develop at a higher temperature range than the less-virulent ''Nosema apis'' ; increased mortality of pollinators due to higher frequency of extreme weather events; food shortage for pollinators due to reduction of flowering length and intensity; and aggravation of other threats, such as habitat loss and fragmentation (González-Varo et al. 2013 <sup>[[#fn:r348|348]]</sup> ; Goulson et al. 2015 <sup>[[#fn:r349|349]]</sup> ; Le Conte and Navajas 2008 <sup>[[#fn:r350|350]]</sup> ; Menzel et al. 2006 <sup>[[#fn:r351|351]]</sup> ; Walther et al. 2009 <sup>[[#fn:r352|352]]</sup> ; IPBES, 2016 <sup>[[#fn:r353|353]]</sup> ). The increase in atmospheric CO <sub>2</sub> is also reducing the protein content of pollen, with potential impact on pollination population biology (Ziska et al. 2016 <sup>[[#fn:r354|354]]</sup> ).

In summary, as with other complex agroecosystem processes affected by climate change (e.g., changes in pests and diseases), how pollination services respond will be highly context dependent. Thus, predicting the effects of climate on pollination services is difficult and uncertain, although there is ''medium evidence'' that there will be an effect.

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