Editing IPCC:AR6/WGII/Chapter-2 (section)

==== 2.4.3.3 Observed Changes in Deserts and Arid Shrublands ====

<div id="h3-17-siblings" class="h3-siblings"></div>

Divergent responses to anthropogenic climate change are occurring within and across arid regions, depending on time period, location, detection methodology and vegetation type (see Cross-Chapter Paper 3). Emerging shifts in ecosystem structure, functioning and biodiversity are supported by evidence from modelled impacts of projected climate and CO 2 levels. While observed responsiveness of arid vegetation productivity to rising atmospheric CO 2 ( [[#Fensholt--2012|Fensholt et al., 2012]] ) may offset risks from reduced water availability ( [[#Fang--2017|Fang et al., 2017]] ), climate- and CO 2 -driven changes are key risks in arid regions, interacting with habitat degradation, wildfires and invasive species ( [[#Hurlbert--2019|Hurlbert et al., 2019]] ).

Widespread vegetation greening, as projected in AR4, is occurring in arid shrublands ( [[#Zhang--2019a|Zhang et al., 2019a]] ; [[#Maestre--2021|Maestre et al., 2021]] ) as a result of increases in leaf area, woody cover and herbaceous production at desert–grassland interfaces ( [[#Gonsamo--2021|Gonsamo et al., 2021]] ). Plant productivity in arid regions has increased ( [[#Fensholt--2012|Fensholt et al., 2012]] ) because of improved water-use efficiency associated with elevated CO 2 ( [[#Norby--2011|Norby and Zak, 2011]] ; [[#Donohue--2013|Donohue et al., 2013]] ; [[#Burrell--2020|Burrell et al., 2020]] ; [[#Gonsamo--2021|Gonsamo et al., 2021]] ) ( ''medium evidence'' , ''high agreement'' ), altered rainfall seasonality and amount ( [[#Rohde--2019|Rohde et al., 2019]] ; [[#Zhang--2019a|Zhang et al., 2019a]] ) ( ''robust evidence'' , ''high agreement'' ), increases in temperature ( [[#Ratajczak--2014|Ratajczak et al., 2014]] ; [[#Wilcox--2018|Wilcox et al., 2018]] ) ( ''robust evidence'' , ''high agreement'' ) and heavy grazing ( ''robust evidence'' , ''high agreement'' ), with the relative importance differing across locations ( [[#Donohue--2013|Donohue et al., 2013]] ; [[#Caracciolo--2016|Caracciolo et al., 2016]] ; [[#Archer--2017|Archer et al., 2017]] ; [[#Hoffmann--2019b|Hoffmann et al., 2019b]] ; [[#Rohde--2019|Rohde et al., 2019]] ). Woody-plant encroachment into arid shrublands is occurring with ''high confidence'' in North America ( [[#Caracciolo--2016|Caracciolo et al., 2016]] ; [[#Archer--2017|Archer et al., 2017]] ) and southern Africa ( [[#du%20Toit--2014|du Toit and O’Connor, 2014]] ; [[#Ward--2014|Ward et al., 2014]] ; [[#Masubelele--2015a|Masubelele et al., 2015a]] ; [[#Hoffman--2019|Hoffman et al., 2019]] ; [[#Rohde--2019|Rohde et al., 2019]] ), and with ''low confidence'' in central Asia ( [[#Li--2015|Li et al., 2015]] ). In North America, sagebrush steppe changes have been attributed to increases in temperature and earlier snowpack melt ( [[#USGCRP--2017|USGCRP, 2017]] ; [[#Mote--2018|Mote et al., 2018]] ; [[#Snyder--2019|Snyder et al., 2019]] ).

Non-native grasses are invading the sagebrush steppes (cold deserts) in North America ( [[#Chambers--2014|Chambers et al., 2014]] ) attributed to warming ( [[#Bradley--2016|Bradley et al., 2016]] ; [[#Hufft--2016|Hufft and Zelikova, 2016]] ). In the eastern semi-desert (Karoo) of South Africa, annual rainfall increases and a rainfall seasonality shift ( [[#du%20Toit--2014|du Toit and O’Connor, 2014]] ) are increasing grassiness as arid grasslands expand into semi-desert shrublands ( [[#du%20Toit--2015|du Toit et al., 2015]] ; [[#Masubelele--2015b|Masubelele et al., 2015b]] ; [[#Masubelele--2015a|Masubelele et al., 2015a]] ) causing fire in areas seldom burned historically ( [[#Coates--2016|Coates et al., 2016]] ).

Interactions of drought, warming and land management have caused vegetation mortality (see [[#2.4.4.3|Section 2.4.4.3]] ) and reduced vegetation cover in shrublands, as projected by AR4 ( [[#Burrell--2020|Burrell et al., 2020]] ). Increased heat and drought are causing the health and abundance of succulent species to decline ( [[#Musil--2009|Musil et al., 2009]] ; [[#Schmiedel--2012|Schmiedel et al., 2012]] ; [[#Aragón-Gastélum--2014|Aragón-Gastélum et al., 2014]] ; [[#Koźmińska--2019|Koźmińska et al., 2019]] ). Hot droughts, in particular, have been shown to reduce population resilience ( [[#Koźmińska--2019|Koźmińska et al., 2019]] ).

<div id="2.4.3.4" class="h3-container"></div>

<span id="observed-changes-in-mediterranean-type-ecosystems"></span>