Editing IPCC:AR6/WGI/Chapter-12 (section)

==== 12.3.7.2 Atmospheric Carbon Dioxide at Surface ====

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Carbon dioxide (CO <sub>2</sub> ) is a well-mixed greenhouse gas with global repercussions on Earth’s energy balance; however, atmospheric CO <sub>2</sub> concentration changes at the land surface also affect plant functions within ecosystems and agriculture (see also Chapter 5). High CO <sub>2</sub> concentration can increase photosynthesis rates and primary production within natural ecosystems ( [[#Norby--2010|Norby et al., 2010]] ; [[#Ratliff--2015|Ratliff et al., 2015]] ; [[#Zhu--2016|Zhu et al., 2016]] ) and agricultural crops ( [[#Hatfield--2011|Hatfield et al., 2011]] ; [[#Leakey--2012|Leakey et al., 2012]] ; [[#Bell--2013|Bell et al., 2013]] ; [[#Glenn--2014|Glenn et al., 2014]] ; [[#Nagelkerken--2015|Nagelkerken and Connell, 2015]] ; [[#Behrenfeld--2016|Behrenfeld et al., 2016]] ; [[#Deryng--2016|Deryng et al., 2016]] ; [[#Kimball--2016|Kimball, 2016]] ). High CO <sub>2</sub> concentration affects total biomass and plant sugar content important to bioenergy production ( [[#Schaeffer--2012|Schaeffer et al., 2012]] ), but also helps some pests and weeds flourish ( [[#Hamilton--2005|Hamilton et al., 2005]] ; [[#Wolfe--2008|Wolfe et al., 2008]] ; [[#Valerio--2013|Valerio et al., 2013]] ; [[#Korres--2016|Korres et al., 2016]] ; [[#Stinson--2016|Stinson et al., 2016]] ; [[#Ramesh--2017|Ramesh et al., 2017]] ), while potentially shifting the effectiveness of herbicides ( [[#Varanasi--2016|Varanasi et al., 2016]] ; [[#Refatti--2019|Refatti et al., 2019]] ). Higher CO <sub>2</sub> concentration reduces transpiration losses during drought conditions ( [[#Cammarano--2016|Cammarano et al., 2016]] ; [[#Deryng--2016|Deryng et al., 2016]] ; [[#Swann--2016|Swann et al., 2016]] ; [[#Durand--2018|Durand et al., 2018]] ), which also changes the energy balance within the plant canopy ( [[#Webber--2017|Webber et al., 2017]] ). Higher CO <sub>2</sub> reduces the nutritional density of crops and forage lands ( [[#Loladze--2014|Loladze, 2014]] ; [[#Müller--2014|Müller et al., 2014]] ; [[#Myers--2014|Myers et al., 2014]] , 2017; X. [[#Li--2016|]] [[#Li--2016|]] [[#Li--2016|Li et al., 2016]] ; [[#Lee--2017|]] [[#Lee--2017|M.A. Lee et al., 2017]] ; [[#Smith--2018|Smith and Myers, 2018]] ; [[#Zhu--2018|Zhu et al., 2018]] ; [[#Beach--2019|Beach et al., 2019]] ) and can increase the production of toxins ( [[#Ziska--2007|Ziska et al., 2007]] ) and allergenic pollen ( [[#Schmidt--2016|Schmidt, 2016]] ).

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