Editing Diffuse sky radiation (section)

==Agriculture and the eruption of Mt. Pinatubo==
[[File: Pinatubo dust layer.jpg|thumb|upright=1.25|A Space Shuttle (Mission [[STS-43]]) photograph of the Earth over [[South America]] taken on August 8, 1991, which captures the double layer of Pinatubo aerosol clouds (dark streaks) above lower cloud tops.]]

The eruption of the [[Philippines]] [[volcano]] - [[Mount Pinatubo]] in June 1991 ejected roughly {{convert|10|km3|cumi|abbr=on}} of magma and "17 million [[metric ton]]s"(17 [[Kilogram#SI multiples|teragrams]]) of [[sulfur dioxide]] SO<sub>2</sub> into the air, introducing ten times as much total SO<sub>2</sub> as the [[Kuwaiti oil fires|1991 Kuwaiti fires]],<ref>{{cite book |author= John C McCain |author2= Muhammad Sadiq |author3= M Sadiq |title=The Gulf War Aftermath: An Environmental Tragedy |publisher=Springer |date=1993 |page=60 |isbn=978-0-792-32278-8 }}</ref> mostly during the explosive [[Plinian eruption|Plinian/Ultra-Plinian]] event of June 15, 1991, creating a [[Volcanic winter|global stratospheric SO<sub>2</sub> haze layer]] which persisted for years. This resulted in the global average temperature dropping by about {{convert|0.5|C-change|F-change|1}}.<ref name="Science News">{{cite web|url=http://www.thefreelibrary.com/Mt.+Pinatubo's+cloud+shades+global+climate.-a012467057|title=Mt. Pinatubo's cloud shades global climate|publisher=Science News|access-date=2010-03-07}}</ref> Since [[volcanic ash]] falls out of the atmosphere rapidly,<ref>{{cite web|url=http://hvo.wr.usgs.gov/volcanowatch/archive/2007/07_03_08.html|title=Hawaiian Volcano Observatory|first=Volcano Hazards|last=Program|website=hvo.wr.usgs.gov|access-date=April 4, 2018}}</ref> the negative agricultural, effects of the eruption were largely immediate and localized to a relatively small area in close proximity to the eruption, caused by the resulting thick ash cover.<ref>{{cite web|url=http://pubs.usgs.gov/pinatubo/mercado/|title=Mercado|website=pubs.usgs.gov|access-date=April 4, 2018}}</ref><ref>{{cite web|url=https://sites.google.com/site/earthsciencesystems/students-faculty/larissa-karan/mt-pinatubo-lk-lithosphere|title=Mt. pinatubo (LK): Biosphere - ESS|website=sites.google.com|access-date=April 4, 2018}}</ref> Globally however, despite a several-month 5% drop in overall [[solar irradiation]], and a reduction in direct sunlight by 30%,<ref>{{cite web|url=http://climate.envsci.rutgers.edu/pdf/TreeRingCorrection3.pdf|title=Cooling Following Large Volcanic Eruptions Corrected for the Effect of Diffuse Radiation on Tree Rings. Alan Robock, 2005. See Figure 1 for a graphic of the recorded change in solar iiradiation|website=rutgers.edu|access-date=April 4, 2018}}</ref> there was no negative impact on global agriculture.<ref name="web.archive.org">{{cite web|url=http://earthobservatory.nasa.gov/Newsroom/view.php?id=22098|archive-url=https://web.archive.org/web/20100316225839/http://earthobservatory.nasa.gov/Newsroom/view.php?id=22098|url-status=dead|archive-date=March 16, 2010|title=Large Volcanic Eruptions Help Plants Absorb More Carbon Dioxide From the Atmosphere : News|date=March 16, 2010|access-date=April 4, 2018}}</ref><ref name="ReferenceA">[https://web.archive.org/web/20090801030547/http://www.gsfc.nasa.gov/topstory/20011210co2absorb.html LARGE VOLCANIC ERUPTIONS HELP PLANTS ABSORB MORE CARBON DIOXIDE FROM THE ATMOSPHERE]</ref> Surprisingly, a 3-4 year<ref>{{cite journal|title=The effects and consequences of very large explosive volcanic eruptions|first=S.|last=Self|s2cid=28228518|date=August 15, 2006|journal=Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences|volume=364|issue=1845|pages=2073–2097|doi=10.1098/rsta.2006.1814|pmid=16844649|bibcode=2006RSPTA.364.2073S}}</ref> increase in global [[Agricultural productivity]] and forestry growth was observed, excepting [[boreal forest]] regions.<ref name="dx.doi.org">[https://dx.doi.org/10.3402/tellusb.v66.21808 Evaluating aerosol direct radiative effects on global terrestrial ecosystem carbon dynamics from 2003 to 2010. Chen et al., ''Tellus B'' 2014; 66, 21808, Published by the international meteorological institute in Stockholm.]</ref>[[File:ZeaMays.jpg|thumb|upright|Under more-or-less direct sunlight, dark [[shadow]]s that limit photosynthesis are [[shadow|cast]] onto understorey [[leaves]]. Within the [[thicket]], very little direct sunlight can enter.]] The means of discovery was that initially, a mysterious drop in the rate at which [[carbon dioxide]] (CO<sub>2</sub>) was filling the atmosphere was observed, which is charted in what is known as the "[[Keeling Curve]]".<ref>{{cite web|url=http://climate.envsci.rutgers.edu/pdf/TreeRingCorrection3.pdf|title=Cooling Following Large Volcanic Eruptions Corrected for the Effect of Diffuse Radiation on Tree Rings. Alan Robock, 2005. See Figure 2 for a record of this|website=rutgers.edu|access-date=April 4, 2018}}</ref> This led numerous scientists to assume that the reduction was due to the lowering of Earth's temperature, and with that, a, slowdown in plant and soil [[Ecosystem respiration|respiration]], indicating a [[deleterious]] impact on global agriculture from the volcanic haze layer.<ref name="web.archive.org"/><ref name="ReferenceA"/> However upon investigation, the reduction in the rate at which carbon dioxide filled the atmosphere did not match up with the hypothesis that plant respiration rates had declined.<ref name="adsabs.harvard.edu">{{cite journal|bibcode=2001AGUFM.B51A0194G|title=Roles of volcanic eruptions, aerosols and clouds in global carbon cycle|first1=Gu|last1=L.|first2=Baldocchi|last2=D.|date=December 1, 2001|journal=AGU Fall Meeting Abstracts|volume=2001|pages=B51A–0194}}</ref><ref>{{cite web|url=http://research.eeescience.utoledo.edu/lees/papers_pdf/gu%20science%20paper%20mar%202003.pdf|title=Response of a Deciduous Forest to the Mount Pinatubo Eruption: Enhanced Photosynthesis. Gu et al., 28 March 2003 Journal of Science Vol 299|website=utoledo.edu|access-date=April 4, 2018|archive-url=https://web.archive.org/web/20160304101728/http://research.eeescience.utoledo.edu/lees/papers_pdf/gu%20science%20paper%20mar%202003.pdf|archive-date=March 4, 2016|url-status=dead}}</ref> Instead the advantageous anomaly was relatively firmly<ref>{{cite web|url=http://www.co2science.org/subject/v/summaries/volcanobio.php|title=CO2 Science|website=www.co2science.org|access-date=April 4, 2018}}</ref> linked to an unprecedented increase in the growth/[[net primary production]],<ref>http://earthobservatory.nasa.gov/Features/GlobalGarden/ Global Garden gets greener. NASA 2003</ref> of global plant life, resulting in the increase of the [[carbon sink]] effect of global photosynthesis.<ref name="web.archive.org"/><ref name="ReferenceA"/> The mechanism by which the increase in plant growth was possible, was that the 30% reduction of direct sunlight can also be expressed as an increase or "enhancement" in the amount of [[Diffuse reflection|diffuse]] sunlight.<ref name="web.archive.org"/><ref name="adsabs.harvard.edu"/><ref>{{cite web|url=http://climate.envsci.rutgers.edu/pdf/TreeRingCorrection3.pdf|title=Cooling Following LargeVolcanic Eruptions Corrected for the Effect of Diffuse Radiation on Tree Rings. Alan Robock, 2005. Figure 1|website=rutgers.edu|access-date=April 4, 2018}}</ref><ref name="ReferenceA"/>

===The diffused skylight effect===
[[File:Canopy.jpg|thumb|left|Well lit understorey areas due to [[overcast]] clouds creating diffuse/[[soft light|soft sunlight]] conditions, that permits photosynthesis on leaves under the canopy.]] 
This diffused skylight, owing to its intrinsic nature, can illuminate under-[[canopy (biology)|canopy]] leaves permitting more efficient total whole-plant [[photosynthesis]] than would otherwise be the case,<ref name="web.archive.org"/><ref name="ReferenceA"/> and also increasing evaporative cooling, from vegetated surfaces.<ref>{{Cite journal|last1=Chakraborty|first1=TC|last2=Lee|first2=Xuhui|last3=Lawrence|first3=David M.|date=2021|title=Strong Local Evaporative Cooling Over Land Due to Atmospheric Aerosols|journal=Journal of Advances in Modeling Earth Systems|volume=13|issue=5|doi=10.1029/2021ms002491|bibcode=2021JAMES..1302491C |s2cid=236541532 |issn=1942-2466|doi-access=free}}</ref> In stark contrast, for totally clear skies and the direct sunlight that results from it, shadows are cast onto [[understorey]] leaves, limiting plant photosynthesis to the top canopy layer.<ref name="web.archive.org"/><ref name="ReferenceA"/> This increase in global agriculture from the volcanic haze layer also naturally results as a product of other aerosols that are not emitted by volcanoes, such, "moderately thick smoke loading" pollution, as the same mechanism, the "aerosol direct radiative effect" is behind both.<ref name="dx.doi.org"/><ref>Impact of atmospheric aerosol light scattering and absorption on terrestrial net primary productivity, Cohan et al. ''GLOBAL BIOGEOCHEMICAL CYCLES'' 2002 VOL. 16, NO. 4, 1090, {{doi|10.1029/2001GB001441}}</ref><ref>Direct observations of the effects of aerosol loading on net ecosystem CO2 exchanges over different landscapes. Niyogi et al. ''Geophysical Research Letters'' Volume 31, Issue 20, October 2004 {{doi|10.1029/2004GL020915}}</ref>
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