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<p class="MsoPlainText">Dear Andrew<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">I don't want to spend as much time on the reply as you did. This material is readily accessible. A few points will suffice I and sure. This is something so easily accessible that I encourage everyone to look into it.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText"><img width="378" height="225" style="width:3.9416in;height:2.3416in" id="Picture_x0020_1" src="cid:image002.jpg@01D3C60A.26CC4450"><o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">That is the increase in productivity from CO2 alone in the past 150 years.
<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">There are many papers on the matter fretting that ‘people use the argument that CO2 enhances plant growth to argue against reducing CO2 emissions’.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Let them fret. Emissions are not going down. AG emissions went up 1.3% in 2018 after levelling off for 3 years.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">>In UK I am aware of increases of crop of the potato family, tomatoes were routinely grown in heated glass houses with CO2 increased.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText"><span style="color:black">In Ontario in greenhouses, those supplementing it with CO2 keep the level at 1200-1500 ppm to optimise the return on water and heat.
<o:p></o:p></span></p>
<p class="MsoPlainText"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoPlainText">>….certain plants have evolved to make better use of CO2,
<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Actually they evolution of C4 plants was a response to the ever-declining CO2 level in the atmosphere. It was the lowest in the last ice age – ever – in the past 4.3 billion years. It was 180 ppm during the
<a href="https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atmosphere">Quaternary Glaciation</a> with most plants in a state of near starvation.
<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">>…they are commonly referred to as C4 plants, because of the more advanced way they photosynthesise, these plants use CO2 so much more efficiently that any concentrations over 200 parts per million is not advantageous to them.
<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">That is not supported the by chart above. The improvement is not nearly as much (see “Corn”). Few plants are C4, most are C3 and benefit enormously from higher CO2. They evolved in 2000-3000 ppm, with the highest long-term level being
7000 ppm. Note that during these 10-20 times higher levels there was no ‘thermal runaway’ and in fact the Icehouse Earth period occurred during one of the highest CO2 levels experienced.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText"><img border="0" width="302" height="215" style="width:3.15in;height:2.2416in" id="Picture_x0020_4" src="cid:image006.jpg@01D3C60A.26CC4450"><o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">>This group that do not benefit from higher than pre industrial levels of CO2 include the food crops typically grown in hotter countries: maize, sugar cane, millet, and sorghum.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText"><span style="color:black">That is not supported by numerous studies published. There is
<b>no</b> benefit to any plant to having a reduced level of CO2 until it exceeds 10,000 ppm (same as people).<o:p></o:p></span></p>
<p class="MsoPlainText"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoPlainText">>The other group of plants generally out competed by the C4 plants in hotter drier climates are known as C3 plants. They theoretically can benefit from increased CO2 in drier areas because they react to water stress by closing their
stomata, this reduces their ability to take up CO2 into their cells when stressed.
<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">This position is not supported by easily accessible publications.
<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText"><img border="0" width="378" height="315" style="width:3.9416in;height:3.2833in" id="Picture_x0020_2" src="cid:image008.jpg@01D3C60A.26CC4450"><o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">For every 1% increase in CO2, the moisture content of dry land soils increases by 0.63% because the plants are more water efficient, and grow faster.
<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Here is NASA on the subject (1982-2015)<o:p></o:p></p>
<p class="MsoPlainText"><img border="0" width="378" height="254" style="width:3.9416in;height:2.6416in" id="Picture_x0020_3" src="cid:image010.jpg@01D3C60A.26CC4450"><o:p></o:p></p>
<p class="MsoPlainText">That is a lot of additional leaf area in only 33 years – up to 50% in places. The Sahel has moved 500 km north into the Sahara during the same time period.<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">>There have been reports of increases of productivity in non food plants up to 23% by Oak Ridge National Laboratory in enhanced CO2 for trees but these are overwhelmed by increase of temperature above 30C and water stress.
<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">Vegetables stop growing in many places between 11 and 3 PM because it is too hot. This is addressed by using shade netting – common in South Africa.
<o:p></o:p></p>
<p class="MsoPlainText"><o:p> </o:p></p>
<p class="MsoPlainText">>Worse to my mind is the way ocean surface concentrations of CO2 have changed so fast in evolutionary terms that marine life has been unable to react so there is a net loss of photosynthetic activity in shallow waters.<o:p></o:p></p>
<p class="MsoPlainText"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span style="color:black">This is the first time I have heard of such a thing. The ocean surface is extremely resistant to changes in CO2 concentration as it has a huge buffering capacity with multiple latent mechanisms that kick in
when they can. The “</span>net loss of photosynthetic activity in shallow waters” because on ‘an increase in CO2’ is unbelievable. Perhaps you can guide me to the source.<o:p></o:p></p>
<p class="MsoPlainText"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span style="color:black">Below is an abstract from an article on the increase in the seed yield (food) rice and wheat yield up to 20,000 ppm CO2. The increase available at 1200 ppm is 30-40%. Since plants developed, only a small percentage
of the time has CO2 been under 1000 ppm.<o:p></o:p></span></p>
<p class="MsoPlainText"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span style="color:black">Regards<o:p></o:p></span></p>
<p class="MsoPlainText"><span style="color:black">Crispin<o:p></o:p></span></p>
<p class="MsoPlainText"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span style="color:black">Available <a href="https://www.ncbi.nlm.nih.gov/pubmed/11540191">
here</a>.<o:p></o:p></span></p>
<p class="MsoNoSpacing">CO2 crop growth enhancement and toxicity in wheat and rice.<o:p></o:p></p>
<p class="MsoNoSpacing"><a href="https://www.ncbi.nlm.nih.gov/pubmed/?term=Bugbee%20B%5BAuthor%5D&cauthor=true&cauthor_uid=11540191"><span style="font-family:"Calibri Light",sans-serif;color:#660066">Bugbee B</span></a><sup>1</sup>, <a href="https://www.ncbi.nlm.nih.gov/pubmed/?term=Spanarkel%20B%5BAuthor%5D&cauthor=true&cauthor_uid=11540191"><span style="font-family:"Calibri Light",sans-serif;color:#660066">Spanarkel
B</span></a>, <a href="https://www.ncbi.nlm.nih.gov/pubmed/?term=Johnson%20S%5BAuthor%5D&cauthor=true&cauthor_uid=11540191"><span style="font-family:"Calibri Light",sans-serif;color:#660066">Johnson S</span></a>, <a href="https://www.ncbi.nlm.nih.gov/pubmed/?term=Monje%20O%5BAuthor%5D&cauthor=true&cauthor_uid=11540191"><span style="font-family:"Calibri Light",sans-serif;color:#660066">Monje
O</span></a>, <a href="https://www.ncbi.nlm.nih.gov/pubmed/?term=Koerner%20G%5BAuthor%5D&cauthor=true&cauthor_uid=11540191"><span style="font-family:"Calibri Light",sans-serif;color:#660066">Koerner G</span></a>.<o:p></o:p></p>
<p class="MsoNoSpacing"><span style="color:#724128"><a href="https://www.ncbi.nlm.nih.gov/pubmed/11540191" title="Open/close investigator list"><span class="ui-ncbitoggler-master-text"><span style="font-family:"Calibri Light",sans-serif;color:#660066">Collaborators
(1)</span></span></a><o:p></o:p></span></p>
<p class="MsoNoSpacing"><span style="color:#724128"><a href="https://www.ncbi.nlm.nih.gov/pubmed/11540191" title="Open/close author information list"><span class="ui-ncbitoggler-master-text"><span style="font-family:"Calibri Light",sans-serif;color:#660066">Author
information</span></span></a><o:p></o:p></span></p>
<p class="MsoNoSpacing"><span style="color:#985735">Abstract<o:p></o:p></span></p>
<p class="MsoNoSpacing">The effects of elevated CO2 on plant growth are reviewed and the implications for crop yields in regenerative systems are discussed. There is considerable theoretical and experimental evidence indicating that the beneficial effects of
CO2 are saturated at about 0.12% CO2 in air. However, CO2 can easily rise above 1% of the total gas in a closed system, and we have thus studied continuous exposure to CO2 levels as high as 2%. Elevating CO2 from 340 to 1200 micromoles mol-1 can increase the
seed yield of wheat and rice by 30 to 40%; unfortunately, further CO2 elevation to 2500 micromoles mol-1 (0.25%) has consistently reduced yield by 25% compared to plants grown at 1200 micromoles mol-1; fortunately, there was only an additional 10% decrease
in yield as the CO2 level was further elevated to 2% (20,000 micromoles mol-1). Yield increases in both rice and wheat were primarily the result of increased number of heads per m2, with minor effects on seed number per head and seed size. Yield increases
were greatest in the highest photosynthetic photon flux. We used photosynthetic gas exchange to analyze CO2 effects on radiation interception, canopy quantum yield, and canopy carbon use efficiency. We were surprised to find that radiation interception during
early growth was not improved by elevated CO2. As expected, CO2 increased quantum yield, but there was also a small increase in carbon use efficiency. Super-optimal CO2 levels did not reduce vegetative growth, but decreased seed set and thus yield. The reduced
seed set is not visually apparent until final yield is measured. The physiological mechanism underlying CO2 toxicity is not yet known, but elevated CO2 levels (0.1 to 1% CO2) increase ethylene synthesis in some plants and ethylene is a potent inhibitor of
seed set in wheat.<o:p></o:p></p>
<p class="MsoNoSpacing"><o:p> </o:p></p>
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