[Stoves] Interesting Video

Andrew Heggie aj.heggie at gmail.com
Tue Mar 27 06:01:46 CDT 2018


On 25 March 2018 at 16:16, Crispin Pemberton-Pigott
<crispinpigott at outlook.com> wrote:

>
> Sixth, if we were somehow to drive the CO2 down to the pre-industrial low
> mark, food production on Planet Earth would drop 30%.

Crispin I'm happy to go along with your first five points but this
last is misleading in the extreme: whilst it is a fact that elevated
levels of  CO2 will increase crop yield in certain cases it is not
true in general, even in those cases where it may be beneficial I can
find no cites that claim more than 23%.

In UK I am aware of increases of crop of the potato family, tomatoes
were routinely grown in heated glass houses with CO2 increased.

 I also played a small part in forest trials in the mid 80s where
circular plots (which I cleared) in a pine forest were replanted and
fumigated with different gases, CO2, SO2 and N2 to measure any
changes.

This was shortly after the 1979 Charney report which commented on the
increasing levels of CO2, in the intervening 40 years I don't see much
to say the predictions were incorrect though personally I didn't
understand the significance until the middle of this millennium’s
first decade.

So my take, and I am not a plantsman nor a biologist and I would have
hoped that there was someone in that field on this list to comment,
certain plants have evolved to make better use of CO2, 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. They have evolved over millions of years in levels of under
and about 280 ppm, now we are at about 400 ppm. 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.

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. Generally these are crops that
benefit from irrigation, like rice and potatoes. I have seen cites of
up to 11% increased crop yield being possible  in these plants but
generally not achieved as other nutrients become limiting,
particularly nitrogen.

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. In UK summer water deficits limit growth
increasingly as weather patterns change and the ratio of
precipitation increases in winter while the total annual rainfall
remains similar.

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.

Andrew




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