Thursday, September 22, 2016

New study undercuts favorite climate myth ‘more CO2 is good for plants’(?)

I have commented on this before but now that The Grauniad has got hold of it, I think I should note it again.  The grasses in the Stanford experiment showed little response to enhanced CO2 because the soil in the area was phosphorous deficient -- and that stopped the plants from taking much advantage of the other growth factors. See here.  There is nothing in the experiment to upset the thousands of studies that show high levels of CO2 enhancing growth.

And the authors below are confused.  In their desperation to show corroboration for the badly implemented Stanford study, they quote a study of corn growth in France.  But that study showed an adverse effect of high temperature, not high levels of CO2.  So it corroborates nothing.  All plants do have a temperature range within which they function best so it is no surprise that the corn cultivars mostly used in France were adversely affected by unusually high temperatures.  Corn grows in a lot of quite warm areas in Latin America and India so it is just a matter of choosing the right cultivar for the climate.  In some places the optimum temperature for maize (corn) germination is given as 33 degrees C!  Toasty!

And the prophecy about wheat yields is just modelling, and we know how good Warmist models are. But wheat cultivars vary too so again the only potential challenge posed by a temperature change as small as one degree would be to choose the right cultivar

And in the grand tradition of Green/Left cherry picking, the crooks below ignore the other effects that a temperature rise would bring -- in particular the larger area that would become available for cropping. Canadian wheat farmers are enormously productive despite farming right up to where the cold limits them.  A temperature rise would open up vast new areas of croplands for them -- leading to glut rather than any shortage of grain crops

A new study by scientists at Stanford University, published in the Proceedings of the National Academy of Sciences, tested whether hotter temperatures and higher carbon dioxide levels that we’ll see post-2050 will benefit the kinds of plants that live in California grasslands. They found that carbon dioxide at higher levels than today (400 ppm) did not significantly change plant growth, while higher temperatures had a negative effect.

The oversimplified myth of ‘CO2 is plant food’
Those who benefit from the status quo of burning copious amounts of fossil fuels love to argue that more carbon dioxide in the atmosphere will benefit plant life. It’s a favorite claim of climate contrarians like Matt Ridley and Rupert Murdoch.

It seems like a great counter-argument to the fact that carbon dioxide is a dangerous pollutant – a fact that contrarians often dispute. However, reality is far more complicated than the oversimplification of ‘CO2 is plant food.’ Unlike in the controlled environment of a greenhouse, the increasing greenhouse effect on Earth causes temperatures to rise and the climate to change in various ways that can be bad for plant life. We can’t control all the other variables the way we can in a greenhouse.

So far, as contrarians like Rupert Murdoch love to point out, the plant food effect has won out. Earth has become greener in recent decades (although that trend may now be reversing). The situation is not unlike a human diet – at relatively low calorie levels, more food is beneficial. But as calorie intake continues to rise, at a certain point it’s no longer benefiting the human body. More food is good, but only up to a certain point, as the global obesity epidemic makes clear.

The experiment

The Stanford scientists set up 132 plots of flowers and grass in California and introduced varying levels of carbon dioxide, temperature, water, and nitrogen. The scientists conducted the experiments over 16 growing seasons between 1998 and 2014. They found that only higher nitrogen levels resulted in higher plant productivity, while higher temperatures caused it to decline.

While this experiment was specific to California grasslands, other studies have similarly undermined the ‘more CO2 is great’ myth. For example, a 2012 paper found that higher temperatures are detrimental to French corn yields. While French corn production has increased steadily in recent decades due to a combination of technological improvements and CO2 fertilization (the former far more than the latter), yields have leveled off in recent years, and were particularly low when struck by heat waves.

Another study published in Nature Climate Change last week concluded that higher temperatures will cause wheat production to decline. Just a 1°C rise in global temperature will decrease wheat yields by about 5% (approximately 35 million tons). Climate change is bad news for several of our staple crops.


1 comment:

Wireless.Phil said...


Experts see few paths to planet-saving climate goal

Yahoo News - ‎1 hour ago‎

Oxford (United Kingdom) (AFP) - The global target to prevent climate catastrophe, crafted at a landmark summit last year in Paris, will be very difficult if not impossible to hit, said some of the world's top scientists meeting this week in Oxford.


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