One of the few upsides found when exploring global warming scenarios is based on the assumption that since green plants thrive on carbon dioxide (and there will be much more of it) for photosynthesis and since warmth tends more than cold to promote growth (and there will be more warmth), farmers who grow green plant crops should, on the whole, thrive.
This hypothesis has been tested in greenhouses with generally positive confirmations.
The problem with this overall proposition is that it has run counter to recent experience for most countries and crops, with China and plantains being notable exceptions. There is substantial agreement that world yields of wheat, rice, and corn (maize), as well as soybeans are trending down with increases in atmospheric CO2 and warmth.
Why would this be so?
Having More CO2 May Not Be All That Helpful If Other Inputs Do Not Match It
Having more CO2 may not help plants if they do not have access to increased water, nitrogen, potash, and the right soil conditions, at the same time. It’s something like having more flour. By itself, more flour does not mean you can bake a bigger cake. You also have to have baking powder, shortening, eggs, water, and other ingredients, or you are just going to get a modestly risen but pasty lump of dough.
Reports of Average Increases In Seasonal Temperature Are Misleadingly Mild
Reports that on average, a region has an increase of 2 degree Fahrenheit over previous years , tend to smooth over a number problems.
The first problem is that spikes of hot temperatures tend to occur more frequently, even if they do not last many days. It is not a case of each day being two degrees warmer; it is generally a case of more incidences of heat spells.
Location, Location, Location
Another poorly understood phenomenon is that temperature spikes tend to have more consequential effects at the margins of the range where a given crop can be cultivated. In other words, if a region was on the borderline of being too hot for the crop, but the crop was still viable most of the time in the past, raises in the frequency of heat spells will tend to shut down the area altogether. This tends to have serious implications for farmers in those marginal regions who depend largely on one cash crop. This is particularly the case in some of the poorest countries, and their farmers often have limited access to retool their operations to make them more viable with some sort of alternative crop.
Bad Timing
A third problem is that the timing of heat waves is often at least as important as their duration. Certain life stages in green plants that reproduce sexually (which are most of the world’s cash crops) can be quite temperature-sensitive.
This is particularly the case with pollen viability, pollen germinative ability, stigma viability, and ovule viability.
Given that an enormous number of crops are essentially providers of food as seeds ( grains, nuts) or fruits with seeds (virtually all tree crops, and many vine crops) failures along these lines have immediate consequences for this year’s crop for the table, and may also diminish the amount and quality of seed for sowing for the follow-on crop.
Pollinator & Pest Problems Tend to Increase with Spikes in Temperature
One consequence of timing disruptions in plant life cycles caused by heat spikes is that pollinators like bees, butterflies, moths, and even birds, end up arriving too late or too early to do their jobs effectively.
Perversely, reductions in killing frosts tend to allow more plant pests or their eggs to overwinter and heat spikes may promote earlier hatching or a higher rate of hatching success among herbivores.
Both of these phenomena may extend to weeds that compete for resources with the crops.
It’s Not All Doom & Gloom
It is nonetheless worthwhile to consider that modern plant breeding has a history of coming up with solutions to changes in climate, and, some colder regions that are now not notably crop productive may well experience a surge in productivity.
Whether either of these will offset downturn in crop yields owing to spikes in temperature, may well be the most important plant science story of our time.
Tony Stankus [email protected] Life Sciences Librarian & Professor
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Posted by: Michael Kors | November 02, 2013 at 03:45 PM
I am not sure if it helps crops to prosper. I have another question popped up in my mind while reading your blog. If this phenomenal activity is uncontrollable and unpredictable, what and how can we avoid it since it will affect our resources?
Posted by: Arnold C. | January 31, 2013 at 06:39 AM