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Does More Carbon Dioxide Mean Increased Crop Water Productivity? (arstechnica.com)
An anonymous reader points us to an Ars Technica report: For the most part, we think of rising levels of carbon dioxide as an environmental problem. But atmospheric CO2 can also boost agricultural productivity by helping plants grow. How do these potential issues balance out? In an investigation recently published in Nature Climate Change, scientists have looked into the global implications of carbon dioxide's ability to enhance agricultural productivity. Increased levels of CO2 can enhance photosynthesis and reduce leaf-level transpiration, the process by which some of the water that plants draw from the ground gets released back into the atmosphere. These changes can reduce growing seasons and water loss. The result could be an increase in what's called "crop water productivity," i.e. the amount of food produced for each unit of water expended. If elevated CO2 levels increase crop yield and reduce water consumption at large scales, this could help ensure water and food security despite the climate disruptions. By combining data from a massive network of field experiments and global crop models, the scientists claimed that depending on the crop type, global crop water productivity will increase by 10 to 27 percent by the 2080s. Arid regions exhibited large increases that were based on crop type.
It sounds good that crops will be more productive. So will other things, though. There was an experiment in which poison ivy was grown in higher CO2 conditions. It grew better and produced more urushiol (the stuff that causes you to have an allergic reaction). Crops may grow better, but so will weeds. It wouldn't surprise me if that included some invasive weeds like kudzu. If it stays warmer, pests might not die off in the cold; the mountain pine beetle is an example. Furthermore, there's not only increased temperatures and longer growing seasons; rainfall patterns will shift, too. Areas that currently grow crops might become arid and either have to grow different crops or not be productive at all. Other areas, such as the northern US, are likely to become wetter. Maybe you have longer growing seasons in some areas, but I'm not sure how much of a real gain there will be if the rainfall moves poleward with the warm temperatures.
Correct. Much as higher CO2 levels and temperatures dominated during the Carboniferous period, spurring massive plant growth and laying down many of the geographic strata that turned into the massive coal fields we mine today, we will likely see greatly increased plant growth which is yet another of the negative feedback mechanisms that keeps the global climate catastrophe from happening the way the alarmists want you to believe.
Globally, water will not become more scarce unless we boil some past the Van Allen belts (not sure how hot it would have to be for that) or launch it to Mars. The point of concern that is often portrayed as "water scarcity" is "potable water scarcity," the reduction in available drinking water as some of the normal sources fade. Many clean rivers start from mountain meltwater that is restocked with snow each winter. If the winters are insufficient to create such a bank of snow on the mountains (too rainy or too dry), the familiar availability of water decreases (even if the annual precipitation does not change at all).
Similarly, subterranean aquifers are a point of concern. Some are restocked by rain, but not always as quickly as they are drained by human use. The recent California drought (like all the ones before it) put a strain on the water supply from the aquifers they have tapped.
This problem can be countered with many known processes, but those all add cost to extract drinkable water from otherwise nonviable sources. (desalinization, transportation, distillation, a few other fun techniques I'm forgetting as I type)
As for the weather predictions, there are equally valid models that warming will lead to more hurricanes, less hurricanes, stronger hurricanes, weaker tropical storms, and a complete cessation of Atlantic currents. So far, with a statistically insignificant set of years since those predictions were first made, the "mostly weaker storms, few making landfall" model seems to fit better but this could be a few years of anomaly.
Increased plant growth does not mean increased yield in food stapple, if we are still limited in Phosporus and nitrogen fixation. But even if it did, the water increase and climate chaotisation would far more offset that. What good is it that Florida could produce more orange, if it loses its coastal city and vast swath of the everglade, or land ? Or if the ocean pH changes destroy the food stapple (fishing) of many countries ? And that is only on top of my head. There are so many factor at play that your typical "AGW is not that bad" is sad.
C. Sagan : A demon haunted world:
http://www.amazon.com/gp/product/0345409469/
visit randi.org
You're also feeding that beef less protein in the same amount of feed.