Saturday, November 9, 2019

Growing Food in a Warming Climate

Plants tend to accumulate in areas where a benign environment is encountered.  When humans were small bands of hunter-gatherers, they could follow the plants and animals to find their food.  They eventually discovered that some plants could be raised under controlled conditions and produce a more reliable source of nourishment.  They also discovered that selective breeding of plants would produce more productive crops.  As food security increased, population could grow, and as the density of people increased, more complex societal organizations would develop.  This was the beginning of civilization as we now know it. 

As time went on science provided more options for producing greater agricultural productivity.  Tremendous improvements in recent generations has allowed the world population to surge during that period.  There are now about 7 billion people on Earth and that population is on track to reach about 11 billion in this century.  If that is to happen, food production must increase even more than proportionately.  This is because people will begin to consume more food and more crop-intensive types of food as their lot in life improves.  The question is whether or not the food supply can continue to be delivered to our current population, let alone one of 11 billion people.

Malthusian predictions have thus far been proved wrong, but that does not mean that will always be the case.  Lester R. Brown provides a survey of all the issues involved in continuing to provide our food supply in Full Planet, Empty Plates: The New Geopolitics of Food Scarcity (2012).  He is not optimistic about the future.

“While the decline of early civilizations can be traced to one or possibly two environmental trends such as deforestation and soil erosion that undermined their food supply, we are now dealing with several.  In addition to some of the most severe soil erosion in human history, we are also facing newer trends such as depletion of aquifers, the plateauing of grain yields in the more agriculturally advanced countries, and rising temperatures.”

Our civilization has developed crops, and techniques for growing them, best suited to the soil, water, and temperature conditions of the past few generations.  The current generation is seeing changes in basic conditions.  Soil and water availability are currently well-understood issues.  Rising temperatures have been added to that list of concerns and are becoming ever more a threat. 

“Agriculture as it exists today developed over 11,000 years of remarkable climate stability.  It has evolved to maximize production within that climate system.  Now, suddenly, the climate is changing.  With each passing year, the agricultural system is becoming more out of sync with the climate system.”

We are concerned here with the effects of climate change.  Perspective will be gained from Brown’s book and one by David Wallace-Wells: The Uninhabitable Earth: Life After Warming.

Since the beginning of the industrial revolution human activities have raised the global temperature almost 1.0 degree Celsius (Centigrade).  The Paris Accord indicated 2.0 degrees as a point which must not be reached.  At current rates of carbon emissions, we will reach 4.0-5.0 degrees.  These changes may not seem like much to some, but the consequences are enormous.  A few plants are the basis of our food supply either as a direct consumable or as food for providing the animal products we consume.  Unfortunately, the plants we depend on are highly sensitive to temperature.  This from Wallace-Wells.

“Globally, grain [mostly wheat and rice] accounts for about 40 percent of the human diet; when you add soybeans and corn [animal feed], you get up to two-thirds of all human calories.  Overall, the United Nations estimates that the planet will need nearly twice as much food in 2050 as it does today—and although this is a speculative figure, it’s not a bad one.”

The needed increase in food supply is hindered by the fact that crop yields decline as the temperature rises.  This from Brown.

“Crop ecologists in several countries have been focusing on the precise relationship between temperatures and crop yields.  Their findings suggest a rule of thumb that a 1-degree-Celsius rise in temperature above the norm during the growing season lowers wheat, rice, and corn yields by 10 percent.”

Temperature plays a critical role in the processes of photosynthesis and pollination, partly explaining the decline in yield as the climate warms.

“…as temperature rises, photosynthetic activity in plants increases until the temperature reaches 68 degrees Fahrenheit.  The rate of photosynthesis then plateaus until the temperature reaches 95 degrees Fahrenheit.  Beyond this point it declines, until at 104 degrees Fahrenheit, photosynthesis ceases entirely.”

“The most vulnerable part of a plant’s life cycle is the pollination period.  Of the world’s three food staples—corn, wheat, and rice—corn is particularly vulnerable.  In order for corn to reproduce, pollen must fall from the tassel to the strands of silk that emerge from the end of each ear.  Each of these silk strands is attached to a kernel site on the cob.  If the kernel is to develop, a grain of pollen must fall on the silk strand and then journey to the kernel site where fertilization takes place.  When temperatures are uncommonly high, the silk strands quickly dry out and turn brown, unable to play their role in the fertilization process.”

“When it comes to rice, the effects of temperature on pollination have been studied in detail in the Philippines.  Scientists there report that the pollination of rice falls from 100 percent at 93 degrees Fahrenheit (34 degrees Celsius) to near zero at 104 degrees, leading to crop failure.”

There are already vast areas too warm to grow grain, and the extent of these regions will increase in the future.  It is often claimed that rising temperatures are not such a severe problem since the crop-growing regions will just drift north.  Life is not so simple.  This from Wallace-Wells.

“…the tropics are already too hot to efficiently grow grain, and those places where grain is produced today are already at optimal growing temperature—which means even a small warming will push them down a slope of declining productivity.  The same, broadly speaking, is true for corn.  At four degrees of warming, corn yields in the United States, the world’s top producer of maize, are expected to drop by almost half.”

“The world’s natural wheatbelt is moving poleward by about 160 miles each decade, but you can’t easily move croplands north a few hundred miles, and not just because it is difficult to suddenly clear the land occupied now by towns, highways, office parks, and industrial institutions.  Yields in remote areas of Canada and Russia, even if they warmed by a few degrees, would be limited by the quality of soil there, since it takes many centuries for the planet to produce optimally fertile dirt.  The lands that are fertile are the ones we are already using, and the climate is changing much too fast to wait for the northern soil to catch up.  That soil, believe it or not, is literally disappearing—75 billion tons of soil lost each year.  In the United States, the rate of erosion is ten times as high as the natural replenishment rate; in China and India, it is thirty to forty times as fast.”

There will be collateral effects that will arrive with climate change that will also hinder crop production.  Rising temperatures will encourage crop pests and diseases from hotter regions to move further north into regions where they were not previously active.  Climate change will also affect rainfall and its distribution.  Too little rain can make vegetation more susceptible to pests and diseases and allow it to become fuel for wildfires.  It will be the change in precipitation at warmer temperatures that will lead to both more intense flooding and more severe droughts.

“Precipitation is notoriously hard to model in detail, yet predictions for later this century are basically unanimous: both unprecedented droughts and unprecedented flood-producing rains.”

“Drought may be an even bigger problem for food production than heat, with some of the world’s most arable land turning quickly to desert.  At 2 degrees of worming, droughts will wallop the Mediterranean and much of India, and corn and sorghum all around the world will suffer, straining global food supply.  At 2.5 degrees, thanks mostly to drought, the world would enter a global food deficit—needing more calories than the planet can produce.  At 3 degrees, there would be further drought—in Central America, Pakistan, the Western United States, and Australia.  At 5 degrees, the whole earth would be wrapped in what the environmentalist Mark Lynas calls “two globe-girdling belts of perennial drought.”

Recently, yet another threat to our food supply has been discovered.  It was long thought that carbon dioxide acted as a plant nutrient and an elevated level in the atmosphere would provide a net benefit in terms of plant growth.  It was true that plants did grow bigger, but the net effect was to replace needed nutrients like proteins, vitamins, and minerals with carbohydrates.  This effect has been referred to as “nutrient collapse.”  In Wallace-Wells’ words:

“Everything is becoming more like junk food.”

If the protein content of our foods has declined by 5-10 percent over the last 50 years, tracking the rise in atmospheric carbon dioxide, we in the developed nations get our nourishment but may be getting a little fatter as a result.  Food is a relatively small portion of expenses for most of us.  But there are many millions of people in the world who must spend half or more of their income on food—assuming it is available.  Diminished nutrient content for them is equivalent to a loss of food supply.  And the nutrient content will continue to fall.

“Recently, researchers have estimated that by 2050 as many as 150 million people in the developing world will be at risk of protein deficiency as the result of nutrient collapse, since so many of the world’s poor depend on crops, rather than animal meat, for protein; 138 million could suffer from a deficiency of zinc, essential to healthy pregnancies; and 1,4 billion could face a dramatic decline in dietary iron—pointing to a possible epidemic of anemia.  In 2018, a team led by Chunwu Zhu looked at the protein content of eighteen different strains of rice, the staple crop for more than 2 billion people, and found that more carbon dioxide in the air produced nutritional declines across the board—drops in protein content, as well as in iron, zinc, and vitamins B1, B2, B5, and B9.  Really everything but vitamin E.  Overall, the researchers found that, acting just through that single crop, rice, carbon emissions could imperil the health of 600 million people.”

The outlook for food production does not look promising—and the future is already upon us.  A consequence of global warming that is often overlooked is that the regions of the Earth where political unrest and violence are endemic are mostly regions where the food supply is unreliable.  As the Earth’s temperature continues to rise the regions of food insecurity will grow and break out in new areas.  The world will become a nastier, more brutal place.

As with other threats from climate change, the wealthy will initially be able to escape its consequences, but the poor will not.  For them it is an existential threat already.  The rest of us will have a few more years to figure out what to do about it—if anything.

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