Food & Climate: A Complicated but Optimistic View

Cynthia Rosenzweig, of NASA Goddard Institute for Space Studies, works with crop models

hide captionCynthia Rosenzweig, of NASA Goddard Institute for Space Studies, works with computer models to see what the future may hold for global food production.

Courtesy Cynthia Rosenzweig

Q&A: Global Warming and Farming

  

Your most direct link to global warming may be the food you eat. All the bounty of your local grocery store depends on natural cycles of rain and sunlight, cool temperatures and warmth in far-flung parts of the world. Now, across the globe, those cycles are shifting and the effects are likely to be profound — not just for farmers, but possibly even for you.

  

Here, a look at some of the most important questions about how climate change will affect food production.

  

Read the Q&A.

For the last 20 years, Cynthia Rosenzweig has been trying to answer a very big and very complicated question: How will Earth's warming climate affect humanity's ability to feed itself?

The question dropped in her lap almost by accident in the 1980s, when she was a graduate student in agricultural science. Because of her husband's job, though, she was living in the decidedly non-agricultural precincts of Manhattan. She found a job at the NASA Goddard Institute for Space Studies (GISS), analyzing pictures that orbiting satellites had taken of farmers' fields.

At that time, few had heard of the greenhouse effect. But several floors above her, other GISS scientists were working on the issue fulltime. They were creating some of the first computer simulations of increasing carbon dioxide in the atmosphere. And one fateful day, Rosenzweig recalls, "a question came filtering down: What would happen to food?"

"I was the only person in the building who could even begin to think about that question," she says. So she took it on and it's dominated her life ever since.

Roots in the Cold War

Rosenzweig turned for answers to another family of computer simulations, which describe the growth of plants like wheat or corn. These so-called "crop models" were created during the Cold War, in part to help the United States predict how much grain the Soviet Union was likely to harvest.

The models predict how a crop will grow and how much grain it will produce under particular environmental conditions. "What the model is actually doing is marching through crop growth, day by day, seeing how much carbohydrate can be produced with the solar radiation, with the water available, and the minimum and maximum temperatures," Rosenzweig says.

Rosenzweig pulled together a large group of collaborators, creating scenarios that included not just information about the future climate, but also how food markets and farmers might respond to these changes. They also factored in the boost the crops are likely to get from higher levels of carbon dioxide in the air. This gas, which traps heat in the atmosphere, also is essential food for plants.

Seeing into the Future

Rosenzweig and her collaborators fed all their data into these crop models. They were among the first to produce a credible estimate of food production in a warmer world. Their estimates are also among the most widely cited. Rosenzweig is co-chair of the working group of the International Panel on Climate Change (IPCC) on this topic.

The result? Well, it's complicated.

"It's not a catastrophe, right away, on a global scale," says Rosenzweig. For the next few decades, climate change probably won't cause a huge change in the total amount of food in the world.

But there will be winners and losers. Canada and some other temperate-zone countries are likely to grow more food, partly because rising temperatures will lengthen the growing season in higher latitudes.

For most developing countries, "it's a negative pressure right away," says Rosenzweig. There are two reasons for this. First, places like India, Pakistan and parts of Africa are expected to get less rain and experience more frequent droughts. Second, while crops need warmth, too much warmth disrupts their development. In the tropics, if it gets much hotter, crops won't do as well.

"Over and over again, our study and many, many following studies have shown that farmers in developing countries are more vulnerable to the changing climate than those in the higher latitudes, where the developed countries are," says Rosenzweig.

And in the long-term, if the globe continues to heat up, even the most optimistic computer models show worsening conditions, not just in the tropics, but across most of the world. By 2080, when today's children are elderly, the models show global food production decreasing, especially in parts of the world that can least afford it. Tens of millions of additional people could go hungry.

A Way Forward

But Siwa Msangi, an economist at the International Food Policy Research Institute in Washington, cautions that these projections aren't set in stone. "In the end, you have to look at these as learning tools," he says.

Msangi, from Tanzania, points out that the models contain many assumptions about human choices, such as how much greenhouse gases we pump into the air, or how much money governments choose to spend on irrigation or on helping poor people buy food. If one enters different assumptions, the computer models show big changes in agricultural production and hunger. "That starts to give you some insight, in terms of what are the really sensitive parameters that policy can affect, what are the levers that policymakers can pull, in order to effect change," Msangi says.

That human ability to learn and adapt is one reason why Rosenzweig says she refuses to be pessimistic.

"First of all, because — I think you can tell — I'm not a pessimistic person," says Rosenzweig, who bubbles with enthusiasm and good cheer, even during a pre-dawn interview.

"This is how I look at it: Global climate change is the most important challenge that we face as a planet," she says. "But it is becoming a major impetus to move the planet toward sustainability."

People are learning, she says. They're learning how to consume less energy, send less heat-trapping gas into the air and, possibly, how to create a world where people everywhere can get enough to eat.

Will a Warmer World Have Enough Food?

An Indian farmer sorts through mangoes at a wholesale fruit market in Hyderabad.

hide captionAn Indian farmer sorts through mangoes at a wholesale fruit market in Hyderabad.

Noah Seelam/AFP/Getty Images

More Climate Change Primers

Your most direct link to global warming may be the food you eat. All the bounty of your local grocery store depends on natural cycles of rain and sunlight, cool temperatures and warmth in far-flung parts of the world. Now, across the globe, those cycles are shifting and the effects are likely to be profound — not just for farmers, but possibly even for you.

How profound? A lot of people are trying to figure this out. Here, a look at some of the most important questions about how climate change will affect agriculture — and how agriculture has helped change the climate.

Will climate change make it easier or harder to grow food?

On average, it probably will be harder. It depends, though, on the crop and on the place. In the tropics, where it's hot already, even more heat will stress plants, resulting in smaller harvests. In colder latitudes, many crops will benefit from warmer temperatures. So Canada's farming areas are likely to expand and become more productive. India and much of Africa, on the other hand, probably will produce less food.

Plants also need water, of course, either from rainfall or rivers fed by melting snow. As the Earth warms up, patterns of wind and rain will shift. No one knows exactly where the water will end up or when it will arrive. But most of the big computer models predicting Earth's future climate, including those created by the Hadley Centre for Climate Change in London or NASA's Goddard Institute for Space Studies, foresee declining rainfall in the tropics. This would also depress harvests in those regions.

Finally, there's a good chance that climate change will produce more extreme weather, such as hurricanes and monsoons that can destroy crops and leave people with no food to eat.

Isn't more carbon dioxide in the air good for crops?

Yes. Carbon dioxide in the air is food for plants; it acts like fertilizer. But some plants can't take advantage of the extra carbon dioxide because their growth is limited by other factors, such as scarce water or nutrients in the soil. Predictions of future food production do include some so-called CO2 fertilization, but there is a lot of controversy about how large that effect will be.

So what's the answer? Will there be more food or less?

Most scientists don't foresee major changes in total food production during the next decade or two, as average temperatures increase by just a few degrees. On average, across the globe, the positive effects of more carbon dioxide in the atmosphere are projected to cancel out the negative effects caused by rising temperatures.

Even during this period, though, some regions will benefit and others will lose ground. Food production is projected to increase in temperate regions, such as North America and Europe. It may fall, however, in sub-Saharan Africa or India. As a result, the world will become increasingly dependent on a handful of major food exporters, such as the United States, Canada, Australia, Brazil and Argentina.

Forty or 50 years from now, as today's children reach middle age, things are likely to get worse. As temperatures continue to rise, along with levels of greenhouse gases in the atmosphere, most models show global food production falling. Many of the areas that will be most affected are those least able to purchase food from abroad. Foremost among these is Africa. According to some estimates, tens of millions of people could go hungry unless there's a major effort to help these countries adapt.

What can be done to avoid the worst effects?

Farmers can adapt in many ways, but it won't be easy, especially in the poorest parts of the world. Take one example: The soil in many parts of Africa is highly degraded. There's very little organic matter — decomposed leaves, roots and grass — left in the soil. It isn't replenished because any leftover vegetation gets harvested and used for fuel. Improving the soil would help Africa prepare for climate change by increasing harvests and also helping the soil store water. Actually accomplishing this, though, will require millions of farmers to change how they manage the land, and they would have to find alternate fuels that they can use for cooking.

Technology is also part of the solution, such as new varieties of crops that are better able to withstand heat, drought and floods; techniques for controlling new pests; and systems for using rainfall and melting snow more efficiently. But developing such technologies, and making them available to millions of farmers, will take a lot of money and time. (Read an NPR report on one example of improved seeds, a new line of rice that can survive severe flooding.)

And, of course, anything that increases the wealth of poor countries will increase their ability to buy food from abroad if domestic production falls short.

Doesn't farming release a lot of greenhouse gases?

Yes. It's estimated that farming is involved in 20 percent to 25 percent of all greenhouse gas emissions worldwide. Large amounts of carbon dioxide are released when farmers burn forests and grasslands in order to make way for fields. Farmers also burn plenty of fossil fuels — to power their tractors, harvesters and other equipment. In addition, when farmers plow their fields, it introduces oxygen into the soil, causing microbes to digest the organic carbon found in decomposed roots and leaves in the soil. This also releases carbon dioxide.

The most important fertilizer that farmers spread on their fields is nitrogen. Some of this nitrogen gets converted into nitrous oxide, a powerful greenhouse gas. And finally, rice paddies around the world produce about 100 million tons of methane, another potent greenhouse gas, each year.

Still, agriculture's emissions of greenhouse gases are holding steady, while other sources — mainly burning fossil fuels for other reasons — continue to increase. So agriculture's share of global greenhouse gas emissions declines each year. Food production is more likely to be a victim of climate change than its cause.

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