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.
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