We have read the headline a number of times now warning us that increasing temperatures are threatening global crop production. One need only to recall the drought and heat wave that hit the mid-western United States last summer, damaging corn and soybean production. Higher temperatures are certainly part of the problem, but a new study led by FSE associate director David Lobell finds its impacts in the U.S. are more indirect. Water stress may be the main culprit.

To validate this hypothesis and to help differentiate the different mechanisms impacting crop yields at higher temperatures, the research team used a model known as an Agricultural Production Systems Simulator (APSIM). High temperatures had a strong negative effect on corn yield response in the United States, in agreement with the data, but the predominate effect of heat in the model was via increased water stress.

As temperatures increase, plants transpire more water into the atmosphere, just as people sweat more on hotter days. With more hot days, the corn plant finds it harder to maintain growth rates, and at the same time loses more water, which sets up the risk of even more drought stress later in the season.

“APSIM computes daily water stress as the ratio of water supply to demand, and during the critical month of July this ratio is three times more responsive to 2 ºC warming than to a 20 percent precipitation reduction,” writes Lobell and co-authors in a new paper published in Nature Climate Change. “Water stress during July is particularly important for overall biomass growth and final yield, with July being the month with the most total biomass growth.”

Direct heat stress on the plant, such as happens on extremely hot days, played a more minor role in determining final yield. The study suggests that increased CO₂ may reduce crop sensitivity to extreme heat by increasing water use efficiency, but gains are likely to be no more than 25 percent.

“The APSIM model has been valuable in its ability to discriminate the importance of these factors,” said Lobell. “Models like these are useful for guiding efforts to develop crops with greater tolerance to increased temperatures, an important component of most adaptation strategies in agriculture, and helping to identify which processes are critical for modeling efforts to consider when projecting climate change impacts.”

The researchers project sensitivity to extreme heat will remain a severe constraint to crop production in the foreseeable future, especially as the region warms. They are now using the models to evaluate different strategies for developing new varieties of corn that can better handle the heat.

Human activities are currently estimated to produce around 40 billion tonnes of carbon-dioxide equivalent every year. Model results indicate that agricultural adaptation measures would prevent around 350 million tonnes of carbon-dioxide emissions annually – equivalent to around 1% of total global emissions.

Adapting to climate change or mitigating climate change – which would you choose to invest your cash in? Mitigation and adaptation are often viewed as separate activities, with the former aiming to reduce greenhouse-gas emissions and the latter helping adjust to expected increases in greenhouse gases. A new study shows that when it comes to agriculture, adaptation measures can also generate significant mitigation effects, making them a highly worthwhile investment.

Food production is big. If farmers fail to adapt to climate change we can expect to see more land being turned over to agriculture, in order to keep up with food demand. With this in mind, David Lobell, from Stanford University, US, and colleagues used a model of global agricultural trade to investigate the co-benefits of helping farmers adapt to climate change, thereby avoiding some of the emissions associated with land-use change.

Running their model to 2050, they show that an investment of $225 bn in agricultural adaptation measures can be expected to offset the negative yield impacts associated with predicted temperature and rainfall changes. But that’s not all – the model revealed that this investment would also save 61 million hectares from conversion to cropland, resulting in 15 Gtonnes carbon-dioxide equivalent fewer emissions by 2050.

"I don't think any of us expected the mitigation benefits to be as big as they were," said Lobell, whose findings are published in Environmental Research Letters (ERL). "We had a hunch that they would be big enough to be an important co-benefit, but the fact they were often big enough to rival other mitigation activities was surprising."

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Africa owns 60% of the world’s uncultivated land suited for crop production, but accounts for 30% of the world’s malnourished and only 3% of global agricultural exports. If there is one thing global agricultural policy experts Paul Collier and Derek Byerlee can agree on, it’s that Africa’s food system is struggling.Their different views on the causes and investment solutions to put Africa on a more prosperous and food secure path made for a provocative discussion at a symposium hosted last week by Stanford University’s Center on Food Security and the Environment.

Collier, a distinguished economist and author of the award-winning book “The Bottom Billion”, was direct in his opening remarks.

“Smallholder agriculture has been a persistent productivity disaster for Africa,” said Collier. “Despite a huge land area to population ratio and higher proportion of its labor force engaged in food production, Africa is still not able to feed itself. The smallholder business model of the last 50 years is fundamentally flawed…maybe it is time for a Plan B.”

African agricultural productivity remains astoundingly low and stagnant at about $500 per person per year. His solution: debunk the ‘myth of the efficient peasant’ and rural romanticism and support commercial agriculture and urban growth.

Commercial agriculture reaps economies of scale that provide advantages often beyond reach for smallholder farmers yet are critical to agricultural production in Africa—risk finance, liquidity, technology, logistics, and knowledge of markets. Collier points to the success of Brazil and Thailand—two emerging economies that differ in scale of commercial organization, but have become major agricultural exporting countries.

Byerlee, a renowned economist and director of the 2008 World Development Report, agreed with Collier that commercial agriculture is likely Africa’s future, but that market-oriented smallholder farmers will play the lead role.

“We have much to learn from emerging business models,” said Byerlee. “Smallholders and agribusiness have complementary assets that can contribute to commercial agriculture, and states and investors must help facilitate smallholder inclusion in these models.”

Byerlee noted that the choice between small-scale or large-scale production models depend on transaction costs and type of commodity, and are context specific. Small- to medium scale production is best suited to most types of products in Africa especially food staples and many labor intensive products (e.g, diary). This follows the example of Thailand that not only has succeeded in food production but alone exports more than the value of all sub-Saharan Africa. Value chains that require stronger coordination with processing and shipping (e.g., sugar and palm oil), demand market standards (e.g, export horticulture) or are taking pioneering risks (e.g., new crops in new areas) may be better suited for large-scale production. Benefits may still be large if they create good jobs—a major challenge for Africa’s future.

Where to invest in Africa’s future?

"Young Africans are voting with their feet in droves to leave smallholder agriculture because it is impoverishing and boring, “ said Collier. “The economic tragedy for Africa is that cities haven’t been the engines of economic opportunity and wage employment.”

Collier argued investments in cities over agriculture are needed to prepare for an urban future and must be done quickly due to one dangerous fact—climate change.

“Climate change is the train coming down the tracks and it is already happening in Africa,” warned Collier. “The continuing deterioration of African agriculture is already set in stone. The last 50 years of carbon emissions are going to continue to devastate Africa’s climate over the next 50 years.”

Collier fears climate change will shift Africa’s competitive advantage in agriculture to Northern Eurasia and North America. Therefore, limited investment dollars must shift to cities which are more climate resilient. Byerlee disagrees.

“There is overwhelming and convincing evidence that agricultural growth is important for poverty reduction and food security,” said Byerlee. “Look at the Green Revolution in Asia and the institutional reforms in China in the early 1980s.”

The 2008 World Development Report also found GDP growth from agriculture benefits the income of the poor two to four times more than GDP growth from non-agriculture. So why isn’t this working for sub-Saharan Africa?

Byerlee points to Africa’s history of poor macroeconomic policies that have disadvantaged African farmers. Smallholder farmers have traditionally been taxed at high levels (as much as 50 percent 20 years ago before liberalization programs started kicking in). Rates have come down dramatically to 15-20 percent, but are still significantly higher than other countries.

“African states must level the playing field,” said Byerlee.

Many of these macropolicies are slowing changing, and that makes Collier and Byerlee hopeful.

“After four decades in sub-Saharan Africa I feel optimistic about Africa’s food systems and future,” said Byerlee. “I see exciting opportunities in terms of market growth, private interest, and improved policies.”

Yields in Africa are low, but there is room for significant improvement. The continent is home to potentially 240 million hectares of uncultivated land and less then 20 percent of irrigation potential has been tapped.

African agricultural systems are transforming rapidly in response to rising rates of income growth, urbanization, and shifts in demand for high value and processed food, and feed for livestock. Higher food prices are incentivizing farmers to enter the market and increasing farmer income. Regional markets now accounting for only 5-10% of trade have much potential to expand, and Byerlee projects the value of African urban food markets to quadruple over the next 20 years.

Renewed investment in Africa is another reason for optimism. After decades of declining support donor agencies are refocusing their efforts on supporting agricultural development in Africa. Private sector investment, ranging from local to foreign investors, is also increasing. Collier spoke of the value pioneer commercial investors are bringing to unused and underutilized, but arable lands in Africa. These larger investors are better able to internalize the benefits of infrastructure supply while creating jobs and opening new markets.

The spur in foreign investment has drawn some fire from opponents worried about ‘land grabbing’. Collier and Byerlee both pointed out the need to differentiate between commercial investors and land speculators. The latter are being scrutinized, and for good reason.

Land speculators are leasing huge tracts of land over long time horizons and banking on the land’s option value if there is a big spike in food prices. This takes potentially arable land out of near-term production and out of the hands of local communities. Byerlee suggests governments impose controls on how rapidly the land is developed as one way of managing this problem.

What will a successful African food system look like in 2050?

"African peasantry as we know it today will not be preserved," projects Collier.

Scientists are making progress in helping millions of wheat farmers adapt to hotter conditions, but the gains have been uneven, reports a new study led by Stanford University. New approaches to breeding are needed to withstand increasingly common heat waves and keep pace with growing global food demand.

Wheat is the most widely grown crop in the world; unfortunately it is also one of the most sensitive to future global warming. Scientists around the world strive to develop new wheat varieties each year that incorporate improved features, much like car companies release new models each year. Different strategies are commonly used; some target fully irrigated conditions that favor very high yields, while others focus on dry and hot conditions where yield maintenance under stress is a priority.

The team, which includes scientists from Stanford and the International Maize and Wheat Improvement Center (known as CIMMYT), evaluated 25 years of data from historical trials around the globe and analyzed the outcome of different past breeding approaches to help prioritize future strategies. The fully irrigated nursery, known as the elite spring wheat yield trials, produces varieties that are released for the majority of wheat farmers in countries like India and Egypt each year. While cultivars selected under stressed conditions showed significant yield progress at higher temperatures, the elite trials did not.

“There has been very impressive progress in improving yields for the elite varieties at the cooler temperatures that wheat prefers,” explains lead author Sharon Gourdji, a post-doctoral scholar in Stanford’s department of Environmental Earth System Science and Center on Food Security and the Environment (FSE).

“However, to date, our analysis shows a lack of yield gains for these varieties in hot environments over the past 25 years. Along with the gains in cool conditions, this means that the yield difference between cool and hot conditions is getting larger.”

A CIMMYT researcher plants wheat seed in pots in the center's greenhouse facilities. Photo credit: X. Fonseca/CIMMYT

"I think we have learned that the current main approach to breeding won't quite cut it in terms of adapting wheat to climate change,” said co-author David Lobell, assistant professor in Environmental Earth System Science and FSE center fellow. “That is useful information as breeding centers try to raise their game to contend with long-term warming."

Lobell notes that there are good reasons why improved heat tolerance for the elite varieties has not happened naturally.

“Breeding is tough since scientists are aiming for so many traits at once – for example, disease resistance, high yields, and good quality for bread making. Adding heat tolerance is like telling a scout looking for a superstar athlete, ‘by the way, make sure he’s a straight A student’,” said Lobell.

One important lesson from the study is that sifting through historical data can help identify what works and what does not.

“It can often be a hard sell to have breeders take the time to send their data back once they have selected their varieties and moved on,” explains CIMMYT wheat physiologist and co-author Matthew Reynolds. “This study clearly demonstrates the advantage of having these data to assess progress. It shows the genetic potential of wheat to adapt to warmer-than-usual conditions, and reinforces the value of screening under stress as a strategy for adaptation to climate change.”

The progress in the nursery targeted towards stress conditions shows that it is possible to make sizable gains in improving heat tolerance. But whether this can be combined with continued high performance under cooler conditions remains to be seen.

“It is critically important for farmers that they not only survive the bad or hot years, but that they can take full advantage of the favorable years” says Gourdji. “What is needed is a breeding strategy that can successfully achieve both.”

This work was supported by a grant from the Rockefeller Foundation. Additional co-authors of the study include CIMMYT’s Ky Mathews and Jose Crossa.