Agriculture throughout much of the world could be threatened in decades ahead as an increase in extreme heat waves, droughts, and floods related to climate change disrupt water supplies, experts said at a symposium co-organized by AAAS.
Significant disruptions associated with climate change already have begun, they said, and as the temperature warms, the impacts are likely to be more threatening, especially to areas in Asia and Africa where poverty and hunger have remained stubborn problems.
In Europe, data show that the annual growing season has expanded by about 30 days in the past three decades, and irrigation demands have risen in some areas of the continent, said Ad de Roo, senior scientist with the European Commission's Joint Research Centre  (JRC). Continued warming could lead to “dramatic” potential change in precipitation, with losses off 30% to 40% in some parts of Southern Europe and increases of 30% to 40% in the north.
Ard de Roo
James W. Hansen
While the climate is inherently uncertain, warming temperatures are expected to intensify the hydrological cycle worldwide, added James W. Hansen, a research scientist at the International Research Institute for Climate and Society at Columbia University.
And, Hansen added: “A lot of the changes that we thought would happen gradually seem to be happening more rapidly than anticipated, making things very difficult to manage.”
Despite their stark assessments, both de Roo and Hansen urged a constructive response to the unfolding changes, saying that measures ranging from new dikes and flood-warning systems to increased research on crop breeding and pest control could help humanity adapt to the coming changes. The emerging challenge should be seen as a “crisis of opportunity,” Hansen said, with public awareness and political will leading “to unprecedented investment in more productive and resilient agriculture in developing countries.”
He and de Roo appeared at the EC Delegation headquarters with JRC Director General Roland Schenkel in the first of three Washington, D.C., symposia, “Beyond Copenhagen: Scientific Perspectives on Adaptation and Sustainability.” The symposia are co-sponsored by the Embassy of Sweden (holding the presidency of the European Union), the U.S. Delegation of the European Commission, and AAAS.
A second symposium, on 5 November at the Swedish Embassy and introduced by Sweden's U.S. Ambassador Jonas Hafström, explored water and urban infrastructure. The final symposium in the series, exploring water and marine services, is scheduled for Thursday 3 December at AAAS headquarters in Washington.
Schenkel moderated the 1 October event, prefacing the discussion with a description of the work of the Joint Research Centre.
As a service of the 27-nation European Commission, he said, the JRC provides scientific and technical support for the conception, development, implementation, and monitoring of European Union policies. Headquartered in the Italian city of Ispra, north of Milan, it has seven institutes spread across five EC nations; it has a staff of more than 2600 and an annual budget of over 330 million Euros.
Schenkel noted that there are two general approaches to climate change—mitigation, or the effort to limit climate change, mostly by limiting emission of heat-trapping greenhouse gases; and adaptation, or preparing humanity to deal with its adverse affects. “Some countries don't want to even start to look into mitigation,” he acknowledged. “We hope this will change. We cannot succeed without mitigation.”
The Necessity of Adaptation
De Roo and Hansen offered a perspective increasingly common among scientists and some policymakers: Climate change has already advanced so far—and greenhouse gas concentrations are rising so steadily—that humanity must prepare now to deal with a range of difficult challenges.
De Roo offered an ominous series of modeling snapshots: Temperatures rising from 3.5 to 5.5 degrees Celsius across much of Europe by 2100; precipitation falling sharply in the south and rising in Scandinavia and the Baltic nations; increases of 30-40 days—or more—through much of Europe in the number of days per year with very dry soil. The risk of floods along Central European rivers—the Rhine, the Elbe, the Danube, and the Po—will increase, with damage costs rising from the current average of 6.5 billion Euros per year to as much as 18 billion by 2100.
Hansen described a world in which the warming climate would make extreme weather events more frequent. “Because of this variability,” he said, “we're not going to experience climate change so much as a gradual change in averages, but as shifts in frequency and intensity of extreme events...[It will] also cause us to experience very hot events we've never experienced before in recent history.”
Focusing especially on Africa and Asia, he said that some areas would experience less frequent rain, and other would experience more. Some areas might experience both increased flooding and increased drought.
“The impacts will be particularly severe in tropical regions that already have high rates of poverty and high rates of hunger,” Hansen said, “particularly in sub-Saharan Africa and Southern Asia—those are hotspots of vulnerability.”
Across much of the globe, these changes would likely have broad impact on human endeavors involving water, the researchers said. Hotter temperatures will mean more evaporation. Drinking water might become more scarce in some areas. Rivers might fall to levels that can't drive hydropower systems; in other areas, swollen rivers might back up behind dams that are old and structurally questionable. Commerce that depends on rivers might suffer as boat transit becomes more unreliable.
To adapt, de Roo said, the JRC is already making great efforts to research and develop early flood-warning systems. Europe also might have to invest heavily in dikes and other flood-control measures, he said.
The Threats to Food Production
Perhaps the most profound impact could be in agriculture, the largest user of surface water supplies in many areas of the world.
Hansen noted that, according to the United Nations' Food and Agriculture Organization, world food supplies must increase 70% by 2050. That is not an impossible goal—the Green Revolution in the second half of the 20th century produced phenomenal gains in farm production, in both developed and developing nations. But because of the increasingly volatile climate, he said, that success will be “much more difficult” to repeat in years ahead.
In Europe, de Roo said, research suggests that farmers may have to shift to different crops in response to changing weather. Yields might suffer. Diseases attacking such essential crops as wheat and potatoes could become more common across a wider part of the continent.
Hansen, in his presentation, said that a moderate increase in temperatures—1-2 degrees Celsius—might actually increase crop yields in many temperate areas, offsetting losses in other areas. But even moderate warming would depress yields in tropical areas. Those factors could make availability of food increasingly inequitable, he said.
If climate change reaches severe levels, with temperatures rising 3 degrees Celsius or more, models suggest that temperate zones could expect moderate losses in the yield of corn, wheat, and rice. In “hotspots” of the lowland tropics in Africa and South Asia, the crop losses could be “severe,” Hansen said.
”No Regret” and “Win-Win” Adaptation
If the picture seems dire, both Hansen and de Roo strongly emphasized that a concerted effort could yield great advances in agricultural practices adapted to the changing climate.
An initial challenge, though, may be getting policymakers to commit to action. “Climate change is an uncertain business,” de Roo said. “We present them with a range of uncertain conditions, and they don't want to deal with that. That's one of the challenges the scientific community faces—decision-making in an uncertain environment.”
Added Hansen: “Adaptation is about decision-making now that is sensitive to climate impacts that can be only partially anticipated. It is about managing uncertainty.”
To address the caution of policymakers and the public, de Roo advocated a focus on “win-win” and “no-regret” measures: not only dikes and early-warning systems, but hazard and risk-mapping, water efficiency strategies, and water pricing to encourage savings.
Hansen favored a balanced approach for agricultural adaptation, in which the substantial uncertainty about future climate is neither ignored nor a deterrent to action. And in strong terms, he rejected “fatalism” in favor of “hope motivating aggressive intervention.”
Generally, he said, vulnerability should be reduced through greater investment in agricultural development, but with more awareness of how climate might affect development outcomes. This includes managing current climate risk more effectively. In deciding on longer-term investment such as agricultural research and crop breeding, it is important to look for strategies that will provide benefits regardless of how local climate changes. And, he said, these strategies can be supported by advancing near-term climate change research, which focuses on understanding and reducing uncertainties over the next 15 to 25 years."
At the same time, creating incentives for agricultural research could drive robust investments; agribusiness will come to recognize opportunities when climate change creates new markets or makes old markets vulnerable.
“The challenge is building the relationships (between science and business) and keeping communication open,” Hansen said. “In some contexts, that is already happening. But also we need to find the common ground where the incentive for agribusiness coincides with the incentives for reducing vulnerability and moving rural populations out of poverty.
“I propose that we learn from the Green Revolution, and see that the current climate crisis could be a crisis of opportunity to respond to the age-old problems of hunger and poverty,” he continued. “The problems are in fact intensified by the variables of a changing climate. But let's approach them in new ways, with the new resources and new energy...on a global scale that seem to be mobilizing around the climate crisis.”