One critical element of the laws of war is a concept known as "belligerent privilege," which stipulates that combatants may legally kill other combatants but may not target civilians. What, then, does a soldier do about the fact that in modern warfare it can be extraordinarily difficult to tell the difference?

Terrorists often choose to move undetected through the ranks of civilian populations. They hide in plain sight by wearing civilian clothes rather than uniforms or distinctive emblems. "They may be farmers by day and fighters by night," said David Luban, a Georgetown professor of law and philosophy, at an event that was part of the Ethics and War series. What's more, civilians may offer food and shelter to enemy soldiers - do they in the process become combatants? And what, finally, should the soldier do about civilians who are being used as a shield to protect combatants?

These are tricky questions. Luban said the phrasing of the Geneva Convention leaves open the possibility that soldiers may legally target civilians in a conflict zone. Article 48 says the military must discriminate between civilians and combatants at all times. Yet Article 51 notes that civilians shall only enjoy full protection in times of conflict "unless and for such times as they take a direct part in hostilities."

Efforts to clarify these issues have proved to be "highly dangerous," said Luban. In 2009, the Obama administration made a change in the Military Commissions Act to label anyone who materially supports hostilities against the U.S. as an "unprivileged enemy belligerent." As a result, civilians who tacitly support an enemy regime or terrorist organization may be lawfully targeted. Unfortunately, the amendment drew no distinction between those who did so voluntarily and those who did so involuntarily. It other words, a civilian actively helping a terrorist might be construed to be a combatant. But less clear, said Luban, is how the U.S. government would consider an Afghan woman who under duress shelters members of the Taliban.

The lack of consensus, he said, has led to widespread confusion within the military. One soldier told Luban that he didn't "think anyone has worked out what to do when civilians take on certain risks by assisting the enemy," or what to do when "soldiers and civilians are indistinguishable."

It is equally difficult to know how far the military is obligated to go to protect innocent civilians. It is often left to the discretion of an individual solider or unit to make that call, and often in a split second. Luban cited one well-known example in which one British soldier, Frank Richards, was ordered to throw bombs into cellars to target German soldiers during the First World War. When Richards chose to issue a warning cry to alert civilians in hiding, he lost a key advantage over his enemy.

The attitude toward civilians is very different today, Luban said. The unspoken sentiment among soldiers is that "we'll not lose another life for these people." But they are wrong to think this way. Luban cited recent studies that indicate it is in the best interests of soldiers to protect the innocent. Brigades that actively try to prevent civilian casualties tend to take the fewest casualties in their own ranks. "If you're careless in protecting civilians," he argued, "you're careless in everything."

The key, Luban said, is establishing clear boundaries. Wars are inevitable, and no matter how compelling the moral arguments, he argued, "the states that ratify treaties like the Geneva Convention will never accept rules that ruin their own military effectiveness." However, the issues surrounding civilians in war zones must be addressed to ensure that soldiers are not left with a dangerous incoherence. Ultimately, he said, "we need analytic clarity."

A hidden trove of historical crop yield data from Africa shows that corn - long believed to tolerate hot temperatures - is a likely victim of global warming.

Stanford agricultural scientist David Lobell and researchers at the International Maize and Wheat Improvement Center (CIMMYT) report in the inaugural issue of Nature Climate Change next week that a clear negative effect of warming on maize - or corn - production was evident in experimental crop trial data conducted in Africa by the organization and its partners from 1999 to 2007.

Led by Lobell, the researchers combined data from 20,000 trials in sub-Saharan Africa with weather data recorded at stations scattered across the region. They found that a temperature rise of a single degree Celsius would cause yield losses for 65 percent of the present maize-growing region in Africa - provided the crops received the optimal amount of rainfall. Under drought conditions, the entire maize-growing region would suffer yield losses, with more than 75 percent of areas predicted to decline by at least 20 percent for 1 degree Celsius of warming.

"The pronounced effect of heat on maize was surprising because we assumed maize to be among the more heat-tolerant crops," said Marianne Banziger, co-author of the study and deputy director general for research at CIMMYT."

"Essentially, the longer a maize crop is exposed to temperatures above 30 C, or 86 F, the more the yield declines," she said. "The effect is even larger if drought and heat come together, which is expected to happen more frequently with climate change in Africa, Asia or Central America, and will pose an added challenge to meeting the increasing demand for staple crops on our planet."

Similar sources of information elsewhere in the developing world could improve crop forecasting for other vast regions where data has been lacking, according to Lobell, who is lead author of the paper describing the study.

"Projections of climate change impacts on food production have been hampered by not knowing exactly how crops fair when it gets hot," Lobell said. "This study helps to clear that issue up, at least for one important crop."

While the crop trials have been run for many years throughout Africa, to identify promising varieties for release to farmers, nobody had previously examined the weather at the trial sites and studied the effect of weather on the yields, said Lobell, who is an assistant professor of environmental earth system science and fellow at Stanford's Program on Food Security and the Environment.

"These trials were organized for completely different purposes than studying the effect of climate change on the crops," he said. "They had a much shorter term goal, which was to get the overall best-performing strains into the hands of farmers growing maize under a broad range of conditions."

The data recorded at the yield testing sites did not include weather information. Instead, the researchers used data gathered from weather stations all over sub-Saharan Africa. Although the stations were operated by different organizations, all data collection was organized by the World Meteorological Organization, so the methods used were consistent.

Lobell then took the available weather data and interpolated between recording stations to infer what the weather would have been like at the test sites. By merging the weather and crop data, the researchers could examine climate impacts.

"It was like sending two friends on a blind date - we weren't sure how it would go, but they really hit it off," Lobell said.

Previously, most research on climate change impacts on agriculture has had to rely on crop data from studies in the temperate regions of North America and Europe, which has been a problem.

"When you take a model that has been developed with data from one kind of environment, such as a temperate climate, and apply it to the rest of the world, there are lots of things that can go wrong" Lobell said, noting that much of the developing world lies in tropical or subtropical climates.

But he said many of the larger countries in the developing world, such as India, China and Brazil, which encompass a wide range of climates, are running yield testing programs that could be a source of comparable data. Private agribusiness companies are also increasingly doing crop testing in the tropics.

"We're hoping that with this clear demonstration of the value of this kind of data for assessing climate impacts on crops that others will either share or take a closer look themselves at their data for various crops," Lobell said.

"I think we may just be scratching the surface of what can be achieved by combining existing knowledge and data from the climate and agriculture communities. Hopefully this will help catalyze some more effort in this area."

Lobell is a Center Fellow at the Program on Food Security and the Environment, a joint program of Stanford's Woods Institute for the Environment and Freeman Spogli Institute for International Studies.

The work was funded by the Rockefeller Foundation

President Obama's vision of a "world free of nuclear weapons" -- first enunciated in Prague in April 2009 -- has been derided by his critics as a utopian fantasy that will have no influence on the nuclear strategies of other nations.

But in a special issue of The Nonproliferation Review, entitled Arms, Disarmament, and Influence: International Responses to the 2010 Nuclear Posture Review, 13 prominent researchers from around the world examined foreign governments' policy responses to Obama's 2010 Nuclear Posture Review (NPR), the landmark document published a year and a day after his Prague speech.

They found that many nations, though not all, had been "strongly influenced by Washington's post-Prague policy and nuclear posture developments," which reduced the role of nuclear weapons in U.S. national strategy, and assured non-nuclear nations that the U.S. would never use nuclear arms against them provided they remained in compliance with their obligations under the Nuclear Non-Proliferation Treaty.

Indeed, the 11 case studies presented "demonstrate that U.S. pronouncements and actions influenced bureaucratic infighting and domestic debates inside a number of important foreign governments, and that some of these governments have adjusted their own policies and actions accordingly."

Read the full report here.

See a presentation about the report here, or listen to a different one here.

Read CISAC co-director Scott Sagan's essay on "Obama's Disarming Influence" in the Bulletin of the Atomic Scientists.  

Read Thomas Fingar's essay on "How China Views U.S. Policy" in the Bulletin of the Atomic Scientists. 

Highlights:

* Russia adopted a nuclear doctrine that was considerably more moderated than it would have been had the United States not pushed ahead with its own policy changes. In the run up to the April 2010 publication of the NPR, Washington "reset" relations with Russia, ended the deployment of missile defense components in Poland and the Czech Republic, and resumed the disarmament negotiations that ultimately led to the ratification of the New START treaty. As a result of this process, and continuous consultation with Russia about the NPR, Moscow narrowed the role of nuclear weapons in its policy and the range of circumstances in which it would consider using them. (page 39)

* "The most important short-term success of Obama's nuclear weapons policy," along with the "Prague Spirit," has been to halt the erosion of the NPT. "Obama's policies helped extract a minimum positive result from the 2010 NPT Review Conference, a favorable outcome compared to the chaos that his predecessor's representatives had created at the 2005 conference." The Obama policy was welcomed as a positive development, which allowed "key players, such as Egypt and Brazil, to strive for compromise, and others, such as Russia and China, not to block it." (page 219)

* The U.S. effort to encourage other governments to reduce the role of nuclear weapons in their policy was successful in the United Kingdom, which adopted a nuclear posture that was very similar to that to the U.S. (page 238)

* Due in large part to the Obama policy, some of the non-nuclear weapons states in NATO began to push for the removal of sub-strategic nuclear weapons from Europe. At the November 2010 NATO summit, members agreed to a new Strategic Concept that called for negotiations with Russia and a linkage between the reduction and eventual elimination of nuclear weapons in NATO Europe to comparable reductions in western Russia. (page 238)

* Obama's new nuclear doctrine was a driving force behind a May 2010 agreement among 189 nations at the Nonproliferation Review Conference to a set of disarmament objectives and steps to reinforce the nuclear non-proliferation regime. (page 238)

* The Obama disarmament initiatives encouraged Indonesia's decision to begin the process of ratifying the Comprehensive Test Ban Treaty. (page 238)

* China continues to view Washington's nuclear doctrine with suspicion. Although Beijing viewed the 2010 NPR favorably compared to its 2001 predecessor, it still found serious cause for concern. This is partly the result of timing: the NPR came out amid a period of rising tension between U.S. and China. It also reflected a tendency among Chinese leaders to view virtually all U.S. doctrine and actions as part of a concerted effort to constrain its rise. In this view, the NPR would foster comparisons between nuclear decreases in Russia and the U.S., and increases in China, and be used as leverage to force Beijing to engage in an expensive conventional arms race. In keeping with this China-centric view, Chinese officials were also concerned about the U.S. military's continued development of missile defense capabilities. (page 243)

* Many non-nuclear weapons states--such as Egypt, Brazil, and South Africa--emphasize their opposition to any constraints being placed on their right to enjoy the benefits of civilian nuclear energy. Some of their opposition is "due to post-colonial sensitivity about any apparent inequality in the terms of international agreements that divide the world into 'haves' and 'have-nots.'" Others are engaged in bargaining, waiting to see what nuclear-weapons states will do regarding disarmament before offering to accept more constraints on nuclear technology development. Some governments also appear to be engaged in "hedging behavior--protecting their ability to enrich uranium or reprocess plutonium" to be closer to acquiring nuclear weapons in the future, should they choose to do so. This may be disappointing for Washington policymakers, but it should not be surprising. After all, the U.S. employs a similar "hedging strategy" in its management of its own nuclear stockpile. As a result, it is imperative to begin discussions of how to reduce the danger of both kinds of nuclear hedging behavior. (page 255)

* The Obama administration must continue "to ensure there is consistency and discipline in the messages" emanating from the military and the government bureaucracy. Some foreign governments viewed the NPR's guarantees as mere rhetoric. "Such a skeptical view is encouraged whenever a senior US military officer makes statements that reflect a lack of understanding or lack of discipline regarding nuclear use policy." Even after the NPR was released, a top U.S. general insisted that the United States had not altered its "calculated ambiguity" policy. (page 258)

The special issue of the Nonproliferation Review was coordinated by Scott D. Sagan, co-director of the Center for International Security and Cooperation at Stanford University, and Jane Vaynman, a PhD candidate at the Department of Government at Harvard University, and a National Security Studies Fellow at the Weatherhead Center for International Affairs. The journal is published by the James Martin Center for Nonproliferation Studies at the Monterey Institute of International Studies, and it is edited by Stephen Schwartz.

Authors:

Irma Argüello is founder and chair of the NPSGlobal Foundation, a private nonprofit initiative that focuses on improving global security and reducing risks stemming from WMD proliferation.

Ralph A. Cossa is President of the Pacific Forum CSIS in Honolulu. He is senior editor of the Forum's quarterly electronic journal, Comparative Connections. 

Ambassador Nabil Fahmy is the founding Dean of the School of Global Affairs and Public Policy at the American University in Cairo. He is also the Chair of the James Martin Center for Nonproliferation Studies' Middle East Project.

Thomas Fingar is the Oksenberg-Rohlen Distinguished Fellow and Senior Scholar in the Freeman Spogli Institute for International Studies at Stanford University.

Brad Glosserman is Executive Director of the Pacific Forum CSIS in Honolulu. Mr. Glosserman is co-editor of Comparative Connections, the Pacific Forum's quarterly electronic journal, and writes, along with Ralph Cossa, the regional review.

S. Paul Kapur is associate professor in the Department of National Security Affairs at the U.S. Naval Postgraduate School and a faculty affiliate at Stanford University's Center for International Security and Cooperation.

Mustafa Kibaroglu is an Assistant Professor at Bilkent University.

Michael Krepon is the co-founder of the Stimson Center, a Washington-based think tank specializing in national and international security problems. 

Harald Müller is executive director of Peace Research Institute Frankfurt and Professor at International Relations at Goethe University Frankfurt.

Pavel Podvig is an independent analyst based in Geneva, Switzerland, where he manages the research project Russian Nuclear Forces.

Scott D. Sagan is the Caroline S.G. Munro Professor of Political Science, co-director of Stanford's Center for International Security and Cooperation, and a Senior Fellow at the Freeman Spogli Institute. He also serves as the co-chair of the American Academy of Arts and Science's Global Nuclear Future Initiative.

Scott Snyder is Director of the Center for U.S.-Korea Policy at The Asia Foundation, Senior Associate at Pacific Forum CSIS, and Adjunct Senior Fellow for Korean Studies at the Council on Foreign Relations.

Jane Vaynman is a PhD candidate at the Department of Government at Harvard University and a National Security Studies Fellow at the Weatherhead Center for International Affairs.

^{The Center for International Security and Cooperation (CISAC), part of the Freeman Spogli Institute for International Studies (FSI), is an interdisciplinary university-based research and training center addressing some of the world's most difficult security problems with policy-relevant solutions. The Center is committed to scholarly research and to giving independent advice to governments and international organizations.}