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Blocking sunlight to cool Earth won’t reduce crop damage from global warming

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Injecting particles into the atmosphere to cool the planet and counter the warming effects of climate change would do nothing to offset the crop damage from rising global temperatures, according to a new analysis by University of California, Berkeley, researchers.

By analyzing the past effects of Earth-cooling volcanic eruptions, and the response of crops to changes in sunlight, the team concluded that any improvements in yield from cooler temperatures would be negated by lower productivity due to reduced sunlight. The findings have important implications for our understanding of solar geoengineering, one proposed method for helping humanity manage the impacts of global warming.

“Shading the planet keeps things cooler, which helps crops grow better. But plants also need sunlight to grow, so blocking sunlight can affect growth. For agriculture, the unintended impacts of solar geoengineering are equal in magnitude to the benefits,” said lead author Jonathan Proctor, a UC Berkeley doctoral candidate in the Department of Agricultural and Resource Economics. “It’s a bit like performing an experimental surgery; the side-effects of treatment appear to be as bad as the illness.”

“Unknown unknowns make everybody nervous when it comes to global policies, as they should,” said Solomon Hsiang, co-lead author of the study and Chancellor’s Associate Professor of Public Policy at UC Berkeley. “The problem in figuring out the consequences of solar geoengineering is that we can’t do a planetary-scale experiment without actually deploying the technology. The breakthrough here was realizing that we could learn something by studying the effects of giant volcanic eruptions that geoengineering tries to copy.”

Hsiang is director of UC Berkeley’s Global Policy Laboratory, where Proctor is a doctoral fellow.

Proctor and Hsiang will publish their findings online in the journal Nature on August 8.

Some people have pointed to past episodes of global cooling caused by gases emitted during massive volcanic eruptions, such as Mt. Pinatubo in the Philippines in 1991, and argued that humans could purposely inject sulfate aerosols into the upper atmosphere to artificially cool Earth and alleviate the greenhouse warming caused by increased levels of carbon dioxide. Aerosols — in this case, minute droplets of sulfuric acid — reflect a small percentage of sunlight back into space, reducing the temperature a few degrees.

“It’s like putting an umbrella over your head when you’re hot,” Proctor said. “If you put a global sunshade up, it would slow warming.”

Pinatubo, for example, injected about 20 million tons of sulfur dioxide into the atmosphere, reducing sunlight by about 2.5 percent and lowering the average global temperature by about half a degree Celsius (nearly 1 degree Fahrenheit).

The team linked maize, soy, rice and wheat production from 105 countries from 1979-2009 to global satellite observations of these aerosols to study their effect on agriculture. Pairing these results with global climate models, the team calculated that the loss of sunlight from a sulfate-based geoengineering program would cancel its intended benefits of protecting crops from damaging extreme heat.

“It’s similar to using one credit card to pay off another credit card: at the end of the day, you end up where you started without having solved the problem,” Hsiang said.

Some earlier studies suggested that aerosols might improve crop yields also by scattering sunlight and allowing more of the sun’s energy to reach interior leaves typically shaded by upper canopy leaves. This benefit of scattering appears to be weaker than previously thought.

“We are the first to use actual experimental and observational evidence to get at the total impacts that sulfate-based geoengineering might have on yields,” Proctor said. “Before I started the study, I thought the net impact of changes in sunlight would be positive, so I was quite surprised by the finding that scattering light decreases yields.”

Despite the study’s conclusions, Proctor said, “I don’t think we should necessarily write off solar geoengineering. For agriculture, it might not work that well, but there are other sectors of the economy that could potentially benefit substantially.”

Proctor and Hsiang noted that their methods could be used to investigate the impact of geoengineering on other segments of the economy, human health and the functioning of natural ecosystems.

They did not address other types of geoengineering, such as capture and storage of carbon dioxide, or issues surrounding geoengineering, such as its impact on Earth’s protective ozone layer and who gets to set Earth’s thermostat.

“Society needs to be objective about geoengineering technologies and develop a clear understanding of the potential benefits, costs and risks,” Proctor said. “At present, uncertainty about these factors dwarfs what we understand.”

The authors emphasize the need for more research into the human and ecological consequences of geoengineering, both good and bad.

“The most certain way to reduce damages to crops and, in turn, people’s livelihood and well-being, is reducing carbon emissions,” Proctor said.

“Perhaps what is most important is that we have respect for the potential scale, power and risks of geoengineering technologies,” Hsiang said. “Sunlight powers everything on the planet, so we must understand the possible outcomes if we are going to try to manage it.”

New tools to systematically build cooperation: Theory of repeated games

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When what we want as individuals clashes with what is best for the group, we have a social dilemma. How can we overcome these dilemmas, and encourage people to cooperate, even if they have reason not to? In a paper released today in Nature, Christian Hilbe and Krishnendu Chatterjee of the Institute of Science and Technology Austria (IST Austria), together with Martin Nowak of Harvard and Stepan Simsa of Charles University, have shown that if the social dilemma that individuals face is dependent on whether or not they work together, cooperation can triumph. This finding was the result of a new type of framework that they introduced — one that extends the entire theory of repeated games. Moreover, as their work pinpoints the ideal conditions for fostering cooperation, they have provided tools to systematically build cooperation.

The tragedy of the commons: if we can (ab)use a public good without seeing negative consequences, we will — without consideration of others or the future. We see examples of this in our daily lives, from climate change and forest depletion down to the stack of dirty dishes in the office kitchen. In game theory, scientists have used repeated games — repeated interactions where individuals face the same social dilemma each time — to understand when individuals choose to cooperate, i.e. their strategies. However, these games have always kept the value of the public resource constant, no matter how players acted in the previous round — something that does not reflect reality of the situation.

In their new framework, Hilbe, Simsa, Chatterjee, and Nowak consider repeated games in which cooperation does not only affect the players’ present payoffs, but also which game they face in the next round. “Repeated games have been studied intensely for over 40 years, and significant new developments are rare — especially such simple ones,” says Martin Nowak. “This addition actually extends the whole theory of repeated games, as a fixed environment is a special case of our new framework.”

When they explored the new model, the scientists found that this dependence on players’ actions could greatly increase the chance that players cooperate — provided the right conditions were in place. “Our framework shows which kinds of feedback are most likely to lead to cooperation,” says first author Christian Hilbe. These include, for instance, how quickly the resource degrades or how easy it is to return to a more valuable state. “Using this knowledge, you can design systems that maximize cooperation, or create an environment that encourages people to work together,” he adds. For example, these ideas could even be implemented by a business or corporation, to create a work community that encourages working together.

 

Protein that causes memory loss in healthy human brains

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A brain protein believed to be a key component in the progress of dementia can cause memory loss in healthy brains even before physical signs of degeneration appear, says a new University of Sussex study, according to IANS.

The study reveals a direct link between the main culprit of Alzheimer’s disease and memory loss. Alzheimer’s disease is characterized by the formation of amyloid plaques in the brain tissue.

These amyloid plaques are made up of an insoluble protein, ‘Amyloid-beta’ (Abeta), which forms small structures called ‘oligomers’ that are important in the disease progression.

Although these proteins are known to be involved in Alzheimer’s, little is understood about how they lead to memory loss.

Neuroscience researchers have investigated how Abeta affected healthy brains of pond snails (Lymnaea stagnalis) by observing the effect of administering the protein following a food-reward training task.

“Because we understand the memory pathways so well, the simple snail brain has provided the ideal model system to enable us to link the loss of established memory to pure Abeta,” said George Kemenes, a neuroscientist at the University of Sussex.

Snails treated with Abeta had significantly impaired memories 24 hours later when tested with the food task, even though their brain tissue showed no sign of damage.

“This demonstrated that Abeta alone is enough to lead to the symptoms of memory loss that are well known in Alzheimer’s disease,” said lead author Lenzie Ford from the University of Sussex.

The work will provide a platform for a more thorough investigation of the mechanisms and effects on memory pathways that lead to this memory loss.

“It is absolutely essential that we understand how Alzheimer’s disease develops in order to find specific targets for therapeutics to combat this disease,” said professor Serpell, who is senior author on the study.