Showing posts with label Science. Show all posts
Showing posts with label Science. Show all posts
Friday, March 6, 2020
To predict an epidemic, evolution can't be ignored
March 2, 2020
College of Engineering, Carnegie Mellon University
Whether it's coronavirus or misinformation, scientists can use mathematical models to predict how something will spread across populations. But what happens if a pathogen mutates, or information becomes modified, changing the speed at which it spreads? Researchers now show for the first time how important these considerations are.
https://www.sciencedaily.com/releases/2020/03/200302153551.htm
When scientists try to predict the spread of something across populations -- anything from a coronavirus to misinformation -- they use complex mathematical models to do so. Typically, they'll study the first few steps in which the subject spreads, and use that rate to project how far and wide the spread will go.
But what happens if a pathogen mutates, or information becomes modified, changing the speed at which it spreads? In a new study appearing in this week's issue of Proceedings of the National Academy of Sciences (PNAS), a team of Carnegie Mellon University researchers show for the first time how important these considerations are.
"These evolutionary changes have a huge impact," says CyLab faculty member Osman Yagan, an associate research professor in Electrical and Computer Engineering (ECE) and corresponding author of the study. "If you don't consider the potential changes over time, you will be wrong in predicting the number of people that will get sick or the number of people who are exposed to a piece of information."
Most people are familiar with epidemics of disease, but information itself -- nowadays traveling at lightning speeds over social media -- can experience its own kind of epidemic and "go viral." Whether a piece of information goes viral or not can depend on how the original message is tweaked.
"Some pieces of misinformation are intentional, but some may develop organically when many people sequentially make small changes like a game of 'telephone,'" says Yagan. "A seemingly boring piece of information can evolve into a viral Tweet, and we need to be able to predict how these things spread."
In their study, the researchers developed a mathematical theory that takes these evolutionary changes into consideration. They then tested their theory against thousands of computer-simulated epidemics in real-world networks, such as Twitter for the spread of information or a hospital for the spread of disease.
In the context of spreading of infectious disease, the team ran thousands of simulations using data from two real-world networks: a contact network among students, teachers, and staff at a US high school, and a contact network among staff and patients in a hospital in Lyon, France.
These simulations served as a test bed: the theory that matches what is observed in the simulations would prove to be the more accurate one.
"We showed that our theory works over real-world networks," says the study's first author, Rashad Eletreby, who was a Carnegie Mellon Ph.D. student when he wrote the paper. "Traditional models that don't consider evolutionary adaptations fail at predicting the probability of the emergence of an epidemic."
While the study isn't a silver bullet for predicting the spread of today's coronavirus or the spread of fake news in today's volatile political environment with 100% accuracy -- one would need real-time data tracking the evolution of the pathogen or information to do that -- the authors say it's a big step.
"We're one step closer to reality," says Eletreby.
Other authors on the study included ECE Ph.D. student Yong Zhuang, Institute for Software Research professor Kathleen Carley, and Princeton Electrical Engineering professor Vincent Poor.
Story Source:
Materials provided by College of Engineering, Carnegie Mellon University. Original written by Daniel Tkacik. Note: Content may be edited for style and length.
Journal Reference:
Rashad Eletreby, Yong Zhuang, Kathleen M. Carley, Osman Yağan, and H. Vincent Poor. The effects of evolutionary adaptations on spreading processes in complex networks. PNAS, 2020 DOI: 10.1073/pnas.1918529117
Tropical forests may be heating Earth by 2035
March 6th, 2020, by Tim Radford
https://climatenewsnetwork.net/tropical-forests-may-be-heating-earth-by-2035/
Climate change so far has meant more vigorous forest growth as greenhouse gases rise. The tropical forests may soon change that.
LONDON, 6 March, 2020 – Within about fifteen years, the great tropical forests of Amazonia and Africa could stop absorbing atmospheric carbon, and slowly start to release more carbon than growing trees can fix.
A team of scientists from 100 research institutions has looked at the evidence from pristine tracts of tropical forest to find that – overall – the foliage soaked up the most carbon, most efficiently, more than two decades ago.
Since then, the measured efficiency of the forests as a “sink” in which carbon is sequestered from the atmosphere has been dwindling. By the last decade, the ability of a tropical forest to absorb carbon had dropped by a third.
All plant growth is a balancing act based on sunshine and atmospheric carbon and rainfall. Plants absorb carbon dioxide as they grow, and surrender it as they die.
In a dense, undisturbed wilderness, fallen leaves and even fallen trees are slightly less likely to decompose completely: the atmospheric carbon in leaf and wood form has a better chance of being preserved in flooded forests as peat, or being buried before it can completely decompose.
The forest becomes a bank vault, repository or sink of the extra carbon that humans are now spilling into the atmosphere from car exhausts, factory chimneys and power station furnaces.
Theory and practice
And in theory, as more and more carbon dioxide gets into the atmosphere, plants respond to the more generous fertilisation by growing more vigorously, and absorbing more carbon.
But as more carbon gets into the atmosphere, the temperature rises and weather patterns begin to become more extreme. Summers get hotter, rainfall more capricious. Then trees become vulnerable to drought, forest fire and invasive diseases, and die more often, and decompose more completely.
Wannes Hubau, once of the University of Leeds in the UK and now at the Royal Museum for Central Africa in Belgium, and more than 100 colleagues from around the world, report in the journal Nature that they assembled 30 years of measurement from more than 300,000 trees in 244 undisturbed plots of forest in 11 countries in Africa, and from 321 plots of forest in Amazonia, and did the sums.
In the 1990s, intact tropical forests removed around 46 billion tonnes of carbon dioxide from the atmosphere. By the 2010s, the uptake had fallen to around 25 billion tonnes. This means that 21 billion tons of greenhouse gas that might otherwise have been turned into timber and root had been added to the atmosphere.
This is pretty much what the UK, France, Germany and Canada together spilled into the atmosphere from fossil fuel combustion over a 10-year period.
“We’ve found one of the most worrying impacts of climate change has already begun. This is decades ahead of even the most pessimistic climate models”
“Extra carbon boosts tree growth, but every year this effect is being increasingly countered by the negative impacts of higher temperatures and droughts which slow growth and can kill trees,” said Dr Hubau.
“Our modeling shows a long-term decline in the African sink and that the Amazon sink will continue to rapidly weaken, which we predict will become a carbon source in the mid-2030s.”
Tropical forests are an integral factor in the planetary carbon budget – a crude accounting system that climate scientists rely upon to model the choice of futures that face humankind as the world heats up.
Around half of Earth’s carbon is stored in terrestrial vegetation and the tropical forests account for about a third of the planet’s primary productivity. So how forests respond to a warmer world is vital.
Because the Amazon region is being hit by higher temperatures, and more frequent and prolonged droughts than forests in tropical Africa, Amazonia is weakening at a faster rate.
But decline has also begun in Africa. In the 1990s, the undisturbed tropical forests alone inhaled 17% of human-made carbon dioxide emissions. In the decade just ended, this proportion fell to 6%.
Catastrophic prospect
In roughly the same period, the area of intact forest fell by 19%, and global carbon dioxide emissions rose by 46%. Even so, the tropical forests store 250 billion tonnes of carbon in their trees alone: 90 years of fossil fuel emissions at the present rate. So their sustained loss would be catastrophic.
“Intact tropical forests remain a vital carbon sink but this research reveals that unless policies are put in place to stabilise the Earth’s climate, it is only a matter of time until they are no longer able to sequester carbon,” said Simon Lewis, a geographer at the University of Leeds, and one of the authors.
“One big concern for the future of humanity is when carbon-cycle feedbacks really kick in, with nature switching from slowing climate change to accelerating it.
“After years of work deep in the Congo and Amazon rainforests, we’ve found one of the most worrying impacts of climate change has already begun.
“This is decades ahead of even the most pessimistic climate models. There is no time to lose in tackling climate change.” – Climate News Network
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