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As humans age, we tend to pass more gas. As trees age, they tend to suck more of it up.
A new paper published Wednesday in the journal Nature has blown away old misconceptions about the roles that the most mature trees in forests play in combating climate change.
It has long been believed that younger trees are better than their older neighbors at absorbing carbon dioxide. But the new research suggests that the opposite is true. It turns out that big trees just keep on growing, at fast rates, and the growth depends on carbon that the trees draw from the air around them.
“In whatever forest you look at, be it old or new growth, it is the largest trees that are the greater carbon sinks,” William Morris, a PhD candidate at the University of Melbourne, told Grist. “Not the smaller, younger trees, as was previously thought.”
Morris and dozens of other scientists studied data related to 673,046 trees belonging to 403 tree species in managed and wild forests across the world. For 96.8 percent of species studied, they found that each tree drew more carbon dioxide out the air each year than it did the year before. The carbon is used to produce leaves, roots, and wood. From the paper:
In absolute terms, trees 100 cm in trunk diameter typically add from 10 kg to 200 kg of aboveground dry mass each year (depending on species), averaging 103 kg per year. This is nearly three times the rate for trees of the same species at 50 cm in diameter, and is the mass equivalent to adding an entirely new tree of 10–20 cm in diameter to the forest each year.
The findings don’t contradict the prevailing notion that young forests are better overall at sucking up CO2 than are old-growth forests. That’s because younger forests contain so many more trees.
That said, it’s still best for the climate that we leave those aging stands in place because cutting them down would unleash the carbon they spent their lifetimes absorbing. “One must take into account the amount of carbon the forests are storing as well as how much they are fixing,” Morris said.
Source
Rate of tree carbon accumulation increases continuously with tree size, Nature
John Upton is a science fan and green news boffin who tweets, posts articles to Facebook, and blogs about ecology. He welcomes reader questions, tips, and incoherent rants: johnupton@gmail.com.
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Climate scientists have looked to the heavens for help with their latest decades-long weather forecast. Their conclusion? “Oh, my god.”
Science has long struggled to forecast how global temperatures will be affected by a doubling of carbon dioxide levels in the atmosphere compared with pre-industrial times, which looks likely to occur this century. Recent consensus suggests that temperatures will rise by between 1.5 and 5 degrees Celsius (2.7 to 5.4 F). With a rise in CO2 levels to 400 parts per million, up from 280 in the 19th century, the world has warmed by nearly 1 C so far.
By modeling how clouds will be affected by the rising temperatures, a team of Australian and French scientists reported Wednesday in Nature that they expect the temperature rise to be “more than 3 degrees” – at the upper end of the projected range.
“4C would likely be catastrophic rather than simply dangerous,” the report’s lead author, Australian climate scientist Steven Sherwood, told the Guardian. “For example, it would make life difficult, if not impossible, in much of the tropics, and would guarantee the eventual melting of the Greenland ice sheet and some of the Antarctic ice sheet.”
Using dozens of computer models, the researchers concluded that water vapor will circulate more extensively than previously anticipated between the different layers of the atmosphere as temperatures climb. That will mean fewer clouds will form, leaving more of the Earth exposed to the sun’s rays. And that means more warming.
“[S]uch mixing dehydrates the low-cloud layer at a rate that increases as the climate warms,” the scientists wrote in their paper. “[O]n the basis of the available data, the new understanding presented here pushes the likely long-term global warming towards the upper end of model ranges.”
The paper is one of several recent studies looking at feedback loops between climate change and clouds, according to Chris Bretherton, a professor of atmospheric science and applied mathematics at the University of Washington. “All of these studies suggest that cloud feedbacks may be at the more positive end of what climate models predict, which would be scary,” Bretherton wrote in an email to Grist. “None of them are without issues of interpretation that will require more research to delve into, so I would not rush to assume the case for strong positive cloud feedbacks and high climate sensitivity is settled.”
In the meantime, we’re all advised to pray for rain.
Source
Spread in model climate sensitivity traced to atmospheric convective mixing, Nature
John Upton is a science fan and green news boffin who tweets, posts articles to Facebook, and blogs about ecology. He welcomes reader questions, tips, and incoherent rants: johnupton@gmail.com.
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Cloud shortage will push temperatures higher as climate warms
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Edible Plants that Self-Seed (Perfect for the Lazy Gardener!)
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This story originally appeared in the Guardian, and has been reproduced here as part of the Climate Desk collaboration.
Meat should be taxed to encourage people to eat less of it, so reducing the production of global warming gases from sheep, cattle and goats, according to a group of scientists.
Several high-profile figures, from the chief of the UN’s climate science panel to the economist Lord Stern, have previously advocated eating less meat to tackle global warming.
The scientists’ analysis, published in the journal Nature Climate Change, takes the contentious step of suggesting methane emissions be cut by pushing up the price of meat through a tax or emissions trading scheme.
“Influencing human behaviour is one of the most challenging aspects of any large-scale policy, and it is unlikely that a large-scale dietary change will happen voluntarily without incentives,” they say. “Implementing a tax or emission trading scheme on livestock’s greenhouse gas emissions could be an economically sound policy that would modify consumer prices and affect consumption patterns.”
There are now 3.6 billion ruminants on the planet–mostly sheep, cattle and goats and, in much smaller numbers, buffalo – 50% more than half a century ago. Methane from their digestive systems is the single biggest human-related source of the greenhouse gas, which is more short-lived but around 30 times more potent than carbon dioxide in warming the planet.
Emissions from livestock account for 14.5% of all human-caused greenhouse gases, according to the UN. It estimates that this could be cut by nearly a third through better farming practices.
Pete Smith, a professor of soils and global change at the University of Aberdeen, and one of the authors of the report, said: “Our study showed that one of the most effective ways to cut methane is to reduce global populations of ruminant livestock, especially cattle.”
He said methane from livestock could only be reduced by addressing demand for meat at the same time.
The scientists say not enough attention has been paid to tackling greenhouse gases other than CO2, especially in the ongoing UN climate talks, which last convened in Warsaw in November.
The only way the world could avoid dangerous tipping points as temperatures rise would be by cutting methane emissions as well as CO2 emissions from sources such as energy and transport, they argue. Reducing livestock numbers, they point out, would also avoid CO2 emissions released when forests are cleared for cattle farms.
William Ripple, a professor in the College of Forestry at Oregon State University, and another of the authors, said: “We clearly need to reduce the burning of fossil fuels to cut CO2 emissions. But that addresses only part of the problem. We also need to reduce non-CO2 greenhouse gases to lessen the likelihood of us crossing this climatic threshold.”
The farming industry said the tax proposal was too simplistic. Nick Allen, sector director for Eblex, the organisation for beef and lamb producers in England, said: “To suggest a tax is a better way to cut emissions seems a simplistic and blunt suggestion that will inevitably see a rise in consumer prices.
“It is a very complex area. Simply reducing numbers of livestock–as a move like this would inevitably do–does not improve efficiency of the rumen process, which takes naturally growing grass that we cannot eat and turns it into a protein to feed a growing human population.”
Allen said reducing emissions was an important goal for the industry. He added: “Grazing livestock have helped shape and manage the countryside for hundreds of years. They bring significant environmental benefits that can significantly mitigate the negative effect of emissions. It is unfortunate that in recent years they have become an easy scapegoat for emissions, despite the fact that the livestock population is generally falling.”
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