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Prehistoric humans may have had a hand in climate change
THIS WEEK
Bye-bye mammoth, hello hotter world Anil Ananthaswamy
AP Photo/Francis Latreille/Nova Productions
HUMANS were fiddling with climate thousands of years before the onset of agriculture – albeit unwittingly. At least, that is if we played a part in the extinction of woolly mammoths. Until recently, anthropogenic climate change was deemed to begin with the burning of fossil
fuels during the industrial revolution. Then in 2003, William Ruddiman, a palaeoclimatologist at the University of Virginia, suggested the advent of agriculture 8000 years ago ramped up levels of the greenhouse gas methane in the atmosphere, warming the world by about 0.8 °C. Now it seems we were toying with
Incredible shrinking proton raises eyebrows HOW big is a proton? The most accurate measurement yet suggests it’s smaller than we thought. This could be due to an error, or it might just hint at totally new particle physics. “The new experiment presents a puzzle with no obvious candidate for an explanation,” says Peter Mohr of the international Committee on Data for Science and Technology, which calculates values for fundamental 10 | NewScientist | 10 July 2010
constants in physics, who was not involved in the new work. The proton’s radius cannot be measured directly but can be inferred from the hydrogen atom, which consists of a proton and an electron. The electron can sit in a variety of energy “shells”, each with a different distribution in space. One shell’s distribution requires the electron to dive in and out of the proton, and another sits entirely outside the proton. The energies of both shells can be combined to deduce the proton’s radius. There is a way to make this measurement more accurate,
climate about 15,000 years ago. Woolly mammoths roamed over much of Eurasia and North America from the mid-to-late Pleistocene about 300,000 years ago until numbers began to decline 15,000 years ago, before the beginning of the Holocene. The transition to the warmer Holocene is characterised by a dramatic change in the type of vegetation, from the open steppe tundra favoured by the coldadapted mammoths to an increase in tree cover. A previous study had shown that when elephants and other large animals are excluded from
a patch of African savannah, tree cover increases by 9 per cent over 36 years. So Christopher Doughty of the Carnegie Institution of Science in Stanford, California, and colleagues wondered whether the extinction of Pleistocene megafauna like the mammoth could be behind the Holocene’s shift in vegetation. To find out, the team focused on Siberia and Beringia, the region that once formed the land bridge between eastern Siberia and Alaska. Previously collected pollen records show there was a rapid growth in dwarf trees of the genus Betula in this area around 15,000 years ago. The researchers plugged this information into a computer model to find out the effect on the climate of increasing tree cover and diminishing grassland and found that it led to a global temperature increase of about 0.1 °C (Geophysical Research Letters, DOI: 10.1029/2010GL043985). “There is a strong connection between when humans arrived, when mammoths went extinct and when you see this big increase in vegetation,” says Doughty. “They overlap almost exactly.” If humans played a role in the extinction of the mammoths, then they had a hand in the climate change that followed. “I see it as humans’ first big impact –Adapted for the chilly steppes– on the planet,” says Doughty. n
however: replace the electron with a muon. This particle is also negatively charged but much larger than the electron, so its energy shells sit closer in and can overlap more with the proton radius. Now, Randolf Pohl of the Max Planck Institute of Quantum Optics in Garching, Germany, and colleagues have successfully created such a “muonic” atom and found that this yields a proton radius 4 per cent smaller than that gleaned using the
“The theorists tell us that an error of such a magnitude in the radius of the proton is ‘impossible’ ”
hydrogen atom (Nature, DOI: 10.1038/nature09250). “The relevant theorists tell us that an error of such a magnitude is ‘impossible’,” says Pohl. Mohr says that the problem is likely to lie with an error in the measurements or a mistake in the calculations. But if such errors are ruled out, the discrepancy would point to a problem with quantum electrodynamics, a theory that underpins much of particle physics. That deficiency opens the door to new physics at work in atoms, such as previously unknown particles or effects. Kate McAlpine n
Bye-bye mammoth, hello hotter world Anil Ananthaswamy
AP Photo/Francis Latreille/Nova Productions
HUMANS were fiddling with climate thousands of years before the onset of agriculture – albeit unwittingly. At least, that is if we played a part in the extinction of woolly mammoths. Until recently, anthropogenic climate change was deemed to begin with the burning of fossil
fuels during the industrial revolution. Then in 2003, William Ruddiman, a palaeoclimatologist at the University of Virginia, suggested the advent of agriculture 8000 years ago ramped up levels of the greenhouse gas methane in the atmosphere, warming the world by about 0.8 °C. Now it seems we were toying with
Incredible shrinking proton raises eyebrows HOW big is a proton? The most accurate measurement yet suggests it’s smaller than we thought. This could be due to an error, or it might just hint at totally new particle physics. “The new experiment presents a puzzle with no obvious candidate for an explanation,” says Peter Mohr of the international Committee on Data for Science and Technology, which calculates values for fundamental 10 | NewScientist | 10 July 2010
constants in physics, who was not involved in the new work. The proton’s radius cannot be measured directly but can be inferred from the hydrogen atom, which consists of a proton and an electron. The electron can sit in a variety of energy “shells”, each with a different distribution in space. One shell’s distribution requires the electron to dive in and out of the proton, and another sits entirely outside the proton. The energies of both shells can be combined to deduce the proton’s radius. There is a way to make this measurement more accurate,
climate about 15,000 years ago. Woolly mammoths roamed over much of Eurasia and North America from the mid-to-late Pleistocene about 300,000 years ago until numbers began to decline 15,000 years ago, before the beginning of the Holocene. The transition to the warmer Holocene is characterised by a dramatic change in the type of vegetation, from the open steppe tundra favoured by the coldadapted mammoths to an increase in tree cover. A previous study had shown that when elephants and other large animals are excluded from
a patch of African savannah, tree cover increases by 9 per cent over 36 years. So Christopher Doughty of the Carnegie Institution of Science in Stanford, California, and colleagues wondered whether the extinction of Pleistocene megafauna like the mammoth could be behind the Holocene’s shift in vegetation. To find out, the team focused on Siberia and Beringia, the region that once formed the land bridge between eastern Siberia and Alaska. Previously collected pollen records show there was a rapid growth in dwarf trees of the genus Betula in this area around 15,000 years ago. The researchers plugged this information into a computer model to find out the effect on the climate of increasing tree cover and diminishing grassland and found that it led to a global temperature increase of about 0.1 °C (Geophysical Research Letters, DOI: 10.1029/2010GL043985). “There is a strong connection between when humans arrived, when mammoths went extinct and when you see this big increase in vegetation,” says Doughty. “They overlap almost exactly.” If humans played a role in the extinction of the mammoths, then they had a hand in the climate change that followed. “I see it as humans’ first big impact –Adapted for the chilly steppes– on the planet,” says Doughty. n
however: replace the electron with a muon. This particle is also negatively charged but much larger than the electron, so its energy shells sit closer in and can overlap more with the proton radius. Now, Randolf Pohl of the Max Planck Institute of Quantum Optics in Garching, Germany, and colleagues have successfully created such a “muonic” atom and found that this yields a proton radius 4 per cent smaller than that gleaned using the
“The theorists tell us that an error of such a magnitude in the radius of the proton is ‘impossible’ ”
hydrogen atom (Nature, DOI: 10.1038/nature09250). “The relevant theorists tell us that an error of such a magnitude is ‘impossible’,” says Pohl. Mohr says that the problem is likely to lie with an error in the measurements or a mistake in the calculations. But if such errors are ruled out, the discrepancy would point to a problem with quantum electrodynamics, a theory that underpins much of particle physics. That deficiency opens the door to new physics at work in atoms, such as previously unknown particles or effects. Kate McAlpine n