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Satellite Finds Greener Hothouse - or Hotter Greenhouse
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| 'When we looked at temperature and satellite vegetation data, we saw that year-to-year changes in growth and duration of the growing season of northern vegetation are tightly linked to year-to-year changes in temperature,' Liming Zhou of Boston University said. | |
On the plus side, things will be greener.
All right, NASA didn't offer any of those most dire predictions this week, although everything but the surfing is widely expected by knowledgeable scientists to coincide with a relentlessly warming globe -- but it did fund a study that found signs that already our hotter home is getting greener.
Specifically, satellite studies show that for the past two decades, the northern latitudes above 40 degrees -- that's a line running through New York, Madrid and Beijing, more or less -- have had lusher and longer growing seasons. "One suspected cause," a press release coyly stated, "is rising temperatures possibly linked to the buildup of greenhouse gases in our atmosphere."
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In fact, it's the only cause the researchers can point to, according to Ranga Myneni of Boston University's Climate and Vegetation Research Group.
"The warming we've seen over the past 100 years, especially over the past 25, is unprecedented, going back more than a thousand years," Myneni, an associate professor of geography, told Wireless NewsFactor. "The amount of warming is over and above natural causes, which points the finger toward the concentration of greenhouse gases in the atmosphere resulting from human activities."
Greenery, lush forests, longer growing seasons -- those are good things. How do these new findings play into the dire predictions of global warming?
"If you accept these findings [of more greenery and warmer seasons], then you have to accept all the consequences of global warming as well," Myneni said. "Those include rising sea levels, an increase in catastrophic weather events such as hurricanes, and human-health consequences."
It's Not Easy Being Greener
"When we looked at temperature and satellite vegetation data, we saw that year-to-year changes in growth and duration of the growing season of northern vegetation are tightly linked to year-to-year changes in temperature," Liming Zhou of Boston University said. The area of vegetation has not extended, but existing vegetation has increased in density, and the phenomenon is more pronounced in Eurasia than in North America.
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'The satellites we have now are the old workhorses, if you will,' Boston University professor Ranga Myneni said. 'If NOAA's satellite is a Chevy, the Terra is a Mercedes.' |
The changes affect small things, and not just things only a farmer would notice. The greening, which NASA described as especially persistent over a broad swath from Central Europe to Siberia, has made its presence known in North America through dramatic changes in the timing of both the appearance and fall of leaves.
This has meant longer growing seasons -- nearly 18 days longer in Eurasia, where spring springs a week early and autumn falls 10 days later. In North America, the green season runs about 12 days longer.
There is a good side to this: It's carbon in the atmosphere that is blamed for global warming, and more plants -- especially long-lived trees -- means more carbon being sucked out of the air and photosynthesized into sugars and starches. But Myneni warned that this is a booby prize at best.
"This is not by any means good news," he said. He pointed to predictions that, if human activities are unchecked, our atmosphere will go from a carbon concentration of 370 parts per million to 700 parts per million in 100 years. "If plants vigorously took up a lot of carbon, maybe they'd reduce that by 100 parts per million. It's quantifiable relief, but not big relief."
As Seen on TV
But Wireless NewsFactor isn't here to scare you. It's here to tell you about satellites. In this case, the researchers relied on the National Oceanic and Atmospheric Administration's polar-orbiting satellite, which among other things provides weather-map images that turn up on evening news programs.
"The instruments we used are the Advanced Very High Resolution Radiometer," Myneni said. "The AVHRR measures reflected solar radiation in the red and near-infrared spectrums."
Green plants absorb a lot of red light. The satellite's readings and a lot of math yielded a fair idea of how much green biomass the satellite was seeing as it orbited the Earth, viewing every portion of the globe at least once a day. Then, past records and temperature measurements taken worldwide were added to the mix.
James Hansen of NASA's Goddard Institute for Space Studies in New York developed the data from satellite observations, weather stations and comparisons to global climate records. "The data were compiled from several thousand meteorological stations in the United States and around the world. The stations also include many rural sites where the data are collected by cooperative private observers," he said.
The Beat-Up Chevy of Satellites
Myneni said making sense of satellite data is an enormous challenge. The raw data itself can be unreliable without corrective calculations to compensate for a variety of factors. The instruments on the satellite degrade over their three- to five-year lifespan, as does the satellite's orbit. So, scientists have to compensate for the orbiter's dimming vision and for the increase in brightness resulting from a lower orbit. Then there's all that air in the way.
"The atmosphere tends to blur things," Myneni said. Major events, such as volcanic eruptions, can throw enough dust into the air to require whole new sets of compensating calculations.
In all, he said, the scientists manage to get reliable data. That doesn't mean, though, that Myneni isn't looking forward to migrating from the NOAA satellite to NASA's Terra platform, launched in December 1999 with a host of more refined and elaborate technology.
"The satellites we have now are the old workhorses, if you will," Myneni said. "We're slowly changing to a better satellite. If NOAA's satellite is a Chevy, the Terra is a Mercedes." 