by Aries Keck for
Friday, December 16, 2011
Boreal Shrubbery Increases
This work has the advantage of been utterly unambiguous in that it is a region that has no direct human impact at all that would ever be measurable. Thus a strengthening of the vegetative cover indicates a generally more supportive growing environment and indirectly a better climate. We can comfortably give it a plus 1.
As noted, we have a clearly warming
Arctic that appears to be brought on
by a significant increase in warm surface water been injected annually during
the past forty years. This has generated
a contraction of the gross sea ice cover and more recently a rather dramatic
decrease in seasonal sea ice cover. All
this allows a somewhat warmer air mass over the Arctic
during the growing season and naturally implies warmer conditions southward
into the tundra and boreal forest. Thus
we have a healthier scrub growing environment.
Thus we continue to have excellent confirmation that the North Polar region is warming up to optimums previously seen in the historical record of previous epochs such as the Bronze Age in particular and the Medieval and Roman optima.
Again as I have previously posted, this appears to be part of a millennium long cycle that repeats around every thousand to twelve hundred years with a sharp two degree drop in general temperatures in the Northern Hemisphere. That last occurred three hundred years ago if you are concerned and we have now entered a long era of pleasant temperatures.
Study Shows More Shrubbery in a Warming World
by Aries Keck for
Comparison of area in
showing increased vegetation between 1986 and 2004. In this false-color Landsat
image, more red color indicates more vegetation. Credit: Jeff Masek. For a
larger version of this image please go here.
Scientists have used satellite data from NASA-built Landsat missions to confirm that more than 20 years of warming temperatures in northern
have resulted in an increase in the amount and extent of shrubs and grasses. Quebec, Canada
"For the first time, we've been able to map this change in detail, and it's because of the spatial resolution and length-of-record that you can get with Landsat," says Jeff Masek, the program's project scientist. He's based at NASA's Goddard Space Flight Center in Greenbelt, Md.
Masek and his co-authors will present their study at the American Geophysical Meeting in
on Friday, Dec. 9. San Francisco
The study, focusing on
Quebec, is one
of the first to present a detailed view of how warmer temperatures are
influencing plant distribution and density in northern areas of North America.
"Unlike the decline of sea ice, which is a dramatic effect that we're seeing as a result of global warming, the changes in vegetation have been subtle," Masek says.
Computer models predict the northward expansion of vegetation due to warmer temperatures. "They predict a dramatic change over the next 100 years, and people have been wondering why we weren't seeing these changes already, Masek says.
The difference between the computer predictions and real-life vegetation may have to do with all the other factors that come into play with plants, like the availability of water and sunlight; the type of terrain; competition from other plants for soil, resources and space; and plant predators like caribou.
"The warm temperatures are only part of the equation," says Doug Morton, the Principal Investigator of the study and a researcher at NASA Goddard.
Scientists track vegetation with satellites by measuring the 'greenness' of a study area. Morton says previous studies used yearly compilations, making it difficult to determine if the increase in 'greenness' was due to expansion of vegetation cover or if what scientists were seeing was instead just the effect of a longer growing season.
For this study, the scientists focused only on 'greenness' measurements during the peak summer growing seasons from 1986 to 2010.
By using Landsat's higher, 30-meter (~98 foot) resolution and viewing the same area at the same time for 23 years, Masek and his colleagues were able to track the areas as they continued to show more 'greenness' over the years.
"It makes sense," Masek says. "This is how shrub encroaching occurs. They increase in size, they increase in density, and then they move northward."
In contrast to the expansion of shrubs, the scientists found little evidence for 'greenness' trends in forested areas, suggesting that forest response to recent warming may be occurring more slowly.
Masek adds that it shows how getting the big picture of warming's effect on forests will rely on continued observations from new
that extend and enhance these data records. U.S.
The Landsat Program is a series of Earth-observing satellite missions jointly managed by NASA and the
Geological Survey since 1972.
They continue to improve and expand this unparalleled record of Earth's
changing landscapes for the benefit of all. U.S.