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Greening
in the North This
view of the top of the world shows enhanced plant growth over the last 20 years,
from the north pole, stretching southward to the 30 degree North latitude line
(the circle). The
color key represents changes in vegetation lushness of the past 20 years. It ranges
from a low increase in the heartiness of vegetation as denoted by the yellow color,
to the highest increase in the lushness of plants as denoted by the purple color. In
addition to the increased "greening," researchers in this study have
also discovered that the growing season from the 40N latitude line and northward
has increased by several days in both Eurasia and North America. Increases in
the heartiness of vegetation and the extended growing period can both be attributed
to rising temperatures as a result of more greenhouse gases being added to the
atmosphere. Looking
at the 40N line, which stretches from New York to Madrid to Beijing, plants have
been growing more vigorously in Eurasia compared to North America. The pattern
of high growth is especially noteworthy in boreal Eurasia, along a broad swath
of land east of 25E and north of 50N. This region includes the grasslands and
croplands of the south central Russian uplands and extends northeast through the
unmanaged mixed and needle forests all the way to the Bolshezemalskaya Tundra. East
of the Urals, there is a contiguous region of high growth over the west Siberian
plain and the central Siberian plateau. East of lake Baikal, there is an area
of strong growth from 50N-55N, that extends east to the Aldan plateau. These regions
in Siberia and eastern Russia consist mostly of natural forests with arctic grasses
and tundra to the north. Outside of this broad swath, there are also large regions
of densely vegetated areas in central Europe and Sweden. About 78% of the vegetation
in these regions between 40N-70N is unmanaged, and almost 58% is forests and woodlands,
an area equivalent to about 78% of the USA. In
North America, changes in the densely vegetated temperate and boreal forest regions
are fragmented and do not show a noteworthy pattern. The most notable increases
in the heartiness of vegetation in North America are located mainly in the forests
of the east and grasslands of the upper Midwest. In
total, only about 30% of the vegetated areas between 40N-70N in North America
show a high amount of greening, compared to more than 61% of the vegetated area
in Eurasia.
The
Temperature Connection: Temperature Influences Greenery Researchers
using satellite data have confirmed that plant life above 40 degrees north latitude,
from New York to Madrid to Beijing, has been growing more vigorously since 1981
due to rising temperatures and buildup of greenhouse gases. According
to ground-based meteorological station temperature measurements, global surface
temperatures in 1998 were the warmest in a record that ranges from 1860 to 2000.
The rate of temperature change was higher in the past 25 years than during any
of the previous 1000 years. On
the graphs, the April to October average temperature changes are designated by
the red bars. The temperature changes directly correspond to changes in vegetation
greenness, shown by the green line. The greenness changes are also April to October
averages (Greenness is measured here as an average change from April to October
of each year). Researchers used satellite data of red and near-infrared solar
radiation reflected back to sensors to determine that vegetation north of 40 degrees
latitude has become more lush. The
northern latitudes (23.6N-90N) have warmed by about 0.8 Celsius (or 1.44 Fahrenheit)
since the early 1970s, but not all areas have warmed uniformly. On the graphs
of North America and Eurasia, the vertical left column designated "Anomaly"
represents the temperature and greenness changes from normal (as compared to the
average). The warming rate in the United States is smaller than in most of the
world, and there is a slight cooling trend in the eastern United States over the
past 50 years. The graph of Eurasia suggests an increasingly "greener"
region as temperatures continue to warm. These
results suggest that warmer temperatures may have promoted plant growth in the
north during the 1980s and 1990s. Eruption
of Mount Pinatubo, Philippines, July 1991 Credit:
U.S. Geological Survey, J.N. Marso, July 1991 Link
for picture can be found here
When
Mount Pinatubo exploded in June 1991, it sent enormous clouds of volcanic ash
and acidic gases into the stratosphere to altitudes in excess of 100,000 feet.
The largest ash cloud, from a June 15 eruption, was carried by upper level winds
to the west and circled the globe in about three weeks. After
the eruption, ash and other particles from the volcano created a haze around the
planet for the next two years and slightly reduced the sunlight reaching Earth's
surface and made the sun's radiation less direct and more diffuse. While overall
solar radiation was reduced by less than five percent, data showed a reduction
of direct radiation by as much as 30 percent. So, instead of direct light, the
sun's rays were reaching Earth after colliding with particles in the air. Scientists
also noticed the rate at which carbon dioxide (CO2) filled the atmosphere slowed
down for the next two years. Many
scientists thought the drop in atmospheric CO2 growth rate was caused by a reduction
in sunlight that lowered the Earth's temperature and slowed plant and soil respiration,
a process where plants and soil emit CO2. But this new research shows that when
faced with diffuse sunlight, plants actually become more efficient, drawing more
carbon dioxide out of the air. While
large volcanic eruptions are rare, this research has big implications for more
regular phenomena such as the effects of aerosols and clouds on an ecosystem's
ability to pull carbon from the atmosphere. Back
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