EARTH'S
BECOMING A GREENER GREENHOUSE
(Images
found below) NASA
satellite data suggest that for more than two decades there's been a gradual greening
of the northern latitudes of Earth. Researchers
confirm that plant life seen above 40 degrees north latitude, which represents
a line stretching from New York to Madrid to Beijing, has been growing more vigorously
since 1981. One suspected cause is rising temperatures possibly linked to the
buildup of greenhouse gases in our atmosphere. Over
this same time period, parts of the Northern Hemisphere have become much greener
and the growing season has increased by several days. Further, Eurasia appears
to be greening more than North America, with more lush vegetation for longer periods
of time. The
results of this NASA-funded research will appear in the September 16 issue of
the Journal of Geophysical Research - Atmospheres. "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 the existing vegetation
has increased in density. The
authors also looked at the differences in vegetation growth between North America
and Eurasia, since the patterns and magnitudes of warming are different on the
two continents. The
greenness data from satellites were strongly correlated with temperature data
from thousands of meteorological stations on both continents. The Eurasian greening
was especially persistent over a broad area from central Europe through Siberia
to far-east Russia, where most of the vegetation is forests and woodlands. North
America, in comparison, shows a fragmented pattern of change notable only in the
forests of the East and grasslands of the upper Midwest. Dramatic
changes in the timing of both the appearance and fall of leaves are recorded in
these two decades of satellite data. The authors report a growing season in Eurasia
that is now nearly 18 days longer. Spring arrives a week early and autumn is delayed
by 10 days. In North America, the growing season appears to be as much as 12 days
longer. The
researchers used a temperature data set developed from the Global Historical Climate
Network. Dr. James Hansen, of NASA's Goddard Institute for Space Studies in New
York, developed this data set and said, "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." Scientists
believe the results indicate a greener greenhouse. "This is an important
finding because of possible implications to the global carbon cycle," said
Ranga Myneni of Boston University. "However, more research is needed to determine
how much carbon is being absorbed, and how much longer it will continue." Carbon
dioxide is a main greenhouse gas and is suspected of playing a role in rising
global temperatures. If the northern forests are greening, they may already be
absorbing carbon -- a process that can impact global temperature changes. Researchers
used the Normalized Difference Vegetation Index (NDVI) to help determine the "greening"
of plant life. Dr. Compton Tucker, of NASA's Goddard Space Flight Center, Greenbelt,
Md., is a co-author of the report and developed NDVI to analyze spectral data
collected by orbiting weather satellites. This
work was made possible through funding by NASA Headquarters' Earth Science Enterprise,
a long-term research program dedicated to understanding how human-induced and
natural changes affect our global environment.
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. Back
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