I’ve tended gardens around the
West for much of my adult life, from the tomatoes and basil I
nurtured through a Laramie winter in a solar greenhouse to the
climbing roses I inherited in our yard in southern New
Mexico’s Chihuahua Desert.
Now I’m writing a
book for Rocky Mountain gardeners, drawing on my education in plant
ecology and experience as a Western gardener, making use of
references on plants and gardening, and the past century or so of
Western climate data.
There’s one large problem
with this gardening information however: it’s all based on
the past, which may no longer be a good predictor of the
future.
For several decades, scientists have been warning
with increasing alarm that levels in of carbon dioxide in the
atmosphere are rising more rapidly than is normal, and that
increased levels of this gas, called a “greenhouse gas,” because it
acts like the glass in a greenhouse to trap and reflect incoming
solar heat, will raise global temperatures.
The theory,
dubbed “global warming,” is controversial. Everyone — from
scientists who may know something about the complicated systems
that maintain our planet’s climate, to the politicians, who
usually don’t — has weighed in on the validity of global
warming.
But the data are increasingly difficult to
ignore. Earlier this month, the World Meteorological Organization,
a body of the United Nations that normally spendsits time on
decidedly non-headline-grabbing tasks such as coordinating weather
data collection among countries, issued an urgent press release.
In careful language, this apolitical body noted that
monthly and annual average temperatures around the globe have
increased gradually for the past 100 years. In fact, the rise in
Northern Hemisphere temperatures during the 20th century may be the
largest rise of any century in the past thousand years.
In Switzerland, according to the press release, the month of June
was the hottest in at least the past 250 years. This year’s
pre-monsoon heat wave in India brought highs from113 to 120 degrees
F, topping the average weekly temperatures by 36 to 41 degrees, and
killing some 1,400 people.
A handful of recent
observations demonstrate that the rise in global temperatures is
already reflected in altered distributions of animals and plants.
In California, for instance, entomologists have mapped changes in
butterfly ranges that show cold-loving species’ territories
shrinking uphill.
Here in Colorado, pikas, the
high-mountain rabbit relatives that whistle from precarious perches
on rockslides, have recently disappeared from seven of 25 sites
where they were once plentiful, as alpine habitats grow warmer and
drier.
On the western Great Plains, blue grama grass, a
cool-season grass that does not grow well when nighttime
temperatures rise, has declined in 23 years of warmer average
temperatures. At the Arnold Arboretum in Boston, tender species
like camellias, never successfully grown outside the greenhouse now
thrive outdoors.
The evidence is impossible to dismiss.
Imagine camellias, those lush flowers epitomizing hot Southern
climates, flourishing in Boston!
Although the global
warming theory is named for its predictions of rising global
temperatures, the heart of the theory is less about warming than
about unpredictability: As the globe heats due to climate change,
the number and intensity of what meteorologists call “extreme
weather events” is expected to increase.
That means more
severe weather, cold as well as hot, rain as well as drought, more
tornadoes, hurricanes, cyclones, blizzards, torrential rains. As
the World Meteorological Organization points out, that data is
compelling, too.
In this year already, we’ve
surpassed several records for extreme weather. The month of May
brought 562 tornadoes to the Great Plains and Southeast, resulting
in 41 human deaths. The record had been 399 tornadoes in June of
1992.
Here in the Upper Arkansas River Valley, a
record-breaking, multi-year drought still grips the landscape, even
after the generous gift of snow brought by the record blizzard that
paralyzed Colorado’s Front Range in March.
Record
highs, record snowfall, record drought, and record storms. With the
number of climate records recently shattered, clearly the past
isn’t a reliable guide to the future, for gardeners or anyone
else.
“All we really know is that the weather is going to
be different than it has been in the past,” writes Peter Del
Tredici of Boston’s Arnold Arboretum in an essay for the New
York Times. “From the garden where I work, the plants seem to be
telling us something we may not want to hear: the world is
changing.”
Writing from a record hot spell in
south-central Colorado, I wish that I didn’t agree.
Susan Tweit is a contributor to Writers on the Range, a
service of High Country News in Paonia, Colorado (hcn.org). She is
a naturalist and the author of several books about the
West.
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