A week ago Sunday, Arctic sea ice
cover reached its lowest extent ever
recorded. For good
reason, there has been significant media focus on how a warming sea gobbles up
the ice that is polar bear habitat and reduces the area's capacity to reflect
the sun's rays. This is roughly equivalent to unplugging one pole's worth of
the Earth's central air conditioning system.
But far less attention has been placed on what a naked Arctic Ocean
means for its closest neighboring ecosystem: the Arctic tundra.
Beyond the images of icebergs and stranded polar bears, I doubt
many people picture the Arctic's vast carpet of lush green plants, chirping
songbirds or highs in the mid-70s -- all of which are typical of summertime on
the tundra. With climate changing at an alarming rate and sea ice extent
slipping away, the tundra stands to change a lot, and this, too, will affect
the rest of the planet. It is time to start familiarizing ourselves with the
tundra, and here's why.
The
tundra biome is huge, covering 15% more of the Earth's surface than all 50 U.S.
states combined. Currently, it stores a significant proportion of the Earth's
carbon in its permanently frozen soils, keeping it locked away and unable to
contribute to the atmosphere's giant pool of greenhouse gases.
However, in much the same way that other bodies of water keep
coastal cities such as San Francisco from having extremely cold winters and
scorching hot summers, sea ice conditions in the Arctic Ocean influence weather
patterns over the nearby tundra. Less sea ice is associated with warmer and
drier summer conditions on the tundra. Consistently balmier summers will cause
soils to warm and thaw to greater depths, unleashing long-stored carbon into
the atmosphere in the form of carbon dioxide and methane, both of which are
potent greenhouse gases.
The previous record low in Arctic Ocean ice cover occurred in 2007,
and the hot, dry summer that accompanied it on the Alaskan tundra was
highlighted by the largest, longest lasting and most severe tundra fire to burn
in northern Alaska in recorded history. The fire covered an area roughly 10%
larger than Manhattan and burned for 2½ months.
Although
lightning frequently strikes the tundra, the landscape is typically fairly
moist and so rarely ignites, and even when it does, the flames don't spread
very far, burn very deeply or remain alight for very long. But the tundra was
very dry in 2007 and fire-fueling winds kicked up the blaze. During this single
event, the immediate combustion of plants and soils and the thawing of frozen
soils injected an enormous amount of carbon into the atmosphere — an amount equivalent
to what the entire tundra biome typically absorbs from the atmosphere through
plant growth every year.
The effect of diminishing sea ice isn't limited to increasing
atmospheric greenhouse gas concentrations. Warmer conditions on the tundra
trigger a cascade of change, including converting its lush but short green
carpet into a taller shag, since warmer soils and deeper thaw enable taller,
woody plants to grow and thrive on the tundra. What my colleagues and I are
discovering from our own work in Alaskan tundra is that this shift in
vegetation cover has implications -- some good, some bad -- for the animals
that depend on it for food and shelter.
Each spring many species of migratory songbirds travel to the
Arctic tundra from all over the world to breed. Some nest in patches of tall
vegetation and may stand to benefit from the expanding taller shag, but those
that nest in short vegetation may not be able to adapt. What may likely benefit
all species is that the taller vegetation harbors significantly more bugs to
eat. We don't yet know which species will benefit, and which will suffer in
response to the changes, but because each species plays a specific ecological
role on the tundra, the downfall of one species or proliferation of another
could have a domino effect that disrupts the tundra's delicate food web.
And in case you thought that what happens on the tundra stays on
the tundra, consider that many of the sparrows, robins and warblers that visit
our backyards in winter, or pass through come fall and spring, spend their
summers breeding on the tundra; so, whatever happens to them there will affect
which ones and how many of them show up at your bird feeder in the future,
potentially setting off a local domino effect.
Since the Arctic as a whole is responding to climate change earlier
and more acutely than the rest of the planet, we should think of it as an early
warning system -- a proverbial canary in a coalmine. Perhaps if we pay closer
attention to how the tundra is changing, we can learn some practical lessons on
what types of changes to expect here at lower latitudes, which would enable us
to mitigate the consequences, or at least plan for how to cope with them.
By Natalie Boelman, Special to CNN September
25, 2012
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