Geology Reference
In-Depth Information
covered by snow that would cool the Earth. If tundra were to expand just a bit, North
America and Eurasia would cool by around 3
0
C, and snow would lie on the ground for
an additional 18 days.
There is a seesaw effect between the boreal forest and the mossy tundra which has
played a major role in the earth's climate by amplifying the swings in and out of ice ages
over the past 2 million years. As we shall see later, the trigger for these swings has been
slight variations in Gaia's orbit around the sun. When our planet's elliptical orbit places
us at our furthest distance from the sun, the tundra spreads its mossy legions southwards
at the expense of the dark boreal forest and the snowy white winter tundra helps to tip
the earth into an ice age. Thousands of years later, when our orbit brings us closer to the
sun, the dark-leaved boreal forest expands northwards, warming the earth even in the
winter months. The boreal forest also cools the earth by fixing carbon dioxide in wood,
but the low albedo of its foliage warms the earth so much that this cooling effect is en-
tirely cancelled out. All of this gives us a Gaian insight that undermines the idea that the
tundra and boreal forest responded passively to climate as an external force. Now we
know that the boreal forest, tundra and climate affect each other. The boundary between
the boreal forest and the tundra is perfectly matched with the position of the boundary
between cold northern air and warm air from the south known as the Arctic front. At
first, it seemed as if the vegetation simply responded to where these two great air masses
happened to meet, but we now realise that the position of the tundra-forest boundary
controls the position of the front—a stunning demonstration of how far-reaching the cli-
matic impacts of vegetation can be. Part of the reason for this is that the forest heats up
much faster because it has a much lower albedo than the tundra.
But it isn't just the trees and mosses that interact with the climate of the high north;
other members of the biotic community may also be involved, including predators and
their prey. It is winter, and a wolf pack howls in the boreal forest in Isle Royale in Lake
Superior, North America, signalling the start of another hunt. The wolves, like so many
others in the far north, prey on moose, those giant ungulates whose males vie for females
in the autumn by sparring with their widely spreading palmate antlers. Far to the south,
over the Azores, warm air has built up during the hot summer, and now it has spilled
northwards across the Atlantic Ocean rolling atop the cold air over Iceland, bringing
high winds and deep snow to the entire western north Atlantic. Isle Royale has just ex-
perienced prolonged heavy snowfall, and our pack responds by combining with other
wolves to make a big hunting group that will find it easier to bring down moose in the
deep snow. The pack sets off to hunt at dawn. Today they will devour one large old
male. Over the snowy winter months, our wolf pack, like many others on Isle Royale,
and perhaps across the entire boreal forest, will feed many new pups with moose meat
from kills facilitated by the deep snow. Fir tree saplings, browsed far less by moose, will
