Cold (15 page)

In the cold air, I can hear Anchorage traffic. The combination of cold air and snow plays tricks with sound. If I turn my
head slightly, or move a bit, the traffic noise is replaced by the sound of fast water coursing through the south fork of
Campbell Creek, some eight hundred feet below me. Sound travels quicker through cold air than warm, but snow muffles sound.
Between traffic and flowing water, I listen, too, for golden-crowned sparrows, for their tweeting song that sounds like “three-blind-mice,
three-blind-mice,” high-pitched and repetitive. But the little birds are gone, headed south toward Washington and Oregon and,
for some, as far as California and the Baja peninsula. I check my thermometer. At this elevation, somewhere close to three
thousand feet, it is thirty-four degrees. It will drop well below freezing tonight. There are no squirrels. They are already
curled up in their burrows, bivouacked. It is snowing hard now. The city is lost behind a curtain of snow, and the mountains
around me appear through a fog of slow-moving white flakes.

The last few hundred feet of the mountain are as steep as the steps of a lighthouse. The trail this high is covered with snow,
and under the snow, from the trampling of other walkers, is ice. Eventually, I am clambering, grabbing rocks to avoid slipping.
The snow — its coolness, but also its texture, crunchy but soft — feels good on my hands. Just below the summit, my right
foot slips, and then my left, and it is only my hands that keep me from falling. That is how it is with snow-covered ice.
Blink and what feels like firm footing becomes slicker than oil. My toes find a purchase, and I look down. I would not die
if I fell from here, but I would be bruised and maybe broken. My fingers are numb. I have no need to crawl up the last twenty
feet to the summit, so I turn and inch my way downward. Thin snow on top of ice has left the trail so slippery that I am trembling
now and crab-walking downward. In places, I slide shamefully along on my behind. The snow eases for a moment, and the city
materializes in the growing twilight. Through the lessening snow, Cook Inlet glows orange and blue with steeply angled rays
of evening autumn sun.

I
t is November fifth in Palawan, an island in the Philippines, 500 miles north of the equator and 250 miles south of Manila.
It has dropped below twenty degrees in Anchorage, and the North Slope has touched zero, but here in Palawan, it is eighty-two
degrees. My migratory compass has, for the moment, acted birdlike, bringing me to warmer climes. Somewhere here on the island,
the arctic warbler should be overwintering, just arrived from Alaska. If these birds are here, they are likely worn out, still
recovering from a self-propelled migration, adjusting to the heat, coping with a new suite of predators, and recuperating
from their own version of jet lag. But I see none of them. Instead, I see resident birds — a tropical kingfisher gliding low
over blue water, a slender white-bellied woodpecker working the trunk of a coconut palm, a Philippine sea eagle riding thermals
up the side of a limestone cliff. These birds will never know the feeling of snow between their toes. They will never know
sea ice.

Underwater, I hold my breath and listen. The water temperature hovers around seventy-two degrees, and the sea is alive with
the clicking of shrimp, sounding something like grains of sand and gravel awash in surf. In the distance, I hear the motor
of a fisherman’s banca, a thin canoe-like craft with twin outriggers for stability and a jury-rigged gasoline motor thumping
through the waves. My companion says she can hear damselfish. I listen again. And there it is, a low-frequency grunt, an unmistakable
burp just at the edge of my hearing. And then another answering the first. Now, my ears attuned to the right frequency, I
hear a chorus of burps, one after another, burp after burp maybe saying something meaningful in damselfish-speak or maybe
just the sound and the fury of three-inch reef fish.

These little fish are stuck here in the tropics. They die in colder water. A near relative, the blacksmith, which broke away
from its tropical cousins some nine million years ago, lives as far north as Monterey Bay, California. The difference between
the two? Enzymes. Enzymes are protein molecules, but unlike other proteins, enzymes are there to encourage reactions important
to life. Bring two molecules together without an enzyme, and they may eventually react. Bring the same two molecules together
on the surface of an enzyme, and a millisecond later they have reacted. To say that enzymes speed up reactions would be to
downplay their importance. They rocket reactions into hyperdrive, increasing reaction rates several million times. And they
are selective. They bring together certain molecules but ignore others. More than four thousand biochemical reactions are
known to be mediated by enzymes. Enzymes are nothing less than the linchpins of metabolism.

But here is the catch: different enzymes work best at different temperatures. Take a damselfish enzyme that works best in
the Philippines, make a few subtle amino acid changes across nine million years of evolution, and you have an enzyme that
works best in northern California.
Molecular Biology and Evolution,
an academic journal, reports on the differences between damselfish and the related blacksmith: “Enzyme adaptation to temperature
involves subtle amino acid changes at a few sites that affect the mobility of the portions of the enzyme that are involved
in rate-determining catalytic conformational changes.” Sketches of fish enzymes, twisted and retwisted ribbons spiraling across
the page, show the difference between the enzymes of the tropical damselfish and the blacksmith. The difference as illustrated
is not profound. The difference in the real world is the difference between life and death.

Anything affecting temperature affects the efficiency of enzymes. So do certain poisons. Temperature — the wrong temperature
— acts like poison. It is not so much an issue of cold taking a single enzyme out of commission as one of cold disturbing
the synchronous behavior of an orchestra of enzymes, leaving one playing too slowly, another too fast, and another barely
playing at all, and in the end reducing the symphony of metabolism to the cacophony of malaise and death.

Temperature limits the ranges of species. Tropical damselfish are tropical not because they like warm water so much, but because
they need warm water. By impairing enzyme performance, cold water kills tropical damselfish, or slows their growth or stops
them from reproducing. The same is true for the corals out here, and the sponges, and the clicking shrimp. Move to the north
or south, and the corals and sponges and shrimp are gradually replaced by other species with other enzymes that work at other
temperatures. First one species drops out, then another, then another. They all play the odds, balancing enzyme efficiency
against other risks. The enzymes of a fish may work best at eighty-one degrees, but if the enzymes of its predators work best
at eighty-one degrees, it may be better off a bit farther north. It might do the same thing to avoid competitors. It may be
better off taking its chances in places where the occasional cold snap could wipe it out. Or it may be better off warm-blooded,
fighting off the cold outside to keep those enzymes at peak efficiency. It would need more food; it would need more insulation;
it would need adaptive behaviors and down jackets and baseboard heat and maybe an electric blanket. But it could live almost
anywhere, while these damselfish are condemned to the tropics.

When I tire of listening to grunting damselfish, I stand in the water. Facing shore, I look at coconut palms growing just
beyond white sand. Farther back, in the hills behind the beach, macaques play in jungle branches. I turn to watch the swells
coming in from the South China Sea. They break on the reef face. A surge of water, the remains of a broken wave, advances
across the shallows, then retreats, leaving white foam behind to slip slowly back. The sun hangs low on the horizon. At this
latitude, sunset comes quickly. I can almost see the sun move as it sinks into the sea. This is the same sun that will rise
in just a few hours over my home in Alaska, but there it will rise slowly, seeming to skim along the horizon, reluctant to
show itself to snow-covered black spruce and frozen tundra.

There was a time during the history of the science of ecology when a few obvious observations could become a rule. Today ecology
relies on advanced statistics, on multivariate models and randomization techniques and the use of Greek letters in place of
actual words. But a hundred years ago, it relied on narrative descriptions and observations. People like Karl Bergmann — working
in the 1840s at the same time that Louis Agassiz was studying glaciers — noticed that animals in cold climates were bigger
than their warm-climate cousins. Siberian tigers were bigger than Bengal tigers, and Bengal tigers were bigger than tigers
in equatorial jungles. Northern badgers were bigger than southern badgers. White-tailed deer in Michigan were nearly twice
the size of those in Nicaragua. Somewhere along the line, Bergmann’s realization that cold-climate mammals were often bigger
than their warm-climate cousins became known as Berg-mann’s Rule. Working with the chaos of nature, ecologists cling to patterns.
They ignore or excuse exceptions. Most ecologists were not troubled by the fact that Arctic brown bears were far smaller than
the brown bears of southern Alaska. An animal in a northern climate, the explanation goes, should be bigger, because a bigger
animal presents less surface area for every ounce of weight. As the size of a cube or a sphere or an irregular shape — the
shape of a bear or a moose or a caribou — increases, its surface area increases less than its volume. For every pound of body
weight, for every ounce of muscle and fat and liver and lung and heart, a big animal has less skin exposed to the cold than
a small animal. A big animal holds on to its heat more effectively than a small one, all else being equal.

Bergmann’s Rule is not so much a rule as a pattern. And there are other patterns. Here you are in an oak forest, and a bit
farther north you are in a spruce forest, and a bit farther you are in a treeless plain with frozen ground. These are the
biomes of ecological maps of the world. The oak forest is temperate deciduous forest, the spruce forest is taiga, and the
treeless plain is tundra. Biomes have clear boundaries on maps of the world, but the boundaries blur on the ground. The taiga
fades to scrubby spruce trees, their enzymes failing them and their roots struggling to find a way through frozen soil. The
spruce trees become more scattered. Seedlings might take hold for a year or two in a patch on the south-facing slope of a
hill or along a river, then die back when a brutally cold, dry gale howls in from the north, blowing them over or sucking
away the moisture that keeps them alive or sand-blasting them with crystals of wind-borne ice. Or the boundary might move
way north, as it would have during the Medieval Warm Period, and then south, as it would have during the Little Ice Age. Stragglers,
unable to reproduce in current conditions, their flowers not maturing or their pollinators no longer present, might hang on
long after the climate has changed, little islands of out-of-place spruce or pine or oak trees.

The ranges of species go where the species work best, destined by the character of their enzymes, destined by how well their
enzymes work at different temperatures. But also: Who will graze on my leaves? Who will eat me? Whom will I eat? Is there
space for my nest? Is the soil right for my burrows or my roots? Who will drive me away? Puffins became scarce around Britain
after 1920 not because of the air temperature, but because the fish they ate followed a shift in water temperature. The birds
followed the fish. When water temperature shifted again around 1950, the fish returned, and with them the puffins. The lives
within the biomes are interwoven, and if one species can go no farther because of the temperature, it may affect another species,
and another, and another, until it appears as though there is some definite boundary and that everything responds in concert.
But zoom in on the map, look a little closer, and the boundaries blur. Brown bears live in tundra and taiga and temperate
deciduous forest. Caribou migrate across biome boundaries. The red fox, the tiger, the wolf, the wolverine, and the raven
all cross biome boundaries as if they did not exist, as if they have never read an ecology textbook or studied a biome map.