of them flock to a handful of caves. Half of the world’s Indiana
bats overwinter in two caves. In 1967, Indiana bats were protected by law because of continuous population decline. What happened?
Cave entrances had been modified to prevent cavers from disturbing the bats. The new entrances — now too small for humans
but big enough for bats — restricted airflow. Caves breathe: as the temperature changes outside, air moves in or out of the
caves. It is not unusual to feel a strong breeze well underground. When the entrances were modified, the caves became asthmatic.
Winter temperatures in the caves rose. At Kentucky’s Hundred Dome Cave, temperatures rose almost twenty degrees. Hibernating
Indiana bats maintain a temperature close to that of the air. At lower temperatures, their hibernating metabolism is very
slow. They survive the winter by slowly burning through limited fat reserves. When the temperature increases, their metabolic
rate increases. Slowly, during their winter sleep, warm Indiana bats starve to death.
It is August fifteenth. It is around sixty degrees. I sit in the rain outside a yurt thirty miles north of my home in Anchorage,
Alaska. A yurt is a round, semipermanent tent modeled after those used by nomadic Mongolians. But this yurt is here in Alaska
rather than there in Mongolia, and it is furnished with a woodstove, bunk beds, and folding chairs. Beneath me, I can see
and hear the Eagle River, which flows from Eagle Glacier, out of sight some fifteen miles upstream. I look periodically for
a grizzly sow and her cub, which were seen by hikers just yesterday feeding on salmon in the river. Now the grizzlies are
as invisible as a North Slope caterpillar.
The Eagle River valley is U shaped, scraped out by a glacier, without the steep-cut angles of valleys cut by flowing water.
Higher up in the mountains around us, other valleys end in waterfalls that stream down the sides of mountains. These hanging
valleys mark the surface of the old ice, hundreds of feet up. In the past, the big glacier, the thick one, flowed through
this valley, extending up beyond what today are the high mountain passes, and the glaciers in the higher mountain passes intercepted
the glacier that flowed through this valley. The glaciers in the high mountain passes flowed into the larger valley glaciers
like shallow streams flowing into a deep river, leaving their beds perched well above the bottom of the deep river, but these
were streams and rivers of ice, moving with leisurely, mountain-grinding power. Boulders carried by the glaciers litter the
valley floor. My son climbs the boulders while I stare at the mountains, imagining this place buried under hundreds of feet
of ice. This makes me imagine Manhattan under ice. Fifty thousand years ago, the Wisconsin Glacier overran what would become
New York. Somewhat famously, it ground grooves into the rocks at Central Park. What would become New York has been overrun
by many glaciers, a complicated coming and going of glaciers that advanced and retreated over thousands of years, a cosmopolitan
mingling of ice and the effects of ice that make the modern world seem inconsequential. The glaciers in New York are gone
now, as is most of the glacier here in the Eagle River valley. All that is left is a pathetic remnant near the head of the
valley. The world has warmed. In national parks, there are signposts marking the extent of certain glaciers in 1959, in 1965,
in 1970, and so on to the present day. Trees grow around these signs. The glacier itself might not be visible until you are
standing next to a sign that says 1959. In ten years, it might not be visible from beyond a sign dated 1970. In twenty years,
it might be gone altogether. People say the glaciers in Alaska have retreated. In fact, they have melted, withered, and in
some cases disappeared, warmed and thawed into miniatures of their former selves or warmed further until
bats overwinter in two caves. In 1967, Indiana bats were protected by law because of continuous population decline. What happened?
Cave entrances had been modified to prevent cavers from disturbing the bats. The new entrances — now too small for humans
but big enough for bats — restricted airflow. Caves breathe: as the temperature changes outside, air moves in or out of the
caves. It is not unusual to feel a strong breeze well underground. When the entrances were modified, the caves became asthmatic.
Winter temperatures in the caves rose. At Kentucky’s Hundred Dome Cave, temperatures rose almost twenty degrees. Hibernating
Indiana bats maintain a temperature close to that of the air. At lower temperatures, their hibernating metabolism is very
slow. They survive the winter by slowly burning through limited fat reserves. When the temperature increases, their metabolic
rate increases. Slowly, during their winter sleep, warm Indiana bats starve to death.
It is August fifteenth. It is around sixty degrees. I sit in the rain outside a yurt thirty miles north of my home in Anchorage,
Alaska. A yurt is a round, semipermanent tent modeled after those used by nomadic Mongolians. But this yurt is here in Alaska
rather than there in Mongolia, and it is furnished with a woodstove, bunk beds, and folding chairs. Beneath me, I can see
and hear the Eagle River, which flows from Eagle Glacier, out of sight some fifteen miles upstream. I look periodically for
a grizzly sow and her cub, which were seen by hikers just yesterday feeding on salmon in the river. Now the grizzlies are
as invisible as a North Slope caterpillar.
The Eagle River valley is U shaped, scraped out by a glacier, without the steep-cut angles of valleys cut by flowing water.
Higher up in the mountains around us, other valleys end in waterfalls that stream down the sides of mountains. These hanging
valleys mark the surface of the old ice, hundreds of feet up. In the past, the big glacier, the thick one, flowed through
this valley, extending up beyond what today are the high mountain passes, and the glaciers in the higher mountain passes intercepted
the glacier that flowed through this valley. The glaciers in the high mountain passes flowed into the larger valley glaciers
like shallow streams flowing into a deep river, leaving their beds perched well above the bottom of the deep river, but these
were streams and rivers of ice, moving with leisurely, mountain-grinding power. Boulders carried by the glaciers litter the
valley floor. My son climbs the boulders while I stare at the mountains, imagining this place buried under hundreds of feet
of ice. This makes me imagine Manhattan under ice. Fifty thousand years ago, the Wisconsin Glacier overran what would become
New York. Somewhat famously, it ground grooves into the rocks at Central Park. What would become New York has been overrun
by many glaciers, a complicated coming and going of glaciers that advanced and retreated over thousands of years, a cosmopolitan
mingling of ice and the effects of ice that make the modern world seem inconsequential. The glaciers in New York are gone
now, as is most of the glacier here in the Eagle River valley. All that is left is a pathetic remnant near the head of the
valley. The world has warmed. In national parks, there are signposts marking the extent of certain glaciers in 1959, in 1965,
in 1970, and so on to the present day. Trees grow around these signs. The glacier itself might not be visible until you are
standing next to a sign that says 1959. In ten years, it might not be visible from beyond a sign dated 1970. In twenty years,
it might be gone altogether. People say the glaciers in Alaska have retreated. In fact, they have melted, withered, and in
some cases disappeared, warmed and thawed into miniatures of their former selves or warmed further until
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