Monday, 8 February 2016

The warming Arctic

T-Shirt Weather in the Arctic

5 February, 2016

WE crested the northern rim of Alaska’s Brooks Range, and from the windows of our truck looked out across the undulating foothills toward the Arctic Ocean. Instead of seeing snow as we had in years past, we were greeted by a landscape already green with spring.

We flew by helicopter to our remote camp and shed our heavy parkas. The fish we had come to study had already disappeared downstream to spawn.

We now realize that what we saw last May was historic — the hottest May for Alaska’s North Slope during what scientists recently concluded was the hottest year on record for the earth. We also saw the future.

Last year, the earth’s temperature passed the mark of 1 degree Celsius above preindustrial levels. Civilization took 165 years to reach that mark, and now the increase could reach 2 degrees Celsius in just 30 more years, a point at which the risks from sea-level rise, drought and other effects could increase significantly.

Despite promises made in Paris to cut greenhouse gas emissions, we will still need to make it through the hottest years of a looming global heat age. Along with the many challenges we face, we must figure out how to protect ecosystems and the benefits they provide.

Each spring for the last 30 years, our team of biologists has traveled to remote field camps in Arctic Alaska. The Arctic is warming faster than anywhere else in the world as seawater replaces sea ice, painting the Arctic Ocean blue and fueling a dangerous feedback loop. The white sea ice reflects the sun’s energy back into space through what is known as the albedo effect. But as the ice melts, the dark Arctic seawater is now absorbing that heat, turning up the earth’s temperature.

With the early spring, snow melted roughly two weeks earlier than in the past and plants turned green soon after. Lakes thawed about 10 days earlier, and Arctic grayling, a fish, bred weeks earlier.

An early spring has long-term consequences. When grayling breed three weeks earlier, for instance, their offspring get a head start on feeding and grow nine times larger. This might seem like a good thing, until you consider that the same warmer temperatures dry the rivers that enable these grayling to swim to lakes where they spend the winter. As these fish wait in shallow pools for the rivers to flow, bears and birds enjoy a captive feast. If rivers do not flow before winter, the fish freeze. The drying of these rivers could threaten some grayling populations.

Last May’s warmth deceived white-crowned sparrows into breeding earlier than usual. When a snowstorm roared in, the sparrows abandoned their ill-timed nests, leaving their eggs behind to perish.

Thunderstorms also raged over our camp. These storms used to be rare in the Arctic, but they strike often now. Lightning has set fire to the tundra, releasing into the atmosphere huge stores of ancient carbon from the permafrost. Sinkholes are also opening up in the thawing tundra. Walk up to one, and you will hear the trickle and clatter as heat dissolves permafrost into cascades of ice age mud and stones.

We are only just beginning to understand these changes. Ecosystems involve a complex web of connections among species and the physical environment. Climate change alters these connections in ways that can surprise and baffle us.

For example, scientists thought they understood Arctic streams until we added nutrients to one to mimic what happens when the tundra thaws. A rare moss materialized and blanketed the streambed. A new set of insects appeared, but they sheltered in the moss instead of drifting into the waiting mouths of hungry grayling. So in a roundabout way, a more productive stream made for skinnier fish.

The surprises pose serious risks because we can’t prepare for what we don’t know. We can no longer be satisfied to watch and document these changes. We must predict and prevent them.

Sustaining life through the coming heat age will require tough decisions as we triage the rising number of climate casualties. We cannot hope to save all species when we haven’t even figured out how many species there are.

We might focus initially on protecting those with the greatest importance to other species and ecosystems, the so-called biotic multipliers of climate change. For instance, top predators are often sensitive to climate change and magnify climate effects by yanking hard on the threads that connect them to other species in the food chain.

Our current approaches to identifying which species and ecosystems are most at risk are primitive. Most predictions rely on the correlation between a map of an animal’s range and a few climate factors. As biologists, we need to develop forecasts that rely on causes, not correlations, as our colleagues studying the atmosphere did years ago. This will require an enhanced effort to comprehend how species survive, reproduce, evolve and move across landscapes, and how changes in the climate alter each of these factors.

We also need experiments that replicate a warming environment. Scientists know how to heat small plots of tundra with open-topped plastic enclosures and forests with heated cables. But the small size of these efforts limits our ability to understand consequences for larger animals and ecosystems. We need to engineer ways to warm bigger ecosystems experimentally by heating up entire lakes, streams, fields and even forests.

We plan to return to the Arctic again in May. This year is predicted to be even hotter than the last. We’ll be ready this time. We understand now that we have already entered the heat age.

Mark Urban is an associate professor in ecology and evolutionary biology at the University of Connecticut in Storrs. Linda Deegan is a senior scientist at the Marine Biological Laboratory Ecosystems Center in Woods Hole, Mass.

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