Someone better tell Santa Claus. First it was polar bears that were threatened by global warming. Now it’s reindeer too. As temperatures in the Arctic skyrocket, reindeer are suffering staggeringly large, rapid population losses. “Herds of reindeer have declined by one-third since the 1990s as their access to food sources, breeding grounds and historic migration routes have been altered,” reports the environmental audit committee of the British Parliament.

The entire planet is getting hotter, but the top of the world is warming twice as fast as the global average. One leading expert, Peter Wadhams, a professor of ocean physics at the University of Cambridge, says the Arctic Ocean could be completely free of ice in summer as soon as 2015. An overheated Arctic in turn threatens catastrophic knock-on effects for the rest of the globe, including more extreme weather; faster sea level rise; and a higher chance of accelerating global warming to where it becomes unstoppable—what scientists refer to as “runaway” global warming.

Yet even as the number of reindeer in the Arctic is declining, the number of warships, cargo vessels and drilling rigs is increasing. In a little-noticed announcement, the United States Defense Secretary, Chuck Hagel, said on November 22 that the Pentagon is increasing its Arctic presence. Citing a “potential for tapping what may be as much as a quarter of the planet’s undiscovered oil and gas,” Hagel declared that the US “will remain prepared to detect, deter, prevent and defeat threats.” For his part, Russian president Vladimir Putin has pledged to turn the Arctic into “an international transport artery” that could cut one-third of the travel time and costs for trade between Europe and Asia compared to the traditional route through the Suez Canal. China, too, is setting its sights upon the Arctic. In May, it gained “observer” status on the Arctic Council—a high level intergovernmental group that coordinates international policies at the top of the world—despite its lack of territorial holdings in the Arctic. Chinese state-owned firms have also signed deals to exploit oil, gas and minerals in the Arctic.

Arctic ice cover has been declining since the 1950s, said professor Wadhams, who has led forty polar expeditions since first visiting the region in 1969. The biggest decline occurred in 2007, when the area covered by ice in summer decreased to roughly half of its usual amount. That left “an ocean of open water at the top of the planet—an unprecedented effect,” Wadhams said in an interview.

There was another large decrease in 2012, but Wadhams and other experts also worry that the thickness of Arctic ice is plummeting. Since satellites cannot accurately measure ice thickness, Wadhams has been going on board British nuclear submarines to map the ice from below with sonar. Arctic ice thickness has declined by 43 percent between the 1970s and 2000s, Wadhams has calculated, “an enormous loss” that he attributes to the higher temperatures of both air and sea in the Arctic.

Secretary Hagel promised in his November 22 announcement that the US military would also work to “preserve the Arctic environment.” That goal will be impossible to achieve if temperatures keep rising, say scientists. The physical momentum of global warming—rooted in the fact that carbon dioxide [CO2] lingers in the atmosphere for many years after being emitted—insures that Arctic and global temperatures will rise for decades to come, even if humanity reduces annual emissions of greenhouse gases. Thus scientists regard further melting of the Arctic as inevitable. The only disputes are over how much and how fast.

“We are going to get into a ghastly situation for the planet at some point and whether it is happening next year or it is going to take a few decades is the only question,” Wadhams testified to Parliament in 2012. Although Wadhams stands alone in projecting an ice-free Arctic as soon as 2015, other scientists agree that the day is coming fast. Tim Lenton, a professor of climate change and earth system science at the University of Exeter who also testified to the parliamentary committee, said in an interview, “My guesstimate is that the first complete loss of summer ice in the Arctic could be as early as 2030 or even 2020. That’s soon enough for me to think that it’s a serious concern.” Julia Slingo, the chief scientist for the Met Office, the United Kingdom’s weather service, testified that the Met’s computer models put the earliest date for an ice-free Arctic between 2025 to 2030, though she added that “further observations are required” to judge how likely that scenario is.

“There is a glimmer of possibility” that humanity could still turn this trajectory around, Lenton told me. Some computer models, he said, indicate that about half of the global warming in the Arctic is driven by methane and soot. Because these two pollutants are powerful but short-lived heat-trapping agents, reducing their emissions could slow the rise of temperatures relatively quickly.

Reducing the amount of CO2 in the atmosphere remains the main challenge, and here too there are more, and more appealing, options than usually recognized. For example, wind and especially solar power are growing exponentially around the world as sharply falling prices lead millions of consumers and businesses to leave fossil fuels behind.

“Solar is growing so fast it is going to overtake everything,” Jon Wellinghoff, chair of the US Federal Energy Regulatory Commission, said in August. In Germany, which has pledged to forsake both fossil fuels and nuclear power, solar has grown to supply roughly 40 percent of the nation’s electricity. In China, renewable energy sources will make up more than half of the power capacity added through 2030, when renewables’ capacity will equal coal’s, Bloomberg New Energy Finance has projected. “There is nothing else like these rates of adopting a new technology,” Danny Kennedy, a founder of the solar company Sungevity, said in an interview. “They’re faster than the adoption rates for cell phones.”

Combined with the other semi-secret weapon in the battle against global warming—dramatically improved energy efficiency for cars, buildings, motors and more—renewable energy’s new competitiveness suggests that emissions could fall much faster than assumed, especially if governments put a price on carbon to discourage fossil fuel use.

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Nevertheless, present trends are moving in the opposite direction, with profound implications for the Arctic and the rest of the planet. World leaders agreed at the Copenhagen climate summit in 2009 to limit global warming to 2 degrees Celsius above the level that pertained prior to the Industrial Revolution—the level to which agriculture and human civilization have adapted over the past ten thousand years. But actions have fallen far short. At the latest international negotiations, held in Poland last month, Japan announced that it would not honor its previous commitment to reduce emissions. More foot-dragging came from traditional laggards China, the US, Canada and Australia.

Because strong action has not been taken, emissions have risen to where dangerous global warming has become unavoidable. Earth is on track to become 4 degrees hotter than pre-industrial levels before 2100, according to a 2012 report from the World Bank. “This would mean a world of risks beyond the experience of our civilization—including heat waves, especially in the tropics, a sea-level rise affecting hundreds of millions of people, and regional yield failures impacting global food security,” explained the Potsdam Institute for Climate Impacts Research, which prepared the report.

The melting of the Arctic—which, remember, is warming twice as fast as the global average—is “a very powerful symbol of what we’re doing to the planet,” said Gavin Schmidt, a climate scientist at the NASA Goddard Space Institute. Some four million people live in the Arctic, Schmidt noted, and “the expectations they have from the climate are a much bigger part of their lives than we have in our air-conditioned and heated buildings…. What [they] eat, how [they] eat, where they build their houses—all of that is going to change tremendously.”

Because some indigenous Arctic peoples rely on reindeer for food, clothing and cultural identity, the precipitous decline in reindeer herds presents “serious challenges to human health and food security and possibly the survival of some cultures,” the British parliamentary report concluded. The Arctic also hosts half of the world’s shorebird species, and many whales and 15 percent of the planet’s migratory birds breed there. Long before sea ice completely disappears, these and many other animals will struggle to survive. Nurturing their young to maturity will be especially challenging, because “earlier melting of snow and ice, or flowering of plants, can cause a mismatch between the timing of reproduction and the supply of food,” a 2013 report by the United Nations Environmental Program explains.

Why should the rest of us care? Beyond simple fairness—after all, the people and wildlife of the Arctic did not cause the global warming that is convulsing their world—there is self-interest. What happens in the Arctic does not stay in the Arctic. What humans do to the reindeer, we do to ourselves.

Scientists warn of three major consequences a warmer Arctic will have on people and ecosystems across the planet:

(1) Nastier weather …and more hunger. A warmer Arctic means that temperature differences with regions to its south are reduced. This shift appears to be slowing the wind patterns that usually propel weather systems from west to east throughout the Northern Hemisphere. As UNEP writes, this slowing may be causing “more intense and longer periods of rainfall and drought, summer heat waves and cold snaps in winter,” such as the record heat wave in Russia in 2010 and prolonged drought in North America in 2011 and 2012.

More volatile weather translates into more difficulty in feeding humanity. The summer of 2012, the hottest ever recorded in the United States, coincided with the worst drought in fifty years. Yields of both corn and soybeans plummeted. Because the US accounts for so much of global food production, the weather troubles in the US drove up world food prices. These higher prices increased hunger and triggered protests in Indonesia and elsewhere that recalled the street riots that afflicted dozens of nations after the last big food-price jump, in 2007—08.

More than any gradual increase in temperature, it is the projected increase in extreme heat and drought that makes the warming of the Arctic such a threat to agriculture. Corn, which is the major crop (by volume) grown in the US, does not reproduce at temperatures higher than 35 degrees C. In the 20th century, the state of Iowa—the center of the US Corn Belt, experienced three straight days of 35 C only once a decade. By 2040, if emissions remain on their current trajectory, Iowa will experience three straight days of 35 C in three years out of four, professors Katharine Hayhoe of Texas Tech University and Don Weubbles of the University of Illinois have calculated.

(2) Faster sea level rise…. and more climate refugees. The warmer Arctic has dramatically accelerated the melting of the Greenland ice sheet. “We are now losing 300 cubic kilometer of ice a year in Greenland,” said Wadhams. “That in itself will double the rate of sea level rise globally. If the melting of Antarctica continues to accelerate as well, which it is, we will certainly get more than one meter of sea level rise by 2100, perhaps as much as two meters.” That will be a “very, very serious problem,” Wadhams said, especially for residents of low-lying coastal regions such as eastern China and Bangladesh.

Unless sea walls and other barriers are installed, a sea level rise of three feet will endanger 145 million people and bring catastrophic flooding to many of the world’s leading cities, including Tokyo, Shanghai, New York and London and the Asian mega-cities of Manila, Jakarta and Dhaka. This is especially so because, along with sea level rise, climate change will also be causing stronger storms. Worldwide, approximately $3 trillion of assets are located at or below three feet above sea level, according to the Stern Review, an analysis of the economic implications of climate change published by the British government. These assets include infrastructure crucial to modern society: water treatment facilities, power stations, railroads, highways, buildings, airports. In theory, it is possible to move or protect these assets, but doing so will be neither quick nor cheap.

As Wadhams notes, for people living in the areas of greatest vulnerability—along low-lying coasts—the most likely response will be to try to re-locate further inland. Such a surge of “climate refugees” will raise the likelihood of social conflict and perhaps violence, which is one reason the US and UK militaries, among others, have identified climate change as a major security threat in the 21st century.

The same global warming that is overheating the Arctic is also melting glaciers around the world, which not only further increases sea level rise but also causes yet more difficulties for growing food. In Asia, at least 500 million people obtain drinking and irrigation water from the 42,298 glaciers atop the Himalayan mountains, a mass of snow and ice long known as the “Third Pole” of this planet. As these glaciers melt—at current rates, scientists expect 40 percent of them to disappear by 2050—both farmers and urban consumers will encounter a paradox: there will be more water available in the short term, raising the odds of costly and destructive flooding, but less water available in the long term, threatening to parch soils and wither crops at the very time human population growth will require more food.

(3) Higher risk of “runaway” global warming. The warmer Arctic has begun unleashing substances—specifically, permafrost and underwater methane—that could sharply accelerate global warming. “[Underwater] methane is leaking from the East Siberian Arctic shelf … at an alarming rate,” the US National Science Foundation wrote in 2010, summarizing research by a team of scientists led by Natalia Shakhova of the University of Alaska Fairbanks. Once it is released to the atmosphere, methane is 23 times more powerful at trapping heat than CO2 is; hence the alarm.

The world’s oceans contain vast quantities of methane, but colder temperatures have kept it stable by transforming it into methane hydrates, an ice-like solid. Warmer Arctic temperatures, however, are freeing more of these methane hydrates. In research published last month in the peer-reviewed journal Nature Geoscience, Shakhova’s team found that the East Siberian sea floor is releasing 17 million tons of methane a year—more than twice as much as previously estimated.

Wadhams fears that if this underwater methane release continues to accelerate, it could “increase the average global temperature by 0.6 degrees by 2040” beyond the sizable amount of warming that is already underway. The mega-question that follows is, could this increase trigger runaway global warming?

Lenton and Schmidt doubt it, though they agree methane release is a problem. Shakhova said in an interview that we “cannot exclude the possibility,” but more data is needed to calculate the odds. Wadhams, however, puts the odds at “one in three or four, unless we take very rigorous action: immediate, very large decreases in carbon emissions and very active research on how to extract carbon from the atmosphere.”

The warmer Arctic, and the methane releases it triggers, are what scientists call a “positive feedback”: higher temperatures release more methane, that methane raises temperatures again, which releases more methane, which boosts temperatures further. It is the warmer Arctic’s potential for turning positive feedbacks into runaway global warming that most worries scientists, because it would make global warming impossible to stop, condemning humanity to an impossibly hot future. “It’s like running a car downhill,” said Wadhams. “You can turn engine off, but you’ll still be gathering speed. [With the Arctic melting] we could get to the point with feedbacks where even if we DO reduce our greenhouse gas emissions substantially, we might think we’re out of the woods, but in fact we would still keep accelerating.”

The melting of the Arctic amounts to a Code Red emergency. The hopeful news is that humans could still alter current trends and limit the damage, not only to the people and wildlife in the Arctic but to their own children and future descendants. One place to start: ban further oil and gas development in the Arctic itself—when the top of the world is melting at record speed, does it really make sense to turn up the heat by burning more carbon? “It’s not completely inevitable that this must all play out like this,” said Schmidt of NASA. “But it depends very much on how we think about the problem, pretty much starting now.”