They partly attribute the observed warming, and preceding cooling trends to ocean circulation changes induced by global greenhouse gas emissions and aerosols predominantly generated in the Northern Hemisphere from human activity.

The research, by scientists from CSIRO and the University of NSW, was published today in Scientific Reports.

Mr Tim Cowan, lead author of the study, says his group was initially interested in the three decade long cooling below the surface of the Southern Hemisphere subtropical oceans from the 1960s and 1990s. “But what really caught our eye was a rapid warming of these subtropical oceans from the mid-1990s, most noticeably in the Indian Ocean between 300 m to 1000 m depth,” said Mr Cowan.

This had the research team asking whether this rapid warming was partly a response to greenhouse gases overcoming the cooling effect of aerosols that peaked globally in the 1980s due to the introduction of clean air legislation across United States and Europe.

To test this, the researchers examined more than 40 state-of-the-art climate simulations that included historical changes to greenhouse gases and aerosols over the twentieth century. “What we found was that the models do a good job at simulating the late twentieth century cooling and rapid warming in the subtropical southern Atlantic and Pacific Oceans, however they show an around 30-year delay in the warming in the Indian Ocean” said Mr Cowan.

“This delay in the modelled Indian Ocean warming is likely due to the presence of atmospheric aerosols, generated through transport emissions, biomass burning, and industrial smog, together with natural emissions of sea salt and dust — these were also the main cause of the late twentieth century subtropical Indian Ocean below-surface cooling” said Mr Cowan.

The researchers found that models with a delayed peak in Northern Hemisphere aerosol levels after the 1980s had a tendency to simulate a delayed rapid Indian Ocean warming until well after 2020, and that the rate of warming related to how quickly the aerosol levels declined after their peak.

“We know that aerosols in the atmosphere generally cool the Northern Hemisphere by scattering incoming sunlight. This, in turn, increases the movement of heat from the Southern Hemisphere oceans to the Northern Hemisphere oceans via a global oceanic conveyor belt, travelling south from the subtropical Indian Ocean, passing the southern tip of Africa into the south Atlantic and then north along the Gulf Stream” said co-author Dr Wenju Cai.

“Together with a greenhouse gas-induced southward shift the Indian subtropical ocean gyres towards the Antarctic, these processes delay the Indian Ocean warming in the models,” Dr Cai said.

“What makes this work fascinating is the fact that human-emitted aerosols have such a large impact on remote ocean temperatures” says Mr Cowan. “For many years aerosols have masked the direct surface warming induced by greenhouse gases in many Northern Hemisphere regions, however in the Southern subtropical Indian Ocean both aerosols and greenhouse gases have historically conspired to produce a net oceanic cooling, and now the reverse of some of these processes is occurring.”

Mr Cowan said that despite the observed rapid ocean warming, quantifying exactly how much is due to declining aerosols or increasing greenhouse gases remains difficult, but as human-generated air pollution is all-together phased out, this will undoubtedly reveal the full impact of greenhouse gases.

The research has been supported by the CSIRO Wealth from Oceans National Research Flagship, The Australian Climate Change Science Program and the Australian Research Council Centre of Excellence in Climate System Science.

Tracking data from Garwood Valley in the McMurdo Dry Valleys region of Antarctica, Joseph Levy, a research associate at The University of Texas at Austin’s Institute for Geophysics, shows that melt rates accelerated consistently from 2001 to 2012, rising to about 10 times the valley’s historical average for the present geologic epoch, as documented in the July 24 edition of Scientific Reports.

Scientists had previously considered the region’s ground ice to be in equilibrium, meaning its seasonal melting and refreezing did not, over time, diminish the valley’s overall mass of ground ice.

Instead, Levy documented through LIDAR and time-lapse photography a rapid retreat of ground ice in Garwood Valley, similar to the lower rates of permafrost melt observed in the coastal Arctic and Tibet.

“The big tell here is that the ice is vanishing — it’s melting faster each time we measure,” said Levy, who noted that there are no signs in the geologic record that the valley’s ground ice has retreated similarly in the past. “This is a dramatic shift from recent history.”

Ground ice is more prevalent in the Arctic than in Antarctica, where glaciers and ice sheets dominate the landscape. In contrast to glaciers and ice sheets, which sit on the ground, ground ice sits in the ground, mixed with frozen soil or buried under layers of sediment. Antarctica’s Dry Valleys contain some of the continent’s largest stretches of ground ice, along the coast of the Ross Sea.

After Levy and colleagues noted visible effects of ground ice retreat in Garwood Valley, they began to monitor the valley, combining time-lapse photography and weather-station data at 15-minute intervals to create a detailed view of the conditions under which the ice, a relict from the last ice age, is being lost.

Rising temperatures do not account for the increased melting in Garwood Valley. The Dry Valleys overall experienced a well-documented cooling trend from 1986 to 2000, followed by stabilized temperatures to the present.

Rather, Levy and his co-authors attribute the melting to an increase in radiation from sunlight stemming from changes in weather patterns that have resulted in an increase in the amount of sunlight reaching the ground.

Sunlight tends to bounce off the white, reflective surfaces of glaciers and ice sheets, but the darker surfaces of dirty ground ice can absorb greater amounts of solar radiation. Thick layers of sediment tend to insulate deeply buried ground ice from sunlight and inhibit melting. But thin sediment layers have the opposite effect, effectively cooking the nearby ice and accelerating melt rates.

As the ground ice melts, the frozen landscape sinks and buckles, creating what scientists describe as “retrogressive thaw slumps.” An acceleration in the prevalence of such slumps has been well documented in the Arctic and other permafrost regions, but not in Antarctica.

Levy’s research shows that even under the stable temperature conditions of the Dry Valleys, recent increases in sunlight are leading to Arctic-like slump conditions.

If Antarctica warms as predicted during the coming century, the melting and slumping could become that much more dramatic as warmer air temperatures combine with sunlight-driven melting to thaw ground ice even more quickly.

Ground ice is not the major component of Antarctica’s vast reserves of frozen water, but there are major expanses of ground ice in the Dry Valleys, the Antarctic Peninsula and the continent’s ice-free islands.

Garwood Valley could tell the story of what will happen in these “coastal thaw zones,” says Levy.

“There’s a lot of buried ice in these low-elevation coastal regions, and it is primed to melt.”

A helicopter view of energy facilities in the Russian Arctic. The company Novatek controls natural gas fields there.

YURKHAROVSKOYE GAS FIELD, Russia — The polar ice cap is melting, and if executives at the Russian energy company Novatek feel guilty about profiting from that, they do not let it be known in public.

From this windswept shore on the Arctic Ocean, where Novatek owns enormous natural gas deposits, a stretch of thousands of miles of ice-free water leads to China. The company intends to ship the gas directly there.

“If we don’t sell them the fuel, somebody else will,” Mikhail Lozovoi, a spokesman for Novatek, said last month with a shrug.

Novatek, in partnership with the French energy company Total and the China National Petroleum Corporation, is building a $20 billion liquefied natural gas plant on the central Arctic coast of Russia. It is one of the first major energy projects to take advantage of the summer thawing of the Arctic caused by global warming.

The plant, called Yamal LNG, would send gas to Asia along the sea lanes known as the Northeast Passage, which opened for regular international shipping only four years ago.

Whatever blame for the grim environmental consequences of global warming elsewhere in the world that might be placed on the petroleum industry, in the Far North, companies like Novatek and Total, Exxon Mobil of the United States and Statoil of Norway stand to make profit.

“It’s a reality of what is available today, and commercially it is a route that cuts cost,” Emily Stromquist, a global energy analyst at the Eurasia Group, said in a telephone interview.

Because of easing ice conditions and new hull designs, the tankers will not even require nuclear-powered icebreakers to lead the way — as is the practice now — except through the most northerly straits.

Novatek’s alternative was extending the natural gas pipeline that goes to Europe over hundreds of miles of tundra, at great cost. While shipping the gas from the field on the Yamal Peninsula, one of the long, misshapen fingers of land that extend north of the Urals in Russia, remains expensive, it is relatively cheap to drill and produce from these rich fields, making the overall project competitive.

In addition to making it easier to ship to Asia, the receding ice cap has opened more of the sea floor to exploration. This has upended the traditional business model of using pipelines to Europe. Thawing has proceeded more slowly in the Arctic above Alaska, Canada and Greenland, but one day what is happening in Russia could happen there.

Still, the Arctic waters are particularly perilous for drilling because of the extreme cold. Tongues of ice that descend from the polar cap for hundreds of miles obstruct shipping and threaten rigs. After a rig ran aground last year, Shell canceled drilling this summer in the Chukchi Sea off Alaska.

This is not the first Arctic venture to benefit from newly cleared sea lanes. The decision to open the Arctic Ocean to drilling passed Russia’s Parliament in 2008 as an amendment to a law on subsoil resources. Exxon and Rosneft, the Russian state oil company, are already in a joint venture to drill in the Kara Sea, and last month they agreed to expand to seven new exploration blocks in the Arctic. Fourteen wells are planned.

With these ventures, Exxon has placed itself in the vanguard of oil companies exploring commercial opportunities in the newly ice-free waters.

In Russia, the mining company Norilsk can now ship its nickel and copper across the Arctic Ocean without chartering icebreakers, saving millions of rubles for shareholders.

Norway is also drilling deep in Arctic waters, but has less territory to explore. Tschudi, a Norwegian shipping company, has bought and revived an idled iron ore mine in the north of Norway to ship ore to China via the northern route.

In northwest Alaska, the Red Dog lead and zinc mine moves its ore through the Bering Strait, which is less often clogged with packed ice than in past decades.

Ice-free Arctic in two years heralds methane catastrophe – scientist

Professor Peter Wadhams, co-author of new Nature paper on costs of Arctic warming, explains the danger of inaction