OSLO (Reuters) - Global warming is likely to disrupt a natural cycle of ice ages and contribute to delaying the onset of the next big freeze until about 100,000 years from now, scientists said on Wednesday. In the past million years, the world has had about 10 ice ages before swinging back to warmer conditions like the present. In the last ice age that ended 12,000 years ago, ice sheets blanketed what is now Canada, northern Europe and Siberia. In a
new explanation for the long-lasting plunges in global temperatures that cause ice ages, scientists pointed to a combination of long-term shifts in the Earth’s orbit around the sun, together with levels of carbon dioxide in the atmosphere. They said the planet seemed naturally on track to escape an ice age for the next 50,000 years, an unusually long period of warmth, according to the study led by the Potsdam Institute for Climate Impact Research. But rising man-made greenhouse gas
emissions since the Industrial Revolution began in the 18th century could mean the balmy period will last for 100,000 years, they wrote in the journal Nature. The findings suggest human influences “will make the initiation of the next ice age impossible over a time period comparable to the duration of previous glacial cycles,” they wrote. “Humans have the power to change the climate on geological timescales,” lead author Andrey Ganopolski told Reuters. He said the lingering
impacts of greenhouse gases in a far distant future did not in any way affect the urgency of cutting emissions now that are blamed for causing downpours, heat waves and rising seas. “The earlier we stop, the better,” he said. Almost 200 governments agreed a deal in Paris last month to shift from fossil fuels to combat climate change. Last week, another group of scientists said humanity had become a force in shaping the planet’s geology and suggested an “Anthropocene epoch” began in
the mid-20th century with factors such as nuclear tests and industrialization. “Like no other force on the planet, ice ages have shaped the global environment,” said Hans Joachim Schellnhuber, director of the Potsdam Institute and an author of Wednesday’s study. He suggested a new epoch might instead be called the “Deglacial”.
Some past studies have suggested that global warming can delay ice ages, but Thursday’s study laid down clear rules.
It said the start of past ice ages coincided with low levels of solar energy reaching the Earth in northern summers, like in current times. But an ice age had not begun because of relatively high, apparently natural, levels of carbon dioxide in the atmosphere since before the Industrial Revolution.
Study at: here; Reporting by Alister Doyle; Editing by Tom Heneghan
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London’s Thames River used to freeze over in winters during the Little Ice Age, providing ice thick enough to support large outdoor festivals known as frost fairs. (Image courtesy of Rijks Museum)
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In the 2004 blockbuster “The Day After Tomorrow,” the Northern Hemisphere experiences an abrupt and catastrophic plunge into Ice Age conditions. The culprit? Extreme rates of melting ice from the poles cause a massive disruption in the ocean currents that distribute heat around the planet. In the movie, North Atlantic currents responsible for the temperate climate along the North American East Coast and Western Europe suddenly grind to a halt, causing the northern United States and the United Kingdom to freeze over and unleashing terrible storms around the world.
It might seem completely off-base to imagine that the heat-trapping gases emitted by humans could cause “global freezing” rather than “global warming.” But in fact, scientists have long hypothesized that greenhouse gases could cause cooling in some places and warming in others due to changes in ocean circulation. There is genuine concern and no shortage of studies looking into whether the unprecedented melting of the Greenland Ice Sheet is impacting the North Atlantic subpolar gyre and Atlantic Meridional Overturning Circulation (AMOC), important drivers of the ocean’s circulation system and Earth’s climate.
So, could we one day see the abrupt climate change depicted in “The Day After Tomorrow”? Or can we expect a more gradual transition to a “mini Ice Age” as some have speculated?
Probably not, says WHOI physical oceanographer Jake Gebbie.
WHOI scientist Jake Gebbie. (Photo by Jayne Doucette, © Woods Hole Oceanographic Institution)
To look into our climate future, we need to review the past. An Ice Age is a “glacial period” in which the Earth’s surface and atmosphere cools by over 5°C, causing the polar ice caps and glaciers to expand. Brought on by naturally-occurring shifts in the Earth’s orbit and tilt, which change where solar energy hits Earth’s surface, these periods occur fairly regularly and can last tens of thousands of years.
A shorter period of cooling, such as the “Little Ice Age” between the 14th and mid-19th centuries, saw temperatures that were half a degree Celsius (about 1°F) cooler in Europe than today’s average temperatures. During the Little Ice Age, volcanic activity blocked solar radiation from reaching the Earth, which, combined with naturally reduced solar activity, the build-up of solar-reflecting ice (the albedo effect), and other potential factors, all conspired to cool the northern hemisphere.
“What caused the Little Ice Age to last for centuries in the Northern Hemisphere is a matter of debate,” Gebbie says. “The ocean had a role, but the driver likely had more to do with volcanoes and solar activity. There is less evidence that it was driven by ocean circulation.”
So, let’s say that, in the next few years, a spate of volcanoes erupt and sunspots reduce solar radiation as much as they did during the Little Ice Age. With today’s record-breaking heat waves, would those natural phenomena be enough to cool the planet to pre-industrial temperatures–or even trigger a Little Ice Age? Not likely, says Gebbie, because there’s now so much heat baked into the Earth’s system that the melting ice sheets would not readily regrow to their previous size, even if the atmosphere cools.
“So far, there may be a balance in the North Atlantic between the energy from atmospheric CO2 ramping up and the countereffects of ocean circulation,” Gebbie says. “But the CO2 is accelerating so much. For that reason, the community consensus is that possibility of the North Atlantic significantly cooling in the near future is very low.”
How do scientists know about the past climate? In some cases, the climate record is preserved in ice cores. In a 2021 research study, WHOI glaciologist Sarah Das and colleagues investigated a 140-meter long cylinder of ice from a mountain range in coastal Greenland. They found that periods of rapid warming over the past 2,000 years actually caused more snow to fall in west Greenland, causing some coastal glaciers to expand.
WHOI glaciologist Sarah Das conducting fieldwork in Greenland (Photo by Chris Linder, © Woods Hole Oceanographic Institution)
“Now we’re past the tipping point. The rapid warming of the past century is accelerating glacier melting so much that the ice caps are shrinking rather than growing,” says Das. “These coastal records are a clue to just how much we’ve already switched the state of the climate system.”
The trajectory of Earth’s orbit is very slowly shifting the Northern Hemisphere away from the summer sun, Gebbie says, so that could help preserve some Arctic ice. But despite this trend–and geological evidence of minor planetary cooling over the last four thousand years–the signs don’t point to an actual glacial period.
“Those changes are very slight, much smaller than what we’ve seen over the last five decades,” Gebbie points out. Based on the growth of ancient marine creatures buried in ocean sediment, Gebbie says these changes likely reflect fluctuations in summertime temperatures rather than Earth’s average temperature.
For those who look to the possibility of an impending Little Ice Age to counterbalance the impacts of human-induced climate change, the scientists say, be careful what you wish for.
“The ocean is acting to slow down global warming now. But even after we figure out a way to decarbonize our economy, the ocean will continue the warming trend because the heat is already in the pipeline,” Gebbie says. “All the evidence we have so far is that the rate we’re changing the planet is greater than what the Earth can account for. It moderates on time scales way beyond our lifetimes.”