Global cooling

As scientists continue trying to sort out exactly how earthly climate works, a group studying the planet’s prehistory has implicated a solidly frozen Bering Strait as a driving force in the arrival of the Ice Age about a million years ago.

One of the biggest environmental shifts in prehistory, the Ice Age has been linked to a drawdown in atmospheric carbon dioxide (CO2) – the colorless, odorless gas now at the heart of climate change concerns about the changes a warming planet could bring.

Human kind’s climate issue has gone from Neanderthal struggles with an atmosphere with too little CO2 to Homo Sapiens fears about an atmosphere with too much of that gas.

The Neanderthals weren’t intellectually advanced enough to worry about it. Homo has advance to the point where we can not only worry about the future, but try to sort out what happened in the past with the hope it might shed light on the what is to come.

Along those lines, a team of researchers from the United Kingdom, the U.S., Japan and Denmark say they don’t know what first disrupted the CO2 equilibrium a million years ago, but they believe based on evidence from sediment samples from the Bering Sea that changes in the sub-arctic Pacific Ocean became the force that sucked so much (CO2) out of the atmosphere that the planet cooled to the point that glaciers surged into what is now the American Midwest or, as the region has proposed rebranding itself, North.

A peer-reviewed study was published in Nature Communications this week. It is titled simply “Closure of the Bering Strait caused Mid-Pleistocene Transition” but there is nothing simple about the paper. Most laymen will struggle to get through the highly technical document.

Fortunately, the University of Exeter in Cornwall helped lead author Sev Kender break it down. Kender is the senior lecturer in geology at the British school.

“The subarctic North Pacific is composed of some of the oldest water on Earth, which has been separated from the atmosphere for such a long time that a high concentration of dissolved CO₂ has built up at depth,” he said in a statement prepared by the university. “When this water upwells to the surface, some of the CO₂ is released. This is thought to be an important process in geological time, causing some of the global warming that followed past glaciations.

“We discovered that the Bering Sea region became more stratified during the Mid-Pleistocene Transition (MPT) with an expanded intermediate-depth water mass, such that one of the important contributors to global warming – the upwelling of the subarctic North Pacific – was effectively curtailed.”

The theory is that the decrease in CO2 escaping the northern ocean fundamentally altered the CO2 concentration in the atmosphere. Atmospheric CO2 is in a constant state of flux with significant variations from season to season, year to year, decade to decade, and millennium to millennium.

Living, breathing planet

“For eons, the world’s oceans have been sucking carbon dioxide out of the atmosphere and releasing it again in a steady inhale and exhale,” as the Earth Observatory at the National Oceanic and Atmospheric Administration puts it.

It is a natural process that was ignored for most of history.

Scientists long ago recognized the big, prehistoric swings in global climate, but for a long time those were believed linked solely to the variations in the Earth’s elliptical orbit around the sun.

The thinking was simple: When the planet is farther from the sun, it is colder; and when it is closer to the sun, it is warmer.

But, as with many things in nature, the situation wasn’t quite as simple as it first appeared scientists studying the planet’s prehistoric geology discovered.

When the planet’s northern glaciers grew and overflowed into the mid latitudes in the mid-Pleistocene, there was no orbital shift that could explain what happened. Enter the greenhouse gases: nitrous oxide, methane and CO2. 

Natural byproducts of life on earth, they are constantly escaping into space, but it is a slow process. Their build up in the atmosphere as they try to escape creates the greenhouse effect that slows the escape of heat from solar radiation beating down on the third planet from our sun.

Without greenhouse gases, earth would just be another cold, dead rock hurtling through space. Natural shifts in the concentrations of these gases over time would eventually be implicated in earthly climate shifts from hot to cold.

“As the MPT occurred during a period when there were no apparent changes in the nature of the orbit cycles,” as the Exeter statement put it, “scientists have long been attempting to discover what drove the changes to take place.”

They now believe that they’ve identified one of the big players in the prehistoric chill, if not the trigger, for the CO2 drawdown of the Ice Age.

“Today much of the cold water produced by sea ice action flows northward into the Arctic Ocean through the Bering Strait,”  Kender said. “As glaciers grew and sea levels fell around 1 million years ago, the Bering Strait would have closed, retaining colder water within the Bering Sea.

“This expanded water mass appears to have stifled the upwelling of deep CO₂-rich water and allowed the ocean to sequester more CO₂ out of the atmosphere. The associated cooling effect would have changed the sensitivity of Earth to orbital cycles, causing colder and longer glaciations that characterise climate ever since.

“Our findings highlight the importance of understanding present and future changes to the high latitude oceans, as these regions are so important for long-term sequestration or release of atmospheric CO2.”

The concern today is, of course, the opposite of what it was in the Ice Age when glaciers over ran northern North America and reached all the way into what are now the U.S. states of  Iowa, Nebraska, Kansas, and Missouri.

Minnesota, the state that would now like to become the focal point of the new U.S. “North,” was once lost beneath the Laurentide Ice Sheet.

Though scientists don’t know what started the shift to less CO2 in the atmosphere that led to the Bering Strait freezing shut and helped create the Ice Age, they do believe they’ve found the culprit that has caused a big spike upward in CO2 since the 1700s:

Us.

Cooling versus warming

Carbon dioxide in the atmosphere has been increasing rapidly since near the start of the Industrial Age. The scientific consensus blames the burning of fossil fuels.

Combustion of oil, gas, grass, firewood or anything else burnable produces CO2 as a natural by-product. The belief is that the natural production of CO2 from animals breathing, vegetation decaying, volcanoes exploding and, especially the ocean  venting was in some sort of global equilibrium before humans invented the internal combustion engine and changed everything.

The steady inhale and exhale, as NASA describes the carbon cycle, appears to have become became more of an exhale due to human forcing.

“…Since about 1750…,rates of increase in levels of (greenhouses) gases are dramatic,” the American Chemical Society observes. “CO2, for instance, never increased more than 30 parts per million (ppm) during any previous 1,000-year period in this record but  already risen by 30 ppm in the past two decades.”

Glacial ice cores have allowed chemists to track C02 levels almost 1 million years back in time. What those records show is a cyclic variation from highs of almost 400 ppm to a lows below 200 ppm.

What sparks the swings remains unknown, but the Chemical Society notes the concentrations of all three gases have increased significantly since 1800 and cites the Industrial Revolution.

“The combustion of fossil fuels produces CO2 with a different carbon-isotope signature than the CO2 present in the atmosphere before the Industrial Revolution,” it adds. “The CO2 from combustion has a lower ¹³CO2/¹²CO2ratio. The ¹³CO2/¹²CO2 ratio of atmospheric CO2 has been dropping steadily as the concentration of CO2 has increased over the past half century. This change is strong evidence that human activity, the burning of fossil fuel, is the major cause of the increase in atmospheric CO2.”

Were the planet on the edge of another Ice Age – with the North Pacific primed to become another big CO2 sink – all this manmade CO2 would be a good thing, but just the opposite appears to be happening.

The Arctic is warming and the flow of water into and out of the region is changing. Whether this is a good thing or a bad thing in the moment only underlines the complexity of climate change.

A 2017 study concluded the warming Arctic is poised to release a lot of methane, but also concluded that the surface waters of the region could absorb up to 2,000 times more CO2 than at present.

“…The cooling effect resulting from CO2 uptake is up to 230 times greater than the warming effect expected from the methane emitted,” reported Ocean Carbon & Biogeochemistry.org.

The study would indicate an open Arctic Ocean today might actually help reduce CO2. The situation, as NASA notes, is complicated.

Humans today know a lot more about the atmosphere than the Neanderthals did, but we remain a long way from knowing it all.