Government scientists are not only blaming global warming for the centuries-long collapse of western Antarctic ice sheets, but global warming is also being blamed for record levels of sea ice in the south pole.
Antarctica sea ice extent set another record this week, reaching 815,448 square miles above normal, breaking a record set this past weekend 800,776 square miles above normal ice coverage.
These two records set within a week of one another shattered the previous ice extent record of 710,428 square miles above average that was set back on December 20, 2007.
But record-breaking ice coverage still worries scientists who argue that it’s being caused by global warming.
“The primary reason for this is the nature of the circulation of the Southern Ocean — water heated in high southern latitudes is carried equatorward, to be replaced by colder waters upwelling from below, which inhibits ice loss,” Mark Serreze, director of the National Snow and Ice Data Center, told author Harold Ambler in an email.
“Upon this natural oceanic thermostat, one will see the effects of natural climate variations, [the rise] appears to be best explained by shifts in atmospheric circulation although a number of other factors are also likely involved,” Serreze told Ambler, who blogs about global warming.
Serreze’s response confused Ambler, who asked him to clarify over the phone what exactly was causing the ocean to warm up. “Was it, simply, global warming?” Ambler asked.
“Exactly!” Serreze responded.
NASA scientist Walt Meier said that growing Antarctic sea ice coverage is less significant a measure than declining Arctic sea ice coverage. Ambler reported that Meier even discounted global sea ice extent as a useful climate indicator.
“While the Arctic has seen large decreases through the year in all sectors, the Antarctic has a very regional signal – with highs in some areas and lows in others,” Meier said last year. “And of course, the Arctic volume is decreasing substantially through the loss of old ice. The Antarctic, which has very little old ice, hasn’t much of a volume change, relatively speaking.”
“A plot of global sea ice is just not informative or useful,” Meier said.
Many scientists have been sounding the alarm on Antarctica despite the record levels of sea ice in the region. Last year, Dutch researchers argued that global warming was causing Antarctic sea ice to expand because “cool freshwater from melt beneath the Antarctic ice shelves has insulated offshore sea ice from the warming ocean beneath,” according to the Herald Sun newspaper.
“Against the background of global climate warming, the expansion of Antarctic sea ice is an exceptional feature, which seems to be associated with decreasing sea surface temperatures in the Southern Ocean,” wrote scientists with the Royal Netherlands Meteorological Institute in the journal Nature Geoscience.
“We predict that this mechanism will be a sizable contributor to the factors that regionally and seasonally offset greenhouse warming and the associated sea ice retreat,” the scientists wrote.
More recently, scientists have focused on collapsing ice sheets in western Antarctica. In May, NASA scientists told reporters that west Antarctic glaciers had gone into “irreversible retreat” which could raise sea levels between 10 and 13 feet.
“Today we present observational evidence that the [ice sheet] has gone into irreversible retreat,” said Eric Rignot, the lead author of a study claiming the western Antarctic was collapsing. “It has reached the point of no return.”
Researchers at the University of Washington corroborated Rignot’s findings by using computer models to determine the western Antarctic ice sheet was collapsing — though the collapse would occur over centuries, between 200 to 900 years.
“Our simulations provide strong evidence that the process of marine ice-sheet destabilization is already under way on Thwaites Glacier, largely in response to high subshelf melt rates,” wrote the University of Washington scientists in their study published in the journal Science. “Similar behavior also may be under way on neighboring Pine Island Glacier.”
But past studies have shown the Antarctic glacier collapses are nothing new. The British Antarctic Survey (BAS) put out two studies in the past year showing that Antarctica has gone through similar periods of glacier collapse in the past.
A BAS study from February 2014 shows that 8,000 years ago Antarctica’s Pine Island glacier thinned just as quickly as it has in recent decades — thousands of years before massive amounts of man-made carbon dioxide emissions were released into the atmosphere.
Not only did the Pine Island glacier melt rapidly in the past, it was also able to naturally reverse the melting.
Another BAS study from last year argued the current melt in the western Antarctic is within the “natural range of climate variability” of the last 300 years.
“The record shows that this region has warmed since the late 1950s, at a similar magnitude to that observed in the Antarctic Peninsula and central West Antarctica,” said a BAS study published in the journal Geophysical Research Letters, “however, this warming trend is not unique.”
“More dramatic isotopic warming (and cooling) trends occurred in the mid-19th and 18th centuries, suggesting that at present the effect of anthropogenic climate drivers at this location has not exceeded the natural range of climate variability in the context of the past ~300 years,” the study continued.
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