When Dr. Ted Scambos, a senior research scientist at the National Snow and Ice Data Center at the University of Colorado Boulder, and co-authors first announced they had found the coldest temperatures on Earth — temperatures of up to minus 93 degrees Celsius (minus 135 degrees Fahrenheit) in several spots on the East Antarctic Plateau — five years ago, they determined that persistent clear skies and light winds are required for temperatures to dip this low. But the team’s new study, published in the journal Geophysical Research Letters, adds a twist to the story: not only are clear skies necessary, but the air must also be extremely dry, because water vapor blocks the loss of heat from the snow surface.
The East Antarctic Plateau is a windswept desolate expanse the size off Australia with few bases or instruments. Image credit: Ted Scambos, National Snow and Ice Data Center / University of Colorado Boulder.
The high elevation of the East Antarctic Plateau and its proximity to the South Pole give it the coldest climate of any region on Earth.
The lowest air temperature ever measured by a weather station, minus 89.2 degrees Celsius (minus 129 degrees Fahrenheit), was recorded there at Vostok Station on July 23, 1983. But weather stations can’t measure temperatures everywhere.
So in 2013, Dr. Scambos and colleagues decided to analyze data from several Earth-observing satellites to see if they could find temperatures on the plateau even lower than those recorded at Vostok.
In the new study, the team analyzed satellite data collected during the Southern Hemisphere’s winter between 2004 and 2016.
The researchers used data from MODIS instruments aboard NASA’s Terra and Aqua satellites as well as data from instruments on NOAA’s Polar Operational Environmental Satellites.
They observed snow surface temperatures regularly dropping below minus 90 degrees Celsius (minus 130 degrees Fahrenheit) almost every winter in a broad region of the plateau, more than 3,500 m (11,000 feet) above sea level.
Within this region, they found dozens of sites had much colder temperatures: nearly 100 locations reached surface temperatures of minus 98 degrees Celsius (minus 144 degrees Fahrenheit).
Shaded relief map of the East Antarctic Plateau with red-yellow-blue color scale indicating occurrences of thermal emission surface temperatures below minus 90 degrees Celsius; small circles indicate nearly 100 regions where observed temperatures of below minus 98 degrees Celsius have occurred, with circle size scaled to number of occurrences. Image credit: Scambos et al, doi: 10.1029/2018GL078133.
The atmosphere in this region can sometimes have less than 0.2 mm total precipitable water above the surface.
But even when it is that dry and cold, the air traps some of the heat and sends it back to the surface. This means that the cooling rates are very slow as the surface temperatures approach the record values.
Conditions do not persist long enough — it could take weeks — for the temperatures to dip below the observed records.
However, the temperature measured from satellites is the temperature of the snow surface, not the air above it.
So the study also estimated the air temperatures by using nearby automatic weather stations and the satellite data.
Interestingly, even though the coldest sites were spread out over hundreds of kilometers, the lowest temperatures were all nearly the same.
That got the study authors wondering: is there a limit to how cold it can get on the plateau?
Using the difference between the satellite measurements of the lowest surface snow temperatures at Vostok and three automated stations, and the air temperatures at the same place and time, they inferred that the air temperatures at the very coldest sites (where no stations exist) are probably around minus 94 degrees Celsius (minus 137 degrees Fahrenheit).
“In this area, we see periods of incredibly dry air, and this allows the heat from the snow surface to radiate into space more easily,” Dr. Scambos said.
“The record of minus 98 degrees Celsius is about as cold as it is possible to get at Earth’s surface.”
“For the temperature to drop that low, clear skies and dry air need to persist for several days. Temperatures could drop a little lower if the conditions lasted for several weeks, but that’s extremely unlikely to happen.”
The scientists also developed a set of instruments designed to survive and operate at the very coldest places through the winter and measure both snow and air temperatures.
They are planning to deploy the instruments in the next year or two, during the Antarctic summer when the temperatures are a comparatively mild minus 30 degrees Celsius (minus 22 degrees Fahrenheit).
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T.A. Scambos et al. Ultra-low surface temperatures in East Antarctica from satellite thermal infrared mapping: the coldest places on Earth. Geophysical Research Letters, published online June 25, 2018; doi: 10.1029/2018GL078133
