The maximum extent of sea ice in Antarctica is expected to have reached a negative record this year since records began, according to US authorities. Ocean extent fluctuates greatly throughout the year, typically reaching its minimum in February and its maximum in September.

According to satellite images this year, the largest ice cover of 16.96 million square kilometers was probably reached on September 10th. This is the lowest value for this so-called maximum expansion in 45 years, as the US space agency NASA announced. For comparison: the average value for the years 1981 to 2010 is 18.71 million square kilometers.

The extent this year is more than one million square kilometers below the previous record low of 1986, said the US National Snow and Ice Data Center (NSIDC) at the University of Colorado in Boulder. It works with NASA.

The current measurements are preliminary and could still be revised, NASA and the NSIDC said. The reason is persistent winter conditions that could further increase the extent of the ice, according to the NSIDC. The final analysis should be published at the beginning of October.

What is the reason?

Both NSIDC and NASA give no reason for the small expansion. Experts say it’s unclear whether this is primarily due to man-made climate change – or rather natural variability.

The Alfred Wegener Institute recently wrote that significant deviations from the long-term average had already been observed. Compared to the Arctic, the Antarctic Sea has a greater range of maximum and minimum extent, largely due to geographical differences between the two regions. Nevertheless, the current small extent of Antarctic sea ice is unusual.