Why Is the South Pole Warming So Quickly? It’s Complicated
Remote Antarctica may feel like the most isolated place on Earth. Secluded at the bottom of the world and surrounded by the turbulent Southern Ocean, in many ways it's a step into another world.
But, as it turns out, the icy continent is more closely connected to the rest of the planet than it appears.
The South Pole is warming at a rate nearly three times faster than the global average, scientists have discovered. And much of that warming is linked to climate cycles happening thousands of miles away in the tropics.
The findings were published yesterday in the journal Nature Climate Change.
The study, led by Kyle Clem of Victoria University of Wellington in New Zealand, examined surface air temperatures at the world's southernmost weather observatory: the Amundsen-Scott station, located almost directly on top of the geographic South Pole. It's a lonely, snow-covered outpost in the middle of the Antarctic continent, in a place where winter temperatures can drop below minus 100 degrees Fahrenheit.
The researchers found that temperatures there have been rising by about a degree Fahrenheit each decade since the start of the 1990s. That's about three times faster than the global average.
Even more surprising, the trend represents a sudden reversal in conditions at the South Pole. For much of the 20th century — at least going back to the 1950s, when the weather station was first established — the South Pole was cooling down.
So why the switch? According to the new study, shifting climate patterns in the tropics probably have played a big part.
The researchers used a combination of observations and model simulations to investigate. They found that changing ocean temperatures in the tropical western Pacific have a big influence on warming at the South Pole.
These ocean temperatures are regulated, in large part, by a natural climate cycle known as the Interdecadal Pacific Oscillation, or IPO. The IPO causes western Pacific temperatures to swing back and forth between warm and cool phases every couple of decades or so.
When the ocean is warmer, it interacts differently with the atmosphere. These atmospheric changes transport more warm air south into Antarctica.
The IPO's influence may be further strengthened by yet another natural climate fluctuation, the researchers added. Known as the Southern Annular Mode, this cycle helps regulate a belt of westerly winds flowing around the Antarctic continent. It can cause these winds to periodically strengthen or weaken.
When the winds are stronger, they help push that warm air over Antarctica, heating up the South Pole. The researchers believe the combination of these two natural climate cycles has strongly contributed to the warming over the last few decades.
In fact, the model simulations suggest that the recent warming could — theoretically — have happened without any influence from human-caused climate change at all.
That said, the researchers do believe climate change has played some role in the recent trends.
Global warming is still happening, and in addition to the rising temperatures it's causing around the world, it's also believed to affect some of the atmospheric circulation patterns — such as the westerly winds around Antarctica — that influence temperatures at the South Pole.
As a result, the researchers suggest that human-caused warming likely strengthened the trends observed at the South Pole in recent decades. But in this case, it's probably not the dominant driver.
It's a finding that speaks to the complexity of the Antarctic climate and of how strongly it's influenced by climate cycles in entirely different regions of the world.
Unlike the Arctic, which has been warming at a breakneck speed for decades now, Antarctic climate change has been notoriously difficult to map out. Different regions of the same continent often have experienced vastly different climate trends at the same time.
While the South Pole was cooling in previous decades, for instance, much of West Antarctica and the Antarctic Peninsula — hundreds of miles away — was warming and melting. More recently, as the South Pole has begun to heat up, the warming trend on the peninsula has declined.
Similarly, Antarctic sea ice has exhibited some puzzling trends.
For most of the last 35 years, sea ice in the Southern Ocean was actually expanding. But starting around 2014, this trend reversed. For the past few years, it's rapidly declined, and scientists are still debating the reasons why (Climatewire, July 2, 2019).
"Antarctic climate is riddled with contrasting changes," wrote climate scientists Sharon Stammerjohn and Ted Scambos, both of the University of Colorado, Boulder, in a published comment on the new research.
Scientists have attributed these complex and shifting patterns to various sources, including natural climate cycles like the IPO or El Niño, as well as the complex influence of climate change on oceanic and atmospheric currents around Antarctica.
Often, though, the impact of human-caused climate change is difficult to parse out. There's so much influence from natural climate variability — what scientists might refer to as "noise" in the climate record — that it often obscures any patterns that could clearly be linked to global warming.
The new study illustrates this issue yet again, Stammerjohn and Scambos note.
"This does not mean that anthropogenic climate change is not playing a role in Antarctica, but its role is often masked by high intrinsic variability," they write.
Still, what's happening at the South Pole is not the most worrisome trend in Antarctica. Even though it's rapidly warming, it's still one of the coldest regions in Antarctica and not in any immediate danger of melting away.
The Antarctic coastline, on the other hand, is another story. Much of West Antarctica, in particular, is home to seaside glaciers that appear to be rapidly melting from the bottom up as warm ocean water seeps beneath the ice.
Scientists have stronger confidence in the role of climate change at these coastal spots, and greater concern about how they may affect the rest of the world. Antarctica is a growing contributor to global sea-level rise, Stammerjohn and Scambos note — its impact on the rest of the planet "could potentially be catastrophic."
By Chelsea Harvey