In the southwest Pacific Ocean, there’s a huge region of unusually warm water covering an area about the size of Australia, known as “the Southern Blob.
“Several thousand miles away, the South American nation of Chile has been experiencing a megadrought for more than a decade, with dwindling rain and water supplies.
On the surface, these two events have nothing to do with each other — but, a new study found, they are linked by invisible forces of global atmospheric pressure and circulation.
The Southern Blob, located east of Australia and New Zealand, emerged about four decades ago, likely caused by a naturally-occurring decline in rainfall over the central tropical Pacific. But over time, climate change has made the Blob bigger and hotter, according to the study.
The drop in rainfall affected atmospheric circulation in the region, creating wind patterns that changed how warm and cold currents flow in the ocean — guiding more warm water to the Blob while pushing cold water deeper down.The warm surface water that makes up the Blob then heats the air above it — and as the atmosphere warms, it expands into a “big, broad area of high pressure,” known as a high pressure ridge, said Kyle Clem, co-author of the study and lecturer in climate science at the Victoria University of Wellington.
This ridge, which stretches across the South Pacific, changes the path that storms usually take as they move across oceans, known as “storm tracks.” Because of the ridge, storm systems shifted south toward Antarctica and away from the west coast of South America.
South America’s coastal region — including central Chile, Argentina and parts of the Andes mountains — relies on those winter storms to replenish freshwater supplies before the summer dry season. With the storms now redirected to Antarctica, Chile has been plunged into serious drought conditions since 2010, with widespread damage to the environment and people’s livelihoods.
The study, published Thursday in the Journal of Climate, marks the first time researchers have made a direct connection between the Blob and the megadrought.
This is Chile’s longest drought on meteorological record, according to NASA. The last megadrought of this scale probably took place in the region more than 1,000 years ago, according to René D. Garreaud, a scientist at the University of Chile and one of the study co-authors.
South America had previously seen an overall decline in rainfall going back decades, coinciding with the emergence of the Blob. But it was sporadic — sometimes there would be drought years, and other times plentiful rain.
But global warming has caused the Blob to expand and grow much hotter over the past decade — and the drought has become one continuous, unending stretch. During the winter season in the southern hemisphere, the Blob warms about three times faster than the global average in other parts of the ocean, Clem said.
“So this thing started in the central tropical Pacific, get some warming, the pattern continues for 40 years — then you just have added heat being pumped into it from increasing greenhouse gases,” Clem said. “That’s what has allowed the Blob to reach such extreme rates of warming … which is why we’re seeing a drought that is so unprecedented.
“The prolonged drought has devastated farms throughout Chile, with crop failures and mass deaths of livestock. Reservoirs are at critically low levels, and residents in some rural areas now rely on water deliveries from tanker trucks.
The Blob’s knock-on effects have also been felt elsewhere. Because the shift causes warmer air to move toward the Antarctic, it has caused a reduction in Antarctic sea ice — which in turn threatens the region’s delicate ecosystems, and could have far-reaching consequences in altering global weather patterns.
It’s not clear when or if the Blob will dissipate, which is what Clem and the team plan to study next. The decline in rainfall is expected to taper off at some point — but researchers don’t know whether that will be enough to break apart the Blob, or if it will be sustained by human-caused heat alone.
“One of the most fascinating things about this is, we have this anthropogenic (human-caused) signal in the climate system, which is the Blob, sitting out there in the middle of nowhere,” Clem said. “But because of the way the ocean’s circulations are configured, it has the ability to influence regional climates where huge amounts of people live, tens of thousands of kilometers away.”
“What our study shows is that, with human-induced climate change, what happens in one place does not necessarily stay there.”
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