Past warming in the Arctic related to the changing winds of Antarctica

In the Earth's past, there are no precise badogues of the rapid warming the world is facing as a result of increasing levels of greenhouse gases in the atmosphere. However, certain periods in Earth's history can reveal valuable details about how different parts of the climate system react and interact.¹. The periods of significant and abrupt warming in the Arctic that occurred episodically during the last ice age (about 115,000 to 11,700 years ago) are particularly interesting. These climate changes are known as the Dansgaard – Oeschger events and have caused temperatures in Greenland to rise by more than 10 ° C in a few decades.². On page 681, Buizert et al.³ report that these events have altered the position of the westerly winds on the southern hemisphere – a finding that has implications for global ocean circulation and atmospheric carbon dioxide.

Recent warming events in the northern hemisphere offer researchers a way to address fundamental questions in climatology. In particular, how do climate changes from one hemisphere affect that of the other? And how and at what rate do these changes spread? The connection between the hemispheres is important for determining how energy moves in the Earth's system and modifies the climate in different parts of the globe.

The simplest model for explaining the observed relationships between Greenland and Antarctic temperatures during the Dansgaard – Oeschger events is the movement of "bipolar alternating current swing" between the hemispheres of the global ocean.⁴. In this model, the temperature of Greenland suddenly shifts into its warm phase when the traffic flips (the ebb of surface waters in the depths of the ocean) in the North Atlantic Ocean accelerates. This adjustment of ocean circulation concentrates heat in the northern hemisphere and causes a gradual cooling of the Antarctic. It takes about 200 years for ocean changes in the North Atlantic to begin to affect the temperature of Antarctica⁵. This shift reflects the time required for accumulated energy to penetrate north of the current around Antarctica and begin to be absorbed by the subsurface levels of the global ocean.⁶.

The opposite occurs when the reverse circulation in the North Atlantic slows or stops, resulting in Greenland's rapid transition to a cold state similar to that badociated with an ice age. It is again about 200 years from the time this rapid change occurs in the Arctic to the onset of warming in the Antarctic. The longer the cold persists for a long time in Greenland, the more Antarctic warms up thanks to this sawtooth mechanism of the deep ocean⁷.

But this is not the complete story. The atmosphere also provides a means by which climate signals propagate between the hemispheres, much faster than by the ocean. The phenomena of brutal warming in the Arctic are causing the meteorological equator – a band of tropical storm clouds that surrounds the globe near the equator – farther north and with it , rainfall patterns badociated with the Asian summer monsoon. In 2017, a reinterpretation of isotopic water signals in an Antarctic ice core revealed an almost instantaneous reaction of atmospheric circulation to changes in the Arctic climate during the most recent ice age, from the south to the west of Antarctica.⁸. However, it is unclear whether this response occurred across the southern hemisphere or whether it was a more localized location.

Buizert and his colleagues present the first evidence at the Antarctic scale of a rapid atmospheric coupling of the position of the westerlies around the entire Southern Ocean to climatic events abrupt past of the Arctic (Fig. 1). The identification of these generalized fluctuations in wind position, which occurred tens of thousands of years ago, in a decade, required the precise timing of ages for the ice cores of the Whole of the Antarctic continent.

The age of the ice cores of Greenland has been linked to that of Antarctica using the methane composition of bubbles in the ice core extremely well resolved ice sheet fracture of the & cal cal car;;;;;;;;;;;;;;. West Antarctic.⁵. Atmospheric methane is rapidly mixed in the hemispheres and can therefore be considered globally synchronous. Past fluctuations in methane abundance mimicked the abrupt changes in temperature in Greenland and thus allowed accurate interrogation of the timing of climate events between the Arctic and the Antarctic.

Buizert et al. took the next step by synchronizing the recording of the division of the Western Antarctic Ice Sheet with four other Antarctic ice cores by identifying the characteristic sequences of volcanic eruptions preserved in the sulphate levels of the Antarctic ice. It was only then that the authors were able to identify the superimposed oceanic and atmospheric signals that occurred in Antarctica in response to the past rapid changes in the Arctic climate.

The clbadic heat swing between the hemispheres across the ocean may account for the delayed and gradual changes in Antarctic temperature that have accompanied the sudden changes in Greenland temperature. But the study by Buizert and his collaborators suggests that these small oceanic changes were superimposed on an almost synchronous movement of the west winds around Antarctica as Greenland entered its warm phase – and conversely, that these winds blew from south to south events. This atmospheric reaction modulated the latitude in the Southern Ocean which was the source of the moisture that fell as snow on the Antarctic.

An unambiguous relationship has already been identified between the duration of temperature events in Greenland and the magnitude of the resulting thermal response in Antarctica through the oceanic mechanism.⁷. Likewise, the authors found that the atmospheric response seemed to be staggering so that more severe events in Greenland would result in a greater weather signal in Antarctica and the Southern Ocean. An atmospheric link linking changes in the Arctic climate to Antarctica has already been hypothesized based on responses of climate models in experiments designed to mimic Dansgaard – Oeschger 's events.⁶. Current work provides observational data to prove the existence of this link.

It is time to no longer consider the Atlantic Ocean and the lag of a century with time when thinking about climate links between the Arctic and Antarctic.⁵. The identification by Buizert and colleagues of a rapid atmospheric link between climates at the poles has implications for our understanding of current climate change. Today, the Arctic is warming about twice as fast as the world average. however, warming at the continental scale of Antarctica predicted by climate simulations has not yet been clearly observed^9,ten. Changes in Antarctic sea ice do not meet model-based expectations either^ten. Meanwhile, the westerly winds of the southern hemisphere have shifted rapidly south, affecting the security of water supply in cities such as Perth Australia and Cape Town in Africa from the South, and may have global consequences by altering heat and carbon dioxide movements between the atmosphere and the climate. l & # 39; Ocean¹¹.

Much more needs to be done to accurately predict how and how fast Antarctic and Southern Ocean behavior will change under global warming. Nevertheless, the authors hinted at the natural changes in behavior – fast and slow – that occurred tens of thousands of years ago. These results provide a foundation for progress in solving the current scientific mysteries of how the ocean and the atmosphere at the poles respond to rapid climate change.