A microcosm of climate

By | Science & Technology
The Antarctic.Credit@NASAonthecommons

New insights into why the Antarctic has evaded the warming seen in the Arctic have been discovered. Currents which cross the Earth transport heat to the Antarctic which appears hundreds of years later.

In the last few years the Earth has been radically warming as a result of natural cycles and human influences. However, Climate scientists consistently point to the Antarctic as evidence contrary to this theory. This is because the Antarctic has experienced little warming in recent years and in certain periods may have actually gained sea ice. This has been a dilemma for scientists and an answer to why this occurs was essential. Attempts to understand these phenomena have focused on the Earth’s ocean currents. In particular, the different layers of water with different properties (eg, salinity, oxygenation, density and temperature) which form barriers to mixing with other layers. The warmest and densest water remains at greater depths confined by these barriers which may have the effect of reducing the upward motion of heat to the atmosphere.

Furthermore, increasing CO2 emissions are believed to be at least partly responsible for the strengthening of the sub polar westerlies cordoning off the Antarctic’s micro-climate from the rest of the planet. This Antarctic circumpolar current prevents warm water from entering Antarctica and therefore allows sea ice to be either maintained or increased. Very little heat is stored locally and the majority is transported to the north. About half of this heat originates from the convergence of currents and at low latitudes experiences an anomalously strong northward transport in comparison to mid-high latitudes where reduced heat movement is seen.

To further explain this, a new study by Armour and colleagues highlights the causes of the rapid warming of the Arctic and the very gradual warming of the Antarctic. Using tracing methods, the team demonstrated how seawater with the most warming from climate change tends to accumulate around the North Pole. The northern flank of the Antarctic circumpolar current was shown to have warmed substantially confirming previous findings. This is explained by the Southern ocean’s meridional overturning circulation, amplified by greenhouse gas forcing; this process occurs on a centennial timescale with warmth stored and released up to one thousand years later.

The increased absorption of energy from the sun may drive these processes as almost all of the energy which affects the climate is originated from the sun. “With rising carbon dioxide you may expect more warming at both poles, it is only seen at one of the poles, so something else must be going on,” said lead author Kyle Armour. “It’s for really simple reasons and ocean currents are the hero here.” “The Southern Ocean is unique because it’s bringing water up from several thousand meters,” Armour said. “It’s deep, past water which is coming up to the surface, all around the continent. You have a lot of water coming to the surface which has had little contact with the atmosphere for hundreds of years.”

Clearly an explanation for this anomaly has been imperative. The observations may further explain the independent weather conditions seen presently in both hemispheres. Recently the northern hemisphere has experienced significant warming followed by cooler and wetter conditions, influenced by the Arctic. The southern hemisphere has seen increasing temperatures and drier drought-like conditions in the last few years, however the Antarctic’s climate has remained near normal and fluctuations in levels of sea ice have been modest compared to the Arctic. “The oceans are acting to enhance warming in the Arctic while damping warming around Antarctica,” said Armour. “Comparisons of warming at the poles are unrealistic, because it’s occurring on top of different ocean circulations.”

The data may still support the theory of global warming if seen in this context. The heat stored around the Antarctic might be released in years to come, having temporary effects on the global climate and inducing a reversal of regional climate. “Climatologists are moving away from this idea of global warming and more toward the idea of regional patterns of warming, which are strongly shaped by ocean currents,” Armour said.

Why does heat accumulate in the Arctic?

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