What's Causing The Tropics To Expand So Quickly?


Robin Andrews

Science & Policy Writer

The expansion of the tropics isn't a good thing, for the most part. Stephane Bidouze/Shutterstock

Climate change is a complex antagonist. Apart from warming the planet and making plenty of natural disasters more potent, it will also create 2 billion climate change refugees, make wine more expensive and taste worse, cause methane bubbles beneath Siberia to explode, and move the North Pole – geographically speaking – to Europe.

As pointed out by Steve Turton, an adjunct professor of environmental geography at CQUniversity Australia, the tropics are set to expand as well, and at a remarkable rate. This, dear readers, is not a good thing.


At present, the tropics are defined as being between 30 degrees north and 30 degrees south of the Equator. Within this roughly defined zone, temperatures are high all year round, and you get both wet and dry seasons featuring thundering rainstorms and sweltering arid conditions, respectively.

On either side of the tropics, you have perma-dry subtropical regions that receive little rainfall. This is where the most expansive and harsh deserts of the world can be found – not including the icy equivalents at the poles, of course.

The tropics are not static, mind you. As Turton points out in his piece for The Conversation, since 1979, something is causing them to expand at a remarkable rate of 56 to 111 kilometers (35 to 69 miles) per decade. By 2100, the expansion will be about 850 kilometers (528 miles), which is the same distance from Rome to London, or from central Florida to North Carolina.

This means that the subtropical zones are also being pushed both northwards and southwards, which will cause an expansion of these dry deserts. In an understandably Australian-centric extrapolation, Turton explains that this new arid region would also stretch between Sydney and Perth, making Australia an even drier continental land mass than it already is.


Much of Africa will experience prolonged heat waves and severe droughts. Water will become sparse, agriculture will fail, economies will crash, and incidences of conflict will increase.

The current position of the tropics, with the intertropic zone highlighted in crimson. KVDP/Wikimedia Commons; CC BY-SA 3.0

The science behind this “tropical bloating” is rather enigmatic. The tropics are generally driven by the high levels of sunlight they receive throughout the year, and that doesn’t change regardless of what happens to Earth’s climate, for the most part.

Part of the cause looks to be man-made climate change. The change in heat distribution in the atmosphere is altering the flow of air in the tropics. Massive convection currents called Hadley Cells are bulging outwards, which are dragging along the associated weather patterns with them.

This expansion appears to be accelerated by natural climate cycles too, including a 15-20 year cycle of massively fluctuating Pacific Ocean temperatures.


Both are conspiring to expand the tropics – and the net result is that almost everyone will sadly suffer.

[H/T: The Conversation]


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