Full Tilt Towards Global Warming

Human activity is causing the earth’s axis to shift. Should we be worried?

Your car is tilting the planet. Your toaster and television, too, if your electrical utility uses coal- or gas-fired power plants. They’re all contributing to a shift in the Earth's axis by changing the distribution of water in the oceans, according to a new paper in Geophysical Research Letters.

The effect isn't large enough for anyone to worry about – at just 1.5 cm, less than an inch per year, Polaris will still be the North Pole star for a while yet – but as Felix Landerer and Johann Jungclaus, the authors of paper, write, the change is “not negligible in comparison to other decadal and secular signals.”

So, not a major cause for concern in terms of the future of civilization, but more evidence of the influence humans have on the big picture.

In some circles, skepticism over the science of anthropogenic global warming can be linked to the difficulty people have getting their minds around the idea that humans are capable of altering something as big as the planet’s ecosystem. This is understandable considering that for most of our 200,000-year history as a species, our numbers were far too small to have a measurable effect.

But there is evidence that even thousands of years ago, our forest-clearing activities changed regional and even global weather and climate patterns. And now, with nearly 7 billion humans on Earth, the cumulative impact goes well beyond measurable. A recently released analysis by the U.S. National Climatic Data Center has discovered that the world's oceans are warmer now than at any time since data-collection began 130 years ago, with July's 62.5 degrees Fahrenheit beating the 1998 record. While air temperatures have remained relatively stable for the last decade – leading less informed observers to wonder if global warming was just a short-term blip – the finding is an important reminder that global warming continues apace, and that things are little more complicated than whatever your backyard thermometer is telling you.

Warming oceans expand, and gravity ensures that the extra volume is distributed as close to the Earth's centre as possible. The upshot being that the oceans' mass gets shifted around, a phenomenon that can change the speed of the Earth's rotation, and, now we learn, can tilt the planet's axis of rotation.

New Scientist's Rachel Courtland explains that:

The changing climate has long been known to move Earth's axis. The planet's North Pole, for example, is migrating along 79 degrees west – a line of longitude that runs through Toronto and Panama City – at a rate of about 10 centimetres each year as the Earth rebounds from ice sheets that once weighed down large swaths of North America, Europe, and Asia. The influx of fresh water from shrinking ice sheets also causes the planet to pitch over. Landerer and colleagues estimate that the melting of Greenland's ice is already causing Earth's axis to tilt at an annual rate of about 2.6 centimetres – and that rate may increase significantly in the coming years. Now, they calculate that oceans warmed by the rise in greenhouse gases can also cause the Earth to tilt – a conclusion that runs counter to older models, which suggested that ocean expansion would not create a large shift in the distribution of the Earth's mass. The team found that as the oceans warm and expand, more water will be pushed up and onto the Earth's shallower ocean shelves. Over the next century, the subtle effect is expected to cause the northern pole of Earth's spin axis to shift by roughly 1.5 centimetres per year in the direction of Alaska and Hawaii.

The Earth's oceans have been expanding, and therefore rising and falling, by dozens of metres over the eons, and there's nothing unusual in that. Consequently, the axis has been shifting around, too. This is not another catastrophe in the making. But it is a humbling finding, one that should give us pause when we think about our species' place in the universe.