More than 20 years after intoning, “The water’s getting warm, so you might as well swim,” Smash Mouth’s “All Star” continues to be prophetic. Case in point: A new study finds that the Atlantic Ocean just had its hottest decade in at least 2,900 years. Someone award Smash Mouth a PhD and calculate the h-index of their discography immediately.
The new findings, published in the Proceedings of the National Academy of Sciences on Monday, rely on a mix of ice and sediment cores as well as thermometer data to track the state of the Atlantic. The ocean has gone through a well-known up-and-down swing in sea surface temperature, known as the Atlantic multidecadal oscillation. Plotted over hundreds of years, the AMO looks like a pretty steady wave pattern. In its warm phase, it can lead to a greater number of intense hurricanes, while the opposite is true in its cool phase. In addition to hurricanes, the phase of the AMO also influences temperature and precipitation over landmasses both immediately adjacent to the ocean and as far away as India.
So the state of the AMO is big deal, especially knowing where it’s heading in a warming climate. To get a handle on where the AMO has been, the researchers turned to a surprising source: the sediment in a lake on Ellesmere Island in the Canadian Arctic. The region is one of the areas heavily influenced by shifts in Atlantic Ocean temperatures. When the Atlantic runs hot, it creates higher pressure over the region, resulting in thinner snowpack; less snowpack means less sediment runoff.
Researchers were able to analyse titanium in layer upon layer of lake sediment to create a time series of the past 2,900 years of Atlantic Ocean temperatures. The finding show the wave pattern of warm and cool periods extends into the past, including a big dip in the heart of the Little Ice Age that ran from 1300 until about 1860. Since then, it’s been rising steadily up, with a sharp peak in the past few decades.
The scientists also compared parts of the new Canadian Arctic to shorter, higher-resolution sediment cores from other locations, including one from off the southern coast of Iceland that covers the past 230 or so years. That record relies on Turborotalita quinqueloba, a tiny, cold-water-loving shelled creature, as a proxy for temperature. The core shows a drop in their numbers over the past century, with the rate of disappearance speeding up.
Taken together, the results show that “recent Atlantic warming is unparalleled” in at least 2,900 years. There are natural factors that could be influencing the shift, but it’s impossible to not consider the impact of climate change. The hallmark of climate change is heat, especially in the oceans. Marine heat waves have become more common and intense. Findings published just last month show rising heat is causing the oceans to stratify. Arctic sea ice plunged to its second lowest levels on record in September as well, again due to hotter oceans.
The new findings add to the growing tire fire that is the world’s oceans. In the case of the Atlantic, the increasing heat raises concerns about how precipitation patterns could shift in places dependent on rain-fed agriculture, as well as the risk of more intense hurricanes in the basin. Of course, these were always going to be of concern on a rapidly overheating planet, but the new study shows just how far outside the bounds of the past climate we are.