Will melting glaciers cool the climate?

Ocean currents and global climate are closely interconnected. Global climate change can alter ocean currents, while at the same time, changes to major ocean currents can have dramatic and cascading effects on regional and global climate.

In the North Atlantic Ocean, warm surface water from the equator flows towards the Arctic. As it travels north, the warm water cools, becomes denser, and ultimately sinks and flows back towards the equator. By transporting warmth to northern latitudes, this “conveyor belt” circulation pattern—known as the Atlantic Meridional Overturning Circulation, or AMOC—tempers high-latitude climates that otherwise would be uninhabitable. 

But today’s rapidly changing climate could disrupt the AMOC. As anthropogenic greenhouse gas emissions increase atmospheric temperatures, glaciers and ice sheets are melting at accelerated rates. Complex climate models show that if enough fresh meltwater floods the surface ocean in the North Atlantic, it could slow the conveyor belt, cooling much of the Northern Hemisphere.

WHOI post-doctoral scholar Simon Pendleton is studying how long-ago flooding of large glacial lakes impacted ocean circulation and climate in the past, to predict how present-day glacial melt could alter currents and climate now and in the future. About 13,000 years ago, the climate began to warm, and the ice sheet that once covered much of North America retreated northward. Large meltwater lakes formed along the ice edge, periodically draining huge amounts of freshwater into the North Atlantic. 

Working with WHOI scientists Alan Condron, Jeffrey Donnelly, and Mark Kurz, Pendleton is drilling into lakebeds in northwestern New York state to collect sediment cores, which provide clues to the dates of those catastrophic floods. Using that chronology, estimates of flood volumes, and a global ocean circulation model, Pendleton is testing whether or not floods from melting glaciers could have slowed ocean circulation and cooled the Northern Hemisphere at the end of the last ice age. His results will provide critical context to help predict whether current warming and glacial melt will have similar impacts in this century.