ENVIRONMENT

Call it the Great Gulf Stream Slowdown: An Atlantic Ocean current that helps regulate the global climate has reached a 1,000-year low, according to two new studies. (NPR)

Use our video resource to help students better understand how the Gulf Stream and other ocean currents contribute to climate.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

• Two new studies document the weakening of the mighty Gulf Stream. What is the Gulf Stream?
  • The Gulf Stream is a warm, fast-moving surface current that starts in the Gulf of Mexico and travels along the eastern coast of the U.S. and Canada before crossing the North Atlantic Ocean. In the North Atlantic, the Gulf Stream splits into two currents: the northern North Atlantic Drift and the southern Canary Current.
  • The Gulf Stream contributes to Earth’s climate.
    • Find the currents of the warm Gulf Stream in our MapMaker Interactive’s ocean currents layer. Compare the temperature of the waters impacted by the Gulf Stream in the Northeast Atlantic with waters at similar latitudes in the Northwest and Northeast Pacific.
    • The Gulf Stream is part of the Atlantic meridional overturning circulation (AMOC). As warm Gulf water approaches the North Atlantic, it cools, releasing its heat to the atmosphere. (Due to this process, AMOC is at least part of the reason why Western Europe enjoys such temperate weather.) As it cools, the water becomes more salty and dense, and sinks (overturns) to the bottom of the ocean.
    • The Gulf Stream and AMOC are part of the larger process of thermohaline circulation, often nicknamed the “ocean conveyor belt.” The ocean conveyor belt describes the interaction of surface currents like the Gulf Stream and deep, slow-moving underwater currents across all ocean basins. These interactions mix ocean waters, salts, and even organisms on a global scale. As ocean temperature and density contribute to temperature change in the atmosphere, the ocean conveyor belt also contributes enormously to climate on our planet.

• What do scientists mean when they say the Gulf Stream has “weakened” over the past 1,000 years?
  • By “weakened,” scientists mean the Gulf Steam has slowed down. According to the new research, the current has slowed 15% since the mid-20th century. In the words of the Washington Post, “That’s a decrease of 3 million cubic meters of water per second, the equivalent of nearly 15 Amazon rivers.”
    • Scientists in one study traced the velocity of the current by collecting ocean sediment and measuring the size of the grains “to determine how the strength of the current has changed. Larger grains mean a faster flowing current.” The results document the Gulf Stream is not strong enough to transport larger grains of sediment.
    • Scientists in the other study assessed temperature changes using thermometer data collected over the past 120 years. The results document a general warming of the current in the North Atlantic.

• Why do scientists think the Gulf Stream is slowing?
  • anthropogenic climate change. Both papers acknowledge the impact of carbon emissions and our warming climate on the ocean conveyor belt.
    • Temperature rise caused by excess greenhouse gases in the atmosphere accelerates ice melt in the Arctic. This is largely due to two feedback loops. Consult and download our spectacular graphic to better understand these processes.
      • 1. Warm air holds more water vapor, creating more clouds and trapping even more heat in the Arctic atmosphere.
      • 2. Dark surfaces such as open water and bare ground absorb heat much more readily than ice and snow. Melting ice exposes more dark surfaces.
    • What does global warming have to do with the Gulf Stream? Increased meltwater from sea ice, icebergs, and, especially, the massive Greenland ice sheet, are gushing into the cold, dense North Atlantic and disrupting the flow of the Gulf Stream.
      • “A key part of the overturning circulation, this AMOC, is the formation of dense water,” says geologist David Thornalley. “The problem is that freshwater isn’t very dense and it stops you forming those dense waters.”
    • The papers do differ in their interpretations about how the Great Gulf Stream Slowdown got it start. The slowdown began in the mid 19th-century, which coincides with both the end of the “Little Ice Age” and the start of the Industrial Revolution. One paper links the slowdown with natural adjustments to the warming climate. The other paper links the slowdown with the burning of fossil fuels associated with the technology of the Industrial Revolution.

• Why is the slowing of the Gulf Stream cause for concern?
  • As seemingly every article on this topic mentions: Have you seen the movie The Day After Tomorrow? The plot for that film is the breakdown of AMOC—even the trailer mentions how “polar melting might disrupt the North Atlantic current.” Commenting on the film, Thornalley (the geologist) says “The basics of the science were portrayed correctly … ‘Obviously it was exaggerated – the changes happened in a few days or weeks and were much more extreme. But it is true that in the past this weakening of Amoc happened very rapidly and caused big changes.’”
  • Any changes to the Gulf Stream and AMOC could impact infrastructure in eastern North America, Canada, and western Europe.
    • With reduced release of heat into the atmosphere of the North Atlantic, climate in Western Europe could become much more erratic.
    • “The circulation is also critical for fisheries off the U.S. Atlantic coast, a key part of New England’s economy that have seen changes in recent years, with the cod fishery collapsing as lobster populations have boomed off the Maine coast.”
    • A slowdown of the Gulf Stream contributes to sea level rise. Sea level rise impacts housing and industry.
    • Biodiverse ecosystems such as coral reefs and deep-sea sponge grounds depend on ocean circulation to “supply their food and disperse their offspring.”
    • Upwelling, the process that brings cold, nutrient-rich seawater to the surface, is impacted by weakened currents. A slowdown of upwelling and the ocean conveyor belt would radically impact marine food webs around the world.

TEACHERS TOOLKIT

NPR: Atlantic Ocean Current Slows Down To 1,000-Year Low, Studies Show

Washington Post: The oceans’ circulation hasn’t been this sluggish in 1,000 years. That’s bad news.

The Guardian: Gulf Stream current at its weakest in 1,600 years, studies show

Nat Geo: Ocean Currents and Climate video resource

Nat Geo: Ocean Surface Currents map layer