Climate Change and Ocean Currents

The Direct and Indirect Effects of Climate Change on Ocean Currents

When people imagine the system of ocean currents that spans this planet, they tend to picture a flawless arrangement of tides, working like an impeccable machine. Unfortunately, human impact has thrown a wrench into this previously-perfect system. The phenomenon known as climate change, caused by pollution, deforestation, and more, is changing ocean currents in ways that can’t always be reversed. This spells out immediate danger for both mankind and our environment.

For thousands of years, ocean currents have regulated the global climate. Wind-driven currents, like the California current, are especially effective at this. But these currents don’t work by themselves; they rely on the very chemistry of the oceans to function properly. The Global Ocean Conveyor Belt is the official name for this system. It’s driven by the exchange between colder, denser water and warmer, lighter water. Through this system, warm water is brought north, to the Northwestern part of the Arctic Ocean. Once it arrives, it gradually becomes saltier and colder, and therefore more dense. As a result, it sinks to the depths of the ocean, where it travels back south, to the tropics. Normally, this entire trip takes about 1000 years (Casey & Haner).

But now, everything could be changed irrevocably.

Ice Melt

As a direct result of global warming, the Greenland ice sheet is beginning to melt. This impacts coastal cities that might be threatened by rising sea levels, but it also affects ocean currents. So much fresh water flooding into the ocean decreases ocean salinity, making the water sink more slowly and less often. This is damaging because, as previously mentioned, the global current system is dependent on the sinking and rising of ocean water. Without it, ocean currents have already begun moving about 15% slower since just the 1950s (“Spring Coming Earlier: Number of Days”).

Slower currents might not seem like such a big deal, but they can have significant impacts on weather. Because of slower currents, less heat is pushed to the northern parts of the Atlantic ocean. Instead, the heat stays longer in the Western Atlantic, fueling more coastal storms along the East Coast. These coastal storms are more likely to cause flooding, too, since warmer water expands and increases sea levels. Slower currents also mean slower circulation of valuable nutrients, nutrients that boost the growth of seaweed and algae. These plants are the base of many marine food chains. If there is a shortage of seaweed or algae, entire ecosystems could starve (“Spring Coming Earlier: Number of Days”).

But the sudden addition of fresh water doesn’t just slow currents down; it can also speed them up, with disastrous consequences. Take Beaufort Gyre, for instance. For centuries, it’s kept the polar area and the Arctic current in equilibrium. Located just above Canada and Alaska, the gyre spins underneath sea ice, collecting fresh water from seasonal glacial melt, runoff, and precipitation. Because it’s composed of mainly freshwater, it protects the sea ice above it from being affected by the saltwater of the ocean. Typically, it slowly releases its freshwater to the Atlantic ocean (“Arctic Ice Melt Is Changing Ocean Currents”).

Since the early 1990s, however, the Beaufort Gyre has been strongly impacted by the melting of land ice, and its behavior has been anything but typical. In the past 30 years, it’s been flooded with a volume of freshwater twice the size of Lake Michigan. So much added water makes the gyre spin faster and become more turbulent, beating against the ice above it. As a result, the ice melts, leaving the gyre vulnerable to the wind, which just makes it spin even faster (“Arctic Ice Melt Is Changing Ocean Currents”).

And the polar winds haven’t been acting typically as of late, either. Usually, these winds change direction every five to seven years. Currently though, they’ve been westerly for over 20 years. Scientists have yet to find an exact answer to why this is happening, but they suspect pollution has impacted the winds. These strong westerly winds drag the current clockwise, increase its size, and force it to move even faster. Since the water is circling so quickly, it’s prevented from being released to the Atlantic (“Arctic Ice Melt Is Changing Ocean Currents”).

The winds add so much energy to the Beaufort Gyre that the energy has to be expelled in some way: eddies. Eddies are circular movements of water, usually formed to counter the main current. These particular eddies balance the system from being overrun with so much kinetic energy. However, they also have their consequences. Because they mix fresh water with the warmer salt water, they lead to further sea ice melt. In essence, there’s a vicious cycle at play here: first, sea ice melts, exposing the gyre to more wind; then, as a result of the wind, the gyre becomes stronger, moves quicker, and forms eddies; then, more sea ice melts, starting the whole cycle over again (“Arctic Ice Melt Is Changing Ocean Currents”).

What will happen at the end of all of this? There isn’t necessarily a simple answer. If the winds were to change direction now, after so long of being westerly, the current would reverse and release all the freshwater it’s accumulated since the 90s to the Atlantic. This would slow the Atlantic current system, called the Atlantic Meridional Overturning Circulation, drastically. Without this system, heat wouldn’t be carried from the tropics to Northern Europe and North America. So much heat trapped in the tropics would undoubtedly affect marine life and change usually-predictable weather patterns (“Arctic Ice Melt Is Changing Ocean Currents”).

The Galápagos Islands

To predict what would happen if the tropics were exposed to more severe heat and more extreme weather events, scientists can only examine what happened in the past. One particularly prime example of these studies took place in the Galápagos.

The Galápagos islands are renowned for their diverse wildlife and unique history. They are kept relatively cool and rainless even though they lie along the equator, a characteristic attributed to the Humboldt current. This current is what allows the islands to be classified as subtropical, meaning penguins and corals can coexist. The islands are also cooled by the Antarctic current, which brings the islands nutrients and fish. However, these islands also have the potential to be destroyed by climate change (Casey & Haner).

The Galápagos lies at the intersection of three major ocean currents: the Cromwell current, the Humboldt current, and the Panama current. They’re also at the “crosshairs” of El Niño, a natural weather phenomenon that causes “rapid extreme ocean heating across Eastern Pacific Tropics” (Casey & Haner). Typically, this isn’t extraordinarily dangerous. A normal El Niño heats up the ocean by about 2.6℉ in a matter of months, causes a few storms and flash floods, then leaves. It’s usually followed by La Niña, which cools off the islands (Casey & Haner).

Now, climate change is changing El Niño, and not for the better. Because of global warming, air is hotter, and can hold more moisture at one time. This accelerates the water cycle, making tropical storms and weather phenomena like El Niño stronger and more frequent. The effects of this could be witnessed in 1982 when the strongest El Niño to date hit the Galápagos. As a result of the warmer waters, nutrients from the cold, more dense water were blocked from rising to the surface. This meant that many marine organisms faced starvation. Many marine iguanas died. Even with an adaptation that allowed them to reabsorb parts of their skeleton and become smaller, there just wasn’t enough food in the warmer waters for them to survive. Galápagos penguins stop trying to breed once temperatures reach about 77℉, so their population decreased dramatically; about 8 out of every 10 penguins died. Flightless cormorants, a seabird species native to only the Galápagos, stopped leaving their nests to look for food, instead staying at their nests to preserve energy. Sea lions, the Galápagos damsel, and countless other species also experienced extreme drops in their population as a direct result of the warmer waters (Casey & Haner).

The 1982 El Niño did more than starve ocean creatures; it also caused stronger storms, which had their own impacts. These chaotic storms flattened forests of scalesia, or giant daisy trees. This in of itself wasn’t too extraordinary; the forests are naturally destroyed by El Niño on a regular basis, as a part of a natural cycle. This frees up space and allows the next generation of trees to take root. However, because of the heat, invasive species were thriving in the Gálapagos. An invasive species of blackberry bushes blocked the young generation of daisy trees from growing, leading to a drastic decrease in the scalesia population. And blackberry species weren’t the only invasive species to thrive in the unnatural heat of the Galápagos. The Fowler’s Snouted Tree Frog ate native insects and invertebrates. Worse, the fire ant ate the eggs and the eyes of giant tortoises. Scientists fear that, as climate change continues, more and more invasive species will be taken to the Galápagos to thrive and take over (Casey & Haner).

A lot of these effects of climate change are caused by the colder waters, containing important nutrients, being kept down by the less dense, warmer waters that global warming brings. But why do colder waters have more nutrients? This might seem counterintuitive—wouldn’t more nutrients and plants grow in the warm, sunny ocean surface?—but there’s actually an important reason why this is not the case. When organisms in the ocean die, they slowly sink down to the bottom, where the water is naturally colder. As they drift downwards, they break down into their core organic materials, a process called rematerialization. This way, when the currents bring these colder waters to the surface, they’re full of organic nutrients and compounds. In summary, it’s not that colder waters inherently have more nutrients; it’s that deeper waters do, and deeper waters happen to be colder (“Sea Surface Temperature & Chlorophyll”).

Currents being slowed down, tropical storms becoming more and more extreme, sea levels rising, sea lions dying, and unique ecosystems being destroyed. The effects of climate change on ocean currents and equilibriums certainly sound scary, and they should be taken seriously. However, there are some solutions, actions the world could take to protect its oceans and marine life. Most of these solutions are more to counter climate change than to target specific areas of the ocean, since all of the issues previously described are occurring as direct consequences of climate change.

How to Help

So, how can climate change be fought?

There are three main categories of actions that can help counter climate change. First, our world needs to reduce its greenhouse gas emissions, and therefore limit global warming. Carpool more. Use less electricity, and more natural light. Switch from the burning of fossil fuels to solar power. Drive more mindfully, using less gasoline. There are countless ways to achieve this (“6 Actions to Fight Climate Change”).

Second, it’s important to be more aware of how everyday actions can impact the environment. Since livestock and agriculture account for acres of deforestation, switch to a low-impact diet consisting more of vegetables and local ingredients than meats. If vegetables aren’t available, plant a garden. Use safe chemicals when treating lawns, killing pests, even when applying sunscreen. Again, these little actions add up to make a big difference (“What You Can Do to Fight Climate Change”) .

Finally, educate others. This is an incredibly important step. Spreading awareness about how marine life and ocean currents are affected by everyday actions can inspire others to learn and become involved in the movement. The only way climate change can be defeated is through cooperation and teamwork. Let's take the first step to the return of the impeccable machine that the ocean currents once were.