Global Warming Is Accelerating Ocean Circulation and Changing Ocean Currents
Wed, April 21, 2021

Global Warming Is Accelerating Ocean Circulation and Changing Ocean Currents

The world’s oceans are being disproportionately affected by multiple environmental issues, particularly global warming and the melting of Arctic ice. The Intergovernmental Panel on Climate Change’s (IPCC) fifth assessment report revealed that humans are responsible for around 110% of observed warming that has led to the average global temperature increase of 0.85 degrees Celsius. The IPCC also issued another report on the impacts of global warming, saying that limiting global warming to 1.5 degrees Celsius will require rapid, far-reaching, and unprecedented changes in all aspects of society.

According to USA Today, an online site that delivers current local and national news, sports, entertainment, finance, technology, and more, the National Oceanic and Atmospheric Administration reported that the past five years have been the five warmest since record-keeping began in the late 1800s. Reports showed that the global average temperature increase was about 1.8 degrees Celsius for the first 10 months of 2018. Our planet has also experienced 42 straight years with an above-average global temperature. 

Meanwhile, the Arctic sea ice melt has also been extremely alarming. NOAA’s 2018 Arctic Report Card showed that we are currently witnessing the fastest decline in Arctic sea ice in at least 1,500 years. The scientists analyzed the state of the frozen ocean by collecting sample ice cores, permafrost records, and tree rings. “The Arctic is going through the most unprecedented transition in human history. This year’s observations confirm that the Arctic shows no sign of returning to the reliably frozen state it was in just a decade ago,” said Jeremy Mathis, director of NOAA’s Arctic research program.

According to Vox, a liberal-leaning American news and opinion website, the largest magnitude decline in sea ice and the greatest sustained rate in sea decline has happened since the start of the 20th century. The growing changes in sea ice can result in greater warming. Reports showed that the melting of the sea surface can cause more melting. The National Snow and Ice Data Center's chart showing the monthly January ice extent for 1979 to 2018 exhibited a decline of 3.3% per decade. This is equivalent to 47,700 square kilometers (18,400 square miles) per year.

“When that ice heats up and melts, it flows off of the land into the ocean, which really does raise sea levels. Greenland's ice sheet is currently 1.9 miles thick and contains enough ice to raise global sea levels by about 25 feet in all. And that ice sheet is indeed shrinking,” Brad Plumer wrote for Vox. 

The increasing global temperatures and the worsening Arctic ice melt heavily impact our oceans, particularly ocean circulation and ocean currents.

The Speeding Up of Ocean Circulation

For years, studies have shown how global warming affected the oceans and marine life. But a recent study focused on how environmental changes influenced the magnitude and extent of the acceleration in ocean currents. According to Phys.org, a leading web-based science, research, and technology news service that covers a full range of topics, ocean circulation plays an integral role in Earth's environment and climate system. It regulates land temperatures in regions where a flow of relatively warm water makes the climate of cities warmer compared to other cities, despite being at the same latitude. 

While it has already been established that ocean circulation in different regions has different responses to global climate warming, there’s still a lack of systematic and continuous direct observations on the planet’s ocean circulation. The researchers led by Shijian Hu, a postdoctoral researcher, used ocean circulation and wind speed data from multiple sources to investigate global mean ocean circulation and global mean sea surface wind speed. Some information includes observations from the global Argo network of robotic floats and numerical simulations. 

The study published in the journal Science Advances showed that global ocean circulation has accelerated during the past two decades. Since the early 1990s, the oceanic kinetic energy has significantly increased, calculating a 36% acceleration of global mean ocean circulation. This is due to the continuous greenhouse gas emissions caused by human activities, giving rise to Earth's energy imbalance and continuous ocean warming. According to the researchers, the continuous acceleration of global ocean circulation may lead to enhanced heat and water mass transport. 

"The magnitude and extent of the acceleration in ocean currents we detected throughout the global ocean and to 2,000-meter (6,560 feet) depth was quite surprising. While we expected some response to the increased winds over the past two decades, that the acceleration was above and beyond that was an unexpected response that is likely due to global climate change,” co-author Janet Sprintall, an oceanographer at Scripps Institution of Oceanography at the University of California San Diego, said. 

The Changing Ocean Currents

Another recent study focused on how the melting of Arctic sea ice alters the ocean currents or the continuous, predictable, directional movement of seawater driven by gravity, wind, and water density. The researchers particularly focused on the Beaufort Gyre, a wind-driven ocean current located in the Arctic Ocean polar region, which is responsible for keeping the polar environment in equilibrium by storing freshwater near the surface of the ocean.

Naturally, the Beaufort Gyre collects freshwater from glacial melt, river runoff, and precipitation, which is significant in the Arctic as it protects the sea ice from melting, helping regulate Earth's climate. However, scientists have observed that this current has accumulated a large amount of freshwater since the 1990s. 

"If the Beaufort Gyre were to release the excess freshwater into the Atlantic Ocean, it could potentially slow down its circulation. And that would have hemisphere-wide implications for the climate, especially in Western Europe," said Tom Armitage, the lead author of the study and polar scientist at NASA's Jet Propulsion Laboratory in Pasadena, California. 

The study published in Nature Communications revealed that the Beaufort Gyre has accumulated more freshwater due to the loss of sea ice in summer and autumn. This has led to the current being more exposed to the wind, which spins the gyre faster and traps the freshwater in its current. According to Science Daily, an American website that aggregates press releases and publishes lightly edited press releases about science, the researchers also discovered that the current is out of balance because of the added energy from the wind. While the acceleration of ocean currents has helped the system balanced, it has the potential to lead to further ice melt.

"What this study is showing is that the loss of sea ice has really important impacts on our climate system that we're only just discovering," said Alek Petty, a co-author on the paper and polar scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.