How the Oceans Currents are Impacted by Climate Change - 338

We may think the local weatherperson controls our weather at 10 PM each evening, but they do not. It is controlled primarily by massive ocean currents, which transport heat away from the equator. Conversely, cold water flows along the ocean floor towards the equator, which evens our temperatures out a bit. The amount of water transporting heat is massive and has its own mathematical term, a Sverdrup, which is 1 million cubic meters of water moving per second. You can use a square yard instead of a square meter and be close enough when attempting to visualize this volume of movement.

Oceanographers and climate scientists have been raising the alarm that one of the ocean currents is getting squirrely. It is the Atlantic Meridional Overturning Circulation (AMOC). Its rate varies from 30 to 150 Sverdrups per second. To give some perspective of how much water is moving, at 100 Sverdrups per second, it is over 35,000 times more water than what goes over Niagara Falls.

 

The (AMOC) is one of the most critical components of Earth's climate system. Often likened to a giant conveyor belt, the AMOC transports warm, salty water from the tropics northward along the surface of the Atlantic Ocean. When it reaches the cooler, higher latitudes, the water cools, becomes denser, and sinks, driving a return flow of cold water southward at depth. This process plays a pivotal role in regulating regional and global climate, influencing weather patterns, sea levels, and the ocean's distribution of heat and nutrients. However, this vital system faces a growing threat from climate change, and its potential disruption could have far-reaching consequences.

 

The AMOC is fueled by differences in temperature and salinity—a process known as thermohaline circulation. Thermo is heat, and saline is saltiness. Warm, salty water from the tropics flows northward, where it cools and sinks due to its density, and then flows south along the ocean floor, creating a conveyor feedback loop. Human-induced climate change is disrupting this delicate balance. Rising global temperatures are rapidly melting the Greenland ice fields, releasing massive amounts of freshwater into the North Atlantic. This freshwater is lighter than saltwater, diluting the ocean's salinity. The resulting reduction in density of the surface waters just south of Greenland weakens the sinking, slowing the AMOC.

 

Recent research indicates that the AMOC is at its weakest point in over a millennium and showing signs of further decline. The Intergovernmental Panel on Climate Change (IPCC) has warned that the AMOC could weaken significantly over the 21st century if greenhouse gas emissions continue unabated (IPCC, 2021). In a worst-case scenario, the system could collapse entirely. Such an event, while uncertain, would be catastrophic, triggering abrupt and irreversible changes in climate systems worldwide.

 

The impacts of a weakened or collapsed AMOC would be profound. The AMOC's role in transporting warm water northward to Europe contributes to the region's relatively mild climate. A significant slowdown could plunge parts of Europe into colder, harsher winters, reminiscent of a "mini ice age." Conversely, the tropics and the Southern Hemisphere could experience intensified warming, as the redistribution of heat by the AMOC would be disrupted.

Coastal regions in North America, particularly along the eastern seaboard, would also see regional sea levels rise. Furthermore, a disrupted AMOC would likely alter precipitation patterns, potentially leading to more severe droughts in parts of Africa and the Amazon basin, regions already vulnerable to water scarcity and ecological stress.

 

Marine ecosystems would not be spared. The AMOC plays a crucial role in nutrient cycling and the oxygenation of deep ocean waters. A slowdown could disrupt marine food chains, harming fisheries and biodiversity. Species that rely on stable ocean temperatures and currents could struggle to adapt, leading to potential collapses in fish populations that many communities depend on for food and economic stability (Caesar et al., 2018).

 

The bottom line is that the ability of humans to feed themselves would become challenging to impossible.

 

Given the stakes, understanding and mitigating the risks to the AMOC is a global priority. The only way to avoid this day of reckoning is to dramatically reduce greenhouse gas emissions, which would limit the melting of ice sheets.

 

Thus, achieving the targets outlined in the Paris Agreement—keeping global temperature rise well below 2°C above pre-industrial levels and pursuing efforts to limit it to 1.5°C—would significantly reduce the risk of an AMOC collapse (UNFCCC, 2015).

 

International cooperation and United States leadership will be key. The AMOC's influence extends across hemispheres, and its potential collapse would have consequences for every nation. Collaborative efforts to cut emissions, share climate data, and invest in sustainable technologies are imperative to address this shared challenge.

 

While the prospect of an AMOC collapse is alarming, it is not inevitable. Humanity still has the tools and knowledge to mitigate the risks and safeguard this vital system. The challenge lies in decisively and collectively prioritizing the health of our planet's climate systems. The AMOC is a reminder of the intricate interconnectedness of Earth's natural processes and the profound impact human activity can have on them. Protecting it is not just a scientific imperative but a moral one, as its stability underpins the well-being of countless ecosystems and communities around the globe.

 

A very interesting read: Wired Magazine SEP/OCT 2024 "The Hole in the Map of the World."

 

Interesting note: The largest waterfall in the world is located southwest of Iceland in the Irminger Sea. The AMOC gets powered here as three million cubic meters of cold salty water plunge nearly two miles every second.

 

Other References:

·       IPCC (2021). Sixth Assessment Report. Intergovernmental Panel on Climate Change.

·       Rahmstorf, S. (2017). "Rising Risk of Abrupt Changes in Ocean Circulation with Global Warming." Proceedings of the National Academy of Sciences.

·       Caesar, L., Rahmstorf, S., et al. (2018). "Observed Fingerprint of a Weakening Atlantic Ocean Overturning Circulation." Nature.

·       UNFCCC (2015). Paris Agreement. United Nations Framework Convention on Climate Change.