Ocean warming has nearly doubled in the last decade

The world’s oceans, often referred to as the “climate’s heat sink,” are now experiencing unprecedented rates of warming. Researchers at the University of New South Wales (UNSW Sydney) have uncovered the acceleration of ocean warming and have pinpointed the areas that are absorbing the most heat. 

Alarmingly, the rate of ocean warming has nearly doubled in the past decade compared to the 1990s, according to the study. 

“The ocean directly impacts the Earth’s climate by absorbing and redistributing large amounts of heat, freshwater, and carbon, and by exchanging these properties with the atmosphere,” wrote the study authors.

“About 91% of the excess heat trapped by greenhouse gases and 31% of human emissions of carbon dioxide are stored in the ocean, shielding humans from even more rapid changes in climate.”

Unprecedented heat stress 

While the heat absorption capacity of the ocean helps to slow the pace of climate change, it is not without costs, noted study co-author Matthew England, a professor at the UNSW Centre for Marine Science and Innovation.

“The world ocean, in 2023, is now the hottest ever recorded, and sea levels are rising because heat causes water to expand and ice to melt,” said Professor England. “Ecosystems are also experiencing unprecedented heat stress, and the frequency and intensity of extreme weather events are changing rapidly, and the costs are enormous.”

Focus of the study

“Right now, the ocean is warming at a dramatically accelerating rate, nearly doubling during the 2010s relative to the 1990s,” said study lead author Dr. Zhi Li. “What we wanted to do in this study was to figure out exactly where this ocean heat uptake has been occurring.”

The researchers investigated the locations of intense ocean heat uptake using a comprehensive set of ocean temperature data – from 1950s ship-based measurements to contemporary readings from the Argo float program. 

The Southern Ocean 

The analysis revealed that while ocean warming is happening on a global scale, the Southern Ocean stands out by storing almost as much excess anthropogenic heat as the Atlantic, Pacific, and Indian Oceans combined.

This variability in regional ocean warming, with hotspots notably in the Southern Ocean within the 300 – 1500 meters depth range, has significant implications.

“Melting ice caps, extreme weather, and marine ecosystems, including coral reefs, are all highly sensitive to ocean temperature changes,” said study co-author Dr. Sjoerd Groeskamp from the Royal Netherlands Institute for Sea Research. “It is critical we understand exactly how and where the ocean warms – both now and into the future.”

Study implications 

The research highlights an urgent need for enhanced global ocean monitoring, particularly in remote and critical areas like polar and subtropical seas, to improve predictions related to sea-level rise and marine ecosystem impacts. 

The researchers are urging for immediate international action, emphasizing that net zero carbon targets need to move from pledges to reality to curb the damage from escalating ocean warming. “Without any action, these net zero pledges are just meaningless,” said Dr. Groeskamp.

More about ocean warming 

Ocean warming refers to the increase in temperature of the Earth’s oceans, which is a direct result of climate change. The oceans absorb much of the increased heat caused by rising atmospheric temperatures due to the greenhouse gas emissions. This has several consequences:

Thermal expansion

As water heats up, it expands. This contributes to sea level rise, which can lead to coastal flooding and erosion.

Melting ice

Warmer oceans contribute to the melting of polar ice caps and glaciers, which also adds to sea level rise.

Coral bleaching

Increased temperatures can cause stress to coral reefs, leading to coral bleaching and the potential death of these ecosystems.

Disruption of marine life

Many marine species are sensitive to temperature and may migrate to cooler areas, altering marine ecosystems and the distribution of life in the ocean.

Weather patterns

Warmer oceans affect global and regional climate patterns, including the strength and frequency of tropical storms.

Ocean acidification

While not a direct result of ocean warming, the process of oceans absorbing more CO2 leads to acidification, which is exacerbated by the overall climate change effects.

Deoxygenation

Warmer water holds less oxygen, leading to areas where there is not enough oxygen to support marine life, known as “dead zones.”

These changes pose significant risks to global weather patterns, marine life, and communities that depend on the ocean for their livelihoods.

Mitigation strategies 

The study led by UNSW Sydney researchers highlights a crucial and urgent need for concerted global efforts to reduce ocean warming. Mitigation strategies are multidimensional and involve both reducing the sources of warming and enhancing the ocean’s resilience. Here’s an overview of such efforts:

Reducing greenhouse gas emissions

The primary driver of ocean warming is the increase in greenhouse gases in the atmosphere. Cutting emissions by transitioning to renewable energy sources, improving energy efficiency, and adopting cleaner transport options can significantly slow the rate of ocean warming.

International climate agreements

Upholding and strengthening international commitments, such as the Paris Agreement, where nations pledge to limit global temperature rise, is vital. Every fraction of a degree in temperature reduction can result in less ocean warming.

Protecting marine ecosystems 

Healthy marine ecosystems can absorb and store carbon more effectively. Protecting areas like mangroves, seagrasses, and coral reefs can aid in regulating the ocean’s temperature and acidity.

Research and monitoring

Investment in oceanic research, like the deployment of Argo floats mentioned in the study, is essential to monitor changes and predict future warming patterns. This knowledge can inform targeted conservation efforts and efficient management of marine resources.

Sustainable fisheries

Overfishing can disrupt the marine food web, affecting the ocean’s ability to regulate climate. Sustainable fishing practices help maintain this balance.

The study is published in the journal Nature Communications. 

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