Accelerating Sea Level Rise: Understanding the Increasing Rates and Impacts

Recent satellite measurements reveal a sudden surge in the rate of sea level rise, accelerating sharply since 2012 and remaining high ever since.

These abrupt shifts may stem from natural variability, or they could indicate the impacts of accelerating global warming, according to Lancelot Leclerc from the University of Toulouse, France.

Over the last 15 years, global warming has contributed to an average sea level rise of over 0.2 meters. This phenomenon is driven by various factors, including the melting of mountain glaciers along with the Greenland and Antarctic ice sheets, which are also expanding as ocean temperatures increase.

Satellite monitoring of sea levels began in the 1990s, initially indicating a consistent rise of approximately 3.6 mm annually. Yet, further analysis showed a significant shift around 2012, with the average increase accelerating from 2.9 mm/year to 4.1 mm/year.

“Though it’s not a drastic change,” notes Jonathan Bamber from the University of Bristol, UK, “we’re not talking about centimeters per year.” He emphasizes that this highlights the importance of tracking these changes over time.

Despite the modest increase, the combination of satellite data trends with tide gauge records spanning a century confirms that sea levels are rising at an accelerating rate.

The analysis indicates that this rise is attributable to multiple factors rather than a single cause. The melting of ice sheets is accelerating, freshwater retention on land is decreasing, and more water is flowing into the oceans.

The acceleration of global warming since around 2010 is largely attributed to reduced aerosol pollution from countries such as China. Aerosols have a cooling effect, and their declines have allowed the warming effects of rising carbon dioxide to become more pronounced.

This increase in sea level rise may also correlate with the reduction of aerosol emissions, as Leclerc indicated during a presentation at the European Geosciences Union (EGU) meeting in Vienna on May 5th.

“The change in trends observed around 2012 appears to be partially linked to increased anthropogenic radiative forcing due to decreased aerosol emissions,” explains team member Annie Cazenave from the University of Toulouse.

Furthermore, another study presented at the EGU gathering indicates that ocean water deeper than 2 kilometers has begun to warm and expand over the last decade, potentially contributing to this acceleration in sea levels.

Prior to 2016, all known contributors to sea level rise aligned with observed global averages. However, Yang Chunxue stated at a conference that after this period, these factors no longer accounted for the complete rise.

This discrepancy suggests an unaccounted factor, likely the deep ocean, owing to the absence of systematic measurements of temperatures below 2 kilometers. While nearly 4,000 robotic probes measure ocean temperatures at various depths, none extend that deep.

Yang and his team employed ocean models to demonstrate that warming below 2 kilometers could resolve this budget discrepancy, identifying that a significant amount of deep warming occurs in the North Atlantic off the U.S. East Coast.

“The Sea Level Budget study indicates that deep ocean warming commenced around 2016,” asserts Kazunabe, who was involved in the research. “Further studies are necessary to confirm the connection with the trend changes of the early 2010s.”

The research team’s findings suggest that deep-sea warming currently accounts for an annual rise of 0.4 mm, representing about 10% of the total sea level increase.