In the summer of 2023, the North Atlantic Ocean experienced an extraordinary marine heatwave of unprecedented intensity and scale, revealing fresh insights into the complex interplay of atmospheric and oceanic processes intensified by climate change. Spearheaded by researchers at the University of New South Wales (UNSW) Sydney, the study published in Nature uncovers the underlying mechanisms driving this extreme warming event and its profound consequences for weather systems, marine ecosystems, and human societies surrounding the basin.
At the heart of this phenomenon lies a confluence of record-breaking weak wind conditions and heightened solar radiation that collectively induced rapid heating of the ocean surface. From Greenland’s icy margins to the sun-drenched coastlines of the Sahara and extending westward toward the Americas, the North Atlantic waters warmed at a velocity equivalent to roughly two decades of typical regional warming, but compressed into a single summer season. According to lead author Professor Matthew England, this abrupt temperature surge defied expectations based on historical climate trends and underscored the accelerative effects of ongoing anthropogenic warming.
Traditionally, the North Atlantic’s surface warming follows predictable seasonal rhythms driven by solar insolation, with winds playing a key role in setting the thickness of the ocean’s upper mixed layer. These winds promote vertical mixing, distributing heat over a greater volume and thus moderating surface temperature rise. However, in June and July of 2023, the winds over this crucial ocean domain were the weakest on record, resulting in an unprecedented thinning of the ocean’s upper layer. Associate Professor Alex Sen Gupta highlights that in some regions, this surface mixed layer was reduced to as little as 10 meters deep compared to its usual 20 to 40 meters, severely limiting the ocean’s capacity to dissipate incoming solar heat.
This exceptionally thin mixed layer acted like a shallow pan of water on a stove, warming rapidly due to concentrated solar absorption. Co-author Dr. Zhi Li, who meticulously analyzed extensive ocean temperature profiles and meteorological data, emphasizes that the synergy between these weak winds and intense sunlight culminated in a marine heatwave encompassing the entire North Atlantic basin. This event dismantled the typical buffering effects the ocean exerts on temperature increases, thereby pushing surface waters far beyond climatological norms.
Compounding this dynamic was a secondary, yet significant, factor involving atmospheric changes linked to international regulations on shipping emissions. The 2020 implementation of stricter rules to reduce sulphur pollution from ships led to clearer skies over key shipping routes in the North Atlantic. Reduced aerosol concentrations diminished the availability of cloud condensation nuclei, resulting in lower cloud cover. This atmospheric clearing further amplified solar radiation reaching the ocean surface, driving localized enhancements in warming. While not the principal driver, this effect accentuated the overall marine heatwave, demonstrating complex interconnections between human activities, air quality policies, and oceanic climate impacts.
Intriguingly, these 2023 warming episodes unfolded against the backdrop of a long-term cooling trend in a portion of the North Atlantic known as the "cold blob," located southeast of Greenland. This cooling, observed over the past half-century, is linked to a weakening Atlantic Meridional Overturning Circulation (AMOC), a critical component of global heat and freshwater transport. The sudden temperature spike in this normally cooling region initially tempted the researchers to speculate whether the AMOC was temporarily rebounding. However, the rapidity and magnitude of warming proved inconsistent with circulation recovery, signifying instead a disruption of normal ocean dynamics due to atmospheric forcing.
The repercussions of this marine heatwave transcended ocean boundaries, reverberating through atmospheric circulation patterns and terrestrial weather extremes. Air masses traversing the warm ocean surface accumulated heat, contributing to historic continental heatwaves that shattered temperature records across Europe. Germany, France, and Italy faced deadly heat surges exceeding 40 degrees Celsius, while torrential rainfall battered parts of Spain and Eastern Europe, underscoring the ocean-atmosphere feedbacks intensified by the heat anomaly.
Simultaneously, marine ecosystems bore the brunt of thermal stress. The Caribbean’s coral reefs, vulnerable to even minor temperature increases, experienced bleaching events indicative of acute physiological stress. The elevated sea surface temperatures also fueled the intensification of tropical cyclones during the 2023 hurricane season. Notably, Hurricane Idalia struck Florida with devastating consequences, inflicting eight fatalities and causing economic damages estimated at $3.6 billion, highlighting the socio-economic toll exacted by climate-amplified ocean warming.
Principal co-author Professor Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research stresses that the scale of this marine heatwave was exceptional. Unlike localized or transient warm patches, this event encompassed the entire North Atlantic, influencing regional weather systems, marine biodiversity, and human livelihoods simultaneously. The spatial extent and duration of the heatwave—persisting over a year—represent a formidable challenge to existing climate adaptation and mitigation frameworks.
Looking ahead, the study’s findings portend a future marked by more frequent and intense marine heatwaves in the North Atlantic as climate change continues to erode the resilience of oceanic upper layers. Long-term warming reduces the density of surface waters, further inhibiting vertical mixing and enhancing the vulnerability of this thin layer to rapid temperature spikes. This positive feedback loop implies that marine heatwaves will increasingly become a dominant feature of the ocean’s climate system, with costly consequences for fisheries, weather stability, and coastal communities.
Professor England calls for urgent and decisive action to arrest these trends. The only viable path to curtailing escalating marine heatwaves lies in an accelerated transition away from fossil fuel dependence. Achieving net zero carbon emissions must be prioritized to stabilize ocean temperatures and safeguard the intertwined natural and human systems dependent on the North Atlantic environment. He underscores that the window for intervention is rapidly narrowing and that delayed responses will magnify the damage from these extreme climate phenomena.
In summary, this landmark study illuminates how record-weak winds and intensified solar radiation, superimposed on chronic anthropogenic warming trends, conspired to trigger the exceptional marine heatwave of 2023 in the North Atlantic. It highlights the intricate linkages between atmospheric conditions, ocean mixing processes, and human-driven climate change, offering critical insights into the mechanisms behind unprecedented ocean warming events. The multifaceted impacts, spanning environmental, economic, and societal spheres, emphasize the urgency of concerted global efforts to limit further warming and enhance resilience to an increasingly volatile climate future.
Subject of Research: Oceanography, Climate Change, Marine Heatwaves
Article Title: Drivers of the extreme North Atlantic marine heatwave during 2023
News Publication Date: 4-Jun-2025
Web References: https://www.nature.com/articles/s41586-025-08903-5
References: 10.1038/s41586-025-08903-5
Image Credits: Richard Freeman, UNSW Sydney
Keywords: Oceans, Climate change, Climate variability, Climate systems, Climate data
