In February, the world’s oceans experienced a heat wave that pushed them well beyond a long-term warming trend driven by human greenhouse gas emissions. The result is a nine-month streak of record-breaking global temperatures, a critical escalation in the climate emergency that threatens marine ecosystems and the planet’s health.
“This February, the average global sea surface temperature was the highest ever recorded in our ERA 5 dataset, which goes back to 1979,” the European Union’s Copernicus Climate Change Service (C3S) reported Thursday. It surpassed the previous 20.98 degrees Celsius (69.77 degrees Fahrenheit) set in August 2023, the warmest month of any year.
C3S’ monthly climate bulletins report on global surface air and sea temperatures and polar sea ice conditions using computer-generated analyses based on billions of measurements from satellites, ships, aircraft, and weather stations. They also report on other climate indicators, such as rainfall and wind patterns.
According to the latest data, a combination of factors has contributed to the escalation of global temperatures: the emergence of an El Nino pattern, which tends to raise ocean temperatures; continuing human-caused greenhouse gas emissions; and changes in atmospheric circulation that alter how warm and cold waters are transported globally. A warmer ocean also causes sea levels to rise through thermal expansion, shifts the distribution of many marine species, affects nutrient availability, and alters the flow of deep-ocean currents.
This month’s heat wave was incredibly intense for the northern hemisphere, where most of Europe and the United States experienced temperatures well above average. But it was also extreme across the tropics and in parts of the Indian and Pacific oceans, where oceans are most directly affected by human-caused climate change.
The increase in ocean temperatures resulted from a strong, ongoing El Nino pattern, which tends to heat the waters. However, human-caused greenhouse gases continue to warm the atmosphere and oceans, contributing to a vicious cycle. Warmer oceans are less capable of absorbing carbon dioxide, further contributing to the warming trend and making it harder for the oceans to cool off again.
A warming ocean also exacerbates other impacts, such as eroding coastlines and disrupting the food web that supports marine life. The warming waters also threaten to displace migratory species, push some species towards extinction, and promote the spread of invasive species that threaten local fisheries.
With the possibility of a third global mass coral bleaching event later this year, the consequences for biodiversity are even more concerning. Warmer waters can cause corals to expel the algae in their tissues, leaving them with a pale skeleton and prone to disease and starvation. This can lead to the collapse of reef ecosystems, leaving coastlines vulnerable and fisheries depleted. And, of course, if the corals die, the habitats of other species are also compromised.