NOAA satellites have been tracking the steady climb in ocean temperatures since April, which is causing unprecedented heat stress conditions in the Caribbean Basin as well as the Atlantic and Gulf of Mexico waters surrounding Florida. The current marine heat wave is raising new concerns about the potential impact on the fragile coral reefs beneath the ocean’s surface.
Derek Manzello, Ph.D., Coordinator of NOAA’s Coral Reef Watch, has researched the impacts of ocean warming around the Florida Keys for more than 20 years. During that time, he has examined five different warm-water coral bleaching events, both on location and with remote-sensing technology.
“If ocean temperatures are higher than the maximum monthly average, for a month or more, especially during the warmest part of the year — even by as little as 1-2 degrees Celsius (2-3 degrees Fahrenheit) — corals will experience bleaching,” said Manzello. “A bleached coral is essentially starving to death because it has lost its main source of nutrition — the algae that live symbiotically within its tissues.”
“The damage corals experience from marine heatwaves is a function of the duration, or how long the heat stress occurs, plus the magnitude of the heat stress,” said Manzello. “Corals can recover from bleaching if the heat stress subsides, but the corals that are able to recover frequently have impaired growth and reproduction, and are susceptible to disease for two to four years after recovery.”
“There are downstream, negative impacts to the corals that are able to survive a heat stress event. If the heat stress does not subside, the coral will die,” said Manzello. “Mortality becomes likely if the corals experience sea temperatures 1°C greater than the historical maximum monthly average for two months, or 2°C greater than the maximum monthly average for one month. Also, if there is a temperature deviation of say 3°C, then the corals would be expected to start experiencing mortality in less than three weeks.”
The Copernicus Climate Change Service (C3S), implemented by the European Centre for Medium-Range Weather Forecasts on behalf of the European Commission with funding from the EU, routinely publishes monthly climate bulletins reporting on the changes observed in global surface air temperature, sea ice cover, and hydrological variables.
This C3S highlighted concerns about sea surface temperature in its most recent press release, which reported findings based on computer-generated analyses using billions of measurements from satellites, ships, aircraft, and weather stations around the world.
Andrew Pershing, a climate scientist with the Princeton nonprofit Climate Central, said that more than 80% of humanity was exposed to climate change-attributed heat in July, when climate change’s influence extended across much of the globe, creating “a tropical band around the planet that includes Africa, South and Central America, the Malay Archipelago and many of the small island nations in both hemispheres.”
Scientists at the United States Environmental Protection Agency (EPA) note that estimating the impact of climate change and its associated costs is challenging due to the difficulty of separating damages that are caused by natural variability in the climate system from those that were made more frequent or intense because of climate change.
However, there is strong evidence that climate change contributed to shocking changes in coral reefs and other marine life, in addition to triggering wildfires, deadly heat in populated areas, and the rising strength of Atlantic hurricanes.
“We just witnessed global air temperatures and global ocean surface temperatures set new all-time records in July. These records have dire consequences for both people and the planet exposed to ever more frequent and intense extreme events,” said C3S Deputy Director Samantha Burgess.
“2023 is currently the third warmest year to date at 0.43ºC above the recent average, with the average global temperature in July at 1.5°C above preindustrial levels,” said Burgess. “Even if this is only temporary, it shows the urgency for ambitious efforts to reduce global greenhouse gas emissions, which are the main driver behind these records.”
Coral reefs are some of the most important ecosystems on Earth. They provide a variety of benefits to humanity, including:
- Coastal protection: Coral reefs act as natural barriers that protect coastal communities from storms and erosion. They can reduce wave energy by up to 97%, which can help to prevent flooding and damage to property.
- Food and income: Coral reefs are a vital source of food for millions of people around the world. They provide a home to many fish and other marine animals that are caught for food. Coral reefs also support tourism and recreation, which provide jobs and income for local communities.
- Biodiversity: Coral reefs are home to a vast diversity of life, including thousands of species of fish, coral, and other marine animals. This biodiversity is essential for the health of the ocean ecosystem and for human well-being.
- Medicines: Coral reefs are a source of new medicines. Scientists are currently studying coral reef organisms for potential treatments for cancer, arthritis, and other diseases.
- Air and water purification: Coral reefs help to purify water and air. They remove pollutants from the water and produce oxygen. This is important for both human health and the health of the ocean ecosystem.
The loss of coral reefs would have a devastating impact on humanity. It would lead to coastal flooding, erosion, food shortages, economic losses, and the loss of biodiversity, so people must take action to protect coral reefs and ensure their survival for future generations.