Parley AIR: Marine Heatwaves
The oceans have never been so dangerously warm
We are currently in a season that’s creating the hottest oceans on record. In the 32 years the National Oceanic and Atmospheric Administration (NOAA) has been keeping track of ocean temperatures, heatwaves have never been this widespread. The last 10 years have brought the warmest ocean surface temperatures since at least the 1880s, when humans started keeping track.
Surface temperatures of about 40% of the global oceans are already high enough to meet the criteria for a marine heatwave – an extended period of unusually high ocean temperatures which can have significant impacts on marine life as well as coastal communities and economies. The new forecast by the Physical Sciences Laboratory (PSL) projects that it will increase to 50% by September, and it could stay that way through the end of the year. That has huge consequences not only for marine wildlife, but for weather patterns and natural disasters. For melting glaciers. For all life on this blue planet. For all of us.
In this Parley AIR Guide, we’re unpacking exactly how heat waves have dire impacts on our oceans, and how we can work together to prevent the trend from getting worse.
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Heat content in the global ocean has been consistently above average since the mid-1990s. (NOAA Climate.gov)
RECORD HEAT WAVES
July 2023 was the hottest month on record here on planet Earth.
Average temperatures in July 2023 were 0.33 degrees Celsius (0.59 degrees Fahrenheit) higher than the previous record, set in July 2019. It’s estimated that the last time Earth was this hot was 120,000 years ago. From Athens, Greece to Death Valley, California, the impact on land has been deadly. Nearly half of the U.S. was under a heat advisory. Crops failed across Southern Europe. Power grids buckled in China.
Unusually high temperatures weren’t just recorded on land, but in the oceans, too. Oceans absorb more than 90% of excess heat created from human greenhouse gas emissions. Normally, the oceans can absorb an extraordinary amount of heat from Earth’s atmosphere without heating, but it’s getting harder and harder to do.
Normally around 10% of the surface of our oceans are in a marine heatwave. The fact that 50% – 5 times the normal amount – could be in a marine heatwave by the end of this year is both astounding and worrying. There’s one other thing: This year, and into early 2024, El Niño, a weather phenomenon that brings unusually hot weather (El Niña brings unusually cool temperatures) in the eastern equatorial Pacific is also exacerbating warming caused by human-driving climate change.
Atlantic Meridional Overturning Circulation. (Nature Journal)
Slowing ocean currents
Warming oceans aren’t a matter of a few consecutive years of heat waves. The problem is much bigger than that. Massive ocean currents – some that span entire oceans – play a crucial role in climate. They act as conveyor belts, moving heat and precipitation from the equator toward the poles. Since the oceans store a massive amount of solar radiation (the energy that comes from the sun and creates heat on Earth), currents help distribute heat around the planet. Ocean water is also constantly evaporating, and almost all rain on Earth begins in the oceans. And currents are in charge of distributing storms and weather patterns.
One, called the Atlantic Meridional Overturning Circulation (AMOC), circulates water in the Atlantic Ocean in a gigantic loop, from the northern part of the globe to south and back again. It takes about 1,000 years for water to complete a full journey along the belt, that is, when the current is healthy.
For years, scientists have been monitoring the AMOC’s slowing. Temperatures in the North Atlantic have been warmer faster than climate models have projected. A study published last month made yet another alarming climate prediction: the AMOC could pass its tipping point as soon as 2025. Reaching its tipping point doesn’t mean total collapse, that the current will stop, but it is a huge, scary step towards it. If the AMOC stopped, it would cause dramatic shifts in temperature and rainfall across the Atlantic Ocean, which separates North, Central and South America in the west, from Europe and Africa in the east. Temperatures would be more extreme, making much of these areas of land along the current uninhabitable.
The study’s researchers noted that a total collapse in the 21st century is unlikely, but if we don’t alter course and drastically reduce human-made greenhouse gas emissions, there is a very real chance the AMOC and other ocean currents will reach a point where they will be increasingly difficult, and likely impossible, to restore.
Coral bleaching in the Maldives. (Ocean Image Bank)
Mass die-offs
In June 2021, a so-called heat dome in the Pacific Northwest was caused by quick and drastic changes in ocean temperatures, particularly off the coast of British Columbia, Canada and Washington State in the U.S. A blob of heat hovered across the area and didn’t move for weeks.
The soaring temperatures and heating oceans were deadly especially for intertidal organisms, those that live in tides along shorelines. The climate change induced heat dome killed an estimated 1 billion sea creatures off the coast of Canada alone. Muscles, snails and clams were cooked alive. The heat took sea stars, barnacles, hermit crabs, worms and tiny sea cucumbers, too. All were washed ashore.
Changes in ocean temperature are also the leading cause of coral bleaching. Coral bleaching happens when the water coral lives in is too warm. When this happens, corals expel the algae, a type called zooxanthellae, that lives in their tissues and creates the vibrant colors we see in healthy coral. Without the algae, the corals turn white (bleached). Bleached corals aren’t dead, but they are weakened and more vulnerable against other threats like pollution and overfishing. In 2020, nearly 80% of corals in the Great Barrier Reef were exposed to heat-induced bleaching. Severe bleaching events caused by abnormally high ocean surface temperatures were also documented in the region in 2015, 2016 and 2017.
In July 2023, oceans off the coast of Florida in the U.S. reached just over 100 degrees Fahrenheit (38 Celsius). This massive heat wave not only bleached coral in the Caribbean Sea, but threatened seabirds, sea turtles, marine mammals and ocean plants, which are important carbon sinks. Warming oceans are also killing plankton, the foundation of the marine food web.
Marine life die-offs disproportionately impact Indigenous Peoples. Native American, Pacific Islander, and Alaska Native communities commonly practice subsistence fishing, with their catch making up a substantial part of their diet, especially protein. Dwindling fish populations can quickly create food scarcity for rural Alaskan villages and erase a cornerstone of already threatened cultures. This happened in 2021, when record low Chinook and chum salmon levels led to the closure of subsistence salmon fishing for most of the year.
Hurricane ‘Irma’ striking Miami, Florida. (Photographer: Warren Faidley)
Supercharged Storms
Sea-level rise has long been the poster child for climate change, and rightfully so. Sea-level rise has more than doubled since the 1990s. As waters warm, they melt sea ice, erasing the once shallow areas that are critical habitats for biodiverse kelp forests, mangroves, coral reefs and salt marshes. These habitats aren’t just important for carbon sequestering and harboring wildlife, they also dampen the impact of waves hitting the shores – by as much as 80%.
The Intergovernmental Panel on Climate Change (IPCC) predicts certain regions, including the western Tropical Pacific, the South-west Pacific, the North Pacific, the South-west Indian Ocean and the South Atlantic, will be impacted by considerably higher sea-level rise. Rising, warming seas also create the perfect environment for intensified natural disasters.
Tropical storms also gain momentum when they hit warm patches of water. When this happens along shorelines, hurricanes, cyclones and other tropical natural disasters are more powerful – and destructive – when they hit land. This exacerbates deadly storm surges, flooding, erosion and landslides, which are now expected to happen at least once a year in many coastal communities where they used to occur only once a century.
IT’S NOT OVER YET
Bleaching corals, slowing ocean currents and mass-die offs of marine plants and animals are huge warning signs that we need to pay attention to. The future is not yet set in stone. We can still act to slow and even reverse some of the damage we’ve caused.
Climate change is at the heart of the matter. The searing temperatures this summer in the U.S. and Europe would have been virtually impossible without climate change, an analysis from the World Weather Attribution found. Climate change made China’s heat wave 50 times more likely than it otherwise would have been.
It can feel like individual actions don’t matter in the face of climate change, but they do. They really, really do. Together, the collective can make small changes in their daily lives that all add up – like avoiding single use plastic, driving less, eating less meat – and, most importantly, push lawmakers and corporations to make the big shifts that will really turn the tide when it comes to climate change. Start with educating yourself and others – our previous guides listed below are a good place to start – and then use what you’ve learned to apply pressure to local and global governments and the carbon-emission giants that are most responsible for our warming planet.
TAKE ACTION
Read up, make noise, spread the word and give others the tools to do the same. Systemic change won’t come unless we demand it.
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