A fever is rising in the ocean. Our rampant burning of fossil fuels has produced a heat-trapping blanket of carbon dioxide (CO2) in the atmosphere that has warmed the Earth. But the situation would be much worse without the ocean, which has absorbed more than 90 percent of that excess heat.
Scientists reported that in 2020, the ocean held the most heat ever recorded. In recent decades (1987-2019), ocean warming has increased by 450 percent, compared to the three decades before that (1955-1986). Last year, the ocean absorbed more than 200 times as much heat as it did on average in the years between 1981 and 2010. That extra heat has dramatic impacts.
Warmer waters are turbocharging the planet’s water cycle. More moisture is evaporating into the atmosphere—powering stronger, wetter, and longer-lasting storms and cyclones. At the same time, historically arid regions are getting even less rainfall and more droughts and wildfires.
As ocean waters warm, they expand in volume. They also hasten the melting of Antarctic and Greenland ice sheets, returning hundreds of gigatons of water previously frozen on land back into the ocean. This combination is raising sea levels at an accelerating pace. Sea levels are estimated to be at least 0.3 meters (1 foot) higher by 2100, perhaps 2.5 meters (8.2 feet) if we don’t curtail greenhouse gas emissions, threatening to inundate wetlands, buildings, and roads.
Warming waters are also affecting the habitats, food sources, metabolisms, and behavior of marine life throughout the food web, from plankton to whales, in interconnected ways that are hard to unravel but increasingly apparent. Some changes are already occurring, among which are more frequent harmful algal blooms and coral bleaching.
“It’s easy to get bombarded with negative projections,” said Dr. Jamison Gove, a National Oceanic and Atmospheric Administration (NOAA) scientist who studies Hawaiian corals. “But I’m generally optimistic.”
Amid dire change, he sees nature’s inherent ability to adapt. “I’m realistic that ecosystems are changing and will be different than today, but coral reefs have a solid chance to persist—assuming we keep learning from our research, and society takes the necessary steps to conserve and manage.”
“Look at Hanauma Bay,” said Dr. Angelicque White, a microbial oceanographer at the University of Hawai‘i at Mānoa (UHM). “During the COVID-19 lockdown, free of thousands of tourists and sunscreen pollution, marine life bloomed again. These ecosystems are resilient.”
The pandemic crisis offers another lesson, she said. “We couldn’t close our eyes and wish it would go away.” Instead, we needed solid research to devise the best strategies to adapt. The same is true for our climate crisis.
What’s the weather forecast?
The surest long-term way to avoid the worst impacts of climate change is to reduce CO2 emissions. In the short term, we’ll have to adapt, said Dr. Malte Stuecker, an assistant professor in the Department of Oceanography and the International Pacific Research Center at UHM.
Stuecker reverse-engineers the complicated cogs in the machinery that produces our climate. His models are dynamic blueprints of ocean-atmosphere interactions, such as the El Niño/Southern Oscillation (ENSO), which seesaws over time and regulates globe-spanning rainfall patterns.
ENSO’s delicately balanced components include variations in trade winds that redirect masses of sun-heated water. Evaporation over these moving warm pools in these trade-wind regions drives water vapor into the atmosphere. That provides the fuel for clouds and moisture-laden storm systems that ripple out in varying far-flung directions, redirecting rainfall to different regions at different times.
Climate modelers have made enormous strides in understanding how the air-sea system operates. With enhanced computing power and more ocean-monitoring instruments feeding in more data, Stuecker and colleagues continually fine-tune their models to provide more accurate and detailed predictions of what will unfold—six months from now and decades into the future—as ocean warming revs up.
Until we can shrink our collective carbon footprint, we won’t be able to prevent extreme storms, floods, and droughts. But we can shore up infrastructure, revise farming practices, ensure water supplies, and take other steps to reduce the damage from them. The key, Stuecker said, is having more precise forecasts.
An ominously rising tide
Along with fiercer storms, add more water, and you have a recipe for more flooding. Higher sea levels supply more
water that storms can push inland. Rising seas also push island water tables higher, which can combine with heavy rainfalls to cause inland flooding.
“People have seen firsthand the impacts of Hurricane Katrina, Superstorm Sandy, and increasing ‘sunny-day’ flooding in Florida,” said Dr. Karen Thorne, a scientist with the U.S. Geological Survey in Davis, California. “More people are no longer in denial about sea-level rise or think it’s a problem for the next generation to solve.”
In 2017, Hawai‘i Sea Grant published a Sea Level Rise Vulnerability and Adaptation Report, which projects that a 1 meter (3.2-foot) sea-level rise would render more than 25,800 acres of state land unusable, and compromise more than 6,500 structures. The publication includes the Hawai‘i Sea Level Rise Viewer, an interactive atlas that people can use to pinpoint their location’s vulnerability. The report also outlines plans to prevent flooding where possible, along with a “managed retreat” policy to identify inland areas to develop.
Ideas once considered too complicated and costly are now being discussed around the world, including massive dike and canal systems to block or distribute floodwaters. Or using dredged sediments in innovative ways: to build up sand dunes as bulwarks, construct large offshore sandbars to block incoming waves, or even re-create new land areas for islands at risk of being drowned. Thorne heads an ongoing experiment to spray dredged sediments atop a subsiding marsh in Anaheim, California, and elevate it by 10 inches.
In other places, scientists are exploring “a green infrastructure approach,” Thorne said, “letting nature work better on our behalf to protect shorelines by protecting wetlands or planting and fertilizing vegetation to help elevate and stabilize them.”
Thorne, for example, led a study to examine whether protective coastal mangrove forests on Micronesian islands can withstand fast-rising seas.
Though they are invasive in Hawai‘i, in many parts of the world mangroves can be nature’s ideal coastal ramparts. They thrive in areas flushed tidally with salt water, pumping oxygen down to intricate, rapidly growing root systems submerged in mud and extending above the sea surface, said Dr. Richard MacKenzie, a research ecologist with the U.S. Forest Service based in Hilo, Hawai‘i.
Sediments suspended in tides hit the roots, settle down, and build up the seafloor, often allowing the mangroves to keep pace with sea-level rise. The root systems also buffer storm waves, protecting coastlines from erosion.
MacKenzie has worked extensively with colleagues in the Forest Service and Western Pacific island nations to educate communities about mangrove forests’ value, suggest ways to prevent their destruction, except in Hawai‘i, investigate where and why mangrove forests aren’t doing well, and devise solutions.
To enhance ways to monitor mangroves, MacKenzie recently spearheaded the invention of a ground-based LIDAR (light detection and ranging) system that emits tens of thousands of laser pulses to scan an entire mangrove forest in seconds, collecting detailed data on how trees are growing.
“It’s like using Star Wars technology in the Dagobah Swamp,” he said.
A bird’s-eye view of corals
Breakthrough technology offers hope for other species. In December, scientists announced that they had flown an innovative airborne laboratory above all the coral reefs around eight Hawaiian islands and created unprecedented comprehensive maps that chart the corals’ health.
Corals normally house symbiotic photosynthesizing algae that provide food to the corals in exchange for shelter. But when waters become too warm, the colorful algae depart, leaving corals starved for food and showing naked, white skeletons—a phenomenon called coral bleaching. At the same time, corals are being stressed by human activities: overfishing, tourism, and pollution.
Using the airborne lab, these scientists can gather data efficiently and repeatedly over wide swaths of ecosystems that are difficult for humans to access. The lab was developed over decades by Dr. Greg Asner and colleagues at Arizona State University’s Center for Global Discovery and Conservation Science (CDCS) in Hilo. The lab is equipped with LIDAR, cameras, and two high-resolution spectrometers that measure hundreds of wavelengths of light across the spectrum from ultraviolet to infrared. The spectrometers detect light emitted by chemicals in organisms, Asner said, and live and dead corals have fundamentally different chemical signatures.
GDCS scientists employed artificial intelligence techniques to interpret collected data and distinguish corals from rocks, waves, and clouds. They then teamed with Gove and other marine biologists, who superimposed their data on waves, water temperatures, fishing, shoreline development, and pollution.
“This is a tremendous leap forward,” Gove said. “Now we can really paint a picture of where and why corals persist or not. We can home in on what traits or conditions allow them to survive despite threats. We can parse our different impacts from climate change versus human activities and determine which factors we need to mitigate to give reefs their best chance of persisting.”
Fish, whales, and walruses
At least corals are stationary. It’s even harder to determine how ocean warming is affecting animals that move around in the vast ocean.
Coral reef fish may lose habitat. Other species may shift their ranges, moving to cooler waters if they can’t tolerate heat or following the migrations of preferred prey, said Dr. Eva Schemmel, a research scientist at NOAA Pacific Islands Science Center.
Warmer temperatures also increase fishes’ metabolic rates, so they grow faster and reach sexual maturity when they are younger. Some species—moi (Pacific threadfin) and ‘ama’ama (striped mullet), for example—have shifted or extended their spawning, and regulations to temporarily close fisheries to protect spawning haven’t kept up.
“Paying attention to shifts that occur as environmental conditions change and adapting harvesting practices is one way to help ensure that fisheries remain sustainable,” said Schemmel, who has worked with community fishers.
Tracking larger ocean life, Dr. Sue Moore of the University of Washington is seeing “boom times for some baleen whales,” but challenging times for other marine mammals in the Arctic. Warmer ocean waters circulating northward are accelerating the melting of sea ice. The summer extent of Arctic Ocean ice has diminished from an average of 2.64 million square miles in the 1980s to 1.44 million in 2020.
For polar bears, walruses, and seals that depend on sea ice platforms to hunt, rest, and rear young, disappearing ice is daunting. But it also opens new expanses of ocean in which plankton can flourish, producing a bountiful buffet for baleen whales.
“We’re routinely seeing more temperate whale species—humpbacks, minke, and fins—joining seasonally migrating gray whales and endemic bowheads coming into the Arctic to feed in summer and early autumn,” Moore said.
Warming waters could also cause ecosystem changes elsewhere that are detrimental to whales. And an open Arctic Ocean also means more commercial and military ship traffic and noise that threaten whales. To cohabit, Moore says, “we have the capacity to add ocean monitoring systems and coordinate with reports from Indigenous communities to better predict regional ocean conditions. For example, if we know where krill are swarming, we know whales will likely be there and can inform ocean users to reduce ship speed and refrain from approaching animals.”
Tiny critters and mammoth geoengineering
How will a warming ocean affect life at the bottom of the food chain? That’s a challenging question for scientists. The adaptive capacities of innumerable species of plankton remain mysterious, and the factors besetting them are myriad, said White, the UHM marine microbiologist.
But could plankton and the ocean help solve our problem? At the sea surface, photosynthetic plankton convert carbon dioxide (CO2) into organic carbon. When they die and decompose, a portion sinks, carrying carbon to the depths. This “biological pump” effectively extracts excess CO2 from the atmosphere and sequesters it in the deep ocean.
White is a member of a National Academy of Sciences committee convened last fall to assess the feasibility and risks of ambitious geoengineering strategies to ramp up ocean CO2 removal and sequestration. Strategies include adding alkaline minerals to seawater to increase CO2 solubility and developing new technologies to extract CO2 from seawater and transport and store it deep in the ocean.
The committee is also investigating ways to speed up the biological pump. Among these are “blue carbon” projects such as protecting and restoring mangrove forests, whose root systems capture and store five to ten times as much carbon as land forests, MacKenzie said; injecting iron and other nutrients into the ocean or devising systems to drive nutrient-rich deep water to the surface to fertilize more phytoplankton growth; and cultivating and harvesting more CO2-extracting algae and seaweed.
“We need a portfolio of solutions and global cooperation,” White said. “Another lesson of the pandemic slowdown is that our carbon dioxide emissions are projected to drop by seven percent in 2020. We see that coordinated actions of humanity can greatly reduce emissions. We shouldn’t feel overwhelmed, because there is still time to take action to protect our environment for generations to come.”
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