A fleet of robots, trolling the oceans and measuring their heat content, has revolutionized scientists’ ability to study how climate change is affecting the seas.
Now the aquatic machines called Argo floats are going into the deepest ocean abyss.
“We know a lot from Argo now that we have over a decade’s worth of temperature data,” said Gregory Johnson, a researcher with the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory. “We now know a lot about the upper ocean and how much heat it’s taking up, but we know less about the deep ocean heat uptake.”
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
A report released last month at the International Union for Conservation of Nature (IUCN) World Conservation Congress concluded that oceans have taken up 93 percent of the warming created by humans since the 1970s. To put that in perspective, if the heat generated between 1955 and 2010 had gone into the Earth’s atmosphere instead of the oceans, temperatures would have jumped by nearly 97 degrees Fahrenheit (E&ENews PM, Sept. 7).
Argo is hardly the only fleet of scientific tools collecting data on ocean warming. But much of what scientists do know about the extent of the ocean’s heat-trapping ability is because of this international program, which has collected more than 1.5 million measurements.
The aquatic robots were first deployed into the watery depths in 2000. Today, the project consists of about 3,500 steel, cylinder-shaped floats that descend 2,000 meters, or 1.25 miles underwater.
At about 55 pounds and 6 ½ feet tall, each battery-powered observation tool takes about 200 pressure, temperature and salinity measurements as it journeys through the ocean, up and down in 10-day intervals like a data-collecting fishing lure. The data are transmitted to satellites when the float reaches the surface. The floats take measurements for four to five years before sinking to the bottom of the sea.
“Argo has made this line of research more comprehensive than it could have ever been with historic data sets,” said Dean Roemmich, a professor of oceanography at the Scripps Institution of Oceanography in San Diego.
Roemmich, who led the original design team, said Argo has expanded global knowledge of the oceans almost uniformly around the globe. Prior to the program, most of the collected ocean data were focused in the Northern Hemisphere. In branching out, scientists have already discovered, for example, that the oceans are not warming uniformly, rather the majority of warming is contained in the Southern Hemisphere.
But scientists continue to struggle with how the heat the ocean absorbs miles under the sea is affecting ocean currents and circulatory systems, ocean ecosystems, and even sea-level rise.
The newest iteration of Argo, Deep Argo, can help.
In June 2014, two Deep Argo floats were deployed north of New Zealand. This year, Johnson said a dozen floats are due to be released into the sea. The goal is to expand the program to have global coverage, although currently the U.S. Argo program, which is funded by NOAA but implemented by five U.S. institutions, has limited funding for the deep divers.
Unlike the original version, deep-ocean Argo floats are made of glass and are orb-like, rather than cylindrical. The design, spearheaded by the Scripps Institution of Oceanography and Teledyne Webb Research, better distributes the crushing pressure almost 4 miles under the ocean’s surface. But like the original Argo, Deep Argo can cycle from the surface to 6,000 meters down in 10-day cycles, relaying information for three years.
“They can survey the whole ocean, with the exception of the deepest ocean trenches,” Johnson said. “That’s revolutionary.”
Hair dryers vs. tea kettles
There are a couple of reasons the oceans currently store more than 90 percent of the excess heat created by human activities.
First, they are 280 times larger than the atmosphere. In addition, the oceans are not that reflective. When sunlight hits the surface, most of that heat is absorbed.
Sea water has high density and holds four times more heat than the air. For example, a 1 degree Celsius change in ocean temperature is equivalent to a 1,000 C change in the atmosphere, Johnson said.
To put the amount of heat collected into perspective, Argo and other ocean measurements have determined the amount of warming that has occurred over the last decade, most of which we know is stored in the oceans, is equivalent to 140 billion 15-watt hair dryers or tea kettles running continuously.
Johnson said that thinking about how hair dryers work versus a tea kettle is actually a good analogy for the oceans.
“When you first turn a tea kettle on, you can touch it for a minute,” he said. “It take a lot longer to warm up water in tea kettle versus the air with a hair dryer. The tea kettle is like the ocean.”
Part of the reason scientists are so interested in learning more about where the heat sucked up by the ocean is being stored is because it ties directly to the ability of mankind to stave off the worst effects of a changing climate.
Johnson said it’s unlikely the oceans will just stop taking in heat, however, because of their massive size—it takes decades for the near surface ocean to come into equilibrium, with the greenhouse gas concentration in the atmosphere.
One of the key services the oceans provide is to shift heat through a handful of global circulation patterns that control our weather, and at certain phases of these patterns the oceans will naturally take up and release heat.
But what is still murky for researchers is how the heat captured by the oceans affects their ability to naturally regulate heat through circulation patterns.
“If we were able to somehow freeze global greenhouse gas emissions right now at 400 parts per million, the surface oceans would continue to warm for a few decades to a century,” Johnson said. “A lot of our ability to make our climate commitments has to do with the time scale of ocean circulation to bring heat back down.”
Although the ocean is very good at capturing human-created heat and preventing it from warming the atmosphere, it does not come without consequences.
The IUCN report summarized scientific literature detailing how warming oceans are accelerating the melting of ice shelves; affecting marine mammal migration patterns, fishery stocks and coral reefs; and contributing to more intense storm systems.
The United Nations’ Intergovernmental Panel on Climate Change is in the process of preparing a special report on climate change, the oceans and cryosphere, but the 80 scientists from around the world that authored the IUCN report noted ocean warming has been largely ignored in international climate change discussions.
They write that ocean warming “may well turn out to be the greatest hidden challenge of our generation.”
Improving scientific knowledge through programs like Argo will be key, they add.
“Future biological monitoring of these open-ocean ecosystems, through an integrated and sustained observational approach, will be essential in understanding the continuing impacts of ocean warming and other stressors on oceanic systems,” the report states.
Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. E&E provides daily coverage of essential energy and environmental news at www.eenews.net. Click here for the original story.