The Sea May Be Absorbing More Heat Than We Thought

If you ever meet a climate scientist, give them a hug. Not only is the work important, it involves an absolute mess of variables-emissions, maybe sequestering those emissions, atmospheric patterns, maybe geoengineering that atmosphere. Data is often sparse or non-existent. So give them a hug.

The data problem is particularly acute in the oceans. A key part of figuring out how much the planet has warmed, and how drastically we need to cut emissions, is determining how the sea is changing. But that's, uh, 325 million cubic miles of water. There's no way to sample all of it.

But scientists are making a tooth. A network of 4,000 sensors, known as Argo, has been providing solid temperature data, but it only covers the upper two meters of ocean. The average ocean depth is about that.

Today, researchers are sharing the results of a different method for determining water consumption. air. And their findings are troubling. The oceans may have warmed 60 percent more than the last month IPCC report cited. That would be more important than it would have been to keep warming up to 2 degrees C above pre-Industrial Revolution levels-the goal of the Paris Climate Agreement-we would have to cut 25 percent more than we thought. The new method needs more scrutiny from other climate researchers, but so far … yikes.

The researchers call their calculations "atmospheric potential oxygen," or APO. It focuses on two gases: CO2 and O2. "When the ocean warms, it loses O2 and CO2, what we call oxygen potential," says oceanographer and climate scientist Laure Resplandy, lead author on a new Nature paper describing the technique. "When it loses that gas, we can track it in the atmosphere."

So far, so simple: As climate change causes the ocean to heat up, the water releases O2 and CO2 into the atmosphere, which a handful of land-based sensors then detect (they've been doing so for decades, giving the researchers lots of data to play with). Except the ocean is not the only source of these gases. Fossil fuels are, too-when oil and coal burn, they release CO2 and use up O2.

That muddies the APO signal, so the researchers had to control for fossil fuels by factoring in worldwide energy use. "We take all the fuel inventories," says Resplandy, "and we say, OK, we've done a lot and much more than we've been doing."

Further complicating matters is that the planet acts as a carbon sink-trees pull CO2 out of the atmosphere, as do plant-like phytoplankton in the oceans. The APO calculations take into account these estimates.

They have collected data from O2, CO2, and temperature readings at the same time. "Using those 80,000 points in the ocean we show that O2 and CO2 combined together are a good tracer of heat," says Resplandy. The atmosphere should mirror that link. They are essentially built up by the ocean, which is used to absorb the ocean. Climate scientists may be able to use this method

The findings are not encouraging. The researchers calculated that each year since 1991, the seas absorbed 13 zettajoules of heat energy, 150 times the energy we as humans produce annually. If a zettajoule sounds vaguely ominous and certainly big, think even bigger-a zettajoule has 21 zeros after it. Previous estimates put the number at 8 zettajoules.

"An ocean warmer than we thought that the earth actually warmed up more than we thought, and that means the earth is more sensitive to emissions than we thought," says Resplandy. It's also bad news for the denizens of the sea, which are struggling to adapt to hotter seas. Corals in particular.

How important is it for scientists to understand how much are the oceans are warming, exactly? "Ocean warming is tea "says University of St. Thomas researcher John Abraham, who was not involved in the new study. "Global warming is really ocean warming."

A potential issue with this new method, though, is the foundational link between the gases and the ocean temperatures, which is based on model calculations. No model, after all, is perfect. "Whether or not these models are accurate enough is an area of ​​concern," says Abraham. "A change of X percent of an atmospheric gas gives you a breakthrough in ocean heat content. How do we really know that quantitative relationship? If they're off by 10 or 20 percent, that's a big error. "It's worth noting, though, that it's worth noting that CO2 and O2 combined is a good tracer of ocean heat.

Another major question is the noise: precisely separating the CO2 and O2 quantities attributed to fossil fuels and other sources, and those from the oceans. "It is a delightfully innovative approach, using global atmospheric oxygen concentration ratios
"NOAA Ocean Scientist Tim Boyer, who has studied ocean heat. He wonders, though, how accurately scientists can isolate the ocean's production of these gases from other sources, and if the new method can calculate the temperature of the water itself.

Other researchers will be in the process of testing. If the authors are right, the APO could become another tool to help scientists by ocean warming. Hugs alone, unfortunately, are not going to make their jobs easier.

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