DAVID GREENE, HOST:
Now we have the story of a strange and elaborate quest that all hinged on a couple decimal points. Scientists today need to figure out how much hotter the oceans are now than in the past, but the old measurements are unreliable. And figuring them out is more difficult than it might seem.
Here's NPR's Rebecca Hersher.
REBECCA HERSHER, BYLINE: If you want to know how much hotter the oceans are today than they were, say, in the 1800s, you need two things - information about how hot the oceans are now and information about how hot the oceans were then. And it's that second part, the historical measurements, that graduate student Duo Chan was interested in.
DUO CHAN: I sometimes joke with my friends - like, oh, I'm not only a climate scientist, I'm a detective.
HERSHER: His detective work started with a tome that sent him down a crazy rabbit hole. The book listed all the ocean temperature measurements taken by sailors going back to the 1800s.
CHAN: Yes. You'll see that there are, like, more than 100 different data sources.
CHAN: So what we...
HERSHER: Wait. Can I read a couple of them?
HERSHER: So a Japanese whaling fleet...
HERSHER: ...Norwegian Antarctic whaling factory ships, Netherlands marine.
CHAN: Yes. And here you have, like, the Japanese Kobe collection.
HERSHER: In all, there are millions of measurements from all over the world. And most of them, up until World War II, were collected using buckets.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED NARRATOR: First, the sea temperature is taken. The movement of warm and cold currents affect the weather a good deal.
HERSHER: This newsreel is from 1947.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED NARRATOR: The met assistant heaves a canvas bucket over the side and collects a sample of seawater and then takes its temperature.
HERSHER: The temperature got written in a logbook. But sailors generally didn't write down other information, like how big the bucket was or what it was made of or how long they waited before putting the thermometer in - all things that could change a temperature reading.
Peter Huybers is the lead scientist on the project.
PETER HUYBERS: This is like if someone left you all their receipts that they had ever spent during their lives and you were trying to piece together what they had been doing.
HERSHER: Duo Chan, the grad student, was undeterred. He had an idea. He took all the measurements and looked for ships that had passed near each other. So they had both measured the temperature of the same piece of ocean at the same time about. He found nearly 18 million pairs of measurements like that and looked for patterns and found one big one. The measurements from Japan in the 1930s seemed to be a little bit too cold - but why?
Duo thought maybe Japanese ships were getting taller, so the water cooled off as it was hoisted all the way up to higher decks. So he found records about Japanese ship sizes. And in order to read them...
CHAN: I learned Japanese.
HERSHER: You did?
CHAN: I did.
HERSHER: Turned out, ships had gotten slightly bigger. But all that work ended up being for nothing because ship size actually had nothing to do with the cold measurements. It was something much more mundane - rounding. A colleague in the U.K. happened to send them some vital information, an old Air Force document. After World War II, the U.S. military had taken all the ocean temperature measurements from Japanese ships and digitized them. And when they did that, they dropped the decimal place.
So if the water was 15.1 degrees on one day and 15.9 degrees on another, both temperatures were recorded as just 15 degrees. Overall, that made the measurements artificially cold by about half a degree.
CHAN: It's amazing. Like, people keep a record of what they did.
HERSHER: The team published their research this spring and it's made waves - because of their work, we now know that the Pacific Ocean used to be slightly warmer than we thought, which will help make climate models more accurate and potentially help avoid catastrophic climate change.
Rebecca Hersher, NPR News.
(SOUNDBITE OF ...OF SINKING SHIPS' "IT'S EASIER WITH NO DESTINATION")
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