To understand the record-breaking warmth this winter in Minnesota, scientists look to the oceans.
For the sixth straight year, surface temperatures of the world's oceans set a new heat record in 2023, according to a study released this month from an international team of scientists. Temperatures soared past the prior record set in 2022 by nearly 0.5 degrees Fahrenheit, spurred by both climate change and a strong El Niño.
What happens in the Pacific Ocean is especially important to Minnesota, said John Abraham, a thermal-science expert at the University of St. Thomas and one of the lead scientists of the study.
"That's because our weather comes from west to east," he said. "As the atmosphere passes over the Pacific, it will pick up moisture and heat, and then it releases that moisture and heat over a place like Minnesota."
December was the warmest in about 150 years of record-keeping for most of the state, according to Minnesota's climatology office. A brief cold spell last week helped bring January temperatures closer to normal, but the month has still been hot. Lakes and ponds across the southern half of the state didn't freeze until mid-January — the latest ice-ins recorded since climatologists started tracking in the 1970s. They have already begun to thaw. The warm winter will have a lasting impact on moose, ticks, deer and other wildlife and the lack of ice and warmer water will increase the likelihood of algae blooms and fish kills in the state's lakes.
Strong El Niños typically drive weather patterns that often, but not always, trap cold air about 1,000 miles north of Minnesota and push moisture about 1,000 miles south. An El Niño began in May and is probably the reason this winter has been so dry, according to the state climatology office.
Climate change is really the story of warming oceans, Abraham said.
Carbon dioxide, methane and other greenhouse gases in the air keep heat from the sun from escaping to space, and instead reflect it back to the Earth. A tiny part of that excess heat warms the air, he said. A small portion melts polar ice and snow. The vast majority of it moves from the atmosphere into ocean water, slowly and steadily warming it.
The average surface temperature of the world's oceans was about 0.5 degrees Fahrenheit warmer in the second half of 2023 than it was in 2022, which was itself a record breaking year. That may not sound like much of an increase, Abraham said, but the energy the oceans absorbed in order for heat to rise that much is "astounding."
Imagine a time you were frustrated watching a pot of water boil, he said. But now imagine that pot is 1.25 miles deep and spans 70% of the Earth's surface. It took 15 zettajoules of energy to create that extra half degree of heat, the study found. A zettajoule is a single joule times 10 to the 21st power, or a one with 21 zeros after it. For reference, the entire world uses about half of a zettajoule a year in its energy systems, Abraham said.
The excess energy from the heat in the oceans compared to 2022 is enough to power the world's economies for 30 years. It's enough to boil 2.3 billion Olympic-sized swimming pools, Abraham said. It's the equivalent of setting off six atomic bombs every second of every day for a year, he said. And 2022 was already a record year, with a heat content that was 10 zettajoules higher than it was in 2021.
That excess energy and heat gets picked up by the atmosphere and supercharges weather systems around the world.
Ocean temperature records were gathered using data from both the National Oceanic and Atmospheric Administration in the U.S. and China's Institute of Atmospheric Physics. Records go back to the 1950s, when scientists would drop little torpedoes called expendable bathythermographs over the sides of boats to collect data as they descended. Starting in 2005, scientists started using "Argo floats," which travel about 7,000 feet under the sea before floating back to the surface. Every stretch of ocean measured is showing a steady temperature increase.
The only answer is to drastically cut the use of greenhouse gases, to give heat a better chance to escape into space, Abraham said. Like a train slamming its brakes, even with massive cuts, ocean temperatures won't stop increasing for the foreseeable future — there is already too much carbon in the air. But what really matters is leveling off the temperature increases, slowing the rate and finding a new normal.
If the world can keep the increase to 4 degrees Fahrenheit or less, that's great, Abraham said. If average temperatures climb 5 degrees or more, the world will likely become one we don't recognize.
