‘Missing’ heat shows gaps in climate research

A photo of the sun.
Colorado scientists are trying to track the missing heat in the global climate equation. PHOTO COURTESY USGS.

Boulder-based scientists say existing data can’t account for all the incoming solar energy

By Summit Voice
SUMMIT COUNTY — Scientists with the Boulder-based National Center for Atmospheric Research say about half the heat that’s built up on Earth in recent years can’t be traced by existing satellites, ocean sensors and other existing instruments.

The “missing” heat may be building up deep in the oceans or elsewhere in the climate system. Pinpointing the buildup of energy in the planet’s climate system is critical to understanding how the climate may change, says NCAR researcher Kevin Trenberth, the lead author of an article published last week in Science.

“The heat will come back to haunt us sooner or later,” says Trenberth. “The reprieve we’ve had from warming temperatures in the last few years will not continue.”

The article suggests that last year’s rapid onset of El Niño, the periodic event in which upper ocean waters across much of the tropical Pacific Ocean become significantly warmer, may be one way in which the solar energy has reappeared.

At issue is the imbalance between energy from the sun that’s entering the Earth’s climate system, and the energy leaving the Earth’s surface. That imbalance is the source of long-term global warming. If the instruments are correct, more energy is building up than is being recorded, thus the “missing” heat.

A percentage of the missing heat could be the result of imprecise measurements by satellites and surface sensors or incorrect processing of data from those sensors, the authors say. Until 2003, the measured heat increase was consistent with computer model expectations. But a new set of ocean monitors since then has shown a steady decrease in the rate of oceanic heating, even as the satellite-measured imbalance between incoming and outgoing energy continues to grow.

Either the satellite observations are incorrect, says Trenberth, or, more likely, large amounts of heat are penetrating to regions that are not adequately measured, such as the deepest parts of the oceans.

Tracking the growing amount of heat on Earth is far more complicated than measuring temperatures at the planet’s surface. The oceans absorb about 90 percent of the solar energy that is trapped by greenhouse gases. Additional amounts of heat go toward melting glaciers and sea ice, as well as warming the land and parts of the atmosphere. Only a tiny fraction warms the air at the planet’s surface.

Some of the missing heat appears to be going into the observed melting of ice sheets in Greenland and Antarctica, as well as Arctic sea ice, the authors say. The rest may be in the ocean. Some heat increase can be detected between depths of 3,000 and 6,500 feet,  but more heat may be deeper still beyond the reach of ocean sensors.
Trenberth and co-author John Fasullo call for additional ocean sensors, along with more systematic data analysis and new approaches to calibrating satellite instruments, to help resolve the mystery.

Ocean buoys used measure temperatures, for example, are separated by about 185 miles and take readings only about once every 10 days from a depth of about 6,500 feetup to the surface. Plans are under way to have a subset of these floats go to greater depths.

“Global warming at its heart is driven by an imbalance of energy: more solar energy is entering the atmosphere than leaving it,” Fasullo says. “Our concern is that we aren’t able to entirely monitor or understand the imbalance. This reveals a glaring hole in our ability to observe the build-up of heat in our climate system.”


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