Has Earth's Missing Heat Been Found?

[Buster's Uncle]

Has Earth's Missing Heat Been Found?
LiveScience.com
By Becky Oskin, Senior Writer  6 minutes ago



This photo from NASA's Suomi NPP satellite shows the Eastern Hemisphere of Earth in "Blue Marble" view. The photo, released Feb. 2, 2012, is a companion to a NASA image showing the Western Hemisphere in the same stunning detail



Where, oh where, is the planet's missing heat?

In 1999, the feverish rise in Earth's surface temperatures suddenly slowed, even as greenhouse gas emissions escalated. This unexpected slowdown has been called a global warming hiatus or global warming pause. Most climate scientists don't think this hiatus means global warming went kaput, but the reason (or reasons) for the slowdown has scientists flummoxed. Researchers have offered more than two dozen ideas to explain the missing heat.

Now, a study published today (Aug. 21) in the journal Science suggests a natural climate cycle in the North Atlantic Ocean gobbled Earth's extra heat. While the study is unlikely to settle the scientific debate, it does support the idea that Earth's global warming continues in the ocean, even when air temperatures stay flat.

"It's important to distinguish between whether ocean heat storage is responsible for the hiatus versus not enough heat reaching the surface of the Earth," said study co-author Ka-Kit Tung, of the University of Washington in Seattle. "We did find enough heat stored in the North and South Atlantic that, if it had remained on the surface, it would have resulted in rapid warming."


Global storage closet

Scientists have blamed the oceans for the global warming pause before, but they pointed their fingers at the Pacific, not the Atlantic. However, in seeking to test this idea with temperature data, oceanographer Xianyao Chen, of the Ocean University of China in Qingdao, and Tung, an atmospheric scientist, said they couldn't find the missing heat in Pacific Ocean temperature measurements.



Top: Global average temperatures. Middle: Heat content measured in the North Atlantic Ocean. Bottom: Seawater salinity in the North Atlantic Ocean since 1950.


"If these models are true, we should be able to find the missing heat, and under the Pacific we couldn't find enough heat to explain the hiatus," Tung told Live Science.

Tung and Chen then searched ocean by ocean until they hit on the North Atlantic, where the heat was playing hooky. The pair primarily relied on Argo floats, which record ocean temperature and salt content down to 6,560 feet (2,000 meters). These worldwide floats reached their most comprehensive levels beginning about 2005. Other records from floats, ships and buoys filled in the timeline since 1970.

But the millions of data points don't conclusively prove that the North Atlantic Ocean is devouring heat. "Unfortunately, the massive array of ocean temperature measurements by Argo floats has only been made after the early 2000s, just when the present hiatus in surface warming was starting," said Matthew England, a climate scientist at the University of New South Wales in Australia, who was not involved in the study. "So being conclusive about each ocean basin is limited by data availability."

Tung and Chen noticed that the North Atlantic's heat content (a measure of stored energy) shifted in 1999, about when the hiatus began. The ocean started absorbing heat at depths below 984 feet (300 m). (The South Atlantic Ocean also took up some heat.) These regions stored more heat energy than the rest of the world's oceans combined, even the enormous Pacific Ocean, the researchers' temperature data show.



Surface currents that form a portion of the Atlantic Meridional Overturning Circulation.


Small basin, big effect

So how does the Atlantic cool an entire planet? The likely culprit is a natural climate cycle linked to the Atlantic Meridional Overturning Circulation (AMOC) current, Tung said. The AMOC is part of a worldwide ocean conveyor belt. Here's how the AMOC works: In the North Atlantic, salty tropical water flowing north cools off and sinks. This water, dense because it is cool and salty, heads south toward the equator, then eventually rises again in the South Atlantic. When the water sinks, it traps heat in the ocean depths. Ocean surface temperatures drive the current: fast when cold, slow when warm.

Between 1945 and 1975, the cycle was in a cool phase, sucking up atmospheric heat at a rapid pace. Toward the end of this cycle, in the 1970s, scientists noticed a suspected "global cooling" that was touted as the beginning of a possible Ice Age. But then the AMOC flipped to warming, corresponding to the rapid uptick in global temperatures. Finally, in 1999, the current switched back to a cold, speedy plunge into the ocean depths, taking extra heat along with it.

Such natural cycles make global warming look more like a staircase than a steady rise in temperatures, Tung said. "Right now, we're on the flat part of the staircase. We still have a few more years of the hiatus."

However, others scientists remain convinced the Pacific plays an important role in the global warming hiatus. Several recent studies affirm the link between the pause and the changes in the Pacific. An Aug. 3 study in the journal Nature Climate Change found that faster trade winds over the Pacific bring up cold water and cool the atmosphere. An Aug. 17 study, also in Nature Climate Change, suggested the Pacific Decadal Oscillation climate cycle might be responsible for the hiatus. That cycle flips every 20 to 30 years.

"I still think the Pacific Ocean is playing the lead role in this ocean heat uptake, but this study is important as it points to an additional role from the Atlantic and Southern Oceans," said England, who co-authored the Aug. 3 Nature Climate Change study.


http://news.yahoo.com/earths-missing-heat-found-182808474.html

[Geo]

Next up: the planet's mantle sucked up the extra heat!

[Buster's Uncle]

Atlantic slows warming, temperature rises seen resuming from 2030: study
Reuters
By Alister Doyle  2 hours ago



OSLO,(Reuters) - The Atlantic Ocean has masked global warming this century by soaking up vast amounts of heat from the atmosphere in a shift likely to reverse from around 2030 and spur fast temperature rises, scientists said.

The theory is the latest explanation for a slowdown in the pace of warming at the Earth's surface since about 1998 that has puzzled experts because it conflicts with rising greenhouse gas emissions, especially from emerging economies led by China.

"We're pointing to the Atlantic as the driver of the hiatus," Ka-Kit Tung, of the University of Washington in Seattle and a co-author of Thursday's study in the journal Science, told Reuters.

The study said an Atlantic current carrying water north from the tropics sped up this century and sucked more warm surface waters down to 1,500 meters (5,000 feet), part of a natural shift for the ocean that typically lasts about three decades.

It said a return to a warmer period, releasing more heat stored in the ocean, was likely to start around 2030. When it does, "another episode of accelerated global warming should ensue", the authors wrote.

Almost 200 governments aim to agree a deal to combat climate change at a summit in Paris in late 2015 and the hiatus has heartened skeptics who doubt there is an urgent need for a trillion-dollar shift from fossil fuels to renewable energies.

Several previous studies have suggested that the larger Pacific Ocean is the likely site of the "missing heat" from man-made greenhouse gases, perhaps linked to a series of La Nina cooling events in the Pacific in recent years.

Other suggestions for the slowdown in warming have included a rise in industrial pollution that is blocking sunlight.


SHIFT IN SALINITY?

A separate team of scientists writing in the journal Nature Geoscience on Sunday said that factors including swings in the sun’s output and sun-blocking dust from volcanic eruptions may account for gaps in understanding the warming trends.

In addition, La Nina cooling events in the Pacific Ocean had played a role, according to the report that examined why computer models of the climate had over-estimated temperature rises in the past decade.

But no one knows for sure.

"It will be interesting to see how and if these ideas are connected" with the theory of the Atlantic, lead author Markus Huber said of the study by the Institute for Atmospheric and Climate Science at ETH Zurich.

Thursday's study said a shift in salinity may have caused more heat to be transferred to the depths of the Atlantic.

Warm, salty water from the tropics flows north on the Gulf Stream in the Atlantic and sinks when it meets cooler water. The "great ocean conveyor belt" then makes cold water flow in the depths to the Southern Ocean.

Even though global warming has slowed, 13 of the 14 warmest years on record have been this century, according to U.N. estimates.

A U.N. panel says it is at least 95 percent certain that human emissions, rather than natural variations in the climate, are the main cause of rising temperatures since 1960 that have caused more heatwaves, downpours and rising sea levels.

(Editing by Gareth Jones)


http://news.yahoo.com/atlantic-slows-warming-temperature-rises-seen-resuming-2030-180401635.html

[Buster's Uncle]

Global warming 'hiatus' means heat is hiding in ocean
AFP
31 minutes ago



An apparent slowdown in the Earth's surface warming in the last 15 years could be due to that heat being trapped in the deep Atlantic and Southern Ocean, researchers say (AFP Photo/)



Washington (AFP) - An apparent slowdown in the Earth's surface warming in the last 15 years could be due to that heat being trapped in the deep Atlantic and Southern Ocean, researchers said Thursday.

The findings in the journal Science suggest that such cycles tend to last 20-35 years, and that global warming will likely pick up again once that heat returns to surface waters.

"Every week there's a new explanation of the hiatus," said co-author Ka-Kit Tung, a University of Washington professor of applied mathematics and adjunct faculty member in atmospheric sciences.

"We looked at observations in the ocean to try to find the underlying cause."

Tung and Xianyao Chen of the Ocean University of China studied deep-sea temperatures from floats that sample the water as deep as 6,500 feet (2,000 meters) depth. They found that more heat began to sink around 1999, just when the rapid warming of the 20th century began to flatline.

The movement of more heat into the water explains how surface temperatures could stay close to the same, even as mounting greenhouse gases trap more solar heat at the Earth's surface, researchers said.

They also found that contrary to earlier studies, the Pacific Ocean was not the hiding place for the heat.

"The finding is a surprise," Tung said.

"But the data are quite convincing and they show otherwise."

The change also coincided with an increase in saltier, denser water at the surface of the northern part of the Atlantic, near Iceland.

This dynamic caused changes in the speed of the huge current in the Atlantic Ocean that circulates heat throughout the planet, the study said.

"When it's heavy water on top of light water, it just plunges very fast and takes heat with it," Tung said.

"There are recurrent cycles that are salinity-driven that can store heat deep in the Atlantic and Southern oceans," Tung added.

"After 30 years of rapid warming in the warm phase, now it's time for the cool phase."

Researchers said the current slowdown may last another decade, then the rapid warming is likely to return.

The study was funded by the US National Science Foundation and the National Natural Science Foundation of China.


http://news.yahoo.com/global-warming-hiatus-means-heat-hiding-ocean-222211103.html