Deep sea marine life, like the anemones shown above, are not yet feeling the heat from global climate change. While the top half of the ocean has warmed measurably over the past decade, the bottom half has not.

(NERC)

Deep below the ocean surface, there's a place global warming hasn't yet reached.

According to a study published Oct. 5 in the scientific journal Nature Climate Change, scientists at NASA's Jet Propulsion Laboratory (JPL) have found that the deepest part of the world's oceans have not warmed measurably over the past decade.

The scientists analyzed ocean temperatures between 2005 and 2013, and found that below a depth of 1.24 miles -- roughly its half-way depth -- the bottom half of the global ocean has not warmed nearly as quickly as the top half, NASA notes.

They collected the temperature data using both satellite measurements and directly using what's known as the Argo array, a network of some 3,000 floating probes scattered throughout the world that measure ocean temperatures and salinity.

This image shows heat radiating from the Pacific Ocean as imaged by the NASA's Clouds and the Earth's Radiant Energy System instrument on the Terra satellite. (Blue regions indicate thick cloud cover.)

(NASA)

While the report's authors say the findings do not question the overall science of climate change, it is the latest in a series of findings that show global warming to have slowed considerably during the 21st century, despite continued rapid growth in human-produced greenhouse gas emissions during the same time.

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"The sea level is still rising," Josh Willis, a JPL project scientist and one of the study's co-authors, said in a news release. "We're just trying to understand the nitty-gritty details."

Sea level rise is caused by a range of factors, the study notes, from things like thermal expansion -- the ocean expanding as it warms up -- to runoff from the melting of the world's glaciers and ice sheets, in places like Greenland and Antarctica.

The study's results came from a "straightforward subtraction calculation," NASA says, using the temperature data gleaned from the Argo array as well as NASA's Jason-1 and Jason-2 satellites and its Gravity Recovery and Climate Experiment (GRACE) satellites.

"From the total amount of sea level rise, they subtracted the amount of rise from the expansion in the upper ocean, and the amount of rise that came from added meltwater. The remainder represented the amount of sea level rise caused by warming in the deep ocean.

"The remainder was essentially zero," NASA added. "Deep ocean warming contributed virtually nothing to sea level rise during this period."

Left unsolved is the riddle of why the world hasn't warmed as quickly as model projections say it should have by now.

Global temperatures have risen by about 0.05°C per decade since the late 1990s, a far cry from the 0.15°C to 0.3°C per decade once projected by the Intergovernmental Panel on Climate Change, the United Nations group charged with delivering periodic assessments of the state of the world's climate.

This has prompted a range of possible explanations in recent years. Some studies have proposed that this is due to a lack of historical temperature data in places like the Arctic and Africa, while others have suggested that a strengthening of trade winds over the Pacific Ocean are to blame.

"The deep parts of the ocean are harder to measure," said William Llovel, the study's lead author. "The combination of satellite and direct temperature data gives us a glimpse of how much sea level rise is due to deep warming. The answer is -- not much."

Read more at NASA's Jet Propulsion Laboratory, or read the full study at Nature Climate Change.

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An emaciated polar bear is seen on a small sheet of ice in this image taken in August in Svalbard, north of mainland Norway. (Kerstin Langenberger)