In a recent edition of NASA's "Ask a Climate Scientist" video series, scientist Joshua Willis stands in front of a black screen, makes a few goofy faces and gives a brief answer to what has become a common question about climate science.
"A lot of people ask me: 'Has there been a pause in global warming because, like, temperatures aren't increasing as fast as they were a decade ago?'" Willis says.
"And I always say, you know, paws are for kittens and puppies, because global warming is definitely still increasing," Willis continues, smiling at his wordplay, as graphics of cute baby animals fill the screen.
It's true that Willis and nearly every other climate scientist dismiss the idea that global warming has paused. Yet the fact remains that average surface temperatures worldwide have not increased since around the turn of the century.
To the casual observer, the lack of warming at the Earth's surface, contrasted to climate scientists' insistence that the planet is still warming, might seem like a conundrum.
As scientists like Willis explain, though, most of the extra heat trapped by greenhouse gases does not warm the Earth's surface anyway.
Why do rising sea levels ignore the pause?
"Over 90 percent of the heat that we trap ... is warming the oceans," Willis said.
So as a measure of global warming, surface temperatures are not a good yardstick, because the atmosphere can only hold a small percentage of the heat that is trapped, he said.
Rather, the oceans should be the primary barometer of global climate change.
And they are certainly changing. Sea levels are going up "like gangbusters," Willis said.
The recent Intergovernmental Panel on Climate Change physical science draft report, released in late September, said it is a near certainty that rates of sea-level rise -- pushed up largely because warmer water expands -- have accelerated over the last two centuries.
The IPCC also reported it was very likely that rates of sea-level rise from 1993 to 2010 had almost doubled, from a 0.067-inch-per-year average rate for the 20th century to a 0.125-inch-per-year average rate.
To Willis and other scientists, this is a clear signal that global warming continues.
"Sea levels are still rising; the ice sheets are still melting; the oceans are still getting more acidic," Willis said. "All of that stuff is still going on just as it has, unabated."
If the heat continues to rise, where is it?
Even if they don't think global warming has paused, scientists are still interested in learning why the rate of surface warming over the last 10 to 15 years has been much slower than in the decades before, even as levels of greenhouse gases continue to increase.
If the Earth is still storing extra heat and that heat is not going into the atmosphere, it must be going somewhere else. Determining where the heat is going could lead to a better understanding of the Earth's climate system, they say.
One of the first researchers to address this question was Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research.
In 2011, Trenberth was a co-author on a paper published in Nature Climate Change that used models to show that pauses in surface temperature warming correspond to additional heat being stored deep in the ocean, below where most of our existing sensors typically measure.
Since then, Trenberth has published additional research (ClimateWire, April 8) showing that more than 30 percent of the warming in the oceans has occurred at depths below about 2,300 feet. He and his co-authors link this change to shifts in winds, especially in the Pacific Ocean, related to decadal weather patterns in the Pacific.