It’s been a busy year for climate scientists, who have been trying to explain why there has been no global warming for nearly two decades.

The Daily Caller News Foundation reported in February there were eight mainstream explanations for the pause, but there are now a whopping 52 explanations for why there has been no warming trend for the last 215 months.

Explanations for the pause in global warming range from ocean oscillation cycles to Chinese coal plant emissions, volcanic activity to some scientists even saying there is no hiatus in warming.

One recent study found that the warming hiatus is due to “heat transported to deeper layers in the Atlantic and the southern oceans, initiated by a recurrent salinity anomaly in the subpolar North Atlantic.”

This oceanic cooling cycle “associated with the latter deeper heat-sequestration mechanism historically lasted 20 to 35 years,” according to Professor Ka-Kit Tung from the University of Washington.

So what’s the latest explanation for why the Earth stopped warming? Europe’s Joint Research Center (JRC) says the hiatus in warming since 2001 is due to “a combination of a natural cooling phase, known as multidecadal variability (MDV), and a downturn of the secular warming trend.”

European Union scientists don’t know the exact what caused the “downturn of the secular warming trend,” but say “ the Earth hasn’t warmed at the same pace during the 20th century.” JRC researchers analyzed surface temperature records going back to 1850 to “separate natural variations from secular” ones.

Scientists discovered three hiatus periods in the temperature records — 1878 to 1907, 1945 to 1969 and 2001 to today — and concluded that these “hiatus periods coincide with natural cooling phases – the multidecadal variability (MDV), most likely caused by natural oceanic oscillations.”

“The scientists therefore conclude that the MDV is the main cause of these hiatus periods during which global warming decelerated,” according to JRC.

Earlier this week, scientists warned that Earth’s atmospheric carbon dioxide concentrations reached 396 parts per million last year, and carbon dioxide levels were set to cross 400 parts per million by 2015 or 2016.

“We know without any doubt that our climate is changing and our weather is becoming more extreme due to human activities such as the burning of fossil fuels,” said Michel Jarraud, secretary-general of the World Meteorological Organization — a United Nation’s weather and climate science bureaucracy.

“The Greenhouse Gas Bulletin shows that, far from falling, the concentration of carbon dioxide in the atmosphere actually increased last year at the fastest rate for nearly 30 years,” Jarraud warned. “We must reverse this trend by cutting emissions of CO2 and other greenhouse gases across the board. We are running out of time.”

But Jarraud’s warning comes after reports that there has been no global warming for the past 215 months, according to satellite data. Furthermore, recent research suggests the “pause” in warming could last another decade.

Some climate scientists who are skeptical of theories that man-made global warming will have catastrophic impacts, say increasing carbon dioxide levels should not be alarming.

“The gradual increase in the rate of the rise of the carbon dioxide concentration is a sign that we are continuing to expand our energy use and availability, primarily in developing countries like India and China,” wrote Chip Knappenberger, assistant director of the Center for the Study of Science at the libertarian Cato Institute.

“With more than a billion people still without much access to electricity… and all the life-improving benefits that come with it, we still have a long way to go,” Knappenberger added. “Consequently, we should anticipate that the atmospheric CO2 concentration will continue to grow for many years to come.”

Note: Readers interested in seeing a complete list of explanations for the hiatus in global warming, the blog Watts Up With That keeps a running tally of all of them.

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Content created by The Daily Caller News Foundation is available without charge to any eligible news publisher that can provide a large audience. For licensing opportunities of our original content, please contact licensing@dailycallernewsfoundation.org.