Climate change deniers frequently point to the global warming “hiatus” to back up their arguments. The hiatus, such as it is, isn’t a global cooling or even a pause in the increase in temperatures. According to the NOAA and NASA, 13 of the 14 hottest years on record have occurred since 2000 and the hiatus began in 1998.

The hiatus, instead, refers to temperatures not rising as rapidly as previously expected. According to new research that trend may soon come to a close.

The Earth’s climate naturally fluctuates due to a variety of factors, unrelated to Co2 production. Under normal circumstances, the period since 2000 should have been abnormally cool.

According to a report published in November, 2014 volcanic activity has caused an unusual amount of global cooling over the last few decades. Volcanoes blast sulfur dioxide aerosols into the air which can reflect sunlight entering the atmosphere and cause a short-term cooling effect. Of course, volcanos also add Co2 to the atmosphere so in the long term they contribute to global warming.

New research published February 26 in the journal Science says that periodically shifting ocean currents have also contributed to cooling over the last few decades. So, while the Earth has gone through an unusual cooling period, human caused global warming has continued to increase.

“We know that it is important to distinguish between human-caused and natural climate variability so we can assess the impact of human-caused climate change on a variety of phenomena including drought and weather extremes. The North Atlantic and North Pacific oceans appear to be drivers of substantial natural, internal climate variability on timescales of decades,” said Michael Mann, Distinguished Professor of Meteorology, Penn State in a statement.

The Atlantic Multidecadal Oscillation (AMO) describes the variation of surface temperatures in the North Atlantic. The AMO oscillates about every 50 to 70 years. The Pacific Decadal Oscillation (PDO), which describes the same variation in the pacific, varies over longer timescales.

The researchers used a wide variety of simulations and found that the AMO and Pacific multidecadal oscillation (PMO) are not interrelated as some have previously claimed. The research showed that the Northern Hemisphere was not warming more slowly because of the AMO, which has been flat, but because of a down-trending PMO.

“Our interpretation is it’s this low-frequency internal variation in the Pacific that’s contributing substantially to the slowdown of the last 10 or 15 years. In our analysis, it very much looks like we’re at a turning point, so it’s likely to turn around and go in the other direction in the decade ahead,” Mann told Discovery News.

Mann’s team concluded that the slowing of warming over the last decade is due to heat burial beneath the tropical pacific.

“Our findings have strong implications for the attribution of recent climate changes. Internal multidecadal variability in Northern Hemisphere temperatures likely offset anthropogenic warming over the past decade,” said Mann.

Volcanic activity is difficult to predict but if the researchers are right and the PMO shifts to deliver warmer air and water into the Northern Hemisphere global warming could begin to accelerate rapidly.