Atmospheric levels of carbon dioxide increased 2.9 parts per million (ppm) in 2013, the biggest year-to-year increase in a 30-year record.  The spike in levels of this heat-trapping greenhouse gas is raising eyebrows because it greatly exceeds the 2.0 ppm average annual increase  observed over the last decade.

Meanwhile, the Earth’s surface temperatures have not recently kept pace with rising CO2 levels – but scientists now have better clues as to why.

News of the record-setting carbon dioxide levels (and updates on other greenhouse gases) was released in a report from the World Meteorological Organization (WMO) today.

Carbon dioxide (CO2) levels have risen inexorably since the Industrial Revolution, from  278 ppm in 1750 to 396 ppm in 2013, a 40 percent increase, the WMO report stated.  The burning of fossil fuels is largely driving the elevated CO2 levels, which are at their highest levels in at least 800,000 years.

It’s not clear if the 2.9 ppm increase in CO2 levels in 2013 is a blip or signals the start of a period in which the gas accumulates in the atmosphere at a faster clip.  If it’s the latter, it would have worrisome implications for the climate.  As the Post’s Joby Warrick reports:

The latest figures from the World Meteorological Organization’s monitoring network are considered particularly significant because they reflect not only the amount of carbon pumped into the air by humans, but also the complex interaction between man-made gases and the natural world. Historically, about half of the pollution from human sources has been absorbed by the oceans and by terrestrial plants, preventing temperatures from rising as quickly as they otherwise would, scientists say.

“If the oceans and the biosphere cannot absorb as much carbon, the effect on the atmosphere could be much worse,” said Oksana Tarasova, a scientist and chief of the WMO’s Global Atmospheric Watch program, which collects data from 125 monitoring stations worldwide.

Multiple scientific assessments have found greenhouse gases, and most importantly CO2, are responsible for the majority of the climate warming observed in recent decades.  However, over the past 15 years, even as greenhouse levels have steadily gone up, the rate of warming of Earth’s surface temperatures has slowed some.  Some scientists have referred to this slowdown as a “pause” or “hiatus.”

(Note that many scientists downplay the significance of this slowdown, as heat has continued to accumulate in the ocean during this so-called hiatus period.)

Related: How global warming can be speeding up, slowing down, and going steady all at the same time

Two significant studies – published today in Nature Climate Change – offer some new insight about the warming slowdown.

One study, published by Japanese researchers, finds natural cycles in the Pacific ocean acted to intensify greenhouse gas-induced warming in the 1980s and 1990s but mask it since 2000.

“These natural cycles increased the global average surface temperature by 0.11 C for the 1980s and by 0.13 C for the 1990s while they decreased temperatures by 0.11 C during the 2000s,” writes the blog ReportingClimateScience.com, which summarizes the study.

Climate models did not predict the recent dampening in the temperature rise and researchers have emphasized the need to improve models to better incorporate natural ocean-atmosphere cycles in the Pacific for improved decade to decade forecasts.

Related: La Niña-like conditions behind gentler global warming, study finds

The second Nature Climate Change study from Gerald Meehl at the National Center for Atmospheric Research (NCAR) – finds the latest generation of computer models are now sophisticated enough to simulate the present slowdown, whereas they were not before.

“If today’s tools for multiyear climate forecasting had been available in the 1990s, they would have revealed that a slowdown in global warming was likely on the way, according to new research,” writes the NCAR news release.

(Nature Climate Change)
Via NCAR: “A series of “hindcasts” successfully captured the plateau in global air temperature observed in the last decade (yellow circle at right). Shown above are observed temperatures for each year (black asterisks) together with hindcasts (red circles) valid for a five-year period centered on each year. ” (Nature Climate Change)

So what do these new, improved models say about the future? Will rapid warming resume to keep pace with the ever increasing CO2 levels?

“There are indications from some of the most recent model simulations that the hiatus could end in the next few years,” Meehl says, “though we need to better quantify the reliability of the forecasts produced with this new technique.”