Gaps in Arctic temperature data caused a misperception that global warming slowed from 1998 to 2012, according to a new study in the journal Nature Climate Change.

A University of Alaska Fairbanks professor and his colleagues in China built the first data set of surface temperatures from across the world that significantly improves representation of the Arctic during the "global warming hiatus."

Xiangdong Zhang, an atmospheric scientist with UAF's International Arctic Research Center, said he collaborated with colleagues at Tsinghua University in Beijing and Chinese agencies studying Arctic warming to analyze temperature data collected from buoys drifting in the Arctic Ocean.

"We recalculated the average global temperatures from 1998-2012 and found that the rate of global warming had continued to rise at 0.112C per decade instead of slowing down to 0.05C per decade as previously thought," said Zhang who is also a professor with UAF's College of Natural Science and Mathematics.

Zhang said their new estimates showed that the Arctic warmed more than six times the global average during that time period.

The team developed new methods of incorporating the Arctic temperature data into global temperature data to better estimate the average temperatures.

Most current estimates use global data that tend to represent a long time span and provide good coverage of a global geographic area. But the remote Arctic lacks a robust network of instruments to collect temperature data.

To improve the dataset in time and space, the team relied on temperature data collected from the International Arctic Buoy Program at the University of Washington. For global data, the team used newly corrected sea surface temperatures from the National Oceanic and Atmospheric Administration.

Zhang said this study expands on NOAA research and other recent studies that have either supported or refuted the idea of a "global warming hiatus" by re-estimating the average global temperatures during that time period with more accurate and representative data.

The global warming hiatus is a much-debated topic among climate researchers. Some scientists theorized that an unusually warm El Nino in the years 1997-1998 and an extended period afterward without an El Nino in the tropical Pacific Ocean may have disrupted the rate of global warming.

The Earth's average global temperatures have been rising over the past century and accelerating as more human produced carbon dioxide enters and lingers in the atmosphere, which is why the idea of "global warming hiatus" seemed baffling to some scientists.

But the new data set and resulting estimates show conclusively that the warming didn't pause.

It also highlights the importance of considering the Arctic when thinking about climate change. Until recently, Zhang said, many scientists didn't consider the Arctic big enough to greatly influence the average global temperatures.

"The Arctic is remote only in terms of physical distance," he said. "In terms of science, it's close to every one of us. It's a necessary part of the equation and the answer affects us all."

Research paper

- SPACE STORY - volcano hg 255 23-DEC-49 Filling the gap: High-latitude volcanic eruptions also have global impact Filling the gap: High-latitude volcanic eruptions also have global impact iss-sarychev-peak-volcano-eruption-hg.jpg iss-sarychev-peak-volcano-eruption-lg.jpg iss-sarychev-peak-volcano-eruption-bg.jpg iss-sarychev-peak-volcano-eruption-sm.jpg Photo of early stages of the eruption of the Sarychev on June 12, 2009 as taken from the ISS. Institute of Atmospheric Physics, Chinese Academy of Sciences
by Staff Writers Beijing, China (SPX) Nov 28, 2017 Volcanic eruptions always seize the attention of climate scientists, because the sulfate aerosols formed in the volcanic plumes may stay months to years in the stratosphere - the second layer of the Earth's atmosphere - resulting in the increase of radiation reflection from the Sun back into space, and therefore cooling the Earth's lower atmosphere or troposphere in a long time period.

It is traditionally believed that because of atmospheric circulation patterns, eruptions in the tropics could have an effect on the climate in both hemispheres while eruptions at mid or high latitudes only have impact over the hemisphere where they erupt.

"Well, it is not always the case", says Dr. Xue Wu, the corresponding author of a recently published study in Atmospheric Chemistry and Physics, "We have found evidences showing that a high-latitude volcano can enhance the aerosol layer in the tropical stratosphere, and also have impact on the climate of both hemispheres."

WU is from the Key Laboratory of Middle Atmosphere and Global Environment Observation (LAGEO), Institute of Atmospheric Physics, Chinese Academy of Sciences. She worked together with Dr. Sabine Griessbach and Dr. Lars Hoffmann from Julich supercomputing center, Forschungszentrum Julich, Germay on a high-latitude volcanic eruption case.

They used the Lagrangian particle dispersion model - MPTRAC, together with multi-source satellite observations to study the transport of the volcanic aerosol from the high-latitude volcanic eruption Sarychev (48N, 153E).

The study revealed that when the Sarychev volcano erupted in June 2009, the Asian summer monsoon (ASM) anticyclonic circulation was developing. The anticyclonic circulation facilitated the meridional transport of aerosols from the extratropical upper troposphere/lower stratosphere to the tropical tropopause region.

Then, the aerosols ascended slowly in the upward branch of the Brewer-Dobson circulation (BDC), the primary circulation in the stratosphere, and dispersed with the poleward branches of the BDC to both hemispheres.

So with the help of the ASM anticyclonic circulation, this high-latitude volcanic eruption will not only influence the climate in the northern hemisphere where the Sarychev located, but also have impact on the southern hemisphere, just as a tropical eruption does.

Based on their calculation, although there was only about 4% of the total SO2 from the Sarychev eruption (1.2+/-0.2106 tons) transported to the tropical stratosphere, it would result in 6 +/-1104 tons sulfate aerosol, which is several times larger than the 1.5-2104 tons per year required to explain the increase trend of the tropical stratospheric aerosol.

On the contrary, if the Sarychev erupted in winter, the aerosol would be confined to the polar side of the strong subtropical jets, deposited or be washed out from the atmosphere in a relatively short time.

WU emphasizes, "It's all about timing. If a high-latitude volcano erupts when the ambient atmospheric conditions are favorable for transport, it is well worth more attention". In the past decade, the Sarychev eruption in 2009 was not the only case that made advantage of the ASM circulation to transport sulfate aerosol to the tropical stratosphere, and "we may expect more in the future." Says Wu.

Research paper

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