The global warming "hiatus" that has been observed over the past 15 years could be largely linked to small volcanic eruptions.
Volcanic eruptions have been known to cool the atmosphere because of the sulphur dioxide they release. Droplets of sulphuric acid form when the gas combines with oxygen in the upper atmosphere and reflects sunlight away from Earth, the Lawrence Livermore National Laboratory reported.
Previous studies suggest eruptions in the early 21st century could account for up to a third of the recent warming hiatus. These new findings further identify observational climate signals triggered by volcanic eruptions using ground, air and satellite measurements.
"This new work shows that the climate signals of late 20th and early 21st century volcanic activity can be detected in a variety of different observational data sets," said Benjamin Santer, a Lawrence Livermore National Laboratory scientist and lead author of the study.
Global warming hit its peak in 1998, but then started leveling off in what has been referred to as a "hiatus." In the past, researchers have suggested the phenomenon is linked to increased heat uptake in oceans and weak solar energy.
In the past, researchers have believed only large volcanic eruptions had the ability to influence global temperature, but these new findings point out previous climate models were missing a vital component. Most satellite measurements of sulfuric acid droplets and aerosols produced by volcanoes are restricted to below 15 kilometers, but cirrus clouds can interfere with these measurements.
To combat this, researchers combined observations from ground, air and space-based instruments to look at these emissions and better observe aerosols at lower altitudes. The improved model estimated volcanoes have created a cooling effect of between 0.05 and 0.12 degrees Celsius since the year 2000.
The team also found late 20th and early 21st century eruptions can be identified though atmospheric temperature, moisture and solar radiation at higher altitudes than what is generally studied.
"The fact that these volcanic signatures are apparent in multiple independently measured climate variables really supports the idea that they are influencing climate in spite of their moderate size," said Mark Zelinka, another Livermore author. "If we wish to accurately simulate recent climate change in models, we cannot neglect the ability of these smaller eruptions to reflect sunlight away from Earth."
The findings were published in a recent edition of the journal Geophysical Research Letters
