Light from a lidar instrument forms a beam in the sky over Boulder, Colo.. NOAA researchers and colleagues used lidar data to better understand recent changes in the amounts of tiny particles high in Earth's atmosphere.
Download here. (Credit: CIRES/NOAA)
A recent increase in the abundance of particles high in the atmosphere has offset about a third of the current climate warming influence of carbon dioxide (CO2) change during the past decade, according to a new study led by NOAA and published today in the online edition of Science.
In the stratosphere, miles above Earth’s surface, small, airborne particles reflect sunlight back into space, which leads to a cooling influence at the ground. These particles are also called “aerosols," and the new paper
explores their recent climate effects -- the reasons behind their increase
remain the subject of ongoing research.
“Since the year 2000, stratospheric aerosols have caused a slower rate of climate warming than we would have seen without them,” says John Daniel, a physicist at the NOAA Earth System Research Laboratory (ESRL) in Boulder, Colo. and an author of the new study.
The new study focused on the most recent decade, when the amount of
aerosol in the stratosphere has been in something of a “background” state, lacking sharp upward spikes from very large volcanic eruptions. The authors analyzed measurements from several independent sources – satellites and several types of ground instruments – and found a definitive increase in stratospheric aerosol since 2000.
Sources of aerosols reach the stratosphere from above and below, as shown in the graph. Sulfur dioxide (SO2), carbonyl sulfide (OCS), and dimethyl sulfide(DMS) are the dominant surface emissions which contribute to aerosol formation.
Download here. (Credit: NOAA)
The reasons for the 10-year increase in stratospheric aerosols are not fully
understood and are the subject of ongoing research, says coauthor Ryan Neely, with the University of Colorado and the Cooperative Institute for Research in Environmental Sciences (CIRES). Likely suspects are natural sources – smaller volcanic eruptions – and/or human activities, which could have emitted the sulfur-containing gases, such as sulfur dioxide, that react in the atmosphere to form reflective aerosol particles.
Daniel and colleagues with NOAA, CIRES, the University of Colorado, NASA, and the University of Paris used a climate model to explore how changes in the stratosphere’s aerosol content could affect global climate
change – both in the last decade, and projected into the future. The team concluded that models miss an important cooling factor if they don’t account for the influence of stratospheric aerosol, or don’t include recent
changes in stratospheric aerosol levels.
“The ‘background’ stratospheric aerosols are more of a player than we thought,” said Daniel. “The last decade has shown us that it doesn’t take an extremely large volcanic eruption for these aerosols to be important to climate.”