It seems that there’s a paper (from JeanPaul Vernier at NASA) out that contradicts the findings of Kaufmann et al 2011, where they blame China’s increasing coal consumption for lack of warming in the past decade saying coal use is adding aerosol particles into the atmosphere that reflect sunlight and therefore cool the planet. [Update, see caveat at end of this post] But in Vernier et al in press at GRL, they say
Recently, the trend, based on ground-based lidar measurements, has been tentatively attributed to an increase of SO(2) entering the stratosphere associated with coal burning in Southeast Asia. However, we demonstrate with these satellite measurements that the observed trend is mainly driven by a series of moderate but increasingly intense volcanic eruptions primarily at tropical latitudes.
Dr B Basil Beamish writes in Tips and Notes:
Here is a new paper hot off the press that seems to contradict the recent concept of cooling temperatures from China’s coal use.
Author(s): Vernier, JP (Vernier, J. -P.)1,2; Thomason, LW (Thomason, L. W.)1; Pommereau, JP (Pommereau, J. -P.)2; Bourassa, A (Bourassa, A.)3; Pelon, J (Pelon, J.)2; Garnier, A (Garnier, A.)2; Hauchecorne, A (Hauchecorne, A.)2; Blanot, L (Blanot, L.)2,4; Trepte, C (Trepte, C.)1; Degenstein, D (Degenstein, Doug)3; Vargas, F (Vargas, F.)5
Source: GEOPHYSICAL RESEARCH LETTERS Volume: 38 Article Number: L12807 DOI: 10.1029/2011GL047563 Published: JUN 30 2011
The variability of stratospheric aerosol loading between 1985 and 2010 is explored with measurements from SAGE II, CALIPSO, GOMOS/ENVISAT, and OSIRIS/Odin space-based instruments. We find that, following the 1991 eruption of Mount Pinatubo, stratospheric aerosol levels increased by as much as two orders of magnitude and only reached “background levels” between 1998 and 2002. From 2002 onwards, a systematic increase has been reported by a number of investigators. Recently, the trend, based on ground-based lidar measurements, has been tentatively attributed to an increase of SO(2) entering the stratosphere associated with coal burning in Southeast Asia. However, we demonstrate with these satellite measurements that the observed trend is mainly driven by a series of moderate but increasingly intense volcanic eruptions primarily at tropical latitudes. These events injected sulfur directly to altitudes between 18 and 20 km. The resulting aerosol particles are slowly lofted into the middle stratosphere by the Brewer-Dobson circulation and are eventually transported to higher latitudes. Citation: Vernier, J.-P., et al. (2011), Major influence of tropical volcanic eruptions on the stratospheric aerosol layer during the last decade, Geophys. Res. Lett., 38, L12807, doi:10.1029/2011GL047563.
It seems the Calipso satellite is designed specifically for this task. From Spie.org:
Since June 2006, the Cloud-Aerosol and Lidar Infrared Pathfinder Observations (CALIPSO) satellite, a joint US (NASA)/French (Centre National d’Etudes Spatiales) mission, has provided high-resolution aerosol and cloud profiles of the Earth’s atmosphere. The long-range transport in the tropics of several small-scale volcanic plumes has been monitored using these observations, which are unprecedented in their scope and detail. Their fate demonstrates the importance of even minor volcanic events on stratospheric-aerosol levels.
CALIPSO offers a unique opportunity to monitor aerosols and clouds in the atmosphere. The instrument is carried on a spacecraft circling the Earth in a polar orbit (see Figure 1), which provides coverage from 82°S to 82°N. The CALIPSO lidar (light detection and ranging) uses a laser that emits light at 532 and 1064nm. The laser light is scattered by molecules and particles in the atmosphere, and a portion is scattered back (backscattered) towards the spacecraft. The backscatter signal is collected by a telescope and sampled at a rate of 10MHz. The 3D location and density of clouds and aerosol layers can be inferred from the vertical backscatter profiles from the ground to the stratosphere.3 Primarily designed for studying tropospheric particles, the nighttime channel at 532nm has a high sensitivity and can, with sufficient averaging, be used to detect small-scale volcanic plumes in the stratosphere for several months, even if the aerosol density is very low.
Since June 2006, CALIPSO observed several volcanic plumes and followed them as they were carried around the world by atmospheric circulation. Figure 2 shows the evolution of the mean scattering-ratio (SR) profile between 20°N and 20°S from June 2006 to May 2010 with a temporal and vertical resolution of 16 days (CALIPSO measurement cycle) and 200m, respectively. The SR is the ratio between the total (aerosol and molecular) and molecular-only backscatter. The maxima, seen in 2006 with an SR greater than 1.2, represent two volcanic plumes, injected at 20 and 17km, respectively, by the Soufriere Hills in the Caribbean on 20 May and the Tavurvur cone of the Rabaul volcano in Papua New Guinea on 7 October. The plume from Soufriere Hills remains at the same level for three months before being slowly lifted in the stratosphere by the general circulation, while the Tavurvur aerosols, at lower levels, disappear within two to three months.
Smaller plumes, with SRs between 1.08 and 1.14, were observed at 17–19km in November–December 2008 and July–December 2009, respectively. These two plumes are further transported into the tropics after the Kasatochi (Alaska) and Sarychev (Kamchatka, Russia) eruptions on 7 August 2008 and 12 June 2009, respectively. The signal seen at 21–22km in March 2009 with an SR of 1.10–1.12 is the signature of soot particles from an extreme biomass-burning episode near Melbourne (Australia) on 7 February 2009 (‘Black Saturday’).
For the first time, those moderate events have been detected over a long period, demonstrating that eruptions with a volcanic explosivity index between three and four and located in the tropics can be an important source of aerosols for the stratosphere, a fact not fully recognized until now. The sulfuric dioxide initially injected at 19–20km is oxidized into sulfuric acid droplets and transported by the general circulation—also called Brewer-Dobson (BD) circulation—into the middle tropical stratosphere, forming a reservoir. Afterwards, those aerosols are released into the global stratosphere according to the season and the phase of the quasibiennal oscillation.5 The vertical velocity of the ascending branch of the BD circulation can be deduced by subtracting the sedimentation from the apparent volcanic-plume uplift, providing an opportunity to evaluate the mean vertical atmospheric motion in the stratosphere.
more at Spie.org here
JP Vernier has done a nice slide show explaining it all, just prior to the publication of the new paper, and you can view it here:
I found this graph most interesting:
They say that small trend starting in 2002 is “No large eruptions over the last decade : but small and frequent ones”.
Update – Caveat: As Jos points out in comments, this Vernier study is about the stratosphere (15-30) where Kaufmann et al is the troposphere (0-15km) , an important distinction that I missed. That’s what I get for posting late at night while tired. However, the premise that Vernier contradicts, the issue of stratospheric aersol increase due to China coal use appears to be falsified. Perhaps though, the authors will turn to the troposphere next as this recent study suggests that the volcanic impact on climate may be significantly underestimated. The secondary nucleation process they cite may work to increase tropospheric aerosols, and also, it stands to reason the smaller eruptions, as cited by Vernier, would also inject into the troposphere as well.