It has recently been proposed that the effects of global warming maybe partially offset by introducing additional sulphate aerosol into the lower stratosphere, which has the potential to increase the fraction of incoming radiation back-scattered out of the Earth's atmosphere. Such technical 'fixes' are part of the geo-engineering approach, whose advocates argue are a viable means of introducing rapid changes to the Earth System which have the potential to mitigate problems caused by anthropogenic activity. One natural phenomenon which introduces similar effects as that proposed above is volcanic eruptions, which can inject significant quantities of both sulphur dioxide (SO₂) and carbonaceous aerosol particles well above the tropopause directly into the lower stratosphere. As well as increasing the attenuation of solar radiation, such volcanic events also perturb stratospheric ozone by increasing the loss due to heterogeneous processes as a result of a high concentration of sulphuric acid droplets. For instance, the Pinatubo Eruption which occurred in the Philippines during 1991 resulted in enhanced stratospheric O₃ loss by ~6% for a number of years after the eruption, as observed by earth-orbiting satellite instruments such as TOMS. These effects can be seen at a global scale as a result of the long-range transport of aerosols once they are placed into the upper atmosphere. A more recent volcanic event has been the eruption of Kasatochi in Alaska (52.2°N, 175.5°W) during August 7th-8th, 2008. An increased aerosol load was subsequently measured in the upper troposphere-lower stratosphere above central Europe on the 15th August, 2008 by in-situ instrumentation operated as part the CARIBIC measurement program (http://www.caribic-atmospheric.com/). Moreover, elevated SO₂ columns were also detected over the region by the Aura/OMI instrument. Scientists in KS-CK performed back trajectories to show that air sampled by the CARIBIC flights containing enhanced particle concentrations originated from the Kasatochi volcanic eruption. Figure 1 below shows the OMI SO₂ column, the elevated SO₂ measured by CARIBIC and the location of the back trajectories. Comparing measurements of the ratio of particulate sulphur against ozone with background values obtained before the eruption show an increase in the ratio between 25-50N. Moreover, the average particulate sulphur and carbon concentrations were elevated by a factor of 3.1 and 3.6,respectively, three to four months after the Eruption. Further details can be found in the associated article linked below.