think climate. think change.
Volcanoes emit water vapour and carbon dioxide, but contribute little to global changes in atmospheric greenhouse gas concentrations.
Large volcanic eruptions, however, can blast huge amounts of sulfur dioxide into the upper atmosphere (the stratosphere). There, the sulfur dioxide transforms into tiny particles of sulfate aerosol. These particles reflect energy from the Sun back into space, preventing some of the Sun's rays from heating the Earth.
Conversion of sulfur dioxide to sulfuric acid aerosol in the stratosphere takes some months, so maximum cooling occurs up to a year after the eruption. It may take many years before the cooling influence of the volcanic aerosol disappears completely.
When Mt Pinatubo in the Philippines erupted in 1991 it blasted up to 26 million tonnes of sulfur dioxide into the stratosphere. This led to a global surface cooling of 0.5°C one year after the eruption. This cooling offset the warming effects of both El Nino and human-induced greenhouse gases from 1991 to 1993.
Australian droughts are closely associated with natural variations in atmospheric and oceanic circulation, such as the El Nino-Southern Oscillation (ENSO). An El Nino event was the main cause of the drought experienced in south-east Australia in 2006.
Since 1975, Australia has experienced more frequent El Nino events than during previous years of the 20th century, but we are unable to say whether this is as a result of climate change. The relationship between long-term climate change and ENSO is a topic of ongoing research.
Although it's not yet possible to say that the frequency and duration of droughts are linked to climate change, there is evidence that rainfall changes in some parts of Australia are due to human influence, as is the warming trend in Australia. With this warming trend, droughts have become hotter. The 2003 drought (which coincided with an El Nino event) was the hottest in the past 100 years.
The decline in rainfall in south-western Western Australia is due to both natural variability and human-induced climate change.
