Volcanic Eruptions Impact Global Sea Level
- Volcanic Eruptions Impact Global Sea Level
Canberra, Australia (SPX) Nov 07, 2005
Clouds of gases and particles sprayed into the stratosphere by
volcanic eruptions cool the oceans and temporarily offset the rise
in global sea level caused by the greenhouse effect, according to
research findings published today in Nature.
Research team leader, Dr John Church from CSIRO and the Antarctic
Climate & Ecosystems Collaborative Research Centre (ACECRC), says
the study is the first to isolate and measure the effect of volcanic
eruptions on sea level variations.
"Using computer models and observations, we tracked sea level
variations and temperatures in the upper 300 metres of the ocean
recorded during and following major volcanic eruptions in the late
20th century" Dr Church says. "What we have seen is a slowing in the
rate of sea level rise immediately after volcanic eruptions followed
by an acceleration over periods of a decade or more."
This temporary slowing of sea level rise following a series of major
eruptions occurring since 1960 (Mt Agung in Indonesia in 1963, El
Chichon in Mexico in 1982 and Mt Pinatubo in the Philippines in
1991) temporarily masked the acceleration of sea level rise that
would otherwise have resulted from the effects of greenhouse gases
in the atmosphere.
Dr Church says although climate scientists generally agree the sea
level has risen by an average of 1.8 mm a year over the last 50
years, there has been little focus on the shorter term variability
in this rate.
"Scientists have known that volcanic aerosols cause a decrease in
the global average surface temperature and other changes in Earth's
climate system. However, until now there has been no study of how
the aerosols impact on sea level and ocean temperatures," he says.
The model results are confirmed by ocean observations. The effect
persists for at least a decade because of the large heat capacity of
the oceans compared to that of the atmosphere and the slow
redistribution of heat by ocean circulation.
Sea level rise occurs in two ways: expansion of the ocean as a
result of ocean warming (thermal expansion); and, changes in the
amount of water in the ocean due to melting glaciers and ice sheets.
Other members of the team are: Dr Neil White of CSIRO and the
ACECRC; and, Ms Julie Arblaster from the National Center for
Atmospheric Research in the US and the Bureau of Meteorology
The team's findings from collaborative research involving the
ACECRC, CSIRO's Wealth from Oceans Flagship and the Australian
Climate Change Science Program will be presented at a major
international climate change conference, in Melbourne from 13-17
November, Greenhouse 2005.