Posted on 11/08/2005 7:28:52 AM PST by blam
Week of Nov. 5, 2005; Vol. 168, No. 19 , p. 294
Volcanic Suppression: Major eruptions can reduce sea level
Sid Perkins
Large volcanic eruptions can temporarily cool Earth's climate and, a team of scientists now suggests, lower sea level worldwide.
BLOWING ITS TOP. Ocean cooling following the June 1991 eruption of Mount Pinatubo in the Philippines caused sea level worldwide to temporarily drop about 5 millimeters. D. Harlow/U.S. Geological Survey
The tiny particles of broken rock and droplets of condensed gases that a volcano ejects high into the atmosphere reflect sunlight into space. So, after an eruption, there's less radiation reaching Earth's surface to warm it, says John A. Church, an oceanographer at the Commonwealth Scientific and Industrial Research Organization in Hobart, Tasmania. In the wake of a major eruption, this deflection of solar energy can cause global air temperatures to drop below average for months.
New analyses by Church and his colleagues suggest that these chilling effects influence the oceans as well. The water would contract as it cooled, with a concomitant drop in sea level.
To estimate the effects of volcanic eruptions on sea level, Church and his colleagues used tide data from around the world, ocean temperature and salinity data gathered by ships, and climate models that include both the atmosphere and the oceans.
After each of several major 20th-century eruptions—including those of Indonesia's Mount Agung in 1963 and the Philippines' Mount Pinatubo in 1991—the oceans cooled subtly for about 18 months, and sea level dropped, on average, several millimeters, or about three times the thickness of a penny. As natural processes scoured the volcanic material from upper levels of the atmosphere, the amount of radiation reaching Earth's surface returned to normal, the oceans warmed and expanded, and sea level recovered over the course of a decade or so.
The analysis by Church's team suggests that after the eruption of Mount Pinatubo, the most powerful one that the researchers examined, sea level dropped about 5 mm but then recovered at a rate of about 0.5 mm per year. Sea level still hadn't fully recovered as of 2000, the last year included in the scientists' analysis. The researchers report their findings in the Nov. 3 Nature.
Between 1950 and 2000, sea level rose, on average, about 1.8 mm/yr. However, scientists using satellite data gathered since 1993 estimate that the rate of sea level rise between 1993 and 2000 was about 3.2 mm/yr. Some of that apparent acceleration can be attributed to post-Pinatubo recovery, says Church.
"I've never thought about how volcanic eruptions would affect sea level, but it makes sense," says Alan Robock, an atmospheric scientist at Rutgers University in New Brunswick, N.J.
Accounting for the temporary effects on sea level of natural phenomena such as volcanic eruptions is essential to accurately predicting sea level rise in response to human-induced climate change, Anny Cazenave of the National Center for Space Studies in Toulouse, France, notes in a commentary accompanying the Nov. 3 Nature article.
FIVE MILLIMETERS!!!
We're DOOMED!
You mean, its effects weren't completely negated by global warming???
I wonder what their margin of error is?
I have often wondered that myself, as I contemplated the difficulty of determining whether a PERCEIVED drop was actually a lowering of the ocean or a raising of the solid-ground point-of-reference! I suppose the ATTEMPT could be made utilizing lasers based in earth orbit; but that is so recent as to render any perceived difference highly suspect.
This is Bush's fault somehow.
How did they measure the drop in sea level? I wondered the same thing and then concluded it is a calculation based on the coefficient of thermal expansion (CTE) of sea water. CTE is the fractional length change per degree C. For a fixed width and length, it is also the fractional volume change.
The CTE of sea water is about 0.00021. Because the length and width of an ocean basin does not change as the ocean is heated or cooled slightly, b also describes the change in height as the water warms or cools. The relation between change of height D h, ocean depth D and temperature change DT is: D h = b D DT.
We should be scraping the bottom of the ocean by now.
Water contacts when it cools? So, the density increases, the colder the water gets? Which is why ice sinks?
If I had a grant, I could research this.
A little elaboration on this, please, and why it is not simple cyclical with seasons.
a number of years ago i read a story that volcanic ash content measured in ice cuttings from greenland showed a significant drop in the last century. like counting the rings of a tree. plus recent articles noted the atmosphere was clearer... all leading to global warming not fossil fuels...
The density of water increases as the temperature drops towards 39 degrees Fahrenheit. Below 39 degrees, water again decreases in density. I believe it is the only substance known to man where the density is at its maximum as a liquid and not a solid.
This is 3rd grade science, but could we get confirmation from a higher authority.
There's a great explanation of how this works and permits life to continue living in frozen lakes and ponds in a Word document at the University of Sussex.
So far so good...assuming the amount of water didn't change.
However, other factors involved in this would include world rainfall totals; runoff totals; rate of evaporation; any changes in volume of sea ice, any net change in basin size due to rift speading vs magma welling/sea mount building....
As we get further and further from the end of the Ice Age, I would expect to see less earthquakes and volcanos because the weight redistribution stresses (water - ice) have been released the further we get from the last major event, 8,000 years ago.
The more important thing is that volcanoes prove Earth's surface can be cooled by putting sun reflectors in the atmosphere. Increasing cloud cover must have the same effect. By inducing cloud generation over the Gulf of Mexico we could cool the earth's surface as well as manage hurricane formation.
Technology solves problems.
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