Volcanoes cool the tropics, say researchers

January 5, 2009
Volcanoes cool the tropics, say researchers
This is Mount Bromo, an active volcano in East Java, Indonesia. Credit: Paul Krusic, Lamont-Doherty Earth Observatory

Climate researchers have shown that big volcanic eruptions over the past 450 years have temporarily cooled weather in the tropics—but suggest that such effects may have been masked in the 20th century by rising global temperatures. Their paper, which shows that higher latitudes can be even more sensitive to volcanism, appears in the current issue of Nature Geoscience.

Scientists already agree that large eruptions have lowered temperatures at higher latitudes in recent centuries, because volcanic particles reflect sunlight back into space. For instance, 1816, the year following the massive Tambora eruption in Indonesia, became known as "The Year Without a Summer," after low temperatures caused crop failures in northern Europe and eastern North America.

More extensive evidence comes in part from tree rings, which tend to grow thinner in years when temperatures go down. This is one of the first such studies to show how the tropics have responded, said lead author Rosanne D'Arrigo, a scientist at the Tree Ring Lab at Columbia University's Lamont-Doherty Earth Observatory. "This is significant because it gives us more information about how tropical climate responds to forces that alter the effects solar radiation," said D'Arrigo. The other authors were Rob Wilson of Lamont and the University of St. Andrews, Scotland; and Alexander Tudhope of the University of Edinburgh, Scotland.

Along with tree rings, the researchers analyzed ice cores from alpine glaciers, and corals, taken from a wide area of the tropics. When things cool, not only do trees tend to grow less, but isotopes of oxygen in corals and glacial ice may shift. All showed that low-latitude temperatures declined for several years after major tropical eruptions. The samples, spanning 1546 to 1998, were taken from Nepal down through Indonesia and across the Indian and Pacific oceans; the ice cores came from the Peruvian Andes. The researchers used materials they collected themselves, as well as samples from the archives of other scientists.

The data show that the most sustained cooling followed two events: an 1809 eruption that probably took place in the tropics, but whose exact location remains unknown; and the 1815 Tambora eruption, one of the most powerful recorded in human history. Following Tambora, between 1815 and 1818, tropical temperatures dropped as much as 0.84 degrees C (1.5 degrees F) below the mean. A slightly bigger one-year drop came in 1731--0.90 degrees C (1.6 degrees F). The researchers say this may be connected to eruptions at the Canary Islands' Lanzarote volcano, and Ecuador's Sangay around this time.

D'Arrigo says that the study shows also that higher latitudes may generally be even more sensitive than the tropics. Some corresponding drops in northern regions following volcanism were up to three times greater. D'Arrigo said higher latitudes' greater sensitivity appears to come from complex feedback mechanisms that make them vulnerable to temperature shifts. This goes along with growing evidence from other researchers that, as the globe warms, the most dramatic effects are being seen with rapid melting of glaciers, sea ice and tundra at high latitudes. The authors say that, overall, eruptions in the 20th century have exerted fewer obvious effects in the tropics. They said this could be because there were fewer major events in that century--but they noted it could also be "because of the damping effect of large-scale 20th-century warming."

"Particularly warm decades may have partially overridden the cooling effect of some volcanic events," said D'Arrigo. Noting that few reliable instrumental records exist from before this time, she said, "This study provides some of the first comprehensive information about how the tropical climate system responded to volcanism prior to the instrumental period."

The paper, "The impact of volcanic forcing on tropical temperatures during the last four centuries," is available at: www.nature.com/ngeo/journal/v2/n1/full/ngeo393.html .

Source: The Earth Institute at Columbia University

Explore further: High-latitude volcanic eruptions affect ocean circulation for decades

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3.3 / 5 (3) Jan 05, 2009
I remember when Mt. St. Helens exploded in May 1981, even being over a 1000 miles away in Alberta, I can clearly remember the ash and that that year didn't have much summer.
4.4 / 5 (7) Jan 05, 2009
Well they say that cooling was "masked" during the 20th century. Now it seems that warming is being "masked" by cooling in the 21st century.

I'm not sure why the term "mask" is being used. The earth actually does get warmer and colder, whatever the reasons. NASA is saying that with the negative Pacific Decadal Oscillation, it appears that we are in for years of cooling.

3.5 / 5 (8) Jan 06, 2009
It would be nice if they would admit that the computer models utterly failed to predict the recent cooling, as well as the expected cooling in the future. It's time to admit the AGW hype was unwarranted, and stop wasting time, money and lives on something that isn't even a problem.
3.9 / 5 (7) Jan 06, 2009
How exactly can they say that recent global warming is masking volcanic eruption cooling when there haven't been any significant eruptions?

Mt. Pinatubo is the scapegoat for the cooling noticed before the "warmest years on record," and now the "warmest years on record" are being heralded as the scapegoat for pinatubo? I don't get it.

This is more of the same "push the issue through deception" that environmentalists blame economists and corporate entities for.
5 / 5 (2) Jan 08, 2009
Velanaris pay no attention to the cooling of the earth. IT IS WARM! If you fail to perceive the warming, it is a failing of your own perception. Sure, the temperature graphs of the five reporting agencies DO show cooling over the last five years. Sure, summers are getting shorter and the global sea ice is at the same level it was in Jan 1979.


Sure many glaciers are advancing.


Sure, the continental USA is currently (Jan 8, 2009) over 40% overed by snow at an average depth of over five inches.


Sure, more and more climate scientists are proclaiming AGW a myth.


Sure the sun is in a very quiet period.


Sure, NASA says we are entering a cooling period because of the Pacific Decadal Oscillation.


Sure, all of your friends and acquaintences have already figured out that they have been fooled.

But, really, those reasons are not enough to have you trying to be reasonable. If you play your cards right, and start believing everything that Al Gore says, maybe you and I will be the last two people on earth to get the joke. You and I will still believe this load of garbage, while the whole world is laughing at the huge practical joke that was played on them....
4 / 5 (4) Jan 09, 2009
You've turned into Noein. Oh no, we need an intervention. Someone get us some common sense STAT!
4 / 5 (4) Jan 09, 2009
We have all been the victim of a huge practical joke. Don't be the last person to figure it out. Your friends and family are realizing that they did not cause global warming. When will you notice that the music has stopped?

5 / 5 (3) Jan 09, 2009
We have all been the victim of a huge practical joke. Don't be the last person to figure it out. Your friends and family are realizing that they did not cause global warming. When will you notice that the music has stopped?


Alright, he's back. That was a close one.
not rated yet Jan 09, 2009
Whats up doc?

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