Impacts of volcanism on climate

Natural events that can trigger global climate changes include:

(1) known astronomical variations in the orbital elements of the Earth (Milankovitch theory)

(2) changes in energy output from the Sun and

(3) airborne volcanic material ejected into the stratosphere

Changes in the composition of the earth’s atmosphere can result in:

1. Ozone effect

2. Greenhouse effect

3. Haze effect

Volcanic eruptions can influence all of the above climatic effects to different extents

Stratospheric ozone depletion

• Ozone (O3) in the stratosphere absorbs ultraviolet radiation

• This ozone is destroyed by chlorine bearing CFC compounds

The region in blue is the hole of ozone depletion, which extended to a record 10.5 million square miles on Sept 19,1998. Image from NASA

• Satellite data showed significant ozone loss after the 1991 Pinatubo eruption

• Volcanic aerosols can play an indirect but significant role in ozone depletion by providing a surface for the chemical reaction to take place

• Short-lived impact

The region in blue is the hole of ozone depletion, which extended to a record 10.5 million square miles on Sept 19,1998. Image from NASA

Volcanic influence on the greenhouse effect

• Volcanoes can create a greenhouse effect

• Deccan Trap volcanism and subsequent greenhouse effect is considered a viable cause for the K-T extinction 65 million years ago

(McLean, D. M., 1982, Flood basalt volcanism and global extinctions at the Cretaceous-Tertiary transition: American Association for the Advancement of Science, 148th National Meeting, Abstract of papers, p. 47.)

http://filebox.vt.edu/artsci/geology/mclean/Dinosaur_Volcano_Extinction/pages/studentv.html

• However, at present a far greater portion of greenhouse gases in the atmosphere are from human actions than from volcanism

• Volcanoes emit between about 145-255 million tons of CO2 into the atmosphere every year

• Emissions of CO2 by human activities, amount to about 24 billion tons per year

• Human activities release more than 150 times the amount of CO2 emitted by volcanoes

http://volcanoes.usgs.gov/Hazards/What/VolGas/volgas.html

http://cdiac.esd.ornl.gov/trends/emis/tre_glob.htm

• Volcanoes in fact produce a GLOBAL COOLING effect that counteracts the current global warming trend

Volcanic influence on the haze Volcanic influence on the haze effecteffect

• Suspended particles, such as dust and ash, can block out the earth's sunlight

• This reduces solar radiation and lowers mean global temperatures (HAZE EFFECT)

• Volcanic eruptions have a far greater impact on the haze effect than on the greenhouse effect

Pacific sunset through haze. Courtesy of NOAA

http://asd-www.larc.nasa.gov/SOLAR/learning-aerosol.html

• The amount of sulfur-rich gases emitted in a volcanic eruption appears to be more effective in causing the haze effect than pyroclastic particles such as ash

• The 1982 eruption of El Chichon had a greater impact on the climate than Mt. St. Helens due to its larger SO2 emission

Pacific sunset through haze. Courtesy of NOAA

• SO2 combines with water vapor to form dense clouds of tiny sulfuric acid droplets which can take several years to settle out

• These droplets absorb solar radiation and scatter it back to space

• This reduces global temperature

Pacific sunset through haze. Courtesy of NOAA

Why Don't All Volcanoes Affect Climate?

Factors which determine whether and how a volcano will affect the climate:

• SIZE. To send gas and ash into the stratosphere, an eruption column at least 15 km high is necessary.

• SHAPE AND DIRECTION. Even a very large eruption will not reach the stratosphere if it explodes sideways.

Example: Mount St. Helens

• LOCATION. To cover the entire earth in volcanic aerosols, the eruption must occur near the equator, so the ash and gases can spread both north and south.

• SULFUR CONTENT. This is important in producing the haze effect

• WATER CONTENT. The more water in the magma that feeds a volcano, the more explosively that volcano will erupt.

PINATUBO: ALL OF THE ABOVE

The Total Ozone Mapping Spectrometer (TOMS) on Nimbus 7 recorded the dispersal of the Pinatubo plume by tracking the sulfur dioxide released.

http://eos.higp.hawaii.edu/education/slide_set1/slides.captions.html

http://eos.higp.hawaii.edu/education/slide_set1/slides.captions.html

http://eos.higp.hawaii.edu/education/slide_set1/slides.captions.html

NASA Langley's SAGE II instrument

AVHRR satellite data Image credit: Dr. Larry Stowe, NOAA/NESDIS

Pinatubo SkiesMany parts of the world experienced vividly

colored sunsets for months following the June 1991 explosion of Mt. Pinatubo in the Philippines. This photo was taken in January 1992 in El Segundo, California, on the west coast of North America, approximately 7500 miles from the Philippines.

http://pages.prodigy.net/pam.orman/joeatmospheric/Atmospheric_9201_3.html

Other climatic effects

• Acid rain and volcanic smogAcid rain and volcanic smog or or “VOG” from sulfur gases (very “VOG” from sulfur gases (very pronounced in Hawaii) pronounced in Hawaii)

• FluorineFluorine from volcanic gases can from volcanic gases can contaminate groundwater and contaminate groundwater and grass, and can cause fluorosis in grass, and can cause fluorosis in livestock (e.g. Hekla, Iceland, livestock (e.g. Hekla, Iceland, 1970)1970)

Lava fountain, Pu`u `O`o cinder and spatter cone