Big Ideas in Volcanology #08:


Is volcanism compatible with life? Is our hydrosphere still receiving significant masses of new volatiles from inside the Earth and comets? And how can these be directly compared to anthropogenic ones? Some food for thought is in this page.

Earth, the water planet, is very poor in volatiles: the ocean is only 0.02 % of its mass. Because of the need of life for liquid water we try to understand how Earth got the way it is, but also other elements are of crucial importance.

For example, during the formation of Earth’s atmosphere a O3 (ozone) layer permitted a progressive protection from UV radiation and played an important role providing additional appropriate conditions for human Life. Nevertheless, Earth’s ozone layer is getting progressively thinner since the late 1970s.

BUV & TOMS ozone concentration on the Arctic region (1971-2000)

Two distinct but related phenomena can be described: a decrease of about 4% per decade in the total volume of O3 in Earth's ozone layer and a much larger springtime decrease in stratospheric ozone over Earth's polar regions (the so called “Ozone hole”).

This is caused by the catalytic destruction of O3 by atomic halogens, mainly due to the photodissociation of man-made halocarbon refrigerants (i.e. CFCs, freons, halons).

Since the ozone layer prevents most harmful UVB wavelengths (280–315 nm) of UV light from passing through the Earth's atmosphere, observed and projected decreases in ozone have generated worldwide concern leading to the adoption of the Montreal Protocol that bans the production of CFCs, halons, and other ozone-depleting chemicals such as carbon tetrachloride and trichloroethane.

NASA projections of stratospheric ozone concentrations on North america if CFCs had not been banned

A diffused idea is that volcanic eruptions can modify the composition of Earth’s atmosphere and impact climate change. Although most of the ash falls from the stratosphere in a short time and has little impact on climate change, volcanic gases like CO2 - a greenhouse gas - has the potential to promote global warming. Conversely, SO2 has impact on global cooling but is also a component of acid rains and a precursor of sulfate aerosol (sulfuric acid droplets), the main component of haze in polluted regions. This causes limits to the visibility, buildings degradation, and represents an hazard for health.

SO2 pollution (average from 2005 through 2007) in similarly sized regions of the US Midwest, Europe and around Beijing.

Bright red indicates the highest pollution levels. Credit: Simon Carn / Ozone Monitoring Instrument Group, University of Maryland.

Research findings indicate that human activities emit more CO2 than volcanoes. In fact, present-day volcanoes emit relatively modest amounts of CO2 if compared to anthropogenic activities, for example about as much annually as emitted by states like Florida, Michigan and Ohio.

However, volcanoes emit CO2 both on land and underwater. Underwater volcanoes are estimated to emit between 66 to 97 Mt of CO2 per year (Morner & Etiope, 2002) but this is balanced by the carbon sink provided by newly formed ocean floor lava. Consequently they are assumed to have marginal effect on atmospheric CO2 levels. The greater contribution comes from subaerial volcanoes, estimated to emit 242 Mt of CO2 per year (Morner & Etiope, 2002).

Surtseyan eruption at Hunga Ha'apai island (Tonga) in March 2009 (left) and nearby El Hierro island (Spain) in July 2011

In contrast, anthropogenic emissions are estimated to be around 29 GT of CO2 per year. This means that human CO2 emissions are over 100 times greater than volcanic ones. Even strong volcanic eruptions such as at Pinatubo (which emitted around 42 Mt of CO2) had little discernible impact on CO2 levels. In fact, aerosols can possibly affect the rate of change of CO2 levels acting as a cooler. Indeed this actually drops only slightly after a large volcanic eruption.

Atmospheric CO2 levels measured at Mauna Loa, Hawaii and Stratospheric Aerosol Optical Thickness, a measure of volcanic activity.

If you are interested in knowing more about this still widely debated topic, here are some suggested lectures:

_ Volcanic Gases and Their Effects

_ Volcanic Gases and Climate Change Overview

_ What Will Cure China’s Sulfurous Skies?

_ Gases: Man versus the Volcanoes

_ Two attempts to blame global warming on volcanoes


Open questions

Earth’s hydrosphere comes from Volcanic Degassing