Flamsteed Astronomy Society

The Climate History of Planets

— by Dr Ben Edwards, Feb 4, 2008

Geology is somewhat off the beaten track as far as the Flamsteed is concerned, but Ben Edwards easily held our attention for an hour on ‘the climate history of planets’, or volcano-ice interactions.

Understanding better the history of the Earth’s climate is clearly most important to us, never more than in the present era of climate change or ‘global warming’.  Has Earth experienced such episodes before, and if so, what is the likely climate outcome?  Equally we have begun on a new phase of detailed examination of our planetary neighbours in the solar system.  The climate history of Mars is of special interest and we are working hard to interpret the avalanche of data coming back from a multitude of space missions to the red planet.  Is there life on Mars and what evidence can we see for the existence of surface water or water-ice in the past?

Examination of sediment cores, ice cores and other sources suggests the Earth’s global average temperature has switched between 17 and 22 degrees over the long term — one or the other, but not spending a long time at any other temperature.  We believe the major factors influencing climate have been —

Plate tectonics driving location of the land masses.  Land masses at the poles support larger masses of ice which reflect back more solar radiation.

Earth’s orbit.  Long-term effects (so-called ‘ Milankovitch cycles’) alter the amount of solar radiation received, and

Vulcanism.  Major eruptions push vast quantities of dust into the atmosphere and can bring about very significant climate changes.  The Mount Pinatubo eruption in 1991 ejected about 10 cubic kilometers of material and caused an average temperature drop of 0.3 degrees.  2.1 million years ago (MYA) the Yellowstone eruption ejected about 2500 cubic kilometers of material and may well have triggered the present ice cycle.

Unfortunately there are few clues left on Earth’s surface about the history of the climate.  Glacial sediments have been eroded and the land record tells us about only 4 episodes of major glaciations in the northern hemisphere.

There are far more clues to be had from the aftermath of volcanic eruptions in ice fields.  A geological record is preserved from eruptions that happened under ice, and when volcanic geology is eroded by ice later in its history.

Ben gave us an engrossing tutorial on the types of geology remaining from volcano-ice interactions, how to recognise them, and what we can learn. 

Finally Ben turned back to Mars and looked at Olympus Mons, the tallest volcano known in the solar system and twice the height of Mt Everest.  Data now being returned from the space missions orbiting Mars suggests it highly likely that Olympus Mons formed with eruptions through thin ice.  As we learn from studies of volcano-ice interactions here on Earth we hope to be able to interpret the data from Mars better and understand when the Olympus Mons eruptions happened, how long they lasted and what was the thickness of the ice.


Olympus Mons from Mars Global Surveyor — courtesy NASA

2004 Grimsvotn eruption, central Iceland.

By Magnus Gudmundsson

Hoodoo Mountain volcano, a trachytic glaciovolcanic edifice in British Columbia, Canada, by B. Edwards.

Dr Ben Edwards  [pic: Mike Dryland]