Geologist Goonie Marsh speaks about current climate change patterns and puts into perspective some of what's happened over the last few billion years.
Geologist Goonie Marsh speaks about current climate change patterns and puts into perspective some of what's happened over the last few billion years.
Are humans causing climate change?
We need to keep perspective here and recognise that the current apparent warming trend may not be caused by rising atmospheric greenhouse gases only. Countless other organisms that have lived on Earth over billions of years have influenced climate, with negative impacts for some and positive for others.
How do rocks tell us about climate change?
Climate leaves fingerprints on natural Earth materials. The character of sedimentary rocks,
accumulating over periods of 10s of millions of years, reflects the climate. More refined records of
climate change over the past few million years have come from measurements of isotopes ice cores,
sedimentary deposits in lakes and in the deep marine environment, in cave deposits and in tree rings
of long-lived tree species.
What has past warming done for the Earth?
Global warming in the past has given Grahamstown a substantial valuable commodity – the clay! Hot,
humid climates generate large-scale sub-surface water circulation systems which dissolve different
rocks, depositing them in the soil layers. Underlying rocks are converted to clay and the soil is
converted to resistant rock such as ferricrete.
How has Grahamstown’s climate varied?
Local rock type, Dwyka Tillite, indicates that 300 million years ago Grahamstown’s climate was
similar to that of Antarctica. At that time, South Africa, and thus Grahamstown, was close to the
South Pole. Subsequently Africa shifted out of the Antarctic climate zone through plate tectonics.
Jump forward to 65 million years ago and Grahamstown’s climate was hotter and more humid than
now.
How has the Earth’s climate changed in the last million years?
Over the last 700 000 years global temperatures have varied in a cyclical fashion. Generally
conditions were significantly colder than today with interruptions by several short-duration
warmer intervals. Changes from colder to warmer climate were abrupt. The last 10 000 years have
been climatically mild and more stable – a climate humankind regards as ‘normal’, but it is not
necessarily ‘normal’ for the Earth system.
Can we stop climate change?
Causes of climate change are many and not well understood. They interact in complex ways and
may result in either warming or cooling. Even if humankind solves the carbon emission issue it
will not contain climate change. Another perspective to keep in mind: humankind is not separate
from the Earth’s system. Arguably, our impact on the environment is just the way the Earth works.
