Geological Climate Change.


When we talk about Climate Change what we are really talking about is Anthropogenic Climate Change, that is, the effect human activities are having on global climate. The increased levels of carbon dioxide in the atmosphere due to the effects of burning coal and oil, the methane output from huge herds of livestock and the nitrous oxide from excessive use of artificial fertilizers are well-known examples of human-induced emissions that are contributing to the rapid global rise in temperature.  Although we are doing it more quickly, we are not the first to do it; here are some examples of how other organisms on Earth have caused Climate Change in the geological past.

From the very first beginnings of life on Earth the organisms that live here have had a direct impact on the climate. As early as 3.5 billion years ago, the first cyanobacteria (blue-green algae) were converting the water and carbon dioxide in the atmosphere into oxygen. This early oxygen was mostly absorbed into rocks but after a billion years or so, oxygen began accumulating in our atmosphere. These simple organisms transformed our atmosphere. They caused global Climate Change.

Much later, around 470 million years ago another new group of organisms, the land plants, evolved. These plants started taking carbon dioxide from the atmosphere and releasing oxygen while their roots contributed to breaking up rock which then absorbed carbon dioxide as well. Very slowly over time (35 million years) this resulted in a significant decrease in the amount of carbon dioxide levels in the atmosphere and there is evidence that the reduction in carbon dioxide resulted in a significant global cooling which triggered an ice age.

This process was repeated 100 million years later when large forests evolved, again the effect was to absorb carbon dioxide from the atmosphere, and again the result was to significantly cool the planet, resulting in another long-lasting ice age. In this case however, the carbon was stored in bogs and swamps when the plants died. This meant that the carbon was extracted from the atmosphere and stored on land. Eventually this plant carbon was turned to coal.

Since the 17th century we have been reversing that process by taking that coal (and more recently oil and gas) and burning it and returning that carbon to the atmosphere as carbon dioxide.  That is the main reason we are now warming the planet.

When these first forests were forming, the rocks in the Burren were forming, and we see evidence of the global ice age. The ice sheets that formed on the South Pole absorbed so much water that sea-level fell globally. We can see that in the Burren limestone, when sea level dropped the limestone on the sea floor became land, was exposed to weathering and soils formed. As the ice melted those soils were then buried by the rising sea level and preserved within the rocks of the Burren.

We are just the latest organism on Earth to significantly change our atmosphere, the difference this time is that we change what that impact is.


Dr. Eamon Doyle, geologist for the Burren and Cliffs of Moher UNESCO Global Geopark.