Palaeoclimatology means the study of climates in the distant past, using ice cores, sea sediments tree rings and the fossil record. Paleoclimatologists research climate events and trends in the past in order to gain better understanding of the current and likely future of the climate.
Because palaeoclimates, or climates in the past, were not originally measured by human beings, palaeoclimatologists use evidence from current environments to find proxy data on climate history.
Historical evidence of climate events is gathered from tree rings of ancient trees, lake sediments and deep-sea cores, coral skeletons and ancient ice cores. In addition to these natural sources of data, climatologists also use more recent evidence from human records of thermometer reading and satellite observations.
For most of the last 400 million years, geologic evidence shows that CO2 levels and temperatures were considerably higher than current levels.
This may have been caused by sun spots and volcanic eruptions spreading massive amounts of CO2, and contributing to the greenhouse effect.
However while volcanoes may have raised pre-historic CO2 levels and temperatures, human activities now emit 150 times as much CO2 as volcanoes.
Data from ice cores suggests that carbon dioxide varied within a range of 180 to 300 ppm over the last 800,000 years. Over the same period, Antarctic temperatures varied according to CO2 concentrations, indicating a close relationship between climate and the carbon cycle.
This relationship shows that human-caused release of CO2 through the burning of fossil fuels and deforestation is likely to directly increase temperatures. Currently, atmospheric CO2 concentrations are at an unprecedented 388.92 ppm (parts per million), a level that has not been seen on Earth for possibly 15 million years.
This rapid CO2 and temperature increase, especially in the last 50 years, is represented in the famous ‘hockey stick’ graph.
This graph was the result of the first comprehensive attempt to use palaeoclimatological data to reconstruct the average northern hemisphere temperature over the past 1000 years.
It shows temperatures as relatively constant until the last part of the 20th century and then suddenly increasing at an exponent rate of change.
The Intergovernmental Panel on Climate Change (IPCC) states that if current warming continues unabated, the result will climate change that is more extreme and rapid than at any other time in geological history.
Ian Ammison, et. al., ‘The Copenhagen Diagnosis: Updating the world on the latest climate science’, Elsevier, 2011, p. 63.; US Environmental Protection Authority, ‘Past Climate Change’, 29 September 2009, http://epa.gov/climatechange/science/pastcc.html.
US Environmental Protection Authority, ‘Past Climate Change’, 29 September 2009, http://epa.gov/climatechange/science/pastcc.html.
Co2 Now, ‘Annual Co2’, http://co2now.org/index.php?option=com_content&task=view&id=171&Itemid=1; Ian Ammison, et. al., ‘The Copenhagen Diagnosis: Updating the world on the latest climate science’, Elsevier, 2011, p. 65.
Jansen, E., J. Overpeck, K.R. et. al., 2007: ‘Palaeoclimate’. In: ‘Climate Change 2007: The Physical Science Basis’. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA,http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter6.pdf.