TAG - Geological Society of Australia

Society UpdateClimate Change StatementThe Executive Committee of the GSA has produced the following draft Climate Change Statement after aprolonged period of consultation with GSA members. In line with feedback from members, the statementemphasises the geological record as an archive of past climate change and how it can contribute to ourunderstanding of future climate change.The Executive Committee recommends that the statement be adopted by the Society, but welcomes furthermember feedback no later than 31 January 2013. This will be followed by consultation with Divisional andBranch committees during February 2013, after which a final statement will be endorsed by the GSA Executiveand placed on the GSA website. All comments should be emailed to climatechange@gsa.org.au.Draft GSA Climate Change StatementThe Geological Society of Australia (GSA) has developedthis document as a science-based statement regardingclimate change, 1 emphasising the contributions that EarthScience can make to the public discussion. This Statementprovides the views of a learned Society dedicated toinvestigation in Earth Sciences and is made by theExecutive Committee of the GSA, after wide consultationwith Society Members who are qualified EarthScientists largely working in or retired from academic,industry, government and public sector organisations.The nature of the geological recordInstrumental records of global climate are short when itcomes to estimating future climate changes because manyof the processes that control global climate operate on verylong time scales by human standards. Current debate aboutthe causes and consequences of global climate change canbe informed by studying the geological record of pastclimate changes on time scales from decades to billions ofyears.The geological record provides the key source ofinformation regarding Earth’s past climates, includingperiods when global climate was both significantly warmerand colder than the present. Important climatic archivesinclude sediment cores from the oceans (up to tens ofmillions of years old), ice cores from Greenland and Antarctica(up to 800 000 years old), as well as marine andcontinental sedimentary rocks that may be hundreds ofmillions of years old. Evidence may include the distributionof fossil plants and animals, the past distribution of ice onthe Earth’s surface, and estimates of temperature andatmospheric composition based on geochemical measurements,to name just a few examples. In some cases, thegeological record may be very detailed and young enoughto overlap with instrumental records of climate (eg, annualgrowth layers in corals).Variability of past climatesGeological evidence clearly demonstrates that Earth’sclimate system is inherently and naturally variable overtime scales from decades to millions of years. 2Some 50 million years ago, mean global temperaturewas about 6°C warmer than today. Since then, Earth’sclimate has fluctuated but has been generally cooling aslarge ice sheets formed, first in Antarctica and then in theNorthern Hemisphere. Over much of the last 2–3 millionyears the climate has typically been colder than today,often much colder, when the growth of ice sheets during‘glacial periods’ caused sea levels to be more than 120 mlower during the largest glacial advances. Theseglacial periods have been interspersed with intervals ofwarmer climate, referred to as interglacial periods. TheEarth is currently in an interglacial period, called theHolocene Epoch. There have been some 50 glacial/interglacial cycles during the last 2.6 million years. Thepresent glacial/interglacial cycle began some 115 000 yearsago with a major global cooling event and growth of icesheets progressively extending from the polar ice-caps tolower altitudes/latitudes. This glacial period peaked about20 000 years ago, when global temperature was some 5°Ccolder than today, and was then followed by progressivewarming, ice melting and sea-level rise that led to thepresent interglacial. We know also that during the last15 000 years interruptions to the gradual warmingoccurred, with both rapid cooling and warming episodessometimes occurring over time periods as short as a fewdecades.6 |TAG December 2012