Past Climate

• Paleoclimatology


  The study of past climates prior to the instrument record, using indirect evidence (data) during past time periods to determine the climate at that time period
• Paleoclimatology


  • It may help us to understand natural climate changes
  • The study of past climates may give us information into future climate scenarios
• Reconstructing Past Climates


  1. Climate reconstruction

  2. Improves our understanding of environmental response to climate variability and climate change

  3. Provides perspective on current climate

  4. Requires identification of a link between quantitative climate forcing and environmental response
• How scientists study climate

  • Satellites
  • Instrument Record
  • Historical Proxy Records
  • Ancient Proxy Records
• Instrument record


  Extends back about 150 years (~1860), during which time Earth's temperature has increased 0.7 °C (1.3 °F)
• Historical Records


  Weather and climate observations can be found in ships logs, farmers' diaries, newspaper accounts, and other written records
• Sediment Cores


  Sediment cores can be taken from lakes, the shallow ocean, or the deep ocean, and the thickness of these layers can be used to infer past climate, or the layers can be composed of organic material that can be analyzed for other climate proxies
• Pollen


  Pollen grains are well preserved in lake and ocean sediment, and the analysis of each of these sediment layers provides information on the vegetation present at that time, which scientists can use to infer past climates (warm or cold) based on the distribution and changes in plant species
• Stable Isotopes


  The most common element used in climate studies is oxygen, and the ratio of O18 to O16 is affected by temperature and can be used as a climate proxy
• Coral Reefs


  Corals are composed of calcium carbonate, which contains isotopes of oxygen that can be used to determine the water temperature when and where the corals grew
• Ice Cores


  As snow and ice accumulate in polar glaciers, a paleoclimate record accumulates of the environmental conditions of the time of formation, which can be analyzed using stable isotope approaches for water or air bubbles within the ice as a record of past atmospheric gas concentrations
• Tree Rings


  Tree growth is influenced by climate, and these patterns can be seen in tree ring width and isotopic composition, with trees generally producing one ring each year, and tree ring records can extend back to the last 1000 years

  
• Paleo-data or proxy data, such as tree rings from Bristlecone Pine (USA) which can extend back up to 10,000 years, can be used to reconstruct past climates
• Ice cores store past samples of the atmosphere, and scientists can analyse oxygen isotopes to infer past temperatures
• Scientists use a drill to extract coral samples from locations like Clipperton Atoll to study past climates
• Speleothems (cave formations) and pollen deposits can also be used as climate proxies
• Sometimes paintings can provide a record of historical climate conditions when precise measurements are not possible
• The European Project for Ice Coring in Antarctica (EPICA) has extracted ice cores to study past climates
• CO2 Atmospheric Measurements


  CO2 has risen from 280 ppm pre-industrial to 315 ppm in 1958 and 419 ppm in 2023
• The global CO2 concentration increased from ~277 ppm in 1750 to 415 ppm in 2021 (up 49%)
• Global fossil CO2 emissions have risen steadily over the last decades, with emissions in 2021 set to rebound towards their pre-COVID-19 levels after an unprecedented drop in 2020
• The top six emitters in 2020 covered 66% of global emissions: China 31%, United States 14%, EU27 7%, India 7%, Russia 5%, and Japan 3%, with international aviation and maritime shipping (bunker fuels) contributing 2.9% of global emissions in 2020
• In 2020, the share of global fossil CO2 emissions was: coal 40%, oil 32%, gas 21%, cement 5%, flaring and others 2%
• Total global emissions were 38.0 ± 3.1 GtCO2 in 2020, 40% over 1990, with land-use change contributing 42% in 1960 and 10% averaged 2011–2020