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Introduction: the evidence for anthropogenic climate change

Explore the evidence for anthropogenic climate change, from climate variation to climate change trends over time. Learn about the impact on weather systems, instrumental data sources, temperature records, and palaeoclimate reconstruction techniques. Sources: IPCC, Canadian Institute for Climate Studies. Discover the changing climatic variables and the importance of proxy data sources.

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Introduction: the evidence for anthropogenic climate change

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  1. Introduction: the evidence for anthropogenic climate change Presented by James Reeler UWC

  2. Climate variation • All manner of human and natural activities are affected by weather and climate • WEATHER is the day to day effect of natural conditions. • CLIMATE refers to an averaging of these conditions over a longer period, obtaining a general picture of trends in conditions over time. • Both systems are highly variable. • Climate is influenced on varying time scales by factors such as fluctuations in solar output, the Earth’s orbit, changes in vegetation cover and in the gaseous composition of the atmosphere (IPCC, 2001). • This short-term variation is termed climate variability, or CLIMATE VARIATION.

  3. Climate change • A long term trend in climatic conditions away from the established conditions is termed CLIMATE CHANGE. • The earth has always experienced climate change due to natural variations in insolation and atmospheric conditions– it is not a new process. • Orogeny, which is the development of new surface features on a geological time scale, can affect the climate gradually. • The most recent ice age ended 10 000 years ago, and what we have been experiencing in recent history may be termed a “climatic optimum” • It is telling that agriculture only arose as a human adaptation strategy within the last few thousand years, corresponding to optimal growth conditions for agricultural crops. Source: Canadian Institute for Climate Studies

  4. Source: IPCC online talks What are we looking for? • Changing climatic variables could be expressed in different ways, depending on how the climate is transformed. • A change in mean temperature would mean we would see more extreme heat and hot weather events. • A transformation in variance of temperature would give a broader spread, resulting in more extremes of both heat and cold. • If there were a change in both mean and variance of temperature, whilst we would see more extreme heat and warm weather, we might still observe extremes of cold weather. • This type of change might therefore hide the signal, since certain areas would be unchanged. Only after extensive observation would the trend be clear. This may be what has happened in recent history

  5. Sources of data - instrumental • Instrumental measurement of climate variables is an important data source, although we only have true records for a short historical period. • Using standard instruments, we record: • Temperature • Rainfall • Wind • Humidity • Atmospheric aerosol and gas concentrations • These standard variables allow measurement of change in the earth’s systems.

  6. Temperature • Temperature is an essential indicator variable, because it provides us with a direct measurement of the energy in the earth’s atmospheric system. • Temperature records date from the middle of the 19th century. • Surface air temperature is usually measured at weather stations by means of mercury or alcohol thermometers. • However, much recent work has been done to allow measurement of the temperature of other atmospheric levels, using the TIROS-N series of satellites. • These atmospheric temperature records start in 1958 (conventional radiosonde network)(Angell, 1988) and 1979 (microwave-sounding unit) (Spencer & Christy, 1990) respectively.

  7. Palaeoclimate reconstruction from proxy data • In order to obtain data prior to the advent of modern measuring devices, climatologists resort to using proxy data from a variety of sources. • Sources of proxy data include: • Glaciological (ice cores) • Oxygen isotopes • Trace elements and microparticle concentrations • Physical properties • Geological • Sediments • Marine – organic/inorganic sediments • Terrestrial – glacial / periglacial/ aeolian/ lacustrine • Sedimentary rocks • Facies analysis • Fossil/microfossil analysis • Mineral analysis • Isotope geochemistry • Biological • Tree rings (dendroclimatology) • Pollen species/abundances • Insects • Historical • Historical meteorological records • Parameteorological records (environmental indicators) • Phenological records (biological indicators)

  8. Palaeoclimatological time scale ProxyTime period before present (years) 10910810710610510410310210 Historical Tree rings, pollen Ice cores Glacial deposits Marine organic sediments Inorganic sediments Sedimentary rocks Decreasing resolution (and accuracy)

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