Also very useful for scenario analysis and to

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-Also very useful for scenario analysis and to estimate relative changes at different locations. But model forecasts are only as reliable as the inputs to the models (initial state, assumptions, processes included…) -Reliability decreases the further we project into the future. Models are limited we can’t take them for face value. But they are improving and only time will tell, since this real-world experiment will take time. Models are good but they are not hard evidence! Historical Climate How has the climate changed in the recent and distant past? Are the changes being observed today historically significant? If not unusual, then perhaps we are witnessing a natural climate variation But even a natural variation could be trouble if it threatens our ability to sustain ourselves If the changes are unprecedented, then we have more reason to believe humans are causing them. The study of past climate is paleoclimatology. Reconstructing Past Climate How can we determine CO 2 concentrations and temperatures from one million years ago? Ice cores: are long cylinders of pack ice obtained by drilling vertically down using a hollow drill. Core samples are extracted in 4-6 m segments, and complete cores can be as much a 4 km long!
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When snow builds up, it becomes compressed and turns to solid ice. Each season is seen as a distinct layer in a core. One 2.5 long core represents a 400,000 year record of climate on Earth—it contains numerous proxies. Isotope ratios are a proxy for temperature (as water vapours move towards to north, the heavier isotopes will condense faster) Small gas bubbles are samples of the atmosphere in the past. (measure the CO 2 concentration) Impurities and dust reveal pollution. (Volcanic, fires, etc). Ice core records are generally regarded as reliable.
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