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Advances in field observation, laboratory techniques and numerical modelling allow geoscientists to show, with increasing confidence, how and why climate has changed in the past. At that time, temperatures rose to levels 2-3°C warmer than today, and sea level rose by up to 20m in places. For example, cores drilled through the ice sheets yield a record of polar temperatures and atmospheric composition ranging back to 120,000 years in Greenland and 800,000 years in Antarctica. M., 2009, Modelling West Antarctic ice sheet growth and collapse through the past five million years. Sea level takes a few hundred years to reach equilibrium in response to changes in atmospheric CO2 and temperature, which may explain why sea level has not yet risen to the same levels seen in the Pliocene. I have newly activated a “Comment Image” plugin for the blog that will hopefully enable commenters to post images in their comments. [Unfortunately “comment images” live in the background do not seem to be working. Studies of the Last Glacial Maximum (about 20,000 years ago) suggest that the climate sensitivity, based on rapidly acting factors like snow melt, ice melt and the behaviour of clouds and water vapour, lies in the range 1.5°C to 6.4°C.If anyone is experiencing difficulty posting long comments then contact me by email.] Those who have not commented on this blog before will find the first comment goes to a moderation queue. and Bischoff, S., 2000, Carbon dioxide emissions from fossil fuel consumption and cement manufacture, 1751-1991, and an estimate of their isotopic composition and latitudinal distribution. Recent research has given rise to the concept of ‘Earth System sensitivity’, which also takes account of slow acting factors like the decay of large ice sheets and the operation of the full carbon cycle, to estimate the full sensitivity of the Earth System to a doubling of CO2.It is based on analysis of geological evidence, and not on analysis of recent temperature or satellite data, or climate model projections. This was due largely to insolation – the solar radiation received by the Earth’s surface – and dictated by the Earth’s orbit and the tilt of the Earth’s axis. This cooling took Earth’s climate into a Neoglacial period, culminating in the ‘Little Ice Age’ (1450 – 1850).
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The Council of the Society is issuing this statement as part of the Society’s work “to promote all forms of education, awareness and understanding of the Earth and their practical applications for the benefit of the public globally”. J., 2008, A new global biome reconstruction and data-model comparison for the Middle Pliocene. This highlights how unusual current temperatures, and estimated future warming, are.
The statement is intended for non-specialists and Fellows of the Society. Before the current warming trend began, temperatures in the Holocene (the last 11,000 years) were declining.
In some cases these changes are gradual and in others abrupt. Atmospheric CO2 is currently just below 400 parts per million (ppm) on average. That so many scientists maintain the opposite is astounding.
Evidence for climate change is preserved in a wide range of geological settings, including marine and lake sediments, ice sheets, fossil corals, stalagmites and fossil tree rings. It last reached similar levels during the Pliocene (5.3-2.6 million years ago).