Global warming
Global warming

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Global warming

2 A 4.6 billion-year history

Climate change is a natural process of warming and cooling that has occurred all through the Earth's history. Throughout geological time there have been ‘hot-house’ periods and ice ages. In order to understand the current situation, it is necessary to have some sense of context and perspective, from historical and geological time-scales. The document below shows a chart showing a generalised temperature history of the Earth.

Click on the link below to see the chart

Temperature history [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)]

We are currently enjoying an interglacial period of an ice age that began approximately two million years ago. (Ice ages are composed of colder ‘glacial’ and warmer ‘interglacial’ periods.) This is at least the seventh ice age in the Earth's 4.6 billion-year history.

During the Cretaceous (65–147 Ma) the whole Earth was up to +15°C (warmer than at present, with tropical forests covering Antarctica, whereas during the Quaternary (~2 Ma) ice sheets spread across much of Europe and the mean surface temperature was up to (5 °C colder than at present. The range of these changes is much greater than the observed increase in temperature over the past century (+0.6 ±0.2 °C) and predictions for the next hundred years (+3 ±1.5 °C).

Click on the link below to read ‘Glaciers past and present’

Glaciers past and present

Click on the link below to read ‘Pollen diagrams and ancient climates’

Pollen diagrams and ancient climates

Activity 1 Past temperatures: before measurement, before people

Measuring temperature is a relatively recent affair. Galileo Galilei invented his thermometer in 1597, but the longest running record of surface temperature to the present day only dates from 1815. For periods prior to these measurements, our understanding of the history of climate change is inferred from geological evidence, primarily:

  • Glaciation (showing that much of the northern hemisphere was covered in ice, some 18 000 years BP).

  • Fossilised pollen (showing that over the past 140 000 years, the mean temperature has varied by almost 15 °C).

Prepare a brief (no more than five minutes) presentation on the information concerning climate change provided by either glaciation or the pollen record. The presentation should close with 3–7 key ideas to explore. Two resources are provided to help you do this: ‘Glaciers past and present’ and ‘Pollen diagrams and ancient climates’. To access these resources, click on the "view document" links above.

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