Geoscience Reference
In-Depth Information
Figure 1: Greenland air temperature: last 10,000 years
Greenland surface air-temperatures over the Holocene (last 10,000 years) as revealed by proxy measurements of oxygen
isotope ratios. Note that all peaks prior to the Little Ice Age were warmer than the late twentieth century warming.
Source: R. B. Alley, “The Younger Dryas cold interval as viewed from central Greenland,”
Quaternary Science
Reviews
, Vol. 19 (2000): 213-226.
Though the Greenland average temperature has warmed by about 1°C since the Little
Ice Age, such warming cannot be shown to have resulted from increases in human-related
CO
2
emissions. The warming was also entirely unalarming in rate and magnitude when
compared with other similar natural warmings that occurred over the preceding 10,000
years.
Context 3—carbon dioxide variations over geological time
It is widely misrepresented in the public domain that Earth's current levels of atmospheric
CO
2
are dangerously and atypically high. Such claims are false, because modern CO
2
levels lie near to an all-time low as assessed against the geological record.
500 million years ago, before land-plant photosynthesis was operating, atmospheric
CO
2
attained about fifteen times present day levels, built by cumulative volcanic
exhalations during four billion years of pre-Cambrian time. Between about 450 and 320
million years ago, levels declined steadily from >4,000 parts per million (ppm) to around
500 ppm, concomitant with the evolution and diversification of land plants, and thereafter
