Mineral deposits formed within the generally stable environment of caves are called speleothems (Greek for “cave deposit”). They provide an archive of climate variations from which indications of mean temperature, rainfall and sometimes surface vegetation data can be extracted on timescales from the subannual to the millennial. They can be remarkably well preserved for millions of years.
Speleothems have a unique ability to be accurately dated over much of the late Quaternary period using the uranium-thorium dating technique. Stalagmites are particularly good because of their relatively geometry and because they contain several different climate records, such as oxygen and carbon isotopes and trace cations.
Prompted by a paper published in the journal Nature looking at speleothem data for China over the past few hundred thousand years Willis Eschenbach looked at the freely available speleothem data from the NOAA Paleoclimatology web site paying attention to the past 10,000 years – the period covering the emergence from the last strong phase of the Ice Age. Eschenbach used data from caves in Borneo, USA, Panama, South Africa, China, Indonesia, Tasmania, Israel, Austria and Costa Rica.
Although based on straightforward calibration the graph produced is fascinating and would be unlikely to change with more detailed processing of the data. It shows that speleothem data indicates that it was considerably warmer 7,000 years ago than it is today. Seen on the timescale of thousands of years today’s warm period is unremarkable. Click on image to enlarge.
A different analysis by Dr Stein-Erik of the University of Bergen a north Norwegian stalagmite, which grew up through the Holocene, showed rates of change from ‘warm’ to ‘cold’ or vice versa, occurred over only a few hundred years. Typical changes were around 1.2 deg C per century, greater than the global temperature changes we have seen in the past century.
Nearer to the present day, speleothem data can also be used to probe the Medieval Warm Period.
It is curious to note that there are hardly any reference to speleothem data in the latest IPCC synthesis report of in any of its supporting documents. Given their importance and the data they produce being able to put today’s climatic period into perspective, it would be beneficial to have them in the next IPCC report at greater length.