Wikipedia defines Palaeoclimatology as "the study of changes in climate taken on the scale of the entire history of Earth". Studies of data stored within rocks, sediments, tree rings, ice sheets, microfossils etc. can provide valuable information on the climate at different stages in the past and also map changes for future trends. Now
     Palaeoclimatologists have used those techniques to support a theory on the decline on the Indus Valley Civilisation (Pakistan) approximately 4,000 years ago. They studied the sediment from the base of an ancient lake (Kotia Dahar) and concluded that the monsoon cycle in that area had been suspended for possibly as long as two hundred years, leading to long term drought.
     The reasons behind the break in the monsoon cycle are unclear but the theory is backed up by similar data from Bronze Age Egypt and Greece, whose civilisations also suffered a decline around that time.
     The lake is not linked to any other water source and so its levels are directly related to rainfall and evaporation. By studying oxygen isotopes in the sediment the team determined that there was a dramatic decrease in rainfall over a 200 year period.
     David Hedell, a palaeoclimatologist from Cambridge University (UK), a co-author of the findings, is quoted as saying "It is an example - there are other examples o this - of how ancient societies have had to contend with climate. There are some lessons for us and our future, in which we will have to deal with anthropogenic climate change".

Edited from Nature (3 March 2014)