Colin Gleadell adds a little historical perspective to the rising value of Contemporary art. Though it is worth noting that the reference point of 2011 might have been an artificially high peak in the Modern and Impressionist Art markets:

It is, however, a measure of the growth of the contemporary market (from 1950 to 2014) that, while it was matched by the earlier period in 2009, its proportion of the fortnight-long sales totals has been increasing with each year since – from 65 per cent in May 2011 to 72 per cent this May.

Art Sales: The $2 billion art bonanza (Telegraph)