From Merchants of Culture, by John Thompson, pg 238. In the United States:
The number of new books published in the US each year prior to 1980 was probably under 50,000. Throughout the 1980s and 1990s, the number of new books published greatly increased, reaching nearly 200,000 by 1998. By 2004 the number had risen to over 275,000 (see table 9 ). 2 After falling off in 2005, the total climbed to over 284,000 in 2007 and continued to rise in the following years, reaching an estimated 316,000 by 2010.
And this has been supplemented greatly by non-traditional outputs. From pg 239-241:
The data from Bowker suggest that the number of non-traditional outputs rose from 21,936 in 2006 to a staggering 2,776,260 in 2010, which, if added to the traditional books published in 2010, would give a total output of more than 3 million titles. The non-traditional outputs include books released by companies specializing in self-publishing, like Lulu and Xlibris, but the vast majority of these non-traditional outputs are scanned versions of public domain works that are being marketed on the web and made available through print-on-demand vendors.
A similar pattern can be seen in the UK. From pg 241:
Prior to 1980 there were probably fewer than 50,000 new books published each year in the UK. By 1995 this number had doubled to more than 100,000, and by 2003 it had increased to nearly 130,000.The total number fell off slightly after that, though by 2009 the number of new books that were published in the UK had risen to more than 157,000 (see table 10 ), spurred on by the growth of print-on-demand, digital and self-publishing.