nearly 20,000 years ago, average temperatures around the world were about 6
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/ice-age-cometh
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/down-earth
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/climate-change
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/global-warming