Sudden global warming 55 million years ago provides evidence for high climate sensitivity to atmospheric CO2, but the source of the carbon remains enigmatic.
Links:
[1] http://admin.indiaenvironmentportal.org.in/feature-article/ancient-carbon-mystery
[2] http://admin.indiaenvironmentportal.org.in/category/author/ken-caldeira
[3] http://admin.indiaenvironmentportal.org.in/category/author/mark-pagani
[4] http://admin.indiaenvironmentportal.org.in/category/author/david-archer-et-al
[5] http://admin.indiaenvironmentportal.org.in/category/journal/science
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/carbon-dioxide
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/climate-change
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/climate-science
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/global-warming