The catastrophic global warming scare was originally propelled by the IPCC with the Mann hockeystick curve of 1998 (called MBH98) that showed the world is now warmer than at any time in the past. The reason for the higher temperature was proclaimed to be due to increased CO2 in the atmosphere that came from 20th century industrialization. It is true that CO2 does absorb infrared radiation in wavelengths of about 2.7, 4.3, and 15 microns. It is also true that correlation is not necessarily causation. Over time other researchers tried to reproduce the results of Mann, et al, something that was not easy since they were not forthcoming with either their data or their methodology. After much work other investigators found serious issues with MBH98. Here is a paper that discusses the investigation into MBH98.

http://www.andrewbostom.org/blog/2008/12/25/horse-hockey-climate-scientology-%e2%80%9cgetting-rid%e2%80%9d-of-the-medieval-warming-period/