When could global warming reach 4 degrees C?

When could global warming reach 4 degrees C?  

Publication Date:  2011
Creator:  Richard A. Betts
Matthew Collins
Deborah L. Hemming
Chris D. Jones
Jason A. Lowe
Michael G. Sanderson
Publisher.Display:  The Royal Society
Subjects.Display:  Climate change
Global warming
Greenhouse gases
unknownIntergovernmental Panel on Climate Change
Source Institution:  Florida International University
When could global warming reach 4 degrees C?