Burden sharing in the actions needed to reduce greenhouse gas emissions has proved so far to be the most intractable problem in the implementation of the Climate Convention and the Kyoto Protocol. We analyzed the contribution of non-Annex I countries to the GHG emissions in the period 1850-2010 to assess their relative contribution to total GHG emissions. In the period 1850-1990 non-Annex I countries represented 44% of the total but this contribution increased in the period 1990-2010 to 56%. If we extrapolate present trends to 2030 they will represent 69% in the period 1990-2030. The "historical responsibility" of Annex I countries is therefore decreasing. If we take 1990 as the starting year in which the Climate Convention recognized clearly that greenhouse gases are interfering dangerously with the climate system, it is evident the need of non-Annex I countries to engage with Annex I countries in the effort to reduce emissions. We present three options for the burden sharing in such effort. (C) 2015 Elsevier Ltd. All rights reserved.