When discussions and negotiations started under the UNFCCC, more than 20 years ago, industrialized countries accounted for about half of global GHG emissions. That was the reason why only industrialized countries had to comply with emission reduction targets under the Kyoto Protocol.
Currently, the share of global GHG emissions has changed.
Upper and lower middle-income countries combined currently account for more than half of global GHG emissions.
The highest rate of increase since 1990 has been in upper middle-income countries. In 2010, upper middle-income countries emitted as much GHGs as high-income (industrialized) countries.
Because middle-income countries are considered as developing countries for the UNFCCC, they were not required to reduce GHG emissions.
This is what triggered the discussions towards an agreement that required all countries to reduce GHG emissions.
IPCC, First Assessment Report – Climate Change: The IPCC Response Strategies (1990)
UN Advisory Group on Greenhouse Gases (1990) – Joint expert group established by the World Meteorological Organization (WMO), the United Nations Environment Programme (UNEP) and the International Council of Scientific Unions (ICSU)
IPCC, Fifth Assessment Report Working (AR5) – Group III (Chapter 1)
Emission Database for Global Atmospheric Research (EDGAR). European Commission, Joint Research Centre/PBL Netherlands Environmental Assessment Agency
UNEP, The Emissions Gap Report (2020)