Discussions at UN climate negotiations tend to focus on which countries have contributed most to climate change. This contribution depends on the methods for calculating both historical and current emissions. For this study, several ways of calculating countries’ relative contributions to cumulative global emissions were compared, showing that outcomes vary significantly as a result of the different choices made in the calculation methods.
Countries’ contributions to climate change are most strongly determined by their emissions over the last two decades
For the calculations, PBL Netherlands Environmental Assessment Agency, Ecofys and the European Commission’s Joint Research Centre (JRC) used data on historical greenhouse gas emissions for individual countries over the 1970–2010 period from the EDGAR data set , supplemented with those from the MATCH emissions data set over the 1850–1970 period. For the period between 2010 and 2030, the business-as-usual scenario was used that was developed for the OECD Environmental Outlook to 2030 . The more recent period (1990–2010) has contributed highly to countries’ cumulative emissions; in particular from the developing countries. Under the business-as-usual emission scenario, total cumulative emissions in China are projected to surpass those in the United States and the EU27 in the coming two decades.
Developing countries’ contributions to climate change approach 50%
Taking into account all greenhouse gas emissions emitted during the 1850–2010 period, the relative contribution by developing countries to global cumulative emissions was 48%. The group of developed countries was responsible for 52%. By 2020, the share of developing countries will probably amount to 51%. Hence, somewhere during the current decade, the share of the cumulative historical emissions in developing countries will surpass that of the developed countries.
|Developed countries||52.0||Developing countries||48.0|
|Australia & New Zealand||1.7||South Korea||0.6|
|Other Europen countries||1.1||Nigeria||0.6|
|Rest of Africa||5.7|
|Rest of Asia||0.6|
|Rest of Latin America||4.6|
|Rest of Southeast Asia||5.7|
Contributions to cumulative greenhouse gas emissions (percentage) according to the reference calculations, including all greenhouse gas emissions, cover the 1850–2010 period
Countries’ contributions vary according to the choices made in calculation methods
Discounting historical emissions for technological progress, for example, reduces the relative contributions by some developed countries and increases those by certain developing countries. The total contribution by the developed countries as a group during the 1850–2010 period came to 48% . This variant takes into account the fact that emerging economies benefit from existing technologies developed elsewhere. Another variant, one that is often used by experts from developing countries, excludes recent emissions (2000–2010), non-CO2 greenhouse gases, and CO2 from land-use change and forestry. This increases the relative contribution by developed countries as a group to as much as 80%. This significantly changes the historical relative contributions by many countries, altering their overall relative contributions by a multiplicative factor that ranges from 0.15 to 1.5, compared to reference values (reference calculations cover the 1850–2010 period and include all greenhouse gas emissions). From a scientific perspective, all greenhouse gases should preferably be included, as well as the most recent emission trends, as was done in the reference calculations included in this study.
The results presented in this paper show the importance of the choices made when calculating the historical contributions by the various countries. Such choices have to be made depending on how calculation results are to be used by policymakers when negotiating a future international climate agreement. Providing transparency on the implications of these choices, such as presented in this paper, may help governments to do so.