Ranking Global Warming Contributions by Country

Human greenhouse gas (GHG) emissions have been the primary contributor to a global temperature rise of ~1 C since pre-industrial times. Industrial processes, energy production from burning fossil fuels and deforestation have been the major contributors to this observed trend in global warming. Even though the overall trend is of global nature, the sources of GHG emissions across the globe have varied drastically between regions and individual countries. A new study by Concordia University’s H Damon Matthews et al. published in Environmental Research Letters last week represents a sound estimate of what countries have historically been the largest GHG emitters and contributors to global warming. The calculations performed in the include an from five different emissions:

  • Fossil Fuel CO2
  • Land-use CO2
  • Methane
  • Nitrous Oxide, and
  • Aerosols, which have a cooling effect on the climate.

The results of the study show that the United States is the clear leader is both GHG emissions and contributions to global warming. Of the 0.7 C increase in global temperature since pre-industrial times, the United States alone has contributed 0.15 C (~20%). The top seven contributors alone account for ~63% of warming contributions, and the top 20 countries account for ~82%. China, which is presently the largest global emitter of GHGs, ranks 2nd on historical contributions to global warming, followed by Russia and Brazil and India. Brazil and India are interesting cases given that most of its CO2 emissions have originated from land-use emissions, meaning that deforestation has contributed to Brazil’s high ranking. This is different from the other top GHG emitting countries, whose main CO2 emissions can be tied back to the burning of fossil fuels. The study also includes the cooling effects that aerosol emissions have on the global climate. Generally, countries that emit larger quantities of CO2 also produce larger amounts of aerosols, which help counteract the warming effects of the CO2 emissions.

National climate contributions due to each of the four components: (a) fossil fuel CO2 emissions; (b) land-use change CO2 emissions; (c) non-CO2 greenhouse gas emissions (methane and nitrous oxide); and (d) sulfate aerosol emissions. Source

The paper also highlights that ~50% of the global CO2 emission budget has already been used if only a 2 C increase in global temperatures is desired by the year 2100. The study also highlights that most countries in the top 20 exceed a desired average of 0.11 C warming contribution per 1 billion people. In a world of 9 billion people, each country should have an average of 0.22 C per billion people in order to achieve the 2 C increase target. Many developed countries are already exceeding this value and do not have much room to increase their contributions and hence their GHG emissions, whereas many developing countries still fall below that value.

Total versus per-capita contributions to temperature change for the world’s top 20 total emitters – Source

The study also introduces an interesting idea of how to account for emissions. Currently, all GHG emissions are accounted for in the country in which they are produced. However, in manufacturing heavy countries such as China, many of the GHG emissions result from products that are shipped for consumption to developed countries. Therefore, if emission accounting were to be performed by consumption, the developed world would have an even larger share of GHG emissions and global warming contributions.