Global Warming Science -


GHG Emissions - Sources


[last update: 2011/01/08]



This document contains the following sections:





Greenhouse Gas Sources By Sector


The sources of greenhouse gases (GHG) come from various sectors including transportation, industrial processes, power generation for residential consumption, agriculture and deforestation. According to the United Nations Food and Agriculture Organization (FAO), deforestation accounts for 25 to 30 percent of the release of GHG []. The report states: “Most people assume that global warming is caused by burning oil and gas. But in fact between 25 and 30 percent of the greenhouse gases released into the atmosphere each year – 1.6 billion tonnes – is caused by deforestation.” From 1990 to 2000, the net forest loss was 8.9 million hectares per year. From 2000 to 2005, the net forest loss was 7.3 million hectares per year.


The ten countries with the largest net loss of forest per year (2000 – 2005) are: Brazil, Indonesia, Sudan, Myanmar, Zambia Tanzania, Nigeria, Democratic Republic of the Congo, Zimbabwe, and Venezuela (combined loss of 8.2 million hectares per year). The ten countries with the largest net gain of forest per year (2000 – 2005) are: China, Spain, Viet Nam, United States, Italy, Chile, Cuba, Bulgaria, France and Portugal (combined gain of 5.1 million hectares per year). []


See: for information on the effects of deforestation.


The following figure (left) shows a generalized source of GHG from various sources. However, this does not include deforestation (the number one cause of GHG). Various studies show various differing contributions by sector, since not all consider the same factors. The right-hand figure shows emissions by sector from another source using 1996 IPCC data []. These are global estimates and do not reflect the fact that GHG contributions by sector vary regionally (for example, in Washington State where a large portion of power generation is hydroelectric, and where there is no net deforestation).




Estimated Greenhouse Gas Emissions by Sector



The above figure ignores one of the largest sources of GHG – deforestation and shows a smaller impact other anthropogenic land use change effects than most studies. See:


The following figure shows GHG by type (pie chart b) and sector (pie chart c) from the IPCC AR4 SPM []. Note that CO2 fossil fuel use is only 56.6 % of GHG.


GHG Emissions by Type and Sector from IPCC AR4 SPM



Becoming vegetarian would be more efficient in reducing greenhouse gases than driving a hybrid car. The United Nations Food and Agriculture Organization (FAO) released a report in November 2006 [ ] that states: “the livestock sector generates more greenhouse gas emissions as measured in CO2 equivalent – 18 percent – than transport…. the livestock sector accounts for 9 percent of CO2 deriving from human-related activities, but produces a much larger share of even more harmful greenhouse gases. It generates 65 percent of human-related nitrous oxide, which has 296 times the Global Warming Potential (GWP) of CO2it accounts for 37 percent of all human-induced methane (23 times as warming as CO2) ” [ ]




United States


The United States has recently stabilized CO2 emissions and has the largest land use based CO2 sink in the world.


A 2009 paper “Trends in the sources and sinks of carbon dioxide” (Nature Geoscience states: “fossil fuel emissions increased by 29% between 2000 and 2008” (worldwide). Not in the US – see the section below on China.


The following figure shows annual total US fossil fuel based CO2 emissions (in green – scale at right) along with the global mean atmospheric CO2. (US emissions in million metric tons from, and atmospheric CO2 from





The EPA (2010) also reports that total US GHG emissions for 2008 are below 2000 levels as shown in the following table []





US Is The World’s Leader in Positive Land Use Change


The following figure shows the net flux of carbon to the atmosphere due to land use change (which results mainly due to deforestation for agriculture and fuel-wood in the tropics and reforestation in the US). The United States has the largest land use change carbon sink in the world – i.e. while much of the world is burning its forests, the US is absorbing the carbon from the atmosphere. This figure shows: Cumulative Emissions of C02 From Land-Use Change measures the total mass of carbon absorbed or emitted into the atmosphere between 1950 and 2000 as a result of man-made land use changes (e.g.- deforestation, shifting cultivation, vegetation re-growth on abandoned croplands and pastures). Positive values indicate a positive net flux ("source") of CO2; for these countries, carbon dioxide has been released into the atmosphere as a result of land-use change. Negative values indicate a negative net flux ("sink") of CO2; in these countries, carbon has been absorbed as a result of the re-growth of previously removed vegetation.” []. 


The same report also states: “While the majority of global CO2 emissions are from the burning of fossil fuels, roughly a quarter of the carbon entering the atmosphere is from land-use change.”




The following figure shows the effect of land-use change on atmospheric CO2 – the US leads the world in land use emissions reduction []


Annual Effect of Land-Use Change on Atmospheric CO2






A study published in 2008 reports that China (which was excluded from the Kyoto requirements) became the largest emitter of CO2 from fossil fuel combustion and cement production in 2006. (Gregg, J. S., R. J. Andres, and G. Marland, “China: Emissions pattern of the world leader in CO2 emissions from fossil fuel consumption and cement production”, Geophysical Research Letters 35, 2008) [].


The following figures are from that study. The left-hand figure compares the US annual carbon emissions with China’s since 1950. The right-hand figure compares the monthly carbon for 2001 – 2007. The study states: “the annual emission rate in the US has remained relatively stable between 2001–2006 while the emission rate in China has more than doubled.






China – the world's largest greenhouse gas emitter – released its plan on climate change in 2007, supporting the rights of developing nations to pursue growth. The Chinese spokesman said "The consequences of inhibiting their development would be far greater than not doing anything to fight climate change … our general stance is that China will not commit to any quantified emissions reduction targets". [,2144,2575639,00.html 




Country Comparisons


March 15, 2010: “CO2 at new highs despite economic slowdown: Levels of the main greenhouse gas in the atmosphere have risen to new highs in 2010 despite an economic slowdown in many nations that braked industrial output … Recession in 2009 in many nations has not apparently affected gains.” []


The Reuters article quoted above ignores a simple fact: the increase in CO2 is from the “developing” nations (especially China), not the “developed” nations that have had the most economic slowdown.

Of course, the alarmists at do their usual blame game: “After global emissions stalled following the worldwide recession around 2008--even falling in some otherwise heavily polluting nations like the US of A--it looks like everyone can rest assured: we're back on track with CO2 concentrations steadily a-risin' in the atmosphere.” They purposefully ignore the facts shown below.


Wikipedia provides a list of countries by CO2 emissions (currently 2007 data). The following figure shows the top 10 []





The following figures provide some country comparisons of global greenhouse gas emissions from the Global Carbon Project []


CO2 Emissions:

The growth of emissions is in the developing nations is outpacing the emissions from developed nations.



CO2 Top Emitters:

China’s emissions have been growing rapidly compared to any other country.



CO2 Emissions by Fuel Type:

Coal has been providing the most emission growth (mainly from China), while oil emissions are flat (close to zero growth).


Change in CO2 Emissions from Coal Emissions:

The US has not been growing coal emissions like China and India.





No Reduction without China


The following figure shows global greenhouse gas emissions (GHG) by type from the 2007 IPCC AR4 SPM []. Note that CO2 fossil fuel use is 56.6 % of GHG globally. In 2004 the United States produced about 22 % of the global fossil fuel based CO2 emissions []. Thus, even if the United States eliminated all automobiles and all fossil fuel based electricity generation, etc – global GHG would be reduced by only 12 %