CO2 - Sources and sinks


Carbon dioxide - Sources and sinks


CO2 - how long in the atmosphere?

About 50% of a CO2 increase will be removed from the atmosphere within 30 years, and a further 30% will be removed within a few centuries. The remaining 20% may stay in the atmosphere for many thousands of years.  

Source: IPCC Fourth Assessment Report, Working Group I (AR4, WG-I chap 7  IPCC publications

CO2 mass balance

Fossil fuels
From Limestone
From deforestation
0.5 - 2.4
Ocean sink  
Land sink  
1 - 1.8
5.5 - 7.9
3.4 - 4.2
Calculated Increase   = 1.3 to 4.5 ppm  
Observed increase     =  2.0 ppm  

These charts are from the 2011 report from the Australian Climate change Commission.

IE - Included Elsewhere in industrial processes.

This next table has been calculated according to the Kyoto Protocol so is slightly different for agriculture and waste. I've included it because it shows farming, forestation and deforestation in more detail.

LULUCF = Land Use, Land Use Change and Foresty.

Agriculture emissions made up 15.2% (84.1 Mt) of total net emissions (excluding LULUCF) in 2011

This tables show land use change and forestry is absorbing 7.3% of emissions. However this is quite changeable and no particular cause for celebration. 

The decreasing trend in emissions from LULUCF since 1990 has been mainly driven by the decline in emissions from forest land converted to cropland and grassland. Changes in LULUCF emissions from year to year are affected by other factors, principally natural disturbances such as wildfires. Emissions from wildfires contribute a large proportion of Australia’s total net emissions in some years.

The source does not say if the peak produced by bushfires is followed by a dip in emissions due to regrowth of the burnt areas, You would expect this to be the case.

Emissions in 2011 Australia excluding land use.

Emissions by sector

LULUCF = Land Use, Land Use Change and Foresty.

How much more can we burn

The UN-sponsored IPCC also concluded that the global economy has a one trillion tonne (1,000Gt C) budget from the beginning of the Industrial Revolution to the end of the 21st century. But only 269GtC is currently left, a fraction of the 779GtC embedded in fossil fuel reserves.

Other estimates are that we can burn 14 or 20% of reserves.


Bushfires vs coal fired power

What about bushfires? They are natural and far worse than power stations.

Coal-fired power stations in Australia emit around 300 million tonnes of CO2 per year.  

Around 30 tonnes of CO2 per hectare are emitted by a serious bushfire

Bushfires must burn an area of forest of 10 million hectares, greater than Tasmania (7 million h) to generate CO2 emissions equivalent to a year of burning coal for electricity.

However, the forest will recover that CO2 over the next few years 

The same cannot be said of coal-fired power stations.  Ref 

Photo: Christine Glassford - The Daily Telegraph

These charts are for U.S.A. All masses are in tons. To convert to tonnes (1,000 Kg) multiply by 0.907.

"CO2 Eq" means the greenhouse warming potential equivalent to CO2. So if methane has 50 times the warming ability of CO2, then the emissions are multiplied by 50 to give the CO2 equivalent.


This figure displays a breakdown of sources of CO2 emissions in the U.S. in 2006. By far the largest source is fossil fuel combustion:

This figure illustrates the relative contribution of the direct greenhouse gases to total U.S. emissions for the period 1990-2009. The primary greenhouse gas emitted by human activities in the United States was carbon dioxide (CO2), representing approximately 83 percent of total greenhouse gas emissions. The largest source of CO2, and of overall greenhouse gas emissions, was the combustion of fossil fuels. Methane emissions, which accounted for 10 percent of U.S. greenhouse gas emissions in 2009, resulted primarily from natural gas systems, enteric fermentation in livestock and decomposition of wastes in landfills. Agricultural soil management and mobile source fossil fuel combustion were the major sources of nitrous oxide emissions. Hydrofluorocarbons that substitute for ozone depleting substances and SF6 emitted from electrical transmission and distribution equipment were the primary sources of fluorinated gas emissions.


Reference: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009, USEPA #430-R-11-005

The U.S. greenhouse gas inventory also presents emissions by more commonly used economic categories: agriculture, commercial, electricity generation, industry, residential and transportation.

Reference: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2009, USEPA #430-R-11-005

Electricity, though produced at power plants, is ultimately consumed in the other economic sectors. When emissions from electricity are distributed among these sectors, the industrial sector accounts for the largest share of U.S. greenhouse gas emissions, about 29 percent. Transportation remains the second largest contributor to emissions, about 27 percent. Emissions from the residential and commercial sectors increase substantially due to their relatively large share of electricity consumption (e.g., lighting, appliances, etc.), with agriculture consuming little electricity.

Land use, land-use change, and forestry activities in the United States result in a net removal of CO2 from the atmosphere. This sector is responsible for offsetting approximately 15 percent of total U.S. CO2 emissions.


(Ag is Agriculture, not silver.)


Gg (Gigagram) = kiloTonne,         PJ = Peta Joule