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Projections for Carbon Dioxide



Global Projections for Carbon Dioxide and Other Greenhouse Gases

By 2100 the atmospheric CO2 concentration (the gas responsible for most temperature change) will be between 540 and 970 ppm depending on the SRES (Special Report on Emissions Scenarios) scenario (see Figure 1)(For a description of the scenarios, see section at the end of this article called Socio-Economic Scenarios). The concentration was about 280 ppm in the pre-industrial era and about 368 ppm in the year 2000.

Since the beginning of the Industrial Revolution (1750),

  • atmospheric CO2 increase: 31%.
  • methane (CH4) increase: 150%
  • nitrogen oxide increase: 17%.

Figure 1. Atmospheric concentrations of CO2, CH4 and N2O resulting from the six SRES scenarios.

Source: Climate Change 2001 Synthesis Report, p. 204

All the emissions scenarios predict an increase in the atmospheric concentration of CO2. The only difference is the size of the increase. This will depend on how much CO2 we continue to pump into the air.

Figure 2 shows the range of emissions for several scenarios.

Figure 2. Anthropogenic (human-produced) emissions of CO2, CH4, N2O and SO2 for six SRES scenarios.

Source: Climate Change 2001 Synthesis Report p 203

Different socioeconomic assumptions (demographic, social, economic, and technological) produce different scenarios (identified by As and Bs in the graphs). They result in different predicted levels of future greenhouse gases and aerosols.
Further uncertainties in the carbon sinks and the size of the climate feedback on the terrestrial biosphere, cause a variation of about -10 to +30% in the year 2100 concentration, around each scenario. The total range is 490 to 1,260 ppm (75 to 350% above the year 1750 (pre-industrial) concentration).

The present concentration of CO2 is at the highest level in the last 420,000 years, the time covered by ice core measurements (see Paleoproxy data), and likely the highest in the past 20 million years. (See Figure 3.)

Figure 3. Observations of atmospheric CO2 concentrations for the years 1000 to 2000 from ice core data and direct measurements. Projections for 2000 to 2100 based on six SRES scenarios. IS92a is the prediction from the earlier SAR (IPCC Second Assessment Report).

Source: Climate Change 2001 Synthesis Report p. 138

Fossil fuel CO2 emissions will be the dominant influence on CO2 concentrations in the twenty-first century. Scientists estimate that, even if all the carbon released to the atmosphere by land use changes such as deforestation, could be replaced (for example, by planting trees), the CO2 concentration would only be reduced by 40 to 70 ppm. Further reduction will depend on burning less fossil fuels.

ACTIVITY 1 Questions
1. What is the general relationship between concentration and time in the graphs in Figure 1?
2. What does the slope of the lines in Figure 1 tell you?
3. What is the relationship between carbon dioxide concentrations in Figure 1 and emissions in Figure 2?

Go to the following website to answer the following questions.


1. Click on “graphics” under the “Greenhouse Gas Emissions” section. Choose Canada and three other countries to investigate. Choose one from Europe and one from the developing world. State the percentage reduction in greenhouse gases required for the country to reach its Kyoto target. Describe any differences you notice in their projected emissions.
2. a) Go back to Greenhouse Gas Emissions and click on “Maps”. Choose “2000 Emissions per capita”. What does “per capita” mean? What are the units for greenhouse gas emissions?
b) What areas of the world produce the most carbon dioxide per capita?
c) Choose “zoom in” and identify countries that have the least emissions per capita.

Socio-Economic Scenarios

Source: Climate Change 2001 Synthesis Report, page 10

Note: In block A1

B = balanced

FI = fossil-intensive

T = non-fossil

A1 – very rapid economic growth and introduction of new technologies, global population peaking 2050.
Subset (A1Fl= fossil-fuel intensive, A1T= non-fossil energy A1B =balanced different energy sources)

A2 – world emphasizing self-reliance and preservation of local identities and economic growth, with global population slowly increasing continuously, and slower, more fragmented technological change.

B1 – rapid change to service and information economy, cleaner, more efficient technologies, global population peaking 2050, emphasizing global solutions to sustainability, improved equity.

B2 – local solutions to economic, social, environmental sustainability, intermediate levels of economic development, less rapid technological change, global population continuously increasing.