State of the Climate - 2014

Greenhouse Gases

Page 9 of 11

Key points:

  • Atmospheric greenhouse gas concentrations continue to increase due to emissions from human activities, with global mean CO2 levels reaching 395 ppm in 2013.
  • Global CO2 emissions from the use of fossil fuel increased in 2013 by 2.1 per cent compared to 3.1 per cent per year since 2000.
  • The increase in atmospheric CO2 concentrations from 2011 to 2013 is the largest two-year increase ever observed.

Carbon dioxide emissions

Global anthropogenic CO2 emissions into the atmosphere in 2013 are estimated to be 38.8 billion tonnes of CO2 (10.6 billion tonnes of carbon), the highest in history and about 46 per cent higher than in 1990. Global CO2 emissions from the use of fossil fuel are estimated to have increased in 2013 by 2.1 per cent compared with the average of 3.1 per cent per year from 2000 to 2012.

Since the industrial revolution more than two centuries ago, about 30 per cent of the anthropogenic CO2 emissions have been taken up by the ocean and about 30 per cent by land vegetation. The remaining 40 per cent of emissions have led to an increase in the concentration of CO2 in the atmosphere.

The origin of CO2 in the atmosphere can be determined by examining the different types (isotopes) of carbon in air samples. This identifies the additional CO2 as coming from human activities, mainly the burning of fossil fuel, and not from natural sources.

Most of the CO2 emissions from human activities are from fossil-fuel combustion and land-use change (top graph). Emissions are expressed in gigatonnes of carbon (C) per year. A gigatonne is equal to 1 billion tonnes. One tonne of carbon (C) equals 3.67 tonnes of carbon dioxide (CO2). CO2 emissions from human activities have been taken up by the ocean (middle graph, in blue, where negative values are uptake), by land vegetation (middle graph, in gold), or remain in the atmosphere. There has been an increase in the atmospheric concentration of CO2 (bottom graph, in red), as identified by the trend in the ratio of different types (isotopes) of carbon in atmospheric CO2 (bottom graph, in black, from the year 1000). CO2 and the carbon-13 isotope ratio in CO2 (δ13C) are measured from air in Antarctic ice and firn (compacted snow) samples from the Australian Antarctic Science Program, and at Cape Grim (northwest Tasmania).

Most of the CO2 emissions from human activities are from fossil-fuel combustion and land-use change (top graph). Emissions are expressed in gigatonnes of carbon (C) per year. A gigatonne is equal to 1 billion tonnes. One tonne of carbon (C) equals 3.67 tonnes of carbon dioxide (CO2). CO2 emissions from human activities have been taken up by the ocean (middle graph, in blue, where negative values are uptake), by land vegetation (middle graph, in gold), or remain in the atmosphere. There has been an increase in the atmospheric concentration of CO2 (bottom graph, in red), as identified by the trend in the ratio of different types (isotopes) of carbon in atmospheric CO2 (bottom graph, in black, from the year 1000). CO2 and the carbon-13 isotope ratio in CO2 (δ13C) are measured from air in Antarctic ice and firn (compacted snow) samples from the Australian Antarctic Science Program, and at Cape Grim (northwest Tasmania). (Source: CSIRO)

Greenhouse gas concentrations

Atmospheric concentrations of major greenhouse gases, including CO2, methane (CH4), nitrous oxide (N2O), and a group of synthetic greenhouse gases, are increasing.

Atmospheric greenhouse gas levels have exceeded the record levels reported in the State of the Climate 2012 report, continuing the increase observed over the past century. The global mean CO2 level in 2013 was 395 parts per million (ppm) — a 43 per cent increase from pre-industrial (1750) concentrations, and likely the highest level in at least 2 million years.

The global CO2 annual increase from 2012 to 2013 was 2.5 ppm, and the increase of 5.1 ppm since 2011 is the largest two-year increase observed in the historical record. Global atmospheric CH4 concentration is 151 per cent higher, and N2O 21 per cent higher than in 1750, and they are at their highest levels for at least 800 000 years.

The impact of all greenhouse gases in the atmosphere combined can be expressed as an ‘equivalent CO2’ atmospheric concentration, which reached 480 ppm in 2013.

Image showing global mean greenhouse gas concentrations.

Global mean greenhouse gas concentrations (‘ppm’ is parts per million, while ‘ppb’ is parts per billion) determined from continuous monitoring by CSIRO, the Bureau of Meteorology and the CSIRO/Advanced Global Atmospheric Gases Experiment at Cape Grim since 1976, in Antarctic firn air samples since the mid-1970s, and globally by CSIRO since the mid-1980s. (Source: CSIRO)

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