Global Sources

The atmospheric concentrations of the greenhouse gases carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) have all increased since 1750 due to human activity. In 2011 the concentrations of these greenhouse gases were 391ppm, 1803 ppb and 324 ppb, and exceeded the pre-industrial levels by about 40%, 150%, and 20%, respectively (IPCC, 2013).

The graph below shows the increase in GHG levels over the last 2,000 years from 0 AD to 2005. As you can see, carbon dioxide and methane are the main GHGs being released. Although the chart from AR5 (2013) is yet to be published, it is anticipated that the upward trend will continue, as evidenced by measurements taken since 1979 to date by the NOAA.

Atmospheric concentrations of important long-lived greenhouse gases over the last 2,000 years. Increases since about 1750 are attributed to human activities in the industrial era. Concentration units are parts per million (ppm) or parts per billion (ppb), indicating the number of molecules of the greenhouse gas per million or billion air molecules, respectively, in an atmospheric sample.
(Source: IPCC AR4, WGI, p.124)

A significant amount of GHGs occur as a result of human activity. Carbon dioxide is the main contributor to the recent surge in GHGs in the atmosphere. This is pricipally due to the burning of fossil fuels and deforestation. The following pages provide more information on the most significant GHGs and their sources in Ireland and globally.

Previous - Greenhouse Gases