Sable Island has participated in greenhouse gases studies for almost three decades. Initially this involved collecting data on background levels of carbon dioxide (CO2), a program which began on Sable Island in 1974 after research in Hawaii which first demonstrated the global increase of CO2. Since then a wide range of research and monitoring relevant to understanding greenhouse gases and global warming has been carried out on the island.

Carbon enters the atmosphere primarily as CO2. Natural sources are emission from ocean surfaces in tropical regions, decay of organic matter, and respiration of plants and animals, and also volcanoes and forest fires. About the same amount of CO2 is removed from the atmosphere by absorption into oceans in temperate and cold regions, and by vegetation which requires CO2 for photosynthesis. Thus there are three natural sinks (or reservoirs) - oceans, terrestrial biosphere (plants and soils), and atmosphere - and carbon in the form of CO2 and its derivatives is constantly transferred from one sink to another.

Since the start of the industrial revolution, however, the burning of fossil fuels has rapidly increased the amount of CO2 entering the atmosphere. Records from the Mauna Loa monitoring station in Hawaii indicate that CO2 concentrations have been increasing at an average rate of about 3% per decade since 1958. Data collected at Sable Island (see figure) and other surface stations in the northern and southern hemispheres show that increases in CO2 concentrations are worldwide.

The global combustion of fossil fuels produces about 7 billion tons of carbon per year, and roughly half remains in the atmosphere as CO2 Although the other half is absorbed by the oceans and by the terrestrial biosphere, the proportion of carbon absorbed by each of these two sinks is uncertain. To understand the uptake of carbon in the northern hemisphere it is necessary to determine the distribution and magnitude of the terrestrial sink. Sable Island is located in the flow of air coming off the North American continent, and thus provides an excellent platform for collecting data on anthropogenic and terrestrial (natural) emissions of carbon from North America. These observations, combined with CO2 measurements from other sites in North America, are used to refine the estimate of large scale CO2 sources and sinks.

Concerns about global warming are not based solely on CO2 - there are other greenhouse gases that have been increasing in modern times because of human activities. In addition to CO2 , other atmospheric chemicals are presently measured at the Sable Island Station as part of greenhouse gases and global warming research:

Methane (CH4) and nitrous oxide (N2O) - both are included in the Kyoto list of the greenhouse gases; and both have significant anthropogenic and natural sources.

Carbon monoxide (CO). This gas is produced by fossil fuel combustion and forest fires, and is useful in separating the anthropogenic and natural sources of CO2 in the levels of CO2 observed. This is particularly important in spring and summer when biological activity is high.

Sulphur hexafluoride (SF6). This is a man-made gas, used primarily in electrical switching equipment, and thus is useful as a marker for pollution derived from human activity.

Radon. This element is a by-product in the decay of uranium which is a trace component in all soils. There are no ocean sources. Radon has a half-life of 3.5 days and serves as a tracer in identifying air masses that have recently resided over land. Thus it's useful in the study of carbon and greenhouse gas emissions from the North American continent.

Oxygen (O2) to nitrogen (N2) ratio. O2 levels are linked to the distribution of CO2, and measurements of the O2:N2 ratio in the atmosphere provide information on atmospheric O2, thus enhancing understanding of the global carbon cycle.

from Trivett et al, 1994

The above graph of the first 20 years of observations collected on Sable Island shows both the long term trend and seasonal cycles in which CO2 levels decrease during spring and summer. The seasonal cycle is driven by biological activity. Plants and other photosynthetic organisms use sunlight, water and atmospheric CO2 to build organic matter (i.e. growth and reproduction). Thus during spring and summer, CO2 levels drop as biological activity increases. Levels rise again during late autumn and winter which are seasons of low biological activity.

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