Carbon Dioxide, Methane & Other Greenhouse Gases

	The atmospheric abundance of carbon dioxide (CO₂), the dominant human-produced greenhouse gas, has increased by about 50% since pre-industrial times due to the proliferation of fossil fuel combustion. Methane (CH₄) is also a strong greenhouse gas; its atmospheric abundance has more than doubled since the pre-industrial era because of human activities. Other significant greenhouse gases include nitrous oxide (N₂O), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride (SF₆).
	Domain:	Atmosphere
	Subdomain:	Atmospheric Composition
	Scientific Area:	Carbon cycle and other GHGs
	ECV Steward:	Paolo Laj, Dale Hurst
	Products:	CO₂ Mole Fraction, CO₂ Column Average Dry Air Mixing Ratio, CH₄ Mole Fraction, CH₄ Column Average Dry Air Mixing Ratio, N₂O Mole Fraction

Atmospheric CO₂ at Mauna Loa

Figure: Monthly mean atmospheric carbon dioxide at Mauna Loa Observatory, Hawaii

Source: Data are reported as a dry mole fraction defined as the number of molecules of CO2 divided by the number of molecules of dry air multiplied by one million (ppm).

ECV Products and Requirements

These products and requirements reflect the Implementation Plan 2022 (GCOS-244).

The requirements are found in the complete 2022 ECVs Requirements document as well: ECV Carbon Dioxide, Methane & Other Greenhouse Gases.

Products			CO₂mole fraction	CO₂ column average dry air mixing ratio		CH₄ mole fraction	CH₄column average dry air mixing ratio	N₂O mole fraction
	(*)	Unit	Values	Values	Unit	Values	Values	Values
Horizontal Resolution	G	km	100	1	km	100	0.3	100
	B		500	5		500	1	500
	T		2000	10		2000	10	2000
Vertical Resolution	G	km	0.1	-	km	0.1	-	0.1
	B		1	-		1	-	1
	T		3	-		3	-	3
Temporal Resolution	G	h	1	1	h	1	1	1
	B		24	12		24	12	24
	T		168	72		168	72	168
Timeliness	G	d	1	1	d	1	1	1
	B		30	7		30	7	30
	T		180	14		180	14	180
Required Measurement Uncertainty (2-sigma)	G	ppm	0.1	0.6	ppb	1	7	0.05
	B		0.2	1		2	10	0.1
	T		0.5	1.6		5	20	0.3
Stability	G	ppm/decade	0.1	0.1	ppb/decade	1	1	0.05
	B		0.1	0.2		1	2	0.05
	T		0.3	0.3		3	4	0.2

(*) Goal (G): an ideal requirement above which further improvements are not necessary. Breakthrough (B): an intermediate level between threshold and goal which, if achieved, would result in a significant improvement for the targeted application. The breakthrough value may also indicate the level at which specified uses within climate monitoring become possible. It may be appropriate to have different breakthrough values for different uses. Threshold (T): the minimum requirement to be met to ensure that data are useful

Data Sources

This list provides sources for openly accessible data sets with worldwide coverage for which metadata is available. It is curated by the respective GCOS ECV Steward(s). The list does not claim to be complete. Anyone with a suitable dataset who wishes it to be added to this list should contact the GCOS Secretariat.