greenhouse gases

While the most prominent greenhouse gas is without doubt carbon dioxide, a number of molecules share properties that group them into this category:

• nitrous oxide (N₂O)
• methane (CH₄)
• water vapor (H₂O)
• fluorocarbons

Equivalence

Carbon dioxide - carbon cycle - speak of - at various times sometimes figures are given in “(million/billion) metric tons of carbon” calculated from carbon dioxide, while at other times only the carbon component of the molecule is used for tracking amount

e.g. annual emissions in the United States have ranged between 5 and 6 billion metric tons for the past three decades. for the world, about 35 billion tonnes CO2 in 2020 compare 10 billion tonnes C in 2015 – 27 CO2

using molecular weights, the conversion is based on the ratio and relative weights of the atomic constituents, two of O compared to one C atom, so 2 × 16 and 12, meaning that 12/32 or 3/8ths of the weight of carbon dioxide comes from its carbon.

The TCRE - transient climate response, different units are used: “Each 1000 GtCO 2 of cumulative CO 2 emissions is assessed to likely cause a 0.27°C to 0.63°C increase in global surface temperature with a best estimate of 0.45°C” “the AR6 reports the TCRE likely range as 1.0°C to 2.3°C per 1000 PgC in the underlying report, with a best estimate of 1.65°C” [AR6 WGI SPM]