Greenhouse Gases

Industrial fossil fuel energy production and industrial food production (30-40%) are the two big sources of GHG emissions. 

Emitting GHGs at all cause is catastrophically dangerous because ​of the extremely long atmospheric lifetime of carbon dioxide (and nitrous oxide) ​and chain reactions of interacting impacts and feedbacks​. ​

​The fossil fuel industry
is actually a source of all GHG emissions 
​(varying extents), ​with the sole exception of halocarbons.

​​​It is also the big source of  health damaging air pollution. Coal combustion is a big source of health damaging mercury and heavy metals. ​

Natural gas (mainly methane CH4)is no better than coal. Though burning natural natural gas emits about half the CO2 as coal, fugitive (leaks) of methane (80X more powerful as CO2) makes natural gas almost as bad as coal (2018 research).

Radiative forcing 
Atmospheric GHG concentration directly correlates with lower atmospheric radiative forcing. The increase in radiative forcing is the increase in the total heat in the climate system. 

This is a far more accurate indicator of warming because it includes future committed global average temperature increase as well as today's temperature increase. 

NOAA publishes its Annual Greenhouse Gas Index, that gives atmospheric CO2 equivalent and radiative forcing​​​

​​​​​​Atmospheric CO2 has increased 50% above pre-industrial
Methane has increased by a factor of 2.6
Nitrous oxide has increased 24%​

Tropospheric  ozone ((ground level, or surface)​ is a
​short lived greenhouse gas ​and a well known toxic ​air
​pollutant caused by fossil fuel combustion. 

Tropospheric O3. Toxic ground level ozone (distinct from
​stratospheric ozone that is the UV radiation shield) is
​a short lasting GHG. It is formed by a chemical reaction
​between oxides of nitrogen and ​volatile organic compounds
​(both from fossil fuels) which is catalyzed by solar warmth.

​It therefore increases with global warming.

​As well as being toxic to human health, it is toxic to green plants,
​so as its concentration increases with warming the capacity
​of green plants to fix carbon from CO2 will decrease, a +ve
​amplifying feedback.  

Also CFCs and HCFCs are artificial chemicals used in industry. ​

Atmospheric CO2 has increased 40% since industrialization.
Methane has increased by 150%.
Nitrous oxide has increased by ​​​​20%.

GHG ice core data goes back 800,000 years. Atmospheric CO2 is nearly 30% higher than its maximum level over the past 800,000 years, from ice core data.​​
Research on ocean sediment indicates this is the highest in 15 million years.
​The rate of atmospheric CO2 increase in unprecedented.  

CO2. Of the GHG emissions CO2 has contributed more than 60% of global warming.
Because it is a very long atmospheric lifetime CO2 emissions are highly persistent and therefore cumulative in the atmosphereThe IPCC gives no set metric on CO2 for atmospheric lifetime. The CDIAC assigns 100-300 years to CO2, but the big thing is that 20-40% of CO2 emissions last for 1000 years (IPCC). In fact the lifetime is over 100,000 years.
​CO2 is also specially important for causing ocean acidification. The main sources are fossil fuel energy, deforestation and cement manufacturing (heating limestone). 

Atmospheric CO2 is the highest in 14 million years
It is increasing at an unprecented rate in tens of millions of years​

​​Multiple lines of evidence show that the rate at which CO2 has increased in the atmosphere during 1900–2019 is at least 10 times faster than at any other time during the last 800,000 years (high confidence), and 4–5 times faster than during the last 56 million years. IPCC AR6 WG1 {5.1.1, 2.2.3; Figures 5.3, 5.4; Cross-Chapter Box 2.1}

​​​​​CO2 equivalent CO2e All the GHGs (as a bundle) are calculated nd expressed as CO2 equivalent.
CO2e therefore is much higher than CO2​
It is essential to control all GHGs in mitigation-which therefore uses CO2e. The 1992 UN climate change convention​ stipulates atmospheric greenhouses gases for climate change monitoring and control, not global warming  

CH4 Methane is classified by the IPCC as a long lived GHG. Methane's warming contribution has been over 50% of CO2's . Methane lasts in the atmosphere 12 years which ​​that means methane emissions exert a warming 100 times that of CO2 over its lifetime. In addition methane disappears because it is oxidized to other GHGs - including water vapour, and  CO2 (that is not accounted in the methane GWP.  Main sources are livestock (ruminants exhale methane), natural gas industry (esp fracking), coal mining, natural wetlands, and rice paddies (wetlands).

A special feature of methane is, the more of it there is in the atmosphere - the longer methane will last in the atmosphere​

Methane feedback. The big thing about methane now is that we are into methane feedback. 
Atmospheric methane increase levelled off at 2000, but since 2007 has been on a sustained fast increase that the scientists say is due to methane feedback emissions from the warming planet. The sources are thought to be warming subarctic and tropical peatlands. 

​​Nitrous oxide (N2O​​) Nitrous oxide contributes the least of these 3 GHGs to global warming, but is increasing fast. It has both an extreme long life time (114 years) and high GWP (298 over 100 years). The main sources are nitrogen chemical fertilizer (made from natural gas), livestock feed production ( same reason)​, livestock waste, and sewage.
Nitrous oxide is even more important now because it is the main cause of depletion affecting the stratospheric ozone UV protective layer
Climate Emergency Institute
EPA Atmospheric Greenhouse gases 800,000 yrs ago and ​1950-2021
The WMO publishes its Greenhouse Gas Bulletin annually for atmospheric concentrations
Atmospheric GHG levels unprecedented in the past 800,000 years
They are is still increasing, because their emissions are still being increased​
The three main GHGs have different atmospheric lifetimes and different global warming ​​​capacities (global warming potential GWP). see NASA below
Climate Emergency Institute
2023, NASA ​Table  GHG Sources, lifetime, heat
Global CO2 emissions by sector
GHGs over geological time 
​The three main GHGs being emitted causing global warming-occur naturally. Ice cores show how they rise and fall alternating with ice ages warm periods.  They are carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O).
​​​They are classified by the IPCC as 'long lasting' atmospheric GHGs, lasting from about a decade (CH4) to over a century (CO2 & N2O).

Water vapour is the top GHG for warming contribution, because it is so abundant in the atmosphere. It is classified by the IPCC as a warming feedback,its most important capacity, rather than a GHG emission. Warmer air/atmosphere holds more water vapour. This +ve (amplifying) feedback about doubles the warming of a GHG alone. 
​​The other GHGs are classified as trace gases only existing in parts per million (CO2) or per billion (methane, nitrous oxide) of air. ​​