Water vapor (H2O)
The most important greenhouse gas is water vapor, which at times can approach 2% in parts of the atmosphere. However, when water vapor condenses into clouds, the white upside reflects sunlight back into space, which has a negative forcing effect.
Water vapor cannot initiate radiative forcing, it can only respond to radiative forcing through feedback mechanisms. Water vapor in the air is fairly constant, and human activities have little impact on this. Since humans have little or no direct impact on the amount of water in the air, and since it is not a forcing factor, water vapor is not included in negotiations on the reduction of emissions of greenhouse gases.
With increasing temperatures there will be increasing evaporation and increased amounts of water vapor in the air. In addition to enhancing the greenhouse effect it means that rainstorms can become more violent, as more water has to come down.
Carbon dioxide (CO2)
Increasing amounts of CO2 in the air may have a fertilizing effect on many plants if other essential requirements for photosynthesis are present. (Water, soil, minerals, right temperature etc)
Carbon dioxide: Pollutant or plant food?
Atmospheric CO2 has increased from a pre-industrial concentration of about 280 ppmv to about 400 ppmv year 2016
(ppmv= parts per million by volume. This refers to the ratio of the number of greenhouse gas molecules to the total number of molecules of dry air. E.g.: 300 ppm = 300 molecules of GHG per million of dry air molecules.).
Atmospheric carbon dioxide (CO2 ) concentration was lingering around 280 ppmv for several thousand years until approximately 1750, the beginning of the Industrial Revolution. At that time large scale burning of fossil fuels started, while at the same time large-scale cutting of timber also took place.
The content of CO2 in the atmosphere has risen continuously since then, reaching 400 ppmv in 2015. This is an increase approaching 40%.
History of CO2 in animated graphic from NOAA
The present atmospheric CO2 concentration has not been exceeded during the past 420,000 years, and likely not during the past 20 million years. The rate of increase over the past century is unprecedented, at least during the past 20,000 years.
With “current energy consumption patterns the amount of carbon dioxide added to the atmosphere (as modified by absorption within natural sinks) is rising at a rate of about one half of one per cent per year” (WMO: Climate into the 21st century).
The present atmospheric CO2 increase is caused by anthropogenic emissions of CO2.
About three-quarters of these emissions are due to fossil fuel burning. Cement production and land use change is responsible for the rest of the emissions.
Nitrous oxide (N2O)
This gas is emitted from artificial fertilizers in modern agriculture, from production of nitric acid and from combustion of fossil fuels. Nitrous oxide is responsible for approximately 4% of the anthropogenic greenhouse effect.
Nitrous oxide (N2O) in the atmosphere has increased from 270 ppbv in 1750 to 324 ppbv in 2011. This is an increase 20%. The increase continues.
Sources of N2O are agriculture, cattle, industry and several other natural sources. N2O is a strong greenhouse gas with a GWP of 310 times that of CO2 .The lifetime in the atmosphere is also quite long, more than 100 years.
Quiz CO2 (NASA)
Quiz: What You Don’t Know About Greenhouse Gases (National Geographic)
UN climate talks often focus on “carbon” pollution as they set guidelines to curb global warming. Yet carbon dioxide, emitted through the burning of fossil fuels, is not the only greenhouse gas that contributes to human-made climate change. So how much do you really know about these gases?
- Greenhouse gases
- Royal Society: CO2 is already in the atmosphere naturally, so why are emissions from human activity significant?
- Carbon dioxide: Pollutant or plant food?
- Explaining how the water vapor greenhouse effect works
- Sources of Greenhouse Gas Emissions (EPA)
- The Atmosphere
- Methane emssions (EPA)
- Agriculture Eyed as Culprit in Global Methane Emissions Spike (Dec 2016)
- Nitrous oxide emissions (EPA)
- Earth Just Permanently Passed Climate Threshold (Sept 2016)
- Overraskende om kull og metan (CICERO, dec 2016)
- The Met Office forecast for the concentration of atmospheric carbon dioxide in 2017 suggests that the increase in atmospheric carbon dioxide over the year will be smaller than the rise seen in 2016 (March 2017)
- Faulty logic fuels fossil fools
- Quite Simply, Earth has a Greenhouse Gas Problem
- Carbon everywhere
- The carbon cycle (NASA)
- The slow carbon cycle (NASA)
- The fast carbon cycle (NASA)
- Changes in the carbon cycle (NASA)
- Effects of changing the carbon cycle (NASA)
- Nature (2014) Carbon is forever