# Which greenhouse gas does the most damage to crops?

While there have been lots of studies looking at the effect of greenhouse gasses on increasing temperatures around the planet, my question is what are the effects of emissions on food production.

• There is a lot of room for interpretation here. Nitrous oxide is a greenhouse gas that also leads to acid rain; its effect on plants is totally different than carbon dioxide increasing temperatures and changing biomes. Plus, the most significant greenhouse gas (water vapor) has a very positive effect on plants (CO$_2$ does also to a certain extent). Can you narrow this down? – kingledion Nov 3 '16 at 20:25
• CO2 is critical for all photosynthetic growth. To say CO2 affects plant growth to 'a certain extent' is very wrong. How funny. Plants need to have CO2 make their own food & O2!! Water vapor is the MAJOR deleterious greenhouse gas...especially for 'global warming'. There is a limit to CO2 and plant growth but it is WAY out there. More CO2=more plant growth. Does anyone know how much atmospheric CO2 comes from TILLING the land? The, (hello)??, OCEANS, melting of permafrost perhaps? Makes anthropomorphic CO2 look just like it is, NO BIG DEAL. Propaganda, to someday tax your exhalations. – stormy Nov 3 '16 at 23:40
• @kingledion Nitrous oxide (N2O) is actually almost inert in lower atmosphere and does not cause acid rain - the other nitrogen oxides do. N2O does cause ozone depletion. – jvir Apr 20 '18 at 0:43

Tropospheric ozone is a significant greenhouse gas (see e.g. IPCC AR4) and has well established negative effects on crop yields. For example, Van Dingen et al (2009) evaluated yield losses of up to about 15% globally, depending on the crop.

Quantitatively hydrogen fluoride is insignificant, except when it is emitted from volcanic sources, in which case it is extremely toxic to crops - far more than any other natural gas. Possibly the worst recorded case was from Iceland when the volcanic eruption of 1783-1794 killed most if not all the crops and livestock downwind. The combination of fluorine poisoning and ensuing famine eventually killed some 10,000 people, or 22% of Iceland's population.

Strictly HF itself is not a 'greenhouse gas', but it reacts rapidly in the upper atmosphere to form other greenhouse gasses, such as CFCs, perfluorocarbons, and the extremely potent GHG, sulphur hexafluoride.

Specifically looking at carbon dioxide, there's been a series of field experiments that involve artificially raising the local CO2 levels for different plant species and seeing how they reallocate this carbon and develop. Results from the Free Air Concentration Experiments (FACE) have been published for the past 25 years and can be found in some pretty major journals.

Some major findings are that the expected yields from carbon enriched plant species aren't as high as previously estimated, and that the rise of ground level ozone associated with higher carbon levels is damaging plant capacity for photosynthesis.

• Your assessment of that article seems overly negative. I didn't see any reference to "yields from carbon enriched plant species aren't as high as expected." However, I did see "The availability of additional photosynthate enables most plants to grow faster under elevated CO$_2$, with dry matter production in FACE experiments being increased on average by 17% for the aboveground, and more than 30% for the belowground" – kingledion Nov 3 '16 at 21:32
• Oh absolutely. I wasn't trying to summarize the article. I just get the impression that most people immediately think that higher atmospheric carbon concentrations might "even out" the negatives when it comes to yields. In practice, there are differences to the growth and development cycle that can mean quicker time to fruition, but we shouldn't expect things like "megacrops". – Trevor J. Smith Nov 3 '16 at 22:25

To add to Trevor's answer, FACE experiments have shown that elevated CO2 can affect grain quality and the food product.