CO2 Is Plant Food

Climate Changes, But Facts Don’t: Debunking Monckton

On the 19th of July in 2011 the National Press Club of Australia held a debate on climate change. In this video I will be analysing the claims Monckton made during the debate and if they are correct or not.

The reason I’m doing this is that Monckton challenges his critics to check his sources, or like he put it in this debate “to do your homework”. I’m going to follow him up on this to see if the scientific literature, and other available sources, corroborate what he’s saying.

28 - CO2 Is Plant Food

Video description

On the 19th of July in 2011 the National Press Club of Australia held a debate on climate change. I will be analysing the claims Monckton made during the debate and if they are correct or not.

In this section Monckton claims that CO2 acts as a fertiliser and will increase food production significantly. I'll be looking into the basis for this claims and if this is supported by the scientific literature.


Final question today from Mark Kenny.

Mark Kenny from The Advertiser.

Lord Monckton, I'll take it from your response to Mr Hart's question that you reject that letter from The House of Lords…

I've told them it impertinent and they should put my reply on their website. They have not so far found the courage to answer.

All right. Look, can I ask you a question, which I guess is a first principles question that would have been maybe better asked earlier, but do you - would you like to see companies and individuals put less pollution skyward than is the case now and than will be the case with a growing population? Or are you unconcerned about it?

Right. Let us distinguish between pollution which usually means particulate pollution such as soot, or the emission of carbon dioxide which on any view is not a pollutant; it is plant and tree food.


If you were - if we were able to manage a doubling of CO2 concentration this century, which is what I expect to happen, regardless of the carbon tax, then what we would find is that at the end of the century, the yield of certain staple crops would rise by up to 40 per cent. And they would be able to survive on less water as well.

The greening of the planet in the 30 years since satellites have been watching as a result of what is known as CO2 fertilisation is absolutely wonderful. It's actually gone up by six percent. The net primary productivity of plants has risen by six percent. So CO2, if you really are a green and you really want to green the planet, is the way to go.

When I asked Monckton what the basis was for the claim that productivity of staple crops would increase by 40% by the end of the century he couldn't provide it to me.

The only thing he could give me was that he heard this number during a presentation by Dr. Leighton Steward at the The Alternative Climate Conference on Sunday December 6, 2009. This was an event where a very select group had access to. For the presentation held by Dr. Steward I couldn't find any transcripts or other materials nor was there a response from Dr. Steward to my enquires for more information.

Monckton also didn't remember anything about how this number was calculated or sourced. This means he has been repeating a number he doesn't know the basis for.

However, lets focus on the numbers and statements made by Monckton. And by now it probably isn't a surprise that they are either incorrect or stretch a fact beyond what it is capable of being used for.

It is true that CO2 in higher concentrations can, and will, act as a fertiliser. For this very reason adding CO2 in greenhouses is used to increase productivity. But the 40% increase in productivity is way beyond what has been demonstrated as achievable by experiments outside of greenhouses. For plants like wheat, soybeans and rice the increase in productivity on average was found to be at 13%; for plants like corn and sugar cane it's 0%. The difference between the plants I mentioned is caused by how they use CO2 during photosynthesis.

This is just the direct effect of CO2, which is already a lot lower than the number cited by Monckton. The advantage of CO2 fertilisation is lost when you start to take into account the indirect effects more CO2 will have.

There are many secondary effects, but I'll take just temperature as an example. If we double CO2 the planet will warm, according to the IPCC, by about 3 degrees Celsius. And here is where the statement by Monckton that “[plants] would be able to survive on less water” will play a role.

It is true that plants use less water if there's more CO2, however this is a double edged sword: plants also use water to cool themselves. If temperatures go up this means plants will experience more heat stress which reduces productivity.

If you start taking into account how weather and precipitation will change due to the increase in temperature it becomes even more obvious that this increase in productivity is not achievable. The drought the U.S. has been experiencing is what has been predicted by climate models, and if we keep increasing CO2 in the atmosphere it is very likely to produce devastating droughts in the grain belt.

Saying that CO2 is a fertiliser doesn't mean that there isn't a point where the effects become negative instead of positive.

But he did get the 6 percent increase in total global plant productivity correct. He probably got this from the paper “Climate-Driven Increases in Global Terrestrial Net Primary Production from 1982 to 1999” which was published in 2003.

Unfortunately the droughts we've seen during the past warmest decade on record have already caused a slight decrease in productivity. Results like this, combined with more advanced research on plants, is why scientists are saying that the increase in CO2 is not a good thing for food production.


  1. H. Leighton Steward
  2. Copenhagen Weathers a Splash of Denial
  3. Climate Scientists Respond
  4. Food for Thought: Lower-Than-Expected Crop Yield Stimulation with Rising CO2 Concentrations
  5. Elevated CO2 effects on plant carbon, nitrogen, and water relations: six important lessons from FACE
  6. What have we learned from 15 years of free-air CO2 enrichment (FACE)? A meta-analytic review of the responses of photosynthesis, canopy properties and plant production to rising CO2.
  7. Smaller than predicted increase in aboveground net primary production and yield of field-grown soybean under fully open-air [CO2 ] elevation
  8. Photosynthesis, Productivity, and Yield of Maize Are Not Affected by Open-Air Elevation of CO2 Concentration in the Absence of Drought
  9. Exceptional Sensitivity of Rubisco Activase to Thermal Denaturation in Vitro and in Vivo
  10. Rubisco activase constrains the photosynthetic potential of leaves at high temperature and CO2
  11. A general relationship between CO2-induced reductions in stomatal conductance and concomitant increases in foliage temperature
  12. Increasing drought under global warming in observations and models
  13. Projections of Future Drought in the Continental United States and Mexico
  14. Climate-Driven Increases in Global Terrestrial Net Primary Production from 1982 to 1999
  15. Drought-Induced Reduction in Global Terrestrial Net Primary Production from 2000 Through 2009
  16. Response to Comments on “Drought-Induced Reduction in Global Terrestrial Net Primary Production from 2000 Through 2009”
  17. Drought Drives Decade-Long Decline in Plant Growth

Media resources

  1. NASA | Plant Productivity in a Warming World
  2. NASA | NASA's Analysis of 2012 Global Temperature
  3. Day 195 - Colorful Canopy by Christie

Climate Changes, But Facts Don’t: Debunking Monckton