2011-04-13 15:44:49Too much of a good thing is a bad thing. Increasing Carbon Dioxide is not good for plants.


An argument, made by those who deny man made Global Warming, is that the Carbon Dioxide that is being released by the burning of fossil fuels is actually good for the environment. Their argument is based on the logic that, if plants need CO2 for their growth, then more of it should be better. We should expect our crops to grow taller and our flowers to bloom brighter.

However, this "more is better" philosophy is not the way things work in the real world There is an older, wiser saying that goes, "Too much of a good thing can be a bad thing." For example, if a doctor tells you to take one pill of medicine, taking three is not likely to heal you three times faster or make you three times better.

It is possible to help increase the growth of some plants with extra CO2, under controlled conditions, inside of greenhouses. It is, based on this, that 'skeptics make their claims. Such claims, however, are simplistic. They fail to take into account that once you increase one substance that plants need, you automatically increase their requirements for other substances.

Plants cannot live on CO2 alone. They get their bulk from more solid substances like water and organic matter. This organic matter comes from decomposing plants and animals or from man made fertilizers. It is a simple task to increase water and fertilizer and protect against insects in an enclosed greenhouse but what about doing it in the open air, throughout the entire Earth?

What would be the effects of an increase of CO2 on plant growth? The following points make it clear.

1. Plants will need extra water. Where will it come from? Rainwater is not sufficient for current agriculture and aquifers are running dry throughout the Earth.

On the other hand, as predicted by Global Warming, we are receiving intense storms with increased rain in certain parts of the world. One would think that this should be good for plant growth. Unfortunately, when rain falls down very quickly, it does not soak into the ground. Instead, it quickly floods into creeks then rivers and finally out into the ocean carrying large amounts of soil and fertilizer.

2. Unlike Nature, our way of agriculture does not self fertilize by recycling all dead plants, animals and their waste. Instead we have to be constantly producing artificial fertilizers from natural gas which will eventually start running out. By increasing the need for such fertilizer you will shorten the supply of natural gas creating competition between the heating of our homes and the growing of our food. This will drive the prices of both up.

3. Denser vegetation can make landscapes more fire-prone. Weeds as well as crops and pastures will be spurred on, raising the cost of farming. Higher concentrations of CO2 also reduce the nutritional quality of some staples, such as wheat.

4. The worse problem by far is that increasing CO2 will increase temperatures throughout the Earth; making deserts and other types of dry land grow. While deserts increase in size, other eco-zones, whether tropical, forest or grassland will migrate towards the poles; shrinking in size as they do. This will reduce the land area in which plants and animals thrive.

5. When plants do benefit from increased Carbon Dioxide, it is only in enclosed areas, strictly isolated from insects. However, when the growth of Soybeans is boosted out in the open, it creates major changes in its chemistry that makes it more vulnerable to insects, as the illustration below shows.

Figure 1: Plant defenses go down as carbon dioxide levels go up, the researchers found. Soybeans grown at elevated CO2 levels attract many more adult Japanese beetles than plants grown at current atmospheric carbon dioxide levels. Science Daily; March 25, 2008. (Credit: Photo courtesy of Evan Delucia)

Figure 2: More than 55 million years ago, the Earth experienced a rapid jump in global Carbon Dioxide levels that raised temperatures across the planet. Now, researchers studying plants from that time have found that the rising temperatures may have boosted the foraging of insects. As modern temperatures continue to rise, the researchers believe the planet could see increasing crop damage and forest devastation. Science Daily; Feb. 15, 2008.

Figure 3: Global Warming reduces plant productivity. As Carbon Dioxide increases, vegetation in Northern Latitudes also increases. However, this does not compensate for decreases of vegetation in Southern Latitudes. The overall amount of vegetation worldwide declines 

In conclusion, it would be reckless to keep adding CO2 to the atmosphere. Assuming there are any positive impacts on agriculture, they will be overwhelmed by all of the other impacts of climate change.

A rise in the level of CO2 will simply increase the size of deserts and decrease the amount of arable land. It will also increase the requirements for water and soil fertility as well as plant damage from insects.

Increasing CO2 levels would only be beneficial inside of highly controlled, enclosed spaces like greenhouses. 


2011-04-13 17:10:03John Cook.


John; concerning your email about merging this post with the "CO2 is plant food" argument.

There weren't any rebuttals started, on any level, for the "CO2 is plant food" argument list but I found a mini post and video when I clicked on the argument title. There wasn't much text there but I incorporated some of it as well as an argument with a footnote that I tuned into a link. I also added the video. 


2011-04-13 17:15:57Question for anyone.


Just out of curiosity, are videos formally referred to as "Figure X" or is there another phrase for them?


2011-04-13 18:04:47
Ari Jokimäki


It would be nice to have some peer-reviewed references in this article, as this is a thoroughly studied subject.

Edited to add: Ok, there is one reference behind the link, but I think adding some more wouldn't hurt.

2011-04-14 00:43:36CO2 is plant food
Dana Nuccitelli

villabolo, Dawei has just about finished the Advanced rebuttal to CO2 is plant food.  He hasn't claimed it in the rebuttal list yet, but his post is in the Advanced forum.

2011-04-14 18:38:28Basic rebuttal and blog post ready to go
John Cook


I've set up the basic rebuttal at:


Blog post here:

Too much of a good thing is a bad thing. Increasing Carbon Dioxide is not good for plants.

I don't think having to include peer review studies are a deal breaker - we can include those in the advanced/intermediate versions. Villabola and reviewers, let me know when this is good to go and I'll add it into the schedule.

2011-04-14 22:45:12
Daniel Bailey
Daniel Bailey

Either keep the video as "Figure 3:" or switch it to "Video:" (no need to number it unless you have more than 1).

2011-04-15 11:26:01John Cook.


John; it's ready to go! I can always make minor corrections or changes later.

Thanks for the suggestion, Daniel.


2011-04-15 12:08:01
Daniel Bailey
Daniel Bailey

"Plants cannot live on CO2 alone."

I like that.

2011-04-15 14:38:36Blog post scheduled for Sunday
John Cook


Thanks for your patience on getting this one through the mill :-)