The Bright Side of Carbon Dioxide

Aug 31, 2017 | Sustainable Agriculture |

The Dirt:

While we are frequently told about the consequences of climate change, what we don’t hear about is how increased levels of carbon dioxide can actually help plants grow. Trees and crops thrive on CO2! They grow faster and better with more carbon in the air. The CO2 fertilization effect has positive implications to help feed our growing population.

Extreme droughts, dangerous flooding, melting ice caps and rising seas are what we picture when someone mentions climate change. The Intergovernmental Panel on Climate Change (IPCC) puts the chance of yield declines on corn, soybeans, and cotton between 30 – 82% due to heat stress caused by increases in temperature. Risky Business, an initiative that assesses the economic risk associated with climate change, tells us that certain crops such as “corn, wheat, soybeans, and cotton, without farmer adaptation, in some Midwestern and southern counties could see a decline in yields of more than 10% over the next 5-25 years and a 1-in-20 chance of yield losses.” By the end of the century, the losses could be even more dire, potentially reaching up to 73%.

While we are frequently inundated with the consequences of excess CO2 and its relationship to climate change— what isn’t making headlines is how increased levels of CO2 can actually grow more food!

There is, however, a degree of uncertainty in these figures. These estimates depend on many different variables, including critical weather patterns, such as temperature fluctuations, how much it rains, how much the soil erodes, if there are fewer frosts, or if there are prevalent droughts. Additionally, the yield losses will not be as severe if the farmer can adapt to any of the changes in climate with technology and smart farming.

What we do know, is that anything that is green gets greener and the overall yield per acre increases when confronted with more CO2. As we mentioned in Carbon: The Dance of Life, plants thrive on CO2 and grow faster and stronger with more carbon in the air. The carbon cycle and photosynthesis is integral to growing any plant life.

So, although it gets a pretty bad reputation, atmospheric carbon dioxide – whether it comes from fossil fuels or just humans exhaling –is good for plants and agriculture. There have been countless studies that have shown that when plants are grown in a CO2 enriched atmosphere, they have a stronger immune system to protect against disease, a better growth rate, and a better chance of survival in a drought.

CO2 fertilization can help take CO2 out of the atmosphere.

CO2 fertilization suggests that the presence of carbon in the atmosphere increases the rate of photosynthesis in plants— i.e. allows plants to grow stronger and faster. The more CO2 that the plant encounters, the more CO2 it utilizes. The estimated decreases in crop yields, due to the anticipated effects of climate change, can actually be mitigated by CO2 fertilization. The Massachusetts Institute of Technology (MIT) has studied this extensively and say:

“We realize that increases in CO2 concentrations and adaptive management can provide significant mitigation of the negative effects of climate change.”

-Massachusetts Institute of Technology

Dr. Craig D. Idso, author of Climate Change: The Facts 2017 and professor at the University of Nebraska, has closely examined the CO2 fertilization effect on agriculture. His site culls a database of over 3,500 studies that include 550 plants that effectively demonstrates how CO2 enrichment increased their yield. Additionally, he references over 2,000 studies on 470 plant species that experienced an increase in their photosynthesis rate when subjected to an enriched carbon environment. To put this in perspective, greenhouse growers use enriched air from 340ppm to 700ppm to maximize their yields – the world right now is at 400ppm.

It is one thing to enrich the air in a greenhouse, but how does this work with crops in practical field applications? Studies indicate that the large-scale crops that we rely on heavily for our food and animal feed (ie. soybeans, wheat, and corn) also react well to more CO2 in the atmosphere. Research collated by Idso and his colleagues note that soybeans showed a 49.9% growth factor when given an additional 300 ppm of CO2. Wheat did almost as well with a 36.7% increase in yield. Corn, while not as prolific as its ‘big-ag’ peers, had an impressive increase in yield of 27.3%.

Most simply put, plants can be categorized into two different types: C3 and C4. While they all use sunlight, carbon dioxide, and water for energy to grow, C3 plants (such as soybeans and rice) are cool season plants. Their perfect growing temperature is between 65-75°F. As temperatures increase, they become less productive. C4 plants (like corn, sugarcane, and sorghum) are plants that can handle the heat and grow well at 90-95°F.  Although corn does better between 77 – 91°F. C4 plants are better at gathering carbon dioxide from the atmosphere and nitrogen from the soil, respectively. Additionally, they expire less water. As a result, they do better in a drought environment. In addition, C4 plants use about 6% of sunlight whereas C3 plants only use about 4.6% of the sunlight’s energy.

CO2 helps plants with drought stress

Plants have something called leaf stomatal pores, this is how they take in ( or “inhale”) carbon dioxide and release water vapor. The more CO2 they have, the fewer pores they create and the less water vapor they release. The plants are essentially storing water and energy in their leaves. Just like humans, when plants are hydrated they grow stronger and stay healthier. This is particularly true for C4 plants such as sugarcane, sorghum and corn.

Nature Magazine published a report by Daniel Taub, Chair of Biology at Southwestern University, which examined the Photosynthetic assimilation of CO2 to the metabolism of plants. He compared photosynthesis under current CO2, at the time of approx. 385 ppm to elevated CO2 of 475 ppm – 600 ppm. Generally, he found that in the higher CO2 environment plants use less water – which can have an added benefit of less run-off and maintaining soil moisture over a period of time. However, it was clear that it depends on the plant type.

Is the entire Earth turning greener?

Australian scientists, Randall Donohue and a group of researchers from the Commonwealth Scientific and Industrial Organization looked at the relationship between annual rainfall, rising CO2 and the greening of the earth. They calculated that global plant growth should have increased by 5-10% through natural sources alone. Through satellite measurements over the years, they calculated, that yes, indeed, there was a global foliage increase of 11%.

A most interesting study, published in November 2016, completed by Trevor Keenan et al, shows that CO2 in the atmosphere is reducing because of the terrestrial and ocean carbon sink!  Using satellites, linear modeling, and global vegetation models, this group found that, beginning in the 21st century, while emissions have grown, the amount remaining in the atmosphere has declined. You can see from their chart below the increase in emissions compared to the basically flat growth of CO2 remaining in the atmosphere.  Their theory and results attribute it to the absorption of CO2 with both land and oceans.

Using global carbon budget estimates, ground atmospheric and satellite observations, and multiple global vegetation models, we report a recent pause in the growth rate of atmospheric CO2 and a decline in the fraction of anthropogenic emissions that remain in the atmosphere despite increasing anthropogenic emissions.” (Recent Pause in the growth rate of atmospheric CO2 due to enhanced terrestrial carbon uptake, Trevor F. Kennan et al)

(a) Observed (solid black line) and modelled (DGVM ensemble—mean (dashed black line) and s.d. (orange area)) changes in the atmospheric CO2 growth rate from 1960 to 2012. The vertical grey line (2002) indicates the point of structural change identified using a linear modelling analysis. The red lines indicate a significant increasing trend from 1959 to 1990 (solid red) and 1959 to 2002 (dashed red) (P<0.1), with no trend evident between 2002 and 2014 (blue). All trends are estimated using the non-parametric Mann–Kendall Tau trend test with Sen’s method. The grey area represents the underlying 5-year dynamic (mean±1 s.d.), estimated using SSA. (b) Fossil fuel emissions (black dashed line) and the fraction of CO2 emissions, which remain in the atmosphere each year (black dots, airborne fraction). Lines indicate significant long-term trends over the periods 1959–1988 (red, increasing) and 2002–2014 (blue, decreasing) at P<0.1. The red dashed line shows a slight increasing trend between 1959 and 2002 (P=0.18). The grey area represents the underlying 5-year dynamic (mean±1 s.d.), estimated using singular spectrum analysis.

Farmers and regions need to adapt to changing conditions too.

While the CO2 fertilization effect helps manage the CO2 in the atmosphere, the question remains: will it be enough? Will the benefits of CO2 fertilization be enough to offset the effects of drought, high heat, excessive rains, or changing temperature?

The FAO acknowledges that elevated CO2 increases the growth, size, and weight of plants. They believe that each farmer or region should adapt best practices and new technologies in order to utilize the effects of CO2 fertilization.

It’s all about the Yield
As a D2D reader, by now you know that a higher crop yield on existing land is the holy grail of farming. As the world population grows and our need for sustainability increases, getting the most out of our land is critical. Using rice as an example, it provides at least 20% of the energy for over 50 percent of the world population.

Paul Quick, from the international Rice Research Institute in the Philippines, is working with scientists in eight different countries from 12 universities to supercharge the photosynthesis process in rice to increase its yield by 50%. According to the IRRI, each hectare of rice (2.5 acres) in Asia produces enough food for 27 people, as 2050 approaches, that same hectare will need to feed 43 people. They are working to convert rice, which is a C3 plant, to the efficient user of CO2 and water, a C4 plant. This would produce the desired 60% increase in yield.

Turbo Charged Plants

It is so much fun to drive a ‘turbo’ car. Because of the additional airflow in the engine, it goes faster and has better engine performance. Think of the C4 photosynthesis process as the same compared to a C3. If important food crops such as soybeans and rice could be genetically altered to have a better use of sunlight and CO2, the yields would be better and less impact on the environment.

The Bottom Line:

There is a positive correlation between higher levels of CO2 and plant growth and resiliency. The more plants we have on earth, be they food crops, prairies, wetlands or tropical rainforests, the more CO2 can be absorbed from the atmosphere. Everyone can do their part by contributing to the restoration of these precious ecosystems.

Resources:

Allen, L. Harwell, et al. “He CO2 Fertilization Effect: Higher Carbohydrate Production and Retention as Biomass and Seed Yield.” FAO Corporate Document Repository, Food and Agriculture Organization of the United Nations, www.fao.org/docrep/w5183e/w5183e06.htm.

Bullis, Kevin. “Speeding Plant Growth to Feed the World.” MIT Technology Review, MIT Technology Review, 8 July 2015, www.technologyreview.com/s/535011/supercharged-photosynthesis/.

Betts, Dusti Lynne. “‘What Is the Difference between C3 Plants and C4 Plants?’” K State Research and Extension.

Challinor, AJ, Watson, J, Lobell, DB, Howden, SM, Smith, DR and Chhetri, N (2014) A meta-analysis of crop yield under climate change and adaptation. Nature Climate Change, 4. 287 – 291. ISSN 1758-678X

Irmak, Suat. “Impacts of Extreme Heat Stress and Increased Soil Temperature on Plant Growth and Development.” CropWatch | University of Nebraska–Lincoln, University of Nebraska-Lincoln, 21 June 2016, cropwatch.unl.edu/2016/impacts-extreme-heat-stress-and-increased-soil-temperature-plant-growth-and-development.

Kellogg, Elizabeth. “C4 Photosynthesis.” ScienceDirect, Elsevier Ltd, 22 July 2014, www.sciencedirect.com/science/article/pii/S0960982213005071.

Lopez, Oscar. “Scientists Are Genetically Modifying Rice so It Can Withstand the Ravages of Climate Change.” Newsweek, Newsweek Magazine, 20 May 2016, www.newsweek.com/2016/02/19/genetically-modified-rice-climate-change-world-hunger-424773.html.

Taylor, James. “Global Warming? No, Satellites Show Carbon Dioxide Is Causing ‘Global Greening’.” Forbes, Forbes Magazine, 10 July 2013, www.forbes.com/sites/jamestaylor/2013/07/10/global-warming-no-satellites-show-carbon-dioxide-is-causing-global-greening/#7841082ee444.