Global Greening

A recent study by a multinational group of scientists has determined that: “From a quarter to half of Earth’s vegetated lands has shown significant greening over the last 35 years largely due to rising levels of atmospheric carbon dioxide”. The study results are based on analyses of data collected by NASA and NOAA satellites. The authors estimate that approximately 70% of the greening is the result of increased CO2 fertilization.

Operating commercial greenhouses under enhanced CO2 conditions to enhance plant growth is a very common practice. Typical greenhouse CO2 levels range from 1000 – 1200 ppm. There have been attempts made in the past to demonstrate aerial fertilization of field crops, but they have achieved limited or no success because of the rapid mixing and dispersion of the CO2 in the open atmosphere.

The increase in atmospheric CO2 concentrations over the past ~70 years, from approximately 270 ppm to approximately 400 ppm has created the opportunity to study the effects of CO2 fertilization on a wide variety of plants, including field crops, grassland species and forest trees. These studies have shown that increased atmospheric CO2 concentrations not only increase plant growth, but also increase the efficiency with which numerous types of plants use water. This has significant implications for areas which receive limited rainfall and are either unsuitable for growing crops or require irrigation for successful crop growth.

Critics have been quick to point out that: “the ultimate benefit to crops has been small — and it doesn’t explain our modern agricultural revolution. The driving factor has to be the fertilizers, the seed varieties, the irrigation”. While this criticism is certainly valid, it is not reasonable to expect that the effects of a 50% increase in atmospheric CO2 concentrations would be as dramatic as the further increase of ~200% imposed in modern commercial greenhouses. However, it is reasonable to assume that the increased atmospheric CO2 concentrations have been a contributing factor to improved crop production, though the effect is not separately measurable.

The development of crop seeds optimized for the higher atmospheric CO2 levels could impact not only the amount of fertilizer required but also the amount of water required for the successful growing of high yield field crops. These effects could potentially both expand the land area suitable for high yield crop production by increasing the efficiency of water use and reduce the cost of crop production by reducing fertilization costs.

Plant growth is a complex process affected by numerous variables. It is critical that these variables and their interactions are understood to optimize crop plant selection and production. The ongoing increase in atmospheric CO2 concentrations offers both the opportunity to study these interactions and the challenge of optimizing them for each of the important field crops over the range of growing conditions experienced around the globe.

Increasing global population will continue to challenge the efficiency and effectiveness of agricultural production. Increasing atmospheric CO2 concentrations will continue to play a role in meeting the challenge.