Carbon Dioxide Plant Outcomes Study Needs More Consideration

7 September 2016 Christopher Johns, Research Manager, Northern Australia and Land Care Research Programme


A series of articles has recently appeared suggesting that more atmospheric carbon dioxide could have a positive impact on climate change outcomes. Based on an article published in the US-based Proceedings of the National Academy of Sciences, the study has received widespread attention because it indicates that as CO2 increases, plants will become less thirsty, resulting in climate change-induced droughts being halved.

Tanami Desert Spinifex

Fig. 1. Tanami Desert Spinifex and Termite Mounds. Source: BRJ Inc, flickr.


The University of Washington led study concludes that when the Earth’s atmosphere holds more carbon dioxide, plants actually benefit from having more of the molecules they need to build their carbon-rich bodies. For instance, plants take in carbon dioxide through tiny openings in their leaves.  But as they do so, moisture escapes. When carbon dioxide is more plentiful, however, these cells do not need to be open for so long and thus plants draw less water from the soil through their roots.

An extension of this assessment suggests that areas likely to be affected by serious drought may halve from what was considered likely over the next 100 years.

But two issues do not appear to have been considered.

First, while the conclusion is correct that less water will be lost with more CO2 in the air, it must also be acknowledged that, with less water moving through a plant, the movement of its vital nutrients will be diminished, thus reducing plant growth.

Second, with less plant growth, it will be harder to absorb and retain water in the soil surface, resulting in more water being evaporated or simply running off into streams or other water courses.

So, while the study is largely correct in its assumptions, it appears to fail to take into account the implications of these assumptions, and we do not have a sustainable outcome that will produce long term benefits.

The impact of climate change is, and will be, increasingly severe and the outcomes of the study need to be assessed more broadly for a final conclusion to be reached.

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