The carbon debate, with shades of grey

Carbon dioxide may not be the villain in global warming, after all. Scientists find it has helped increase earth’s green cover

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Sreelatha Menon | May 2, 2017


#Science   #Global Warming   #Carbon dioxide   #Environment  


Is the world getting greener? That would be a paradox when nations are putting their heads together to find ways to fight global warming.
While the world is condemning carbon dioxide (CO2) as the culprit for global warming, there are some who are fighting for the cause of CO2. And they cite scientific data to support their stand. They say that CO2 is in fact leading to an increase in green cover. Studies dealing with CO2 intake by plants are often cited by these lobbies.

The latest such study comes from the University of California, Merced, published in the Nature journal in April. It has found that there has been a 30 percent increase in global photosynthesis in the past 200 years compared to the amount of CO2 being converted to food by plants prior to that period.

In simple terms, it means that in the last two centuries, when the world got industrialised and its global emissions of CO2 began to spike, the plant world was ingesting more CO2 than in the past and turning it into food in the presence of sunlight (which is what photosynthesis means). In other words, the number of plants absorbing CO2 increased in these years.

So was that the result of increased CO2 emissions?

The researchers have not identified the cause for this increase in photosynthesis. They have proposed some possible reasons: “Rising atmospheric CO2 levels, a result of emissions from human activities; longer growing seasons, a result of climate change caused by CO2 emissions; and nitrogen pollution, another result of fossil fuel combustion and agriculture.”

Now these researchers led by Elliott Campbell, associate professor at the University of California, Merced, are not exactly singing praises of CO2. Says Campbell: “The rising CO2 level stimulates crops yields, but it also benefits weeds and invasive species. Most importantly, CO2 emissions cause climate change, which will increase flooding of coastal cities, cause extreme weather and ocean acidification.”

The rise in photosynthesis is defintely good as it removes CO2 from the atmosphere. But human intervention nullifies this blessing. Says Campbell: “Another effect of the rise in photosynthesis is that it can cause plants to remove CO2 from the air and store it in ecosystems. Unfortunately, CO2 emissions from fossil fuel burning overwhelm any uptake by plants.”

A co-author of the paper, Joe Berry from the Carnegie Institution for Science, adds: “The increase in photosynthesis has not been large enough to compensate for the burning of fossil fuels. Nature’s brakes have already been overwhelmed. So now it’s up to us to figure out how to reduce the CO2 concentration in the atmosphere.”

The researchers sourced their data from air trapped in bubbles in different layers of Antarctic ice. Photosynthesis, or use of CO2 can be measured by the presence of carbonyl sulphide, or COS, which plants absorb with CO2.

The key was finding COS stored in the ice, and that provides a record of Earth’s plant growth as photosynthesis is closely related to the atmospheric COS level.

Campbell agrees that his study “suggests that the world is getting greener. But the research did not identify the cause of the increased photosynthesis. However, previous research using computer models has shown several processes that could, together, create such a large change in global plant growth”.

Do these findings change anything for the world? For instance, do these mean that the world can go slow on the temperature targets set by the Paris agreement?

Campbell says that no such dramatic change is expected. “The climate models used to forecast climate change already account for plant uptake of CO2. Our study provided new evidence to confirm that the plant uptake in the models is indeed happening,” he says.

Nor do these findings mean that we are better off than we thought we were given that plant growth has increased. “The results only confirm what the IPCC [Intergovernmental Panel on Climate Change] model projects,” says Campbell.

“In fact, confirmation of the IPCC models is the most significant part of this study,” he says, thus blunting any hopes of those who may want to use the findings to further the arguments against the efforts to fight climate change.

Another significant result of the study is methodological, says Campbell. “We have demonstrated a new line of evidence to track plant uptake of CO2. If we continue to make these measurements, we will have an early warning of when/if the plant uptake of CO2 slows down when/if nutrient limitations take effect,” he says.

Earlier studies have estimated current levels of plant activity, which is where the present study differs. “Our study estimates the change in plant activity over the last 200 years,” says Campbell.

Chandra Bhushan, deputy director general of Centre for Science and Environment, says that the data on global photosynthesis only reveals the extent of the concentration of CO2. “If there is enhanced plant growth, one cannot ignore the ill effects of CO2 emissions,” he says.
Meanwhile, lobbies in favour of CO2 are working towards changing national and international policies that seek to bring down global emissions of greenhouse gases.

In the US, a coalition for CO2 is actively working to dilute the position on emissions taken by the Obama administration. A parallel coa­lition for cutting down on CO2 emissions is also working to strengthen the position against emissions. A group of scientists from across the world sent a petition to US president Donald Trump in February, asking him to not only water down the US position on emissions but also to quit the United Nations Framework Convention on Climate Change (UNFCCC) and have nothing to do with the UN-led discourse on climate change.

In a covering letter to this petition, Richard Lindzen, professor emeritus of atmospheric sciences at MIT, wrote: “Carbon dioxide is not a pollutant. There is clear evidence that increased atmospheric carbon dioxide is environmentally helpful to food crops and other plants that nourish all life. It is plant food, not poison.”

Others criticised the UNFCCC-led Paris agreement for targeting “minor greenhouse gases like CO2 for harsh regulation”.

The petition said: “We urge the United States government, and others, to withdraw from the UNFCCC. We support reasonable and cost-effective environmental protection. But carbon dioxide, the target of the UNFCCC, is not a pollutant but a major benefit to agriculture and other life on Earth. Observations since the UNFCCC was written 25 years ago show that warming from increased atmospheric CO2 will be benign – much less than initial model predictions.”

Menon is a freelance journalist

(The article appears in the May 1-15, 2017 issue)

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