widenews desk: For decades, scientists have been trying to figure out what all the carbon dioxide we have been putting into the atmosphere has been doing to plants. It turns out that the best place to find an answer is where no plants can survive: the icy wastes of Antarctica.
As ice forms in Antarctica, it traps air bubbles. For thousands of years, they have preserved samples of the atmosphere. The levels of one chemical in that mix reveal the global growth of plants at any point in that history.
“It’s the whole Earth — it’s every plant,” said J. Elliott Campbell of the University of California, Merced.
Analyzing the ice, Dr. Campbell and his colleagues have discovered that in the last century, plants have been growing at a rate far faster than at any other time in the last 54,000 years. Writing in the journal Nature, they report that plants are converting 31 percent more carbon dioxide into organic matter than they were before the Industrial Revolution.
The increase is because of the carbon dioxide that humans are putting into the atmosphere, which fertilizes the plants, Dr. Campbell said. The carbon in the extra plant growth amounts to a staggering 28 billion tons each year. For a sense of scale, that is three times the carbon stored in all the crops harvested across the planet every year.
“It’s tempting to think of photosynthesis at the scale of the entire planet as too large to be influenced by human actions,” said Christopher B. Field, the director of the Stanford Woods Institute for the Environment, who was not involved in the study. “But the story here is clear. This study is a real tour de force.”
Starting in the Industrial Revolution, humans began to pump carbon dioxide into the atmosphere at a prodigious rate. Since 1850, the concentration of the gas has increased over 40 percent.
Since plants depend on carbon dioxide to grow, scientists have long wondered if that extra gas might fertilize them. The question has been hard to answer with much certainty.
For one thing, a plant relies on more than just carbon dioxide. It also needs water, nitrogen and other compounds. Even with a perfect balance of nutrients, plants may grow at different rates depending on the temperature.
To get some real-world measurements of plant growth, some scientists have built enclosures so that they can determine the precise amounts of carbon dioxide as well as the growth of plants. They can even run experiments by flooding the enclosures with extra carbon dioxide.
Trees and other plants in these enclosures have indeed grown faster with more carbon dioxide. But it has been hard to extend these results to the planet as a whole. Scientists found that plants responded differently to carbon dioxide in different parts of the world. The logistical challenge of these experiments has mostly limited them to Europe and the United States, leaving huge swaths of forests in the tropics and the far north little studied.
More recently, scientists have turned to satellites to get clues to what plants have been doing. They have measured how green the land is, and from that data they have estimated the area covered by leaves.
But this method has its shortcomings, too. Satellites cannot see leaves hiding under clouds, for example. And the size of leaves serves as only a rough guide to a plant’s growth. If a plant builds bigger roots, that growth will be hidden underground.
In the mid-2000s, atmospheric scientists discovered a powerful new way to measure plant growth: by studying an unimaginably rare molecule called carbonyl sulfide.
Carbonyl sulfide — a molecule made of a carbon atom, a sulfur atom and an oxygen atom — is present only in a few hundred parts per trillion in the atmosphere. That is about a million times lower than the concentration of carbon dioxide. Decaying organic matter in the ocean produces carbonyl sulfide, a gas that then floats into the atmosphere.
source: science time