A new report shows that increased carbon dioxide in the atmosphere since the industrial revolution has sped up the growth of plants throughout the world. The information helps solve a question among scientists, of how the carbon dioxide released from human activity has been affecting plant life on earth.
The study, published in the journal Nature, and led by Dr. J. Elliot Campbell of University of California, Merced, examined air bubbles trapped in Antarctic ice. When ice forms there, it traps bubbles of air preserving samples of the atmosphere at various points in history. By studying the levels of one particular chemical, scientists can learn about the global growth of plant life at any point in time.
“It’s the whole Earth — it’s every plant,” said Campbell.
The team discovered that plants have grown at a faster rate over the past century than at any other period in the past 54,000 years. They found that plants are converting 31 percent more carbon dioxide into organic matter than prior to the industrial revolution.
According to Christopher B. Field, director of the Stanford Woods Institute for the Environment:
“It’s tempting to think of photosynthesis at the scale of the entire planet as too large to be influenced by human actions. But the story here is clear. This study is a real tour de force.”
Field was not involved in Campbell’s study.
Since 1850, concentrations of carbon dioxide in the atmosphere have increased by more than 40 percent. Scientists have hoped to determine whether the increase in CO2 would help fertilize plants, but have faced difficulty reaching a definite conclusion – plants rely on other nutrients, such as water and nitrogen, and growth can vary based on other factors like temperature. Scientists have also found that plant responses to increased CO2 can vary based on geography, and most experiments on the subject have been limited to Europe and the United States.
Recently, however, scientists found a new way to measure plant growth, using a very rare molecule called carbonyl sulfide, which is present in only several hundred parts per trillion in the atmosphere. It is produced by decaying organic matter in the oceans, after which it floats into the atmosphere. The molecule is processed by plants alongside carbon dioxide, but is destroyed as it enters plant tissues, which means that carbonyl sulfide levels in the air drop as plants grow.
By the time air reaches Antarctica, it is so well mixed that levels of the substance there reflect the growth of plants worldwide. Samples of that air are captured in the ice bubbles, and preserved for thousands of years. Campbell and his team studied samples going as far back as 54,000 years.
“The pace of change in photosynthesis is unprecedented in the 54,000-year record,” Capbell said, noting that the current rate is 136 times fast as at the end of the last ice age, when there was another drop in the carbonyl sulfide as glaciers receded.
The absorption of extra CO2 has slowed the rates of climate change. However, scientists are still uncertain how plants will respond to a continued rise in carbon dioxide While it could spark even more growth, that potential is ultimately limited.
“I’ve been referring to this as a carbon bubble,” according to Campbell. “You see ecosystems storing more carbon for the next 50 years, but at some point you hit a breaking point.”