Study Measures Vulnerability Of Earth’s Lungs
February 7, 2013

Scientists Gauge Vulnerability of Earth’s “Lungs” To Climate Change

April Flowers for - Your Universe Online

Because they draw in carbon dioxide and breathe out oxygen, tropical rainforests are often called "the lungs of the planet." However, yearly variations in climate can cause the amount of carbon dioxide absorbed and released by these forests to vary considerably.

A new study conducted by a team of scientists from the University of Exeter, the Met Office-Hadley Centre and the Natural Environmental Research Council´s (NERC) Centre for Ecology & Hydrology demonstrates that these variations reveal the rain forests´ vulnerability to climate change.

Professor Peter Cox of the University of Exeter explained: "We have been struggling for more than a decade to answer the question 'will the Amazon forest die back under climate change?' Our study indicates that the risk is low if climate change is associated with increased plant growth under elevated carbon dioxide.”

“But if this effect declines, or climate warming occurs due to something other than a carbon dioxide increase, we expect to see a significant release of carbon from tropical ecosystems.”

The findings of the study were recently published in the journal Nature and point to a new method for determining just how sensitive biological systems are to changes in climate. The key to this new method was learning how to read the yearly variations in the concentration of carbon dioxide in the atmosphere.

Each year carbon dioxide in the atmosphere increases, in part as a result of burning fossil fuels and deforestation. If the amount goes up from one year to the next depends on whether or not tropical forests are absorbing carbon dioxide or releasing it — which, in turn, depends on whether the tropical climate was warmer and dryer, or wetter and cooler than the previous year. This means that trace levels of carbon dioxide in the atmosphere create a record of how the Earth´s "lungs" are responding to warming or cooling trends in the climate.

How these year-to-year variations in carbon dioxide concentration levels relate to long-term changes in carbon absorption in tropical rainforests was the focus of the team's research.  According to their findings, climate models that predicted tropical forest dieback caused by climate change also had large year-to-year variations in carbon dioxide concentrations. By contrast, models that showed the rainforest as more robust to climate change had more realistic year-to-year variations in carbon dioxide concentrations.

The team was able to determine that about 50 billion tons of carbon would be released for each degree Celsius of warming in the tropics, which was initially a relief.

"Fortunately, this carbon release is counteracted by the positive effects of carbon dioxide fertilization on plant growth under most scenarios of the 21st century, so that overall forests are expected to continue to accumulate carbon," said Cox.

However, if the release of carbon dioxide doesn't fertilize tree growth as strongly as climate models suggest, the team is certain that tropical forests will suffer.

"The long-term health of tropical forests will depend on their ability to withstand multiple pressures from changing climate and deforestation. Our research has shed light on the former, but the latter remains a significant pressure on this ecosystem," said Chris Jones of the UK´s Met Office in closing.