A breath of fresh air

By | Science & Technology
Tropical forest. Credit@kriskrugviaflickr.com

A new NASA-led study suggests tropical forests are responsible for absorbing more of the world’s carbon dioxide (CO2) than previously thought. This research estimates that tropical forests absorb 60% of Earth’s carbon dioxide, far more than other forests. This is encouraging considering CO2 uptake by boreal forests, such as those in Canada and other northern regions, is slowing. This is the first study to compare CO2 estimates from a number of alternate approaches and using different scales, appearing to reconcile what have previously been viewed as contradictory results.

Forests and other vegetation form part of the biosphere and play an important role in the carbon cycle on Earth. They take up carbon dioxide from the atmosphere through photosynthesis and expel it through respiration. Both photosynthesis and respiration are affected by changes in climate conditions such as temperature and precipitation. The global climate has veered from its norm ever since the industrial revolution and this has altered how forests operate as part of the carbon cycle.

Global warming has drawn major attention from scientists, politicians and businesses, and is considered one of the most pressing environmental challenges of the twenty-first century. The undeniable consensus among the scientific community is that the majority of the warming over the last half of the twentieth century is a result of human activity on the planet, which has increased greenhouse gas concentrations in the atmosphere. The Intergovernmental Panel on Climate Change (IPCC) also predicts that this behaviour may drive climate change rapidly in centuries to come. Paramount to these greenhouse gases is CO2 of which human activity has greatly increased its concentration in the atmosphere. This has primarily been through the burning of fossil fuels.

Earth’s biosphere naturally absorbs some of this CO2 through its oceans and other ecosystems – like forests. Forest ecosystems act as “sinks”, removing almost 30% of net carbon dioxide from the atmosphere. If the rate of CO2 removal by forests were to drop, the rate of global warming may speed up.

The NASA-led study performed a global reconciliation of all the available information regarding the effects of CO2 on climate change and came to one conclusion: tropical forestry is a far greater carbon absorber than expected. The team estimated that tropical forests absorb 1.4 billion tons of CO2, out of a total 2.5 billion tons. This is because forests across the world use the CO2, which is being increasingly pumped into the atmosphere, to grow faster by photosynthesis; an effect called carbon fertilisation. This effect is greater in warmer climates, explaining why tropical forests might appear more active in the carbon cycle.

Green areas have the highest uptake of carbon dioxide from the atmosphere; red have the least. Schimel’s team found that tropical forests were responsible for about 60% of global uptake and worldwide forests accounted for about a third of fossil fuel emissions. Credit@DavidSchimel

Green areas have the highest uptake of carbon dioxide from the atmosphere; red have the least. Schimel’s team found that tropical forests were responsible for about 60% of global uptake and worldwide forests accounted for about a third of fossil fuel emissions. Credit@DavidSchimel

Lead author of the paper, Dave Schimel told The Positive, “We determined more accurately where that [CO2] uptake is occurring. However, tropical forests are more likely to carry on uptake into the future, while forests in North America and Europe are likely to slow their growth. This is because most northern uptake is due to forest regrowth, in forests harvested over the last century, while tropical uptake is likely due to increasing CO2 itself.”

This study helps to understand how terrestrial ecosystems might continue to offset human carbon emissions or whether it will intensify global climate change. Schimel’s analysis demonstrates how carbon uptake by tropical forests depends on how they respond to climate change and how the balance of the carbon cycle requires protection from deforestation.

NASA monitors Earth from space via satellites to study the interaction of Earth’s natural ecosystems and understand how the planet is changing. This information is shared globally to work towards the goal of protecting and preserving life on Earth.

How else might Earth’s ecosystems help counteract the effects of global warming?

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