Tropical rainforests are often referred to as the Earth’s “lungs” because they typically absorb carbon dioxide and emit oxygen. However, the extent of carbon dioxide absorption or emission varies significantly due to year-to-year fluctuations in climate. A recent study published in the journal Nature demonstrates how these fluctuations highlight the rainforest’s susceptibility to climate change.
Dr. Chris Huntingford, a climate modeler at the Centre for Ecology & Hydrology (CEH), collaborated with researchers from the University of Exeter and the Met Office Hadley Centre on this study.
The research introduces a novel approach to gauge the sensitivity of biological systems to climate changes. It involves interpreting the year-to-year changes in atmospheric carbon dioxide levels.
Professor Peter Cox, the lead author of the study from the University of Exeter, explained that scientists have long grappled with the question of whether the Amazon forest will decline due to climate change. He stated, “Our study suggests that the risk is minimal if climate change stimulates increased plant growth under elevated carbon dioxide levels. However, if this effect weakens or if climate warming occurs independently of carbon dioxide increase, we anticipate a substantial carbon release from tropical ecosystems.”
The annual increase in atmospheric carbon dioxide is influenced by whether tropical forests absorb or emit carbon dioxide, which, in turn, depends on whether the tropical climate experiences warmer and drier conditions or cooler and wetter conditions. Thus, the carbon dioxide levels in the atmosphere serve as a record of how rainforests respond to climate fluctuations.
The team examined how these year-to-year variations in carbon dioxide concentration correspond to long-term changes in carbon storage in tropical rainforests. They observed that climate models predicting rainforest decline under climate change exhibited significant year-to-year variations in carbon dioxide concentration, whereas models indicating rainforest resilience had more realistic fluctuations.
By integrating this relationship with real-world carbon dioxide variations, the team estimated that approximately 50 billion tonnes of carbon would be released for every degree Celsius of warming in the tropics. Initially, these findings were relieving, as Peter Cox noted, “Fortunately, this carbon release is offset by the beneficial effects of carbon dioxide fertilization on plant growth in most 21st-century scenarios, allowing forests to continue accumulating carbon overall.”
However, the researchers emphasize that tropical forests will face challenges under climate change if carbon dioxide fertilization does not enhance tree growth as much as predicted by climate models. They assert that the long-term viability of tropical forests hinges on their ability to withstand various pressures from climate change and deforestation.
