Central Pacific type El Nino events can increase by 11.7%, La Nina events by 14.6%
Trees logged for agriculture in Southeast Asia. Photo: iStock Deforestation in the Maritime Continent (MC) — the Southeast Asian region between the Indian and Pacific Oceans — can strengthen subtropical El Nino-Southern Oscillation (ENSO) dynamics, causing more Central Pacific and multi-year ENSOs, according to a new climate modelling study.
The archipelagos of Indonesia, Borneo, New Guinea, the Philippine Islands, the Malay Peninsula and the surrounding seas are part of the MC region.
Darker areas show Maritime Continent. Source: Bureau of Meteorology, Government of Australia
Deforestation in the region has the potential to alter ENSO’s complexity, making El Nino more complex and less predictable, the study suggested. ENSO is an important climate phenomenon on Earth due to its ability to change the global atmospheric circulation, which in turn influences temperature and precipitation across the globe.
Logging trees is a common land-use change, especially in tropical regions like the MC. However, deforestation reduces evapotranspiration and alters surface albedo, which measures how much sunlight the Earth's surface reflects. As surface albedo warms the ambient environment, this further impacts land-atmosphere-ocean interactions to modify the local climate.
These local effects have the ability to affect land-atmosphere interactions, such as the land-sea breeze.
Ting-Hui Lee of the University of California led the study, which used the community Earth system model to simulate hypothetical future deforestation over 100 years, converting native broadleaf evergreen and deciduous trees to warm-season grasses.
When compared to control experiments, the deforestation model increased the occurrence of the Central Pacific and multi-year types of ENSO. This change in the complexity of the climate phenomenon can be attributed to the MC’s intensification of subtropical ENSO dynamics.
“This idealised coupled climate modelling study suggests that MC deforestation has the potential to alter ENSO’s complexity,” making El Nino more complex and less predictable, said the study published in journal Geophysical Research Letters.
The likelihood of Central Pacific type El Nino events occurring increased by 11.7 per cent as a result of deforestation compared to background levels in the models, while La Nina events were exacerbated by 14.6 per cent in the same simulations.
Further, if deforestation continues, more multi-year La Nina events are likely to occur in the coming decades. Simulations suggest a 13.8 per cent increase in La Nina events. Multi-year El Nino events may increases from 40.2-44.7 per cent after deforestation.
A study published in journal Nature Climate Change by Bin Wang & et al found that five out of six La Nina events since 1998 have lasted two to three years. Ten multi-year La Nina events over the past century had an accelerated trend, with eight of these occurring after 1970. The two types of multiyear La Nina events over this time period followed either a super El Nino or a central Pacific El Nino.
The United Nations’ Food and Agriculture Organization (FAO) estimated that around 420 million hectares (ha) of forest were lost between 1990 and 2020. Even though the rate of deforestation has declined, it was still 10 million ha per year in 2015–2020.
Trees and forests are major means for combating climate change. Forests contain 662 billion tonnes of carbon, which is more than half the global carbon stock in soils and vegetation. Despite a continued reduction in area, forests absorbed more carbon than they emitted in 2011–2020 due to reforestation, improved forest management and other factors, stated State of the World’s Forests 2022 by FAO.
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