Rapid Urbanization in Brazilian Amazon Threatens Rainforest

By Rachel Mucha

RIO DE JANEIRO, BRAZIL – A landmark study in the Journal of Nature Communications revealed that urban pollution in Manaus, Brazil, has caused a 400 percent spike in Secondary Organic Aerosol (SOA) particles in nearby areas of the Amazon, that is likely to alter regional rainfall, tree growth, and photosynthesis patterns.

Authored by a 36-member research team at the bilateral US-Brazil Green Ocean Amazon initiative (GOAmazon) and published in March of 2019, the study corroborated environmentalists’ concerns that rapid development and urbanization in the Amazon region will damage nearby rainforest ecosystems.

In pristine rainforest ecosystems, SOA is integral to the maintenance of balanced solar radiation levels and the formation of rain clouds. In excess, however, SOA particles can impede cloud formation and elevate terrestrial solar radiation to unhealthy levels, thus diminishing rainfall and stunting tree growth.

In the Amazon, these ecosystem changes are the cause for international concern; the rainforest produces about 20 percent of the planet’s oxygen and houses one-fifth of earth’s fresh water.

According to the GOAmazon study, SOA particle production in Manaus — an industrial hub of two million inhabitants — has been drastically accelerated by nitrogen oxides produced by motor vehicles, air conditioners, deforestation-related fires, and other urban pollutants.

The conclusion is based upon a comparative analysis of SOA levels in pristine rainforest ecosystems in the Amazon with forested regions that are proximate to Manaus and consequently have been impacted by urban pollution.

The researchers recorded large enhancements in SOA (60-200 percent on average, 400 percent maximum) in the urban-peripheral sample, as well as a higher prevalence of greenhouse gases and ozone in comparison to the pristine rainforest.

“The general effect and the forest’s sensibility to these changes are still not fully understood, but the increase in the presence of [SOA] particulates and ozone levels could affect the forest’s climate, ecology, and rainfall patterns, not to mention human health,” said Dr. Manish Shrivastava, one of the study’s principal authors, in an interview with the Manaus-based journalistic organization, Amazonia Real (AR).

Dr. Luiz Candido, a meteorologist and head of graduate studies in Climate and Environment at the National Institute of Amazonian Studies in Manaus, told AR that the GOAmazon findings demonstrate the importance of “rethinking the development not just of Manaus, but of other cities.”

Candido prodded: “Do we need major cities? Would it not be better to prioritize the quality of the environment and the health of the population?” He advocated for the limitation of urban growth and the creation of smaller settlements and villages in the region, as a way to minimize future damage to the rainforest.

In a separate conversation with AR, environmental researcher Charles Clement echoed Candido’s fears about urbanization and lamented the GOAmazon findings evidencing Brazil’s faltering commitment to the Paris Climate Accords.

Although Brazil is a signatory to the 2016 accords, the country has fallen short of its climate pledges since newly-elected president Jair Bolsonaro weakened environmental regulations and opened the Amazon to new development.

“To put the Paris Accords into practice in Brazil, we have to put people back in the forest, as it is a socially and environmentally acceptable option,” said Clement. “The indigenous people have shown us how to do this for centuries, and indigenous knowledge must be highlighted in Amazonian conservation and environmental education programs,” he concluded.

Ultimately, GOAmazon posits that its results provide “a clear picture of how anthropogenic emissions are likely to have greatly modified [SOA] formation since pre-industrial times over the Earth and imply that rapid urbanization in future years might substantially enhance [SOA] formation in the pristine forested region of the Amazon.”

The Brazilian government’s response to this clear warning about the negative impacts of urban pollution on ecosystem health in the Amazon will be globally significant, given the region’s role in mitigating climate change and conserving natural resources.

The international community must hold Brazil accountable for its Paris Accords commitment to limiting urban pollution, lest SOA particles drastically alter Amazonian rainfall patterns and tree growth in the future.