State of the Planet

News from the Columbia Climate School


Understanding the ‘Rain’ in Rainforest

High levels of evapotranspiration within rainforest canopies result in high levels of moisture in the air. Here, moisture condenses into clouds over the Amazon; these clouds eventually return water to the rainforest via precipitation and are also dispersed by winds, watering countries throughout the Americas. (Source: NASA MODIS, 2009

Try talking to anyone about the importance of forests and there’s a high likelihood that one or both of the following will happen: first, you may be labeled a tree-hugger (at this juncture, people may start to look for dreadlocks or hair wraps, piercings, and threadbare attire); second, your audience will immediately disengage and assume that they have already heard and understood your message. Their internal dialogue may go something like, “Trees are important, I get it. I recycle my paper and buy seventh generation tissues. Please don’t waste my time telling me things that everyone knows.”

The problem with this line of thinking is that, well, it’s wrong. While recycling is hugely important, it does not safeguard forests. And no, most of us definitely do not get just how important trees are. How could we when the world’s preeminent arboreal experts themselves acknowledge an incomplete understanding of the issue? We – as individuals and as a society – cannot presume to know how important any one species, region, or ecosystem is; to do so begets an incredibly dangerous thought process. Deforestation the world over, especially in the rainforests of South America, illustrates the dire consequences that are a product of such thinking.

That forests in general, and rainforests in particular, provide vital ecosystem services is a fact we have long known. That razing forests to make way for agriculture and human development has negative ramifications is also a fact we have known for quite some time now.  In recent decades, both the scientific community and the general public have come to better understand the potential for and implications of habitat loss, extirpations, and mass extinctions cased by deforestation.  In recent years, the scientific community and, to a certain extent, the general public, have also come to understand the impact of deforestation on the accumulation of atmospheric carbon. And since people first began felling forests, we have known that they play a role in water cycles.

For a long time (read: millennia), the connection between forested areas and water cycles focused on flood mitigation, regulation of run-off, and other localized ecosystem services.  Now, however, there is increasing evidence that forests – and subsequently, deforestation – may have impacts on global water cycles. A recent article in The Economist, explored the potential connection between deforestation in the rainforests of South America and drought in countries from Brazil to the US.

According to the article, the decrease in evapotranspiration that occurs when vast areas of rainforest are cleared results in less downwind precipitation. This has dire implications for places that depend on the transportation of moist air from the Amazon basin to bring rainfall.  It is becoming increasingly apparent that not only could continued, large-scale deforestation in the Amazon result in diminished precipitation throughout the Americas; it may also affect global weather patterns.

Farms like this one in Iowa may face prolonged droughts should deforestation in the Amazon continue. (Source: wikimedia, 2006)

The Economist article discusses a new and controversial theory proposed by two Russian scientists, which posits that forests, through their participation in cycles of condensation and precipitation, may actually be the main determinant of wind patterns. This challenges the long-held belief that temperature drives winds. The theory uses this contentious proposition to explain the observation that deforestation in coastal areas often results in drought farther inland, claiming that forests act as biotic ‘pumps’ that transport moisture inland from oceans and other water bodies.

While the theory discussed in the article has not yet been widely accepted by the scientific community, it highlights (as does the article itself) the interconnectedness of the environmental crises we face today. Considering the relationship between deforestation and drought is a prime example of why we as a global community cannot continue to discuss ecological destruction as a series of disaggregated problems nor continue to create disjointed policies to address them.

The biosphere is made up of countless ecosystems, all of which influence each other and the organisms that inhabit them in complex and intricate ways. To put it simply, everything is connected – every tree, every animal, every person has an impact that resonates across oceans and continents.  If this is a new revelation for you, take a second to really process it, because it’s a hugely important concept to grasp. Take a deep breath, have a sip of water… and then consider that you wouldn’t be able to do either of those things without trees. It almost makes you want to hug one, doesn’t it?

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13 years ago

How can the dam project slated to be built within 3yrs in the Amazon be stopped?