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Nature does not always have to be green

By Jo-Anne Nina Sewlal BSc., MPhil., FLS., AMSB Dept of Life Sciences, University of the West Indies

The media projects the image that a healthy terrestrial ecosystem is a green one. But a sign of a healthy ecosystem is a variety of colours and shades.

The word albedo is Latin for whiteness, in this context referring to the amount of sunlight reflected by the object it is shining on. This may sound quite trivial, after all what does the amount of sunlight reflected off your earrings or belt buckle have to do with the environment.

But with respect to the environment, the amount of sunlight that is reflected off the surface of land, water and mountains has a great impact on the conditions necessary to support life on this planet.

There is one simple rule that must be kept in mind; dark surfaces absorb more radiation while surfaces lighter in colour reflect more radiation. Albedo is measured on a scale of zero to one, with a totally black surface having an albedo of zero meaning that all the radiation is absorbed.

This is in contrast to a perfectly white surface which has an albedo of one meaning that all the radiation is reflected. However, the actual albedo that a surface exhibits depends on how light or dark it is.

Objects in our environment that have typically low albedos include, the ocean and land, while ice, snow and clouds have very high albedos (ranging from 0.7 to 0.9).

But when you think of the planet in terms of albedo, you can see that not all land or ocean is equal, for instance a dense forest reflects more radiation than one with an open canopy and exposed dark soil. Just to give you an idea of the variation of albedo in a terrestrial ecosystem, grass has an albedo of 0.25 while dark soil has an albedo of 0.12.

Basically in areas where there is vegetation the soil is darker thus affecting the environment in three ways; heating the soil, causing evaporation of water from the soil and vegetation and finally adding heat to the atmosphere. Overall, the planet has an average albedo of 0.3 so that 30% of solar radiation is reflected while the remaining 70% is absorbed.

So you can see where this is going, if the average global albedo decreases, global warming and the detrimental effects it brings with it like increasing sea levels, reduced land for terrestrial ecosystems and loss of biodiversity will become more prevalent. But as I mentioned earlier albedo refers to how white an object is. So let's take a closer look at the white things in our environment.

The first thing are clouds, which may not seem environmentally influential but they help to regulate the global temperature as they reflect sunlight but they also function to trap warmth against the planet's surface.

Other white components include snow and ice. So how does ice and snow fit into all of this especially here in the Caribbean, after all, when people hear the word, "Caribbean" images of sun and sand spring to mind. Ice plays an important function in our environment in particular temperature regulation as they reflect sunlight. However, due to human activities like combustion there is an increase the amount of greenhouse gases like carbon dioxide therefore increasing the average global temperature and causing the polar ice to melt.

This is unfortunately a vicious cycle, because as the ice melts, more land and ocean beneath are exposed, therefore an increased surface area to absorb radiation is available, thus increasing the albedo and causing more ice and snow to melt.

Human activities can also have an impact on the average albedo, such as deforestation which exposes much dark soil decreasing the overall albedo.

Then there is air pollution where the amount of fine particles in the air (referred to as aerosols) which affects albedo both directly and indirectly. Direct effects of aerosols on albedo include their ability to both scatter and absorb radiation.

The scattering of radiation has the effect of cooling the atmosphere whereas radiation absorption as mentioned earlier has the opposite effect. Aerosols indirectly affect albedo by causing a "seeding effect" in the clouds that is they provide a surface which water droplets can condense and form around, therefore the number of droplets in the cloud increases so it rains more frequently and the cloud does not stay dark but is much whiter and reflective for much longer.

Additionally the soot produced from combustion can settle on the ice and snow thus changing them from a reflective surface to an absorptive one, thus decreasing the albedo.

So basically what the combustion we carry out in Trinidad and Tobago can affect another location a great distance away and contribute to our planet's environmental problems. But artificial surfaces also contribute to albedo, the most common one being concrete.

Concrete has a low albedo therefore it can absorb a lot of solar radiation, thus becoming a concern in urban areas where they contribute to the "heat island effect".

"Heat islands" is the term given to developed or urban areas that are hotter than nearby rural areas. The tall buildings provide many surfaces which light can be reflected off of or absorbed. However, heat loss which usually takes place during the night is prevented as the buildings block the cool air from moving in to replace the hot air that rises at this time of day.

Therefore there is little or no air flow in these urban areas and thus no escape for pollutants, thus affecting air quality and in turn human health. Other manmade structures that influence albedo include roads, where the dark asphalt absorbs a lot of heat.

So when designing our urban areas urban planners, architects and the government needs to keep albedo in mind can have some beneficial effects, for example, lighter coloured pavements and parking lots require less lighting at night thus using less electricity and less energy.

So if we are to fully understand our environment, how it functions and how to protect it we need to put this idea of lush green hills aside and look at all ecosystems as well as urban areas as they all have a role to play in the survival of our planet.

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guest said on Friday, Apr 20 at 9:58 AM

I understand the point you are making but green is a concept of a healthy ecology not a colour.

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Anonymous said on Monday, Apr 16 at 8:02 PM

Good subject matter but i expect better punctuation from you.

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