We start our A–Z journey on global warming with the Amazon Rainforest, which has an incredibly important role to play in maintaining balance in the Earth’s climate, in ways that are only just being understood. The Amazon is inextricably linked to the issue of global warming and therefore a very good place to start our inquiry into what may be the biggest threat to our existence on this planet.
The Amazon river basin contains the largest rainforest on Earth and covers approximately forty per cent of the South American continent. The rainforest is located in eight countries. Brazil has sixty per cent, with Colombia, Peru, Venezuela, Ecuador, Bolivia, Guyana, Suriname and French Guyana between them containing the rest. The Amazon forest is a natural reservoir of genetic diversity, containing the largest and most species-rich tract of tropical rainforest that exists. The Amazon contains an amazing thirty per cent of Earth’s species. One square kilometre can sustain about 90,000 tons of living plants! It’s also amazing to consider that one in five of all the birds in the world make the rainforest their home. The Amazon basin is drained by the Amazon River, the world’s second longest after the Nile. The river is essentially the lifeline of the forest. It is the most voluminous on Earth and its daily freshwater discharge into the Atlantic is enough to supply New York City’s freshwater needs for nine years! New measurements recently taken by scientists, however, suggest that the Amazon may actually be the longest river in the world. No doubt this will be confirmed if true, at some point in the future!
A few thousand years ago tropical rainforests covered as much as twelve per cent of the Earth’s land surface, but today the figure is below five per cent. The largest stretch of rainforest can be found in the Amazon river basin, over half of which is situated in Brazil.
Why is the Amazon so important in the context of global warming?
The rainforest acts as a major store of carbon and produces enormous amounts of oxygen. The Amazon has been referred to as ‘the lungs of the Earth’ because of its affect on the climate. The way this is achieved is of course through photosynthesis, the process by which green plants and trees use the energy from sunlight to produce food by taking CO2 from the air and water and converting it to carbon. The by-product of this is oxygen. The Amazon therefore helps recycle CO2 by turning it into oxygen, and it is estimated that the Amazon produces about twenty per cent of this essential gas for Earth’s atmosphere.
Trees, plants and CO2
Levels of CO2 in the atmosphere have been measured since 1958, from a monitoring station located on Mauna Loa volcano in Hawaii. They show sharp annual increases and decreases in CO2 levels, similar to the tooth on a saw. The readings seem to mimic a breath of air being taken in and out, almost as if the Earth is breathing. They correspond to the amount of vegetation on the planet (most of which is in the northern hemisphere, as the landmass there is greater), taking in CO2, and giving out oxygen. During summer in the northern hemisphere, when the Earth is tilted towards the sun, Earth’s vegetation is able to photosynthesise, resulting in an uptake of CO2, causing worldwide CO2 levels to drop. In winter in the northern hemisphere, when Earth’s axis is tilted away from the sun, the opposite happens, causing CO2 levels to rise again. When one becomes aware of the correlation between the Earth’s vegetation and CO2 levels, it is easy to understand why the Amazon, and rainforests in general, are such an important part of Earth’s ecosystem.
The problem is, however, that although the measurements taken at the volcano in Hawaii show sharp up and down annual readings, the measurements also show a simultaneous steady upward trend in CO2 levels. The importance of CO2 in relation to global warming will be a recurring theme throughout this book, and will be looked at further in Chapter C.
What has been happening in the Amazon?
A worrying trend is the Amazon having experienced two consecutive years of drought, in 2005 and 2006. The drought in 2006, which left rivers dry, stranded thousands of villagers, and put regional commerce at a standstill, was the worst on record. A second year of drought is of great concern to researchers studying the Amazon ecosystem. Field studies by the Massachusetts-based Woods Hole Research Centre in the USA, suggest that Amazon forest ecosystems may not withstand more than two consecutive years of drought without starting to break down. Severe drought weakens forest trees and dries leaf litter leaving forests susceptible to land-clearing fires set during the July-October period each year. According to the Woods Hole Research Centre, it also puts forest ecosystems at risk of shifting into a savannah-like state.
A recent experiment carried out by a team of researchers suspended 5,600 large plastic panels between 1 and 4 metres (3.2– 13.1 feet) above the ground to mimic severe drought conditions, where as much as eighty per cent of a one-hectare plot is deprived of eighty per cent of rainfall. Measuring rainfall, soil moisture, leaf and canopy characteristics over time, it was found that after four years the rainforest trees began to die while leaf litter dried and became tinder for wild fires.
Another factor is the El Niño Southern Oscillation (ENSO) event, a climatic phenomenon that influences much of the climate in the region, particularly Northeast Brazil, and the northern Amazon. ENSO brings with it dry conditions in the above areas, and manmade climate change is thought to increase this naturally occurring phenomenon in the future. ENSO is further looked at in Chapter W. Some climate models have suggested that temperatures in the Amazon may increase by 2 to 3°C (3.6–5.4°F) by the year 2050, together with a decrease in rainfall during the dry period. If the drought continues, based on the results of the aforementioned experiment, 2007/8 could be a turning point for the forest, which may mean that a tipping point will be reached where the forest will start to die, with catastrophic consequences for Earth’s climate. If this trend continues, according to the WWF, between thirty and sixty per cent of the Amazon rainforest could become dry savannah, rendering the forest a source of CO2 instead of a sink/store of it, which it currently is.
There are ways in which we can all help try and sustain this vast and ecologically important expanse of rainforest, and these will be discussed in Chapter Y. The Amazon will be further considered in Chapter D, where the problem of deforestation is looked at.
The Amazon rainforest contains about thirty per cent of Earth’s species.
World rainforest cover has over thousands of years decreased from twelve per cent to five per cent.
The Amazon helps to recycle CO2, a gas which contributes to global warming and while doing so produces about twenty per cent of Earth’s oxygen.
CO2 levels rise and fall with the seasons. There is greater landmass and hence vegetation in the northern hemisphere, which means that when Earth is tilted towards the sun during northern summertime, CO2 levels drop as a result of there being greater uptake of CO2 from photosynthesis. During the winter, the opposite happens and CO2 levels rise again.