2021-04-08

Under excessive human intervention, the Amazon rainforest may become an accomplice to global warming

By yqqlm yqqlm

In our impression, plants absorb carbon dioxide through photosynthesis, so forests should be a powerful weapon to curb global warming.

However, a paper published in the journal Frontiers in Forests and Global Change in mid-March argued that the current Amazon rainforest is contributing to global warming.

Previously, a study published in the journal Nature Climate Change pointed out that in some areas of the tropical rainforest, the current carbon dioxide emissions have exceeded the absorbed share.

But the absorption and emission of carbon dioxide is only one aspect of the Amazon rainforest that affects the climate. All human-made and non-human-made events in the Amazon are exerting unpredictable consequences on global warming.

Human activities have broken the fragile balance that originally existed in the rainforest, making the situation out of control. Eventually, the lush and dense Amazon rainforest may transform into a dry savanna over a wide area.

Not only does it sequester carbon, it also produces greenhouse gases

The Amazon rainforest is the ultimate biodiversity on the planet.

Plants in rainforests, especially tall trees, convert carbon dioxide in the air into carbohydrates through photosynthesis. Although the efficiency of this process is only about 6%, considering the large amount of solar energy and the huge amount of plants that the earth receives from space, the total amount of carbon stored in the Amazon rainforest reaches 200 billion tons, which is about the total amount of humans in 4 to 5 years. carbon emission.

However, the Amazon rainforest is also a world of water. Water vapor from the Atlantic Ocean pours into this land in the form of rainfall. Plant photosynthesis releases a large amount of absorbed water, which will return to the rainforest in the form of precipitation again. In the process of Atlantic water vapor moving up and west on the South American continent, on average, one water molecule circulates more than 5 times in the Amazon rainforest.

When the rainy season comes, the water level of the Amazon River Basin will rise several meters, and floods will inundate a lot of woodland. In the soil rich in water and nutrients, the activity of various methanogens has increased, and the organic matter in the soil is converted into methane in a large amount, making the methane emission of the entire Amazon basin reach 3.5% of the global methane emission.

In absolute terms, methane emissions cannot be compared with carbon dioxide, but the warming coefficient of methane is more than 25 times that of carbon dioxide. They contribute at least 16% of the greenhouse effect, and they are not negligible carbon. Source of emissions.

Under excessive human intervention, the Amazon rainforest may become an accomplice to global warming

Unruly humans, runaway rainforest

If we take the human factor into consideration, the carbon emissions problem of the Amazon basin will become more complicated and completely messed up.

Wetland drying and forest logging activities carried out by humans for the purpose of increasing arable land seem to reduce the area of ​​wetlands, thereby controlling the rainfall intensity in rainforest areas, but this practice will cause soil compaction and release at the same time. Nitrous oxide. The release of nitrous oxide itself is not large, but its warming coefficient has reached dozens of times that of methane and 300 times that of carbon dioxide. In terms of share, the greenhouse effect caused by nitrous oxide accounts for about 7% of the overall situation.

The most common method used in the logging process is arson. In the forest fire that obscured the sky, large areas of rainforest were reduced to ashes, and amorphous carbon and carbon black were released into the atmosphere. These small black particles absorb a lot of sunlight, causing local heating. The loss of a large number of forests has led to a sharp drop in water vapor transpiration, and the local climate has become increasingly dry and high temperature, which in turn will encourage the release of nitrous oxide.

On the other hand, in order to develop shipping, hydropower and other industries, humans have built a large number of dams in the Amazon Basin. The increase in wetland area caused by the construction of dams will increase methane emissions.

Therefore, no matter how humans dispose of or use Amazon’s water systems and wetlands, it seems that greenhouse gases will always emerge to play the role of “thorns”, leaving humans with no idea where to go.

If the balance is lost, the rainforest may become grassland

What role does the Amazon rainforest play in global warming has always been a problem that plagues academics.

The author of this recent paper pointed out: Deforestation will affect the absorption of carbon dioxide, but if we consider the overall situation, we will find that it is indeed a very important issue to see whether the Amazon rainforest contributes to global warming. Emission and absorption of carbon dioxide is only one aspect of difficult topics.

For this reason, this study did not use carbon dioxide as a single indicator, but comprehensively considered various factors. In particular, all other factors except carbon dioxide were superimposed to assess how strong they are. .

The research results clearly show that the various forms of human production, such as resource collection, river water storage, crop planting, and livestock breeding, all change the natural ecological and climatic system, and most of them will Promote global warming.

In addition, methane is indeed the most important greenhouse gas in the Amazon basin, and its largest natural source is still the rainforest itself. In the past, rain forests were able to offset the greenhouse effect caused by their own release of methane, but human activities are severely weakening this ability. The consequences of this will not only be the increasingly uncontrolled emissions, the rain forest itself will also face a turning point in its destiny.

According to analysis, with the further intensification of deforestation, the water cycle of the Amazon rainforest will be very different from now, which will eventually lead to the conversion of the Amazon rainforest into a drier savanna in a wide area. This conversion will occur when the rainforest harvest area reaches 20%-25%. According to an assessment made by the Brazilian government, the current rate of deforestation in the Amazon rainforest has reached 17%, and the situation is precarious.

Although the ecosystem is fragile, the adaptability of species and the ability to rebuild the ecosystem often exceed human expectations. In this sense, even if it is disturbed more, the rainforest will not fall into desolation.

But any slight changes to the rainforest ecology and climate may start a cycle of constant deterioration, affecting the entire South America and even the world. As for the scale and extent of this impact, we still know very little.

(According to “Science China Central Kitchen”)