Editor’s Note: While climate is the focus of this diary, the impacts of deforestation and ecosystem destruction on the people of the forest and their livelihood are all important.
Introduction: Deforestation of the Amazon from land use
Deforestation of the Amazon River basin has been going on since the 1970s, to clear land for agriculture and cattle ranching to supply beef to, ultimately, the world. And the local inhabitants have to be fed as well. From 1961 to 2017, the population of Brazil increased from about 80 to about 205 million people, a 156% increase, as shown in the graphic below.
The pace of deforestation rapidly increased as first the arable grassland in southernmost Brazil and later, the Cerrado savanna ringing the Brazilian rain forest. were consumed by maize, cattle and, later, soybean production. The region became an important source for strong, lightweight wood like balsa as well. The amount of land, in hectares (ha), devoted to agricultural endeavors is shown in the graphics below.
The bar graphic below shows the amount of rain forest lost to cultivation and cattle ranching from 1988 through 2018 in square kilometers (km2). Note that the peak near the center of the time series in 2004 corresponding to peaks in soy and cattle production. Also note the slowing of deforestation after 2004, as a result of pressure from world conservationists and the indigenous peoples of the Amazon rain forest. This period ended with the election of Jair Bolsonaro, a right-wing populist modeled after Donald Trump and other authoritarian leaders. Since his election, deforestation has been increasing at rapid rates, with deforested land area records being set for the last four months (11/21, 12/21, 1/22, 2/22). These records were set during what is usually a lull in forest removal; the Amazon rainy season.
A Rain Forest Deforestation Example from the State of Rondonia, Brazil
The banner graphic for this post is a satellite view of Rondonia state in Brazil, taken in August 2016 by the NASA TERRA satellite, using the Moderate Resolution Imaging Spectrometer (MODIS). The area in the red rectangle from that graphic are shown next in a series, to show the evolution of deforestation from 2000 to 2005 to 2012.
Compare the graphic above with the next one from 2005. Large areas to the upper left and lower center of the 2000 graphic have been developed with roads and clearings, in preparation for farming. Other areas toward the Buritis town center (middle right) have been further cleared.
Areas around some 2005 cleared roads had more trees cleared by 2012, but new development is not as extensive.
As stated above, forestation once again increased in the last several years as ways were found to get around forest preservation law, and after the 2018 election of Jair Bolsonaro to the Brazilian presidency.
Bolsonaro and Accelerated Deforestation
This video tweet from Greenpeace gives a good description of what has happened in the Amazon rain forest since Bolsonaro took office in January 2019.
There are new laws being considered in the Brazilian Congress, prominent among them “The Land Grabbers’ Bill”, which will allow land barons and corporations to use methods of deforestation that had been made illegal under previous land reforms intending to protect the Amazon. This land grab ignores the rights of the indigenous peoples of the area, and will accelerate the decline of the rain forest into single crop agriculture, and after the limited productivity of the soil is used up, range land and savanna.
Climate Change and Deforestation: Drying of the Amazon Basin
Vegetation Is a Moisture Source for 50% of Amazon Precipitation
In general, moisture depends on two sources, soil moisture and water vapor converging into a region by the general atmospheric circulation. Their relative importance varies from place to place on the globe. There are areas of the world that significantly depend on the “exhaling” or evapotranspiration of local vegetation to provide moisture for precipitation. Interestingly, the U.S. Great Plains has been shown, using climate models, to be one of them. But another that has implications both locally and far afield of it is the Amazon rain forest, both because of its vastness and its location straddling the equator.
As things stand, local vegetation is responsible for about half of the precipitation in the Amazon River Basin. It’s been shown in observations that the rainy season initiates before the ocean air reaches the area, through thunderstorms fed by moisture from the local vegetation. Only later does moist ocean air begin to travel inland through the Amazon basin with the onset of the South American monsoon, further augmenting rainy season precipitation. The data suggest that deforestation has delayed the onset of the Amazon rainy season about one month since the 1970s, when deforestation of the Amazon began.
Tropical Ocean Response to Greenhouse Gases Will Dry out the Amazon
But another problem is sea surface temperatures (SSTs). Both the tropical Atlantic and the tropical eastern Pacific are projected to warm up about 2oF from their current levels in climate model projections forced with increasing greenhouse gas concentrations. Additionally, more frequent El Niño events in the Pacific are suggested by climate models. In the current climate, an anomalously warm tropical Atlantic and the El Niño in the tropical eastern Pacific are observed to suppress precipitation in the Amazon. The trends in tropical ocean SSTs forced by global warming will serve to compound the drying of the Amazon from deforestation.
A Tipping Point for the Amazon Rain Forest?
There were several articles published recently regarding the possibility that conditions conducive to resilience of the Amazon rain forecast may be approaching a tipping point beyond which recovery will not be possible without massive amounts of human help. Some of the reasons are discussed next.
Resilience of the Amazon Rain Forest to Environmental Stress Is Decreasing
By using satellite imagery over several decades, scientists can assess how well the rain forest can bounce back from stresses like deforestation, drought, and anomalous warmth. According to a study published in the journal Nature Climate Change, more than 75 percent of the rain forest is losing its ability to bounce back (“resilience”). The vegetation is drier and takes longer to regenerate after a drought, even in the most densely forested areas.
Reduction in resilience could be an early warning sign that the Amazon is nearing its “tipping point,” according to the study’s authors. Between humans destroying large swaths of the forest and the change brought about by that and exacerbated by global warming, we may witness a sudden dieback of trees requiring a substantial wet season and their replacement with trees that are more able to adjust to drought and heat, i.e. savanna vegetation. This transition has already been observed in a study of 100 sites in the Amazon over the period from 2016-2019. The same study has found that the rain forest tree dieback has not been sufficiently compensated by the increase in drought-resistant trees.
What Will Be Lost Without the Amazon Rain Forest
Research of the combined impacts of deforestation and global warming on the Amazon suggest that over half of the rain forest could transition into savanna in mere decades. This in turn would result in reduced biodiversity and shifting regional weather patterns.
On a larger scale, consider that the Amazon has been one of Earth’s most important “carbon sinks,” pulling billions of tons of carbon dioxide from the air and storing it in vegetation. Current data has suggested that the Amazon has now become a carbon source, to the tune of one billion tons of CO2 per year. What are the sources for this CO2?
- Burning to clear land for agriculture and range land
- The loss of vegetation available to absorb CO2, and
- The byproducts of producing cattle for beef, including the cattle itself.
The loss of the Amazon would put limiting temperature rise to 1.5 degrees Celsius (2.7 degrees Fahrenheit) out of reach.
It’s not clear what the tipping point is; it’s possible we are already there if the decline in resilience has reached the point where the trees of the Amazon rain forest die whenever there is a drought, with or without curtailment of deforestation for whatever purpose.
Conclusions
The Amazon rain forest is an important component of the Earth system, providing a important buffer to rapid climate change, because:
- It is a vital sink for the Earth system’s carbon cycle, essential to the mitigation of greenhouse gas emissions.
- If the Amazon rain forest degrades into savanna, it will become a source for CO2 rather a sink, which will increase the pace of global warming.
- It has historically been self-sustaining, with moisture from its vegetation providing half of its annual precipitation.
- Deforestation disrupts this cycle and delays the rainy season, because:
- Fewer trees are available to draw moisture from the soil into the atmosphere to be recycled as precipitation.
- Deforestation disrupts this cycle and delays the rainy season, because:
- Its degradation beyond a “tipping point” will result in the permanent loss of this vital resource.
- Loss of rain forest resilience suggests that this tipping point is imminent, or even already exceeded.
- Such a result will make it all but impossible to keep the mean annual Earth temperature from increasing only 1.5oC above the 20th century value.