The Amazon rainforest is potentially on the cusp of a climatic transformation, moving towards conditions not seen on Earth for tens of millions of years. Recent scientific research suggests the region is approaching a state termed a ‘hypertropical’ climate. This new climate is characterized by increased heat, reduced rainfall, and greater volatility, posing a significant threat of widespread tree mortality and diminishing the Amazon’s crucial role as a global carbon sink.
Scientists involved in the study have issued a stark warning: without substantial reductions in greenhouse gas emissions, the Amazon could experience up to 150 days of ‘hot drought’ annually by the year 2100. These periods are defined by intense dryness exacerbated by extreme heat. Alarmingly, such conditions are projected to occur even during months typically associated with the wet season, such as March, April, and May – a scenario virtually unheard of in the present day.
Uncovering the Amazon’s Breaking Point
The comprehensive study, spearheaded by researchers at the University of California, Berkeley, analyzed over three decades of data. This included measurements of temperature, humidity, soil moisture, and light intensity collected from research plots situated north of Manaus in central Brazil. A key element of the research involved sensors embedded within tree trunks, enabling scientists to directly observe how these trees respond to escalating temperatures and decreasing moisture levels.
During recent El Niño-driven drought events, the research team identified two critical stress points for Amazonian trees:
- Leaf Pore Closure: When soil moisture levels plummeted to approximately one-third of their normal values, a significant number of trees began to close their leaf pores. This physiological response, aimed at conserving water, had a detrimental effect on their ability to absorb carbon dioxide. Carbon dioxide is essential for the trees’ growth, repair, and overall health.
- Sap Embolism: Prolonged exposure to high temperatures led to the formation of bubbles within the trees’ sap. This phenomenon disrupted the vital transport of water throughout the tree, a process researchers likened to an embolism in the human circulatory system – a sudden blockage that can lead to a stroke.
The study found that fast-growing tree species with low wood density were particularly susceptible, exhibiting higher mortality rates compared to trees with denser wood. This suggests that secondary forests, which are characterized by a larger proportion of these fast-growing species and have regenerated naturally after human or natural disturbances, may be more vulnerable to these climatic shifts.
The researchers observed these same warning signs across multiple research sites and during various drought events, indicating a consistent and predictable response of the Amazonian ecosystem to heat and dryness. While annual tree mortality in the Amazon currently hovers just above 1 percent, the researchers estimate this figure could climb to approximately 1.55 percent by 2100. Although seemingly a minor increase, even a half-percentage-point rise across the vast expanse of the Amazon rainforest translates to a substantial loss of trees.
Defining ‘Hypertropical’ and Its Global Significance
The researchers define ‘hypertropical’ regions as those experiencing temperatures hotter than 99 percent of historical tropical climates, coupled with significantly more frequent and intense droughts. Such a climate is unprecedented in modern history and has only been observed in tropical regions during periods of much higher global temperatures, specifically between 10 and 40 million years ago.
In contrast to current tropical zones, which generally maintain relatively stable temperatures and consistent rainfall that supports dense vegetation year-round, a hypertropical climate would usher in extreme heat, prolonged dry spells, and the potential for severe storms. The implications of such a transformation extend far beyond the Amazon basin.
Tropical forests are unparalleled in their capacity to absorb atmospheric carbon. However, when subjected to environmental stress, their carbon uptake diminishes considerably. In particularly dry years, the Amazon has even been observed to release more carbon than it absorbs. As global temperatures continue to rise, any reduction in the Amazon’s carbon storage capability could accelerate worldwide warming and potentially contribute to it.
Recent years have already witnessed severe fire seasons in parts of rainforests, fueled by extreme heat and drought. These fires not only decimate ecosystems but also release vast quantities of stored carbon. The cascading effects observed in the Amazon could easily impact other rainforests globally. The study’s authors emphasize that rainforests in western Africa and Southeast Asia may face similar risks as temperatures climb, with the severity dependent on the pace and scale of global emission reductions.
The future of the Amazon, and indeed other vital ecosystems, hinges on human action. As lead author Jeff Chambers stated, “It all depends on what we do. If we’re just going to emit greenhouse gases as much as we want, without any control, then we’re going to create this hypertropical climate sooner.” The scientific evidence points to a critical juncture, where decisive action on emissions is paramount to averting a profound and potentially irreversible climatic shift in one of Earth’s most vital natural systems.