"Around the Amazon River, and specifically in its central section, there is a series of extremely unique forest and aquatic ecosystems that maintain a continuous interdependence with the river and are still only superficially understood. The river is also a transport route between isolated human populations along its course and defines a way of life. Among the relevant ecosystems are large, shallow lakes, the result of the river's own geomorphological dynamics, which are the focus of the study. The study details the trend of warming waters over decades and extreme fluctuations during a period of drought, when water temperatures reached over 40 degrees, a phenomenon without precedent even in the tropics. This extreme situation dramatically affected aquatic life and human activities, with the death of hundreds of pink dolphins, characteristic of these waters, being particularly striking.

The study combines intensive measurements during the drought episode, decades of monitoring data, which are essential for identifying trends, satellite information to assess the extent, and explanatory models of the physical processes associated with the observations. This provides an accurate description of what happened and a convincing analysis of the relevant processes, among which the importance of low wind speeds stands out as a necessary factor in reaching the thermal peaks observed in the water. This understanding of the physical processes will be fundamental to understanding and predicting the biological consequences of these large climatic fluctuations, although the study only speculates partially on them, due to a lack of adequate data.

In general terms, climate change predictions include long-term trends for certain meteorological variables and also highlight that these trends will be accompanied by an increase in the magnitude of fluctuations and the frequency of extreme events. These predictions are gradually materialising in a very concrete way in many parts of the planet and, in some cases, dramatically for the ecosystems and populations of the affected areas, as in this case study in a region as unique and emblematic as the Amazon. It would be desirable for the publication of the study to coincide with COP30, which is being held in Belém at the gateway to the Amazon, to reinforce the conviction and determination of the body responsible for taking the necessary decisions to implement the commitments made by countries in the fight against climate change.

Is the study of good quality?

‘The study very conclusively combines information from high-frequency measurements during the drought event with decades of temperature measurements in some lakes, satellite information and analysis of the processes using mathematical models of physical dynamics. This multiple and complementary approach allows us to reach robust and convincing conclusions about the specific causes of some exceptional episodes, such as the very high water temperatures reached.’

What are the implications and how does it fit in with existing evidence?

"Year after year, if not month after month, we are witnessing extreme weather events across the planet. That the Amazon is being affected so dramatically is perhaps no longer surprising. Climate change predictions already indicated a general increase in the frequency of extreme events over the long term. The study is particularly valuable because it describes an extreme phenomenon in an emblematic and unique ecoregion of the planet, but it also demonstrates the importance of thoroughly analysing data through the prism of existing theoretical knowledge to identify the relevant processes underlying the observed patterns. In this case, a set of meteorological conditions (drought, high air temperatures, low wind) led to an exceptional and dramatic situation in the ecosystems, evidenced by the death of fish and hundreds of pink dolphins.

Are there any limitations to be taken into account?

The study itself points to the difficulty of understanding the biological and ecological consequences of the physical phenomena observed, beyond the verification of certain facts. For example, why the dolphins did not seek refuge early enough in cooler waters that they could presumably access.

Its publication coincides with COP30, which starts on Monday in Belém, at the gateway to the Amazon. Will it serve as a wake-up call about the effects of climate change?

‘It would be desirable for the publication of the study to coincide with COP30 to reinforce the conviction and determination of the body responsible for taking the necessary decisions to implement the commitments made by countries in the fight against climate change. The wake-up calls are piling up, this is just one more, but it is set in an emblematic location on the planet. Let us hope that its proximity will encourage decision-making in the desired direction and manner.’

EN