Climate observation at high level - Amazon Tall Tower Observatory (ATTO)

In the first research phase (also known as the pilot phase) from 2017 to 2021, scientifically and socially relevant results were achieved and a total of 55 scientific publications were published in well-respected international scientific journals.
New findings from ATTO research include, for example:

• In the forests of the central Amazon region, 60 per cent of precipitation is returned to the atmosphere, with the majority being brought into the atmosphere by the transpiration of trees.
• A study analysing satellite data and ground-based methane measurements (including measurement data from ATTO) shows an increase in methane emissions from the Amazon since 2014, which most likely contributes to a global methane increase.
• The Amazon makes up only about four per cent of the land surface, but is responsible for about 25 to 40 per cent of global emissions of biogenic volatile organic compounds (BVOCs), such as those emitted by trees, into the atmosphere.
• The study of the pristine atmosphere around ATTO during the rainy season has provided the first insights into how human-induced climate change has fundamentally altered aerosols and possibly cloud properties and precipitation in the Amazon.
• ATTO researchers have found that long-range transport of Saharan dust and smoke from African savannah fires affect the nutrients and sunlight reaching the forest.

In the ATTOplus research phase from 2021 to early 2025, the ATTO team was able to gain the following insights in collaboration with Brazilian researchers:

(1) The Amazon rainforest: source or sink for greenhouse gases?

One of the most important questions for climate research in the Amazon rainforest is: Is the Amazon rainforest still a global sink for carbon dioxide (CO2) or can it no longer fulfill this function due to climate change, increasing emissions, slash-and-burn as well as drought?

Researchers are working to answer these questions with the help of digital climate models. However, many of the climate models have not yet been able to reproduce the seasonal cycles of the Amazon rainforest with its highly complex absorption and release of greenhouse gases with sufficient precision. ATTO researchers have therefore collected new data series at the ATTO measuring tower and used them to develop a regional inversion model.

Among other things, atmospheric CO2 signals were used to improve the land surface models. It has now been shown that the Amazon rainforest – despite major regional differences – still represents a sink for atmospheric CO2.

(2) On average, carbon remains in the biomass of the Amazon rainforest for only ten years

Plants in general, and the trees of the Amazon rainforest in particular, absorb carbon from the atmosphere in the form of CO2 through photosynthesis. So ATTO researchers have investigated how long this carbon remains in the biosphere, or in the soil, before it is released back into the atmosphere through respiration and decomposition processes.

The researchers were able to demonstrate the following processes: A large proportion of the CO2 circulates through the ecosystem within days to weeks, so in fact it is not stored long-term at all.

Another part is used for the production of short-lived plant material, such as leaves. This is released again after a few months to years through the decomposition of dead plant parts.

Only a smaller proportion of the carbon is used for the production of long-lived plant material, such as stems and roots, or is released into the soil where it is stored long-term as mineral carbon.

On average, all these areas result in a retention time for carbon in the Amazon forests of only around ten years (see also ATTO educational materials). This is a shorter duration than previously assumed and is therefore of great importance when considering the Amazon rainforest as a carbon sink.

(3) Storms are central to gas flows, biodiversity and carbon storage

Several meteorological studies have shown that weather events, such as storms, have a major influence on gas flows in and above the Amazon rainforest. They influence the mixing of the air layers and can thus ensure that gases or aerosols are transported from very high atmospheric layers to lower ones, where they are relevant for cloud formation, among other things. At the same time, they also ensure that gases and particles that are transported by the forest itself reach higher atmospheric layers, where they can influence atmospheric chemistry and thus also the weather and climate.

Based on a new study, ATTO researchers can now prove that the number of major storm damages in the entire Amazon basin – so-called windthrow events – quadrupled in the period under investigation from 1985 to 2020. This is partly due to the increase in severe storms as a result of climate change.

After storm damage, the regrowing plant species often differ significantly from the previous composition: they are less diverse and often store less carbon. A complete recovery after devastation caused by storms often takes several decades.

(4) Some of the aerosols detected at the ATTO measuring tower come from great distances

Some of the aerosols measured in the atmosphere at the ATTO tower have traveled very long distances: For example, they originate from the continent of Africa, over 10,000 kilometers away. In addition to the already known inputs of Saharan dust, ATTO researchers were also able to detect soot particles produced by African bush fires. At times, more than half of the particles around ATTO came from Africa. This shows just how global the atmosphere is, as natural events on other continents can influence the natural productivity of the rainforest (through nutrient input), atmospheric circulation and precipitation (through cloud formation), as can human activities such as slash-and-burn agriculture, right up to the Amazon region.

Research Analyses of aerosols within the framework of ATTO were also able to detect PFAS (per- and polyfluorinated alkyl compounds), so-called perpetual chemicals. The particles have most likely reached the Amazon region through atmospheric transport from large cities such as Manaus over long distances, proving that the Amazon is no longer an untouched natural area of the earth.

(5) Mosses and lichens are as relevant as trees

It has long been known that trees produce volatile gases, so-called biogenic volatile organic compounds (BVOCs). These play a major role in the chemistry of the atmosphere, as they can be converted into cloud condensation nuclei. The Amazon rainforest is a very large producer of the most important group of BVOCs, the isoprenes.

ATTO researchers have now discovered that mosses and lichens also produce BVOCs. In tropical rainforests, mosses and lichens are omnipresent and grow on every conceivable surface. Due to their large numbers, the amount of BVOCs they release is comparable to that of trees. These BVOCs from mosses and lichens also influence the atmospheric composition and have an impact on air quality, climate and ecosystem processes. Until now, digital atmospheric and climate models had not taken mosses and lichens into account

Detailed information on ATTO research can be found on the research infrastructure website: https://www.attoproject.org/de/

The third ATTO research project was launched in May 2025: ATTOsynthesis. The German project partners will receive around five million euros in funding from the BMFTR until 2028.

The participating institutions from Germany are the Max Planck Institute for Biogeochemistry in Jena (MPI-BGC), the Max Planck Institute for Chemistry in Mainz (MPI-C), the Karlsruhe Institute of Technology (KIT) and the University of Mainz. On the Brazilian side, a large number of research institutes and universities are involved as cooperation partners, coordinated by the owner of the tower, the Amazon Research Institute INPA (Instituto Nacional de Pesquisas da Amazônia). These also include the University of São Paulo and the National Institute for Space Research in Brazil (INPE).

The ATTO tower was already equipped with numerous measuring instruments during the construction and pilot phase. Fundamental series of measurements have been started and new findings evaluated.

The ATTOsynthesis funding project will now help to intensify German-Brazilian research and cooperation in order to prepare the ATTO research infrastructure for broader scientific use. This will also facilitate networking and synergies with other internationally established research infrastructures such as ACTRIS and ICOS.

With the help of the measurements on the tower, the carbon dioxide released and stored by the forest can be quantified. This allows reliable conclusions to be drawn about the rainforest as a carbon source or sink. This measurement data is of enormous importance in order to be able to make more precise statements on climate development.

Furthermore, measurements of aerosols on the tower provide insights into the processes that lead to cloud formation and therefore play a major role in the water cycle. For example, the scientific understanding of the significance of the "flying rivers" in the Amazon can be deepened. These are large masses of water that evaporate from the humid forest and can thus transport the water further afield in the form of clouds.

Overall, however, the Amazon rainforest is already severely affected by climate change and ongoing deforestation. The investigations at ATTO therefore also serve to develop an understanding of the "tipping points" – the tipping points of the global climate system - and to make predictions about how resilient the Amazon forest is and what impact human activities and climate change have on this important ecosystem.

The Amazon region is one of the most important regions for the global climate system, as it is the largest water and CO2 reservoir on earth. It therefore influences the overall stability of the Earth system and its global carbon cycles. Due to its chemical and physical processes in the atmosphere, the Amazon makes an important contribution as a regulator of the global climate. The gigantic evaporation from its forests creates clouds and currents that cool and influence the entire climate. Changes to this system therefore have a global impact.

A location was deliberately chosen for the ATTO research infrastructure where the influence of humans would hardly be felt. Located far from the nearest major city, Manaus, ATTO's central location in the Amazon region offers unique opportunities for climate, atmospheric and ecosystem research. The air over the central Amazon basin is the cleanest in the world during the rainy season. Here, the interaction between forest and atmosphere can be studied under conditions close to those of pre-industrial times. Due to its altitude, the ATTO measurements can record processes within a radius of several hundred square kilometres and thus cover a large part of the Amazon basin. This means that the effects of climate change and the influence of humans on one of the most unspoilt areas of the world can be researched particularly well.