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Paulo Artaxo

Paulo Artaxo: Physics in service of the planet

Researcher comments on the COP21 agreement and highlights the Amazon’s importance for the global climate

Paulo ArtaxoLéo RamosAn appreciation of all things practical and problems of social importance led São Paulo native Paulo Artaxo to follow an unusual path compared to his professorial colleagues at the Physics Institute at the University of São Paulo (IF-USP). Following a quick flirtation with nuclear physics during his master’s studies in the late 1970s, he turned his efforts toward an area that was then relatively new and only beginning to receive some recognition: the study of environmental problems caused by aerosols—fine particles suspended in the atmosphere—in cities such as São Paulo, and particularly in the Amazon Region. Over time, Artaxo’s research became an international reference on the role these particles play in rain formation and control of solar radiation levels over the immense tropical forest. “Aerosols and greenhouse gases are the key to climate effects caused by man,” says Artaxo, who co-coordinates the FAPESP Research Program on Global Climate Change (RPGCC).

The elevation of climate change to one of the major scientific issues of the 21st century brought Artaxo’s work to the forefront. The nearly 2,000 scientists who made significant contributions to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) shared the Nobel Prize in 2007, along with former U.S. Vice President Al Gore. Among these scientists were Paulo Artaxo and 11 other Brazilians. In more recent years, he has figured among the world’s most influential researchers—the elite 1% of scientists whose papers receive the most citations and have the highest impact rating, according to a survey by the firm Thomson Reuters. In this interview, Artaxo comments on the outcomes of the agreement reached at the Paris Climate Conference (COP21) in December 2015 (see also the report on the agreement), and talks about his career and research.

Physics applied to environmental problems
Undergraduate, Master’s and PhD at the Physics Institute, University of São Paulo (IF-USP). Four postdoctoral appointments (University of Antwerp, Lund University, Harvard University and NASA)
Scientific production
586 scientific papers and over 26,000 citations

What is your overall assessment of the COP21 agreement?
It was without a doubt an excellent beginning for a new era in our global society. For the first time in history, after 21 years of climate conferences, the majority of the 195 countries responsible for 90% of greenhouse gas emissions has set clear goals for reducing emissions. One of the guidelines is to replace fossil fuels with renewable energy. We are faced with an enormous challenge, however. Climate change is already happening, and we will need to make an effort to adapt to the new climate, especially in the less industrialized countries. We will also need a strong scientific effort in order to understand the processes through which change occurs in the various ecosystems and to develop strategies for minimizing the environmental impacts. Our energy production and usage systems will have to be revised to sustainable levels.

Even if the emission reduction goals—the so-called Intended Nationally Determined Contributions (INDCs)—spontaneously adopted by countries under the COP21 agreement are fully met, they are insufficient to ensure a global temperature increase of only 1.5 to 2 degrees Celsius (ºC) by 2100, the objective sought by the signatories. What can be done about this situation?
The Earth’s temperature has already risen 1ºC over that of the preindustrial era. Even if the emission reduction commitments assumed in Paris are honored, the planet is expected to heat up by about 3ºC over the course of this century. This will cause profound and rapid change in the way ecosystems function, and it will have significant socioeconomic impacts. The combined commitments to the INDCs provide for a 40% reduction in global emissions. But we will need a global reduction of 70% to 90% if we really want to limit the temperature increase to 2ºC by the end of this century. This means we will have to cut emissions faster and more extensively. In the meantime, we need a system of global governance to guide implementation of the INDCs in each country. We also have to conduct periodic reviews—right now the reviews are scheduled for every five years—until our planet is able to stabilize the atmospheric concentrations of carbon dioxide (CO2) and reduce them to acceptable levels. This will not be an easy task. The needed reduction will take several decades to implement. In the final analysis, there are economic, social and political issues to be resolved.

Are Brazil’s proposed goals timid or ambitious?
The problem we have to solve is a global one, and it relies on emissions cuts in every country, especially the more industrialized ones. The combined emissions of China and the United States account for over 50% of global emissions. What those countries do will serve as a strategic model for the entire planet. The United States is promising to cut emissions to 27% of its 2005 levels. For comparison purposes, Brazil, for example, is promising a 42% reduction by 2030. The U.S. proposal is very timid. There has to be equity among countries, in both emissions and the pattern of consumption of natural resources across the globe. Everyone will have to make a greater effort than promised up to this point. That includes Brazil, which will have to further reduce deforestation of the Amazon and invest heavily in solar and wind energy, which are abundant in the Northeast.

And what about China, the largest contributor to greenhouse gas emissions today?
China’s industrialization has been relatively recent, and most of its products are exported to other countries. Some of its emissions, therefore, are not properly attributable to China because the consumer goods produced there are sold in the United States, Europe and the rest of the world. U.S. and European manufacturers have set up plants in China to make products for their own markets. So in practice, it’s the more industrialized countries that consume these products, but the emissions are counted as China’s, and that is not really accurate. We have to develop mechanisms to account for emissions more fairly and accurately.

But that logic holds true for any exporting economy, doesn’t it?
Yes. Today we have a global economy, but we don’t have a system of global governance and accountability for greenhouse gas emissions. We’ve globalized the economy, but no other sociopolitical aspect. China’s INDC, for example, offers no pledge to reduce emissions. Its commitment is to increase its CO2 emissions efficiency per unit of GDP growth. In other words, the country’s emissions will continue to grow, but more slowly than the pace of the economy. In practice, countries still industrializing, such as India and China, will continue increasing their emissions to meet people’s legitimate demand for more consumer goods. People in more industrialized countries already use those goods. India is still much further behind in that process than China. At the point when every one of the more than two billion Chinese and Indians wants to have a car in the garage and a house with a microwave, TV and other goods, there will simply not be enough natural resources to sustain that level of consumption. But although it is a crucial issue, the question of equity was not even on the discussion table at COP21. We have to understand that COP21 is only the beginning of a necessary process.

Is stopping illegal deforestation in Brazil feasible?
Brazil has had the greatest success story of any country in reducing greenhouse gas emissions. Through public policy, it reduced deforestation from 27,000 square kilometers (km2) in 2005 to about 5,000 km2 in 2014. In other words, it drastically reduced its emissions. Still, stopping deforestation will be very difficult because it requires new instruments, new legislation and economic incentives. That is an absolutely essential task for Brazil to perform, because it is in our interest to maintain the Amazon biome for future generations. The Amazon forest, left standing as an ecosystem, is invaluable. The worst thing we can do is turn it into carbon dioxide by burning it down.

Let’s change topics. Why did you decide to become a scientist?
Ever since the age of 12 or 13, I realized I had a lot of talent for exact sciences, mathematics, physics and chemistry. In addition, I read a lot and had tremendous curiosity for understanding how our planet works. I was also lucky enough to have good physics teachers in high school, which is rare nowadays. The combination of those factors motivated me to become a scientist.

Why physics?
I wanted to understand nature’s processes, from mechanical questions to broader things like how the Universe works as a whole. I read a lot about physics from the time I was a child. From there to becoming a scientist was a simple step. I graduated from USP and did my master’s in nuclear physics under Professor Iuda Goldman. Then I decided to do something more applicable and of more direct social interest. I started doing research on the environment. First, I worked on processes associated with urban air pollution. In the 1980s, São Paulo had serious air pollution problems, although they were not yet recognized by the public. Later on I started working on understanding processes that govern how the Amazon ecosystem works in an interdisciplinary fashion.

In a tower in the Amazon: forest as research differential

Personal archivesIn a tower in the Amazon: forest as research differentialPersonal archives

At the time, studying climate physics was not an obvious choice. Why did you choose that field?
I was at a very traditional physics institute, working in fields such as nuclear physics, particle physics and solid state physics. Everyone looked half askance at applied physics and my work. They would ask what I was trying to do mixing physics with environmental issues. Happily, I made the right choice. We later showed that physics has much to contribute to our understanding of processes associated with air pollution and global climate change. My research group evolved from being the ugly duckling at the institute to a reference at USP and even in other countries.

You specialize in the study of aerosols. What are these particles?
Atmospheric aerosols are tiny solid or liquid particles that are suspended in the atmosphere, which makes them invisible to the naked eye. In a city like São Paulo, people breathe about 30,000 of these particles per cubic centimeter of air. Aerosols, which are a component in air pollution, are deposited in the lungs and can cause cardiorespiratory illnesses and other health problems. In the Amazon, aerosol particles are very important for the basic operation of the ecosystem. Clouds do not form from water vapor alone. They need vapor and a particle that is hygroscopic, that is, having affinity with water—an aerosol. Vapor is deposited onto the particle and forms a cloud droplet. The cloud develops, and eventually it rains. Understanding these physical and chemical processes is an important challenge for climate science.

Does this process of cloud formation and development hold true for cities?
Yes, it’s a universal mechanism. In São Paulo, aerosols come from industrial smokestacks and automobile exhaust, to name two sources. The black smoke put out by bus and truck diesel engines consists of particles in very high concentrations. Aerosols have two important properties that affect climate. First, they intercept and reflect solar radiation, which affects the radiation balance and alters the amount of sunlight that reaches the ground. Second, they are absolutely essential for cloud formation. Without clouds, there is no rain. And without rain, there is no agriculture. Aerosols and greenhouse gases are, in fact, the key to climate effects caused by man. The curious thing is that, in the Amazon, the biological life of the forest controls the concentration of these particles in the atmosphere and determines the regional climate. That was one of the discoveries in our research.

How so?
In the Amazon, we noted that plants were the principal source of the aerosols that control cloud formation and the radiation balance over the forest. They emit volatile organic compounds, such as terpene gases and isoprene, that are converted into aerosol particles. Other constituents of these particles include leaf fragments, pollen grains, bacteria, fungi, and ashes from burning. In other words, the vegetation itself controls the climate over the forest. It governs rainfall and the radiation balance by emitting aerosols. The forest also processes water vapor, which is the second key ingredient in clouds. Understanding these biological, physical and chemical processes is fascinating business.

Have you worked on aerosols since your PhD?
Yes, I’ve worked on aerosols in climate, particularly in the Amazon. In the 1980s, this was completely novel. I was lucky to have Professor Paul Crutzen, a Nobel Prize winner in chemistry [1995], working with me during my doctoral studies. I participated in the first major experiment in the Amazon in 1979, called Brushfire. It was led by Professor Crutzen, who was researching the effect of fires on the regional climate. He had an idea, not yet well-established at the time, that the emissions in the Amazon could affect global climate. The question really fascinated me, and motivated me to try to understand the integration of the biological, physical and chemical processes that control the overall functioning of the Amazon. As innovative results were being produced, important new questions arose.

Why did you become interested in studying aerosols in particular?
In the 1970s, research on pollution looked almost exclusively into the gas component, such as the photochemistry of ozone and its effects on plants and human health. In the scientific community, no one was talking about atmospheric aerosols. But I realized there was very important science behind these particles, and I devoted myself to discovering that role.

What brought you to do four postdoctoral stints abroad?
Early in my career I realized that in areas associated with the environment and global climate change, it makes no sense to work in isolation. Strong international partnerships are absolutely necessary and play a strategic role. So, three months after finishing my PhD, as a professor on the staff of USP, I went to the University of Antwerp, where I spent two years working. I learned a lot there. Then I spent two more years at Lund University and Stockholm University, both in Sweden. After that, I realized I had to learn remote sensing techniques and how to use satellite environmental measurements. I then went to NASA and worked there, from 1993 to 1994. More recently, I worked at Harvard University in 2008, collaborating with good researchers who study the balance between carbon and aerosols. I’ve maintained strong international partnerships for more than 25 years.

How does the climate of the Amazon affect the climate in the rest of the country and the world?
The forest is a gigantic processor of water vapor. The forest converts the water through biological mechanisms—a process that is very intensive and important for maintaining the regional and global climate. Looking at the regional picture, 60% to 70% of the water vapor that reaches central South America originates in the tropical Atlantic and is transported to and processed by the Amazon. This water vapor transport influences rainfall in southern South America. From a global perspective, since the Amazon is in a tropical region, it is subject to strong convective processes. Ascending air masses draw the water vapor from the surface and bring it up to high altitudes, where it is efficiently transported to the temperate regions of our planet. So the Amazon and the Pacific Ocean are the two main sources of moisture for the global climate. Besides being an important greenhouse gas, water vapor is essential for cloud formation and for controlling the radiation balance and precipitation.

Artaxo receiving an honorary doctorate from Stockholm University in 2011: partnerships abroad

Personal archivesArtaxo receiving an honorary doctorate from Stockholm University in 2011: partnerships abroadPersonal archives

Can the recent drought in São Paulo be associated with the deforestation of the Amazon?
Not as an exclusive factor. And the reason is simple. On average, about 30% of the water vapor that reaches the city of São Paulo comes from cold fronts in southern Brazil. Another 30% comes from the South Atlantic by way of maritime winds. São Paulo is, after all, near the coast. About 40% of the moisture in the city comes from the North. Up to this point, Brazil has deforested about 19% of the original area of the Amazon. This means that if only 40% of the water vapor here in the Southeast comes from the Amazon, and if no more than 20% of the water vapor processed by the forest is affected, a 7% or 8% reduction of moisture in São Paulo could be attributed to deforestation of the Amazon, under the worst-case scenario. The processes are not linear, but this very simple calculation shows that it is impossible, from a climatological standpoint, to attribute the drought in São Paulo directly to deforestation of the Amazon. According to the latest analyses, the situation in São Paulo was due to very dry, abnormally stationary air masses over the Southeast—a phenomenon that is not yet understood by meteorologists. It goes without saying that lack of preparation for dealing with climate anomalies and lack of medium- and long-range planning also contributed to the water crisis in that region.

Is it certain that extreme events such as major droughts and heavy rainfall are linked to climate change?
The increased frequency of extreme climate events is statistically linked to climate change. The reason is simple. When you inject more energy into the climate system—which is what is happening now with higher concentrations of greenhouse gases—that energy has to be dissipated in some way. The atmosphere is accumulating much more heat than it did 200 years ago. This raises the frequency of extreme events, regionally and across the globe. We’re also observing small-scale changes, such as the rainfall in the city of São Paulo. In the 1950s, São Paulo was the city of drizzle. Now it’s the city of big storms. Now, when it rains, it rains heavily and causes socioeconomic damage. But the question remains: Is this due to climate change or not? We still don’t have a direct, conclusive answer. But the answer will probably come when we have accumulated more solid, long-range information. In the case of the Amazon, the droughts of 2005 and 2010 cannot be unequivocally associated with global climate change. We can say confidently that these droughts were the largest in the past 100 years and that they occurred in a very short time interval—probably caused by climate change as we’ve been saying.

What is it like to do research with colleagues with different backgrounds?
Doing interdisciplinary research is harder than researching in a single field. We’re learning something the entire time. As an example, I have to understand the effect of radiation on the Amazon ecosystem, I have to study photosynthesis, how the stomata in a leaf open to let in atmospheric CO2 and how the flow of radiation affects this process. The important thing is to understand that in nature, processes occur simultaneously, and things are not divided into physics, chemistry and biology like at the university. Early in my career, I understood the interdisciplinary question, so my first postdoctoral appointment was in the chemistry department at the University of Antwerp. In my research, I have to look at the planet through an interdisciplinary lens in all of its dimensions.

How is it that you became one of the world’s most cited Brazilian researchers?
I never thought my scientific career would have that kind of repercussion. I coordinate many projects, I publish a lot, I advise a lot of students. The scientific community engages in dialogue through publications and conferences. I followed that model of having strong international partnerships, and I don’t have a single scientific paper without contributions from researchers in other countries. That results in international visibility, but the importance of the work, especially on the Amazon, also stimulates citations. The Amazon is an ecosystem for which the research is recent and full of important new developments. Another point is that practically all the articles I’ve published are interdisciplinary. My citations come from different audiences in more than one subject area. I have 11 papers in Science and Nature, which few scientists in other countries have achieved. From that standpoint, I’ve been very lucky. It shows the dynamic nature of Brazilian science. Brazil is one of the most important partners in science today on a global level, and not just in environmental science. With the current economic crisis, it’s not very clear how we’re going to maintain that leadership in the coming years, but we have to find a solution. The research we did on the Amazon was extremely important for the outcomes of the IPCC. Some cloud processes occur only in very clean environments like the Amazon—processes we discovered through measurements taken in large-scale experiments in that region. There is no way to study natural processes in clean environments in the United States, Europe or Asia, where air pollution has entered the picture. We need to use the strategic advantages Brazil has in the scientific realm.

What research are you working on now?
I’m juggling several projects, the main one being the Green Ocean Amazon (GOAmazon) program. We’re studying the impact that an urban center like Manaus, with a population of two million, has on the surrounding atmospheric properties. We want to know how the pollution generated by Manaus interacts with the natural forest emissions. Manaus is unique in the world; the situation exists only in the Amazon. There is no other large city that is isolated in every direction by 1,500 kilometers of forest. So the question arises: How do the gases and aerosols produced by automobiles in Manaus interact with the aerosols from the forest, and what are the effects of this type of pollution on the ecosystem? That is the central theme of the GOAmazon experiment, which involves more than 250 scientists in Brazil, the United States and Europe.

Has GOAmazon already produced new data?
The pollution from Manaus has a very large impact on the functioning of the Amazon ecosystem. Nitrogen oxide emissions from combustion processes in the city, such as those put out by automobiles and the power plants that supply Manaus, interact with the volatile organic compounds that vegetation emits, and produce ozone. We found ozone concentrations coming from Manaus that were similar to those from the city of São Paulo—over 40 parts per billion, which is the level at which ozone starts becoming toxic to plants. The natural ozone concentrations in the Amazon are 8 to 10 parts per billion at mid-day. When these concentrations become high, the stomata do not open, which enables plants to avoid tissue damage. But in so doing, plants carry out less photosynthesis, fix less carbon and have a substantial decline in growth rate. That is a direct effect of urban pollution on the carbon cycle of the Amazon forest. The effect appears hundreds of kilometers downwind from Manaus. These data are important for Brazil. The Amazon absorbs approximately half a metric ton of carbon per hectare per year. Because the forest area is so enormous, this has a huge impact on the global carbon cycle. If the Amazon loses a percentage of its capacity to store carbon, the greenhouse gas effect is exacerbated. We need to understand the factors that influence the carbon cycle in the Amazon. In GOAmazon we’re also observing major changes in the properties of clouds influenced by the Manaus pollution plume, as compared to “clean” clouds. This has a dramatic effect on the hydrologic cycle.