C2GTalk: An interview with Paulo Artaxo, Professor at the Institute of Physics at the University of São Paulo, Brazil

How will global warming impact society, both economically and socially?

6 February 2023

How should the world protect the Amazon forest, and why?

What is the impact of aerosols on the global temperature?

What is the state of science about stratospheric aerosol injection?

Could research on solar radiation modification cause a delay in emissions cuts?

What role should the Global South play in researching solar radiation modification?

What are the challenges climate scientists face in the Global South?

This interview was recorded on 13 December 2022 and is also available with interpretation into 中文, Español and Français.

Research on solar radiation modification is needed, especially in the Global South, to understand whether it could be an option for reducing climate risk, said Professor Paulo Artaxo during a C2GTalk. The planet is currently headed for 3°C global warming, yet the world is still not doing enough to phase out fossil fuels and net zero goals look extremely difficult to achieve.

Paulo Artaxo is a professor at the Institute of Physics at the University of São Paulo, Brazil. He is a member of the IPCC – UN Intergovernmental Panel on Climate Change. He has developed his career working with the Amazon environment and global climate change. He is a member of the Brazilian Academy of Sciences (ABC), and the World Academy of Sciences (TWAS). He is vice president of the Academy of Sciences of the State of São Paulo (ACIESP). He is also vice president of The Brazilian Society for the Advancement of Sciences (SBPC). He received several awards, including the Almirante Álvaro Alberto award in 2016 and the TWAS Earth Science Prize. He received the Doctorate Honoris Causa from the University of Stockholm, Sweden. He was included in the Clarivate Analytics list as belonging to the top 1% of the most cited researchers worldwide in 2014, 2015, 2018, 2019, and 2020.

Below are edited highlights from the full C2GTalk interview shown in the video above. Some answers have been edited for brevity and clarity.

You recently attended the Conference of the Parties 27 (COP 27) climate summit, I understand.  Commentators have welcomed a deal on loss and damage there but expressed quite a lot of disappointment at the lack of strengthened commitments to reduce CO2 emissions.  How would you describe the outcome of that meeting and basically the state of climate diplomacy right now? 

I was the whole time during COP 27 in Sharm el-Sheikh, and basically everyone who left the meeting was very disappointed.  Let’s say this: I cannot find a single person who left the meeting with optimism for several reasons.   

The first one is that the final official communication documents from COP 27 do not even mention that we have to phase out fossil fuels.  It does not mention a clear mechanism for loss and damage, as you mentioned, and it does not make any significant contribution or reduction of greenhouse gas emissions.   

So basically, we are going to a planet that is about 3°C hotter.  This will bring tremendous impacts on our society, both economically and also socially, and certainly we are on the wrong track here to build up a sustainable society.  That was the reason for my disappointment after COP 27. 

What makes you think that we are heading for 3°C at the moment? 

Actually, it is not me who thinks that.   

Nature did an interview with hundreds of climate modelers just after the Sixth Assessment Report from IPCC was released, and there is an update from Nature in November 2021.  Nature asked a single question to hundreds of climate scientists: “Which is your best guess of how much will be the increase in temperature along this century?” 

Ofcourse the answers varied significantly between 2°C to 4.5°C, and the average result was 3°C.  Actually, if you fulfill all the Paris Agreement expected reductions in greenhouse gas emissions, we will heat up the planet by 2.6°C, but as we know very well most of the countries will not fulfill their commitments on the (NDC) nationally determined contributions associated into the Paris Agreement. 

So basically, we are going to an average of 3°C in continental areas.  That means an increase of about 4°C to 4.2°C in cities, where 80 percent of the population will be living in 2050.  With an increase in the urban heat island this means an increase in temperature somewhere between 4.5°C to 5°C.  This is what our economic system is driving the planet to right now, and certainly we need clear action to avoid this kind of scenario.  

One bit of progress that people sometimes point to is that a growing number of countries have committed themselves to net zero by a certain year.  Is that actually possible? 

That is a very good point.  For instance, the European Union wants to become net zero in 2035, the United States in 2040, Brazil in 2050, China in 2060, and India in 2070. 

The problem is that right now production of food is responsible for 30 percent of global greenhouse gas emissions.  With a growing population and billions of people who have very little food in developing countries, the demand for food will increase.  Right now we have 30 percent of the emissions from food chain production. 

How are we going to mitigate this?  How are we going to compensate for 30 percent of the total greenhouse gas emissions today?  That is in my opinion basically an impossible task. 

Food production is the major challenge we will have in terms of reducing emissions.  We can change the energy system to stop burning fossil fuels.  That is easy.  We have the technology for that.  That is economically feasible in the next few decades, but the major challenge is actually food production for a growing, 10 billion people in 2050.  We can try to reduce emissions, but it will be extremely difficult to get to net zero as committed in the national determined contributions for most of the countries by 2030, 2050, or 2070.  This for me is a major challenge for our society.  

I understand you are recently back from Amazonia.  One of the few highlights I guess of COP 27, at least from the reporting that I covered, was the speech by Brazilian President-Elect Lula, who said Brazil is back and committed to ending the destruction of the Amazon.  At the same time, we saw a warning from the World Wildlife Fund saying it is on the brink of a tipping point, becoming permanently degraded, and as far as I read the Amazon has already become a net carbon emitter since 2016 or so. 

Perhaps you could just summarize.  How serious is the situation facing the Amazon right now, and what consequences would its continued destruction have for the global climate? 

A few weeks ago the Brazilian government released deforestation numbers for 2021 to 2022, and Brazil had deforested an additional 11,300 km2 of primary forest.  So a huge amount of carbon is being released into the atmosphere without any benefit for Brazilian or global society. 

Of course the very first task that Brazil has to do is to get to zero deforestation as quickly as possible.  The commitment from the new government, which will take office on January 1st, is for zero deforestation by 2028.  This is possible, and there is no cheaper, easier, or faster way to reduce greenhouse gas emissions than stopping deforestation. 

Another important advancement is the joint effort between Brazil, Indonesia, and Congo signing an agreement to jointly reduce tropical deforestation because of course it is essential to stop deforestation in all tropical countries and not just in Amazonia.  But — and there is a very important “but” — the problem is that the Amazonian forest, because of increasing temperature, is suffering very important degradation and is starting to lose carbon to the global atmosphere. 

Why is this important?  Because Amazonia itself, only the Brazilian Amazonia, holds 120 billion tons of carbon in the ecosystem.  This is roughly ten years of all fossil fuels burning on the whole planet.  If a fraction of this carbon goes to the atmosphere due to the increase in temperature and the reduction in precipitation in Amazonia, then bye-bye to all of us. 

Basically in addition to stopping deforestation it is absolutely essential to stop the burning of fossil fuels.  Even if Brazil lowers deforestation by 2028 to zero and if the developed countries continue to burn fossil fuels, Amazonia and all the other tropical forests do not have a future, and the carbon that is stored in this critical ecosystem will be released into the atmosphere, aggravating the climate emergency that we have right now.  This is clearly the scenario I see in terms of global carbon emissions.  

Is there any way of helping to protect the Amazon from that temperature increase?  Are there forest management techniques that can avoid permanent degradation?  

Mark, the only way to protect the forest in addition to zero deforestation is to reduce the greenhouse gas emissions because if you allow the global temperature to increase by 3°C, in Amazonia, a continental region, the increase in temperature will be about 4°C.  What happens is that the enzymes that control the photosynthetic process in Amazonian plants have evolved over the last million years to a certain temperature, so they are all optimized to make photosynthesis in a certain temperature.  If you increase this temperature by three or four degrees, the enzymes do not work properly anymore as they were designed to do, and then we will have a reduction in photosynthesis, and the carbon will go to the atmosphere. 

This is a process that has already started.  It is not forecast for the future.  Several recent studies using remote-sensing techniques or using in situ measurements using aircraft in Amazonia show clearly that parts of the Amazon forest are already becoming a source of carbon to the global atmosphere due to increasing temperature and reduction of precipitation in the Amazon region caused by global warming. 

I wonder if we could switch to another of your areas of expertise, aerosols and air pollution and their impact on the climate.  It is one of those aspects that is not probably widely known, the masking effect that aerosols have on the temperature.  Perhaps you could explain a little bit to what extent pollution other aerosols are and how much they are masking global warming and what kind of impact we might see from efforts to reduce air pollution. 

What is the impact of aerosols on the global temperature? 

That is a very important issue. In the atmosphere you have three main ingredients.  The first one is the trace gases — oxygen, nitrogen, and the greenhouse gases like CO2, methane, ozone, and so on.  The second component is aerosol particles, particles that are suspended in the atmosphere.  The third component is clouds. 

Aerosols are small particles that have a size similar to the wavelength of visible light, so they scatter radiation back into space, making a huge benefit to the climate system of cooling down the surface temperature, scattering back radiation into space and not letting the extra radiation reach the ground and increase our temperature.  Right now the IPCC report from Working Group One estimates that globally aerosols are responsible for cooling down the planet by one-third of the amount that is being heated up by greenhouse gases, and that is a very important issue, first because the aerosol particles have a very short lifetime in the atmosphere of a few days to a few weeks, so any change in the aerosol particles reflects very rapidly to the global temperature.  Instead greenhouse gases like CO2 have a lifetime of several thousand years, and methane has a lifetime of about 11 years, but the aerosols have a very short lifetime. 

This means that aerosols right now are masking one-third of the heat caused by greenhouse gases, and if you clean up our cities — for instance, changing our transportation fleet from burning diesel or gasoline, which produces a lot of particles to the atmosphere, by electrical vehicles we will strongly reduce in urban areas the amount of particles.  If you change the energy system from burning coal or oil by, let’s say, aeolic or photovoltaic electricity generation we will also emit much fewer particles.  What this means is that in the next few decades we will see that the masking effects of aerosol will be strongly reduced, and this will accelerate global warming.  That is another important issue in the global climate change arena.  

It was this issue, if I understand correctly, that inspired the famous Nobel Prize-winning scientist Paul Crutzen, who coined the term “Anthropocene,” to suggest in an article on climate change that you could introduce I guess artificially aerosols into the stratosphere to counter that effect of cleaning up aerosols lower down. 

This idea has gained increasing attention of late.  Stratospheric aerosol injection may even be finding itself more in the spotlight given the lack of sufficient progress on emission cuts.  In October the U.S. White House announced it was funding a five-year research plan to look at solar radiation management (SRM), or as the IPCC calls it, solar radiation modification. 

Just to take a step back, what do you see as the current state of scientific knowledge about this potential technology, its risks, costs, and benefits?  Where are we in our learning process about this idea? 

Basically science is looking for ways to give options to the society to deal with the extreme danger of climate change if we do not reduce greenhouse gas emissions.  The science of the interactions between aerosols in the stratosphere with solar radiation is still in its infancy, so we know actually very little of the physics of the interactions between aerosols and radiation in the upper atmosphere, and there are a lot of new experiments designed to study better this effect. 

These experiments are very important in case we fail to reduce emissions and we wind up in a climate emergency that could destroy the Earth’s ecosystems like the tropical forests and like the ice on the icecaps both in the Arctic and Antarctic, and science has to provide the society with possible options, and one of them is solar radiation modification. 

At the same time that you need to understand better the process we also need to understand better the undesirable effects of such techniques.  They can also be dangerous to the climate system, and we need to study better the possible impacts from physical, biological, and chemical points of view.  

I guess those impacts would vary in their expression at local and regional levels.  You can have a global temperature impact and then varying impacts at the local level. 

As people start to consider and do science on this but also as policymakers start to engage on it, a key question is how to assess risk and how to measure the risks of SRM and pit them against the risks of a warmer world without SRM.  How does one actually go about doing that in practice?  It seems an extremely difficult assessment to make.  What does one do? 

Yes, you are right.   

It is an extremely difficult assessment to do.  I remember two decades ago James Lovelock, the person who elaborated the Gaia hypothesis, saw the danger of allowing the planet to heat up by 3°C to 4°C degrees was so big that he was defending building up let’s say hundreds of nuclear power plants worldwide to avoid a catastrophic failure of the global ecosystem.  Of course nuclear energy has its own problems with proliferation and with residuals from nuclear reactors, but this is just to give an idea of the kinds of options that some people were thinking about actually 20 years ago. 

Now the situation is even more dangerous for the whole society.  We are not reducing emissions.  The governments are completely controlled by the energy and fossil fuel industries that do not want to reduce emissions, even if it puts 8 billion people and all the life on our planet in a very difficult situation right in the next decade. 

We are not talking anymore about climate change at the end of this century.  Actually climate change is already with us right now, increasing climate extremes enormously and bringing important societal impacts for both developed and also developing countries right now.  So the balance between action and the impacts is a very delicate issue that needs to be better discussed by the whole society.  

One common objection or concern put out there is that pursuing this research — and then eventually questions about potential deployment — could undermine efforts to cut and remove emissions, the so-called “moral hazard.”  What are your views on that concern? 

There is no question that any action that could delay the ending of fossil fuels is actually very bad for the whole planet.  The only way that you can avoid a catastrophic failure of the Earth’s ecosystem is basically to change the whole society to clean energy generation, less consumption, and many other systemic changes that you have to do very urgently. 

Actually science has warned society since the Stockholm Conference in 1972, fifty years ago Science is warning society  “Uh oh, you are going in the wrong direction.  This is not building up sustainability on our planet.  You are tracking to a very dangerous situation.” 

Then there was the Rio 1992 Conference that was actually already 30 years ago.  The same message was that, and then we have had 27 COPs so far with absolutely no reduction in terms of global emissions.  Global emissions are still going up this year by 1.2 percent according to the Global Carbon Project instead of being reduced by 7 percent a year as required by the IPCC 1.5°C report.  So basically society, driven by the fossil fuel industry and the deforestation industry, is going in the wrong direction unfortunately. 

That is happening with or without, as it were, discussion or research in SRM.  Do you think that doing research and discussing SRM makes it less likely as the moral hazard argument goes that the necessary reductions are taken or is it not effective at all? 

I think that just doing research and not starting doing deployment are completely different things.  Doing research on possible ways on how the society could get rid of this dangerous situation does not directly of course impact in terms of fossil fuel emissions.  I think that doing research, increasing knowledge for society on possible options for the next generation, does no harm in terms of fossil fuel emissions because actually in my opinion any of the solar radiation modification strategies could have also perceived dangerous environmental consequences, but these need to be quantified, these need to be properly studied, and this is what you have to do right now. 

Another critique which some people hold strongly is that SRM is a “techno fix” to a problem that is actually rooted in unsustainable human behavior and falling out of sync with nature.  There is a critique that says you don’t start messing with nature and why are we looking at this. 

You have an interest in SRM.  You also have a great interest in nature.  How do you see the relationship between this kind of technology and a respect for nature?  Can these two be held at the same time? 

No question that in the ideal situation we would not even think about solar radiation modification.  That is very, very clear.  If we would be intelligent beings on our planet, we would not even consider that.  But of course we are already geoengineering the climate, releasing 42 billion tons of carbon every single year, so we are already doing solar radiation management through the emissions of fossil fuels. 

Industry does not recognize that of course —it is not in their economic or political interest — but science has to advance and find ways of alternatives to society in case society decides to use solar radiation management in the future or if this becomes absolutely necessary, and that is a real possibility because of the control of the governments on our planet by the energy industry, which is very short-sighted.  Basically the industry just wants to increase their profits in the next two, three, five, or ten years.  Nobody is thinking of the global climate in ten, 20, or 50 years.  This is something that needs governance globally as soon as possible to change this picture. 

The Global South would likely have the most to gain or lose from SRM.  To what extent do you see experts in the Global South involved in research discussions and taking part in the governance of SRM right now? 

There are tremendous gaps in terms of knowledge from the developed countries to the Global South.  It is extremely important that the Global South be engaged in all possible future solutions for the climate crisis, including solar radiation management and other techniques that are being considered, direct air capture or whatever, capture of CO2 by the oceans, and so on. 

Especially, as you mentioned, the Global South will be the most impacted by climate change, and certainly it is in their own interest to design a possible fix for the global climate.  It could be solar radiation management or any other strategy.  Working on increasing the knowledge on possible strategies for society is critical for the Global South also.  That is a very important point.  This needs coherent global action from developed countries as well as developing countries.  

What challenges do you see facing climate scientists in the Global South getting more involved in the science of SRM and the governance, and what kinds of measures could overcome some of those challenges? 

One of the major challenges is that many countries in the developing world have critical needs in terms of feeding their population, in terms of housing, in terms of providing water, and in terms of providing electricity for their own population.  Their needs are much more basic for today than thinking of climate in ten, 20, or 30 years.  That is the first point. 

The second point is that the investment in science and technology in the Global South is a small fraction of the investment that is generally done in developed countries.  This means it is much more difficult to do science in a competitive way with developed countries because of much lower budgets and resources available, like supercomputers, like training personnel, like strong universities, strong research institutes, and so on.  Unfortunately the developing countries have a long way to enter on this agenda, but this means that we need to emphasize the role of The World Academy of Sciences in developing countries to join this important activity, which is basically to find ways for our society to minimize the potential impacts of climate change on our planet. 

 You were recently at a conference on SRM organized by the Inter-American Institute for Global Change Research in Jamaica.  What were the big themes?  What were you hearing from the participants there? 

That was a very interesting conference.  The Inter-American Institute for Global Change Research has solar radiation management in their scientific agenda because they see that Latin American countries, countries from the Americas themselves, need to enhance the science in this area. 

One of the outcomes was very, very interesting because most of the countries are not really worried about mitigation, and they are much more involved in adapting their societies to climate change.  We asked all the countries that were present in the conference how they would allocate resources in terms of solar radiation management research, mitigation, or adaptation.  The answer for most of the countries is that they would put 80 percent in adaptation to climate change, 20 percent in mitigation, and virtually nothing in terms of solar radiation management research. 

This means that developing countries are desperate to adapt their societies to climate change because the impacts they are seeing right now, today, in their societies are very, very big, and they are really worried about the future in terms of water availability, increasing climate extremes, and so on. 

This is a tricky one, but is there any way in which solar radiation modification could be considered as a form of adaptation, or is it something different entirely? 

Some think it is different.  It is not an adaptation per se, although if it is properly done certainly it could be one of the strategies that societies could use, let’s say in the second half of this century, to mitigate the impacts of climate change.  In this sense it could be viewed as a kind of adaptation, but of course it is not properly an adaptation strategy per se. 

One last question on SRM:  

The first thing would be TWAS (The World Academy of Society).  TWAS has started a climate change assessment group that is putting together scientists, especially from developing countries, to drive a common agenda for adaptation and mitigation but with a view on developing countries.  This is very, very important. 

For instance, if you follow the development track from developed countries like in North America, Europe, Africa, Southeast Asia, or Latin America we would be in very bad shape.  So we need to change the whole society.  We need to change the whole economy. 

Economic growth ad infinitum in a planet with resources that are limited only exists in the heads of economists.  This does not have any background in science, so we need to promote actually a decrease in development in order to fit our society to the limited natural resources we have in our planet, and developing countries have a critical role for that. 

I would like to end, if I may, on a more personal kind of note.  Some of the things you have said today, if you go away and think about them, oh, my goodness, it is quite challenging to look and see where we are heading on climate and also, as you say, this sort of continued failure by governments to take sufficient action.  Yet here you are doing this after so many decades, still full of energy.  How do you keep motivated?  How do you actually keep your morale up as you deal with this very grim topic? 

There is no other way.  My main research area is the Amazon.  Now we have to find two things — how to implement policies that are effective to reduce deforestation and second, how to regrow forests in degraded areas in Amazonia.  To do that properly in an optimized way you need science.  If you leave this important issue just for, let’s say, the landowners in Amazonia, this will not work out. 

We need public policies that are based on science, and we are developing these public policies.  They are available, and now we have to put pressure on politicians with solid science actually to change the course of Amazonian deforestation, make recuperation of degraded areas a top priority for the new Brazilian government and not just in Brazil but all over tropical countries — Congo, Indonesia, Paraguay, Bolivia, and so on. 

Of course in terms of personal motivation that is what drives my research, to help society and make alternatives in terms of science for the very best public policy to minimize the suffering of our population.  I think that personally is an obligation as a human being. 


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