The goal of limiting global warming to 1.5 °C cannot be abandoned

The margin must be defined as a reference point in the COP30 negotiations, assess members of the Scientific Council of the climate conference presidency.

By Elton Alisson, from Belém  |  Agência FAPESP – Even if it is exceeded, the goal of limiting the increase in global average temperature to 1.5 °C above pre-industrial levels should not be abandoned. This goal is considered the maximum point for avoiding the worst climate scenarios, and it must be the starting point for negotiations at the 30th United Nations Climate Change Conference (COP30). 

This assessment comes from a group of 11 renowned climate scientists, six of whom are from Brazil, and the rest from South Africa, the United States, Germany, China, and England. They are members of a Scientific Council established as an advisory body by the COP30 presidency.

The council is chaired by Thelma Krug, a member of the FAPESP Board of Trustees. It includes, on the Brazilian side, Paulo Artaxo, a professor at the Physics Institute of the University of São Paulo (IF-USP) and a coordinating member of the FAPESP Research Program on Global Climate Change (RPGCC); Carlos Nobre, a senior researcher at the Institute of Advanced Studies (IEA) at USP and co-chair of the Scientific Panel for the Amazon; Ima Vieira, a researcher at the Emílio Goeldi Museum of Pará; Tatiana Sá, a researcher at EMBRAPA Amazônia Oriental, one of the decentralized units of the Brazilian Agricultural Research Corporation; Moacyr Araújo, a professor and vice-rector of the Federal University of Pernambuco (UFPE); and Marina Hirota, from the Serrapilheira Institute.

“One of the basic core messages is that 1.5 °C [global warming limit] isn’t just a target or goal. It’s something we need to take seriously and we must maintain it as the starting point and the limit that negotiations should always aim for,” said Johan Rockström, director of the Potsdam Institute for Climate Impact Research in Germany and one of the foreign members of the council, during the group’s first public event at COP30.

According to Krug, one of the council’s goals is to provide scientific data to support the COP presidency. ”The first question we were asked was whether it’s still feasible to keep global warming to the 1.5 °C limit. From that question arose a series of other questions that had to be addressed as part of the answer,” he said.

When the Intergovernmental Panel on Climate Change (IPCC) began publishing its first reports in 1990, the assessment at the time was that up to 5 °C or 6 °C global warming would not pose a risk of causing irreversible changes to the climate system. However, as knowledge advanced and subsequent assessments were made, the risk temperature range decreased. In the sixth and final report published by the Panel in 2022, this range was between 1.5 °C and 2 °C, Rockström recalled.

“This shows that the more we learn about how the Earth system works and the impacts of global warming, the greater we see the problem of it damaging the Earth’s ability to support life. We conclude that 1.5 °C is a very serious level of global temperature increase beyond which we have ample evidence that people around the world will suffer from a sequence of extreme events, and we also run the risk of approaching points of irreversible change in the functioning of the Earth system,” he said.

New scientific evidence also indicates with high probability that the 1.5 °C warming limit will be reached within the next five to ten years due to the Earth system being overloaded with cumulative emissions of greenhouse gases, such as carbon dioxide (CO₂), Rockström pointed out.

“Science shows that we can still limit this excess and return to 1.5 °C. The best-case scenario indicates that we can return to this level still in this century, but that, unfortunately, we have a period of overheating of 50 to 60 years still in this century, somewhere between 1.6 °C and 1.7 °C, before reversing this trend,” he said.

However, these climate scenarios are very optimistic. They assume that countries will be able to reduce global carbon emissions this year or next and quickly transition to a global economy with net-zero emissions within 25 years, Rockström says. He emphasized that this will also depend on the world’s ability to promote the transition of the Earth system from a source to a sink without exceeding any tipping points in the biosphere’s ability to absorb carbon and on the ocean remaining stable and absorbing 90% of the heat and 25% of CO₂.

“This represents a bet on a resilient Earth system and very important guidance for negotiators that we need to take the implementation of mitigation measures seriously,” he said. “The message we’re conveying to the COP presidency is that, whether we like it or not, we need to seriously increase the scale of carbon dioxide removal. We need to act simultaneously on all fronts, such as mitigation, the environment, agriculture, and carbon dioxide removal, to have a chance of minimizing the 1.5 °C warming breach,” he said.

Use with moderation

Despite being promising, the available carbon dioxide removal (CDR) solutions are slow and expensive and cause a wide range of intentional and unintended consequences, said Chris Fields, a professor at Stanford University in the United States and one of the international members of the Scientific Council.

“When restoration and reforestation are used as CDR solutions, they can generate a wide range of benefits; but when we use industrial techniques to capture CO2 from the air or regenerative geological formations, it may not work,” said Fields.

According to the American scientist, there are several technologies being discussed today for removing CO₂ from the atmosphere, in addition to restoration and reforestation. These include capturing CO₂ from the air and injecting it into the ground to form sedimentary rocks and ocean fertilization, which can alter the biological and chemical composition of marine ecosystems.

“There are dozens of CDR options, but we can say that, in the current context, forest restoration tends to be the cheapest option, with many species available at a cost of USD 50 per ton or less. Industrial processes, on the other hand, tend to be the most expensive, with a current cost of USD 200 per ton or slightly less,” Fields compared.

Krug said that reforestation is also the easiest way to start implementing CDR initiatives because there are already successful examples around the world, including in Brazil, although they are still on a small scale.

“We need much more ambitious commitments and a much faster energy transition because many parts of the world have already committed to zero deforestation. So what we need now is a commitment to energy transition and to be very clear about the reduction and phasing out [of fossil fuels]. I’m hopeful that this will happen,” said the scientist.