The scientific journal Nature has published a correspondence signed by 34 international scientists warning that "most current voluntary carbon offsets are neither robust nor capable of neutralising fossil fuel emissions” and claiming that numerous studies "have found significant and widespread problems with many carbon credit protocols and programmes". In a letter necessarily brief by Nature's editorial standards, they claim that numerous scientific studies have been published to back this up. The 34 scientific voices sign in their personal capacity and are specialists in forest carbon cycling, climate policy and carbon markets from universities and research centres mainly in the US and the UK, followed by Australia, the Netherlands, Norway, Spain and Switzerland. The only representatives of a Spanish organisation are CREAF researchers Josep Peñuelas (also a CSIC researcher), Jordi Martinez Vilalta (also a professor at the Autonomous University of Barcelona) and Maurizio Mencucini (who is also an ICREA researcher).

The reaction of the international group of experts follows the recent statement by the board of trustees of the Science-Based Targets initiative (SBTi), which they believe lowers the criteria for carbon offsets by companies and relaxes the founding values of SBTi. According to science representatives, the Science-Based Targets initiative statement opens the door for companies to use voluntary carbon market offsets to meet Scope 3 emissions targets. Specifically, Scope 3 covers greenhouse gases that are not emitted directly by the company but result from its value chain and are therefore carried out by intermediaries. This includes, for example, offsetting emissions from the transport of goods, business operations or the disposal of a by-product.

The voluntary carbon offsetting is the financial contribution a company makes to participate in projects aimed at balancing the tonnes of CO2 it has generated.

In simplified terms, voluntary carbon offsetting is the financial contribution a company makes to participate in projects aimed at balancing the tonnes of CO2 it has generated. The contribution is dedicated to purchasing carbon credits, each of which is roughly equivalent to one metric tonne of CO2 reduced, avoided, or captured. Examples of projects are reforestation - to boost the carbon sink effect of trees -, replacing fossil fuels with renewable energy, avoiding deforestation or waste treatment. Following the Science-Based Targets initiative's mitigation hierarchy, organisations should resort to carbon offsetting only after having exhausted all other efforts to avoid and reduce emissions in their value chain that impact on climate change.

Scientific rigor

CREAF and CSIC researcher Josep Peñuelas is firmly committed to imposing scientific rigor, which is why he has signed up to the letter published in Nature. "Rigor is needed when interpreting decarbonization and emissions compensation targets", he says, while recalling that "Science-Based Targets was created on the basis of a commitment linked to research and evaluation and is now loosening its founding values". Peñuelas points out that, instead of prioritising scientific evidence, SBTi is based on voluntary reports from large companies. He reminds us that "scientific evidence is not perfect, but it is the closest tool we have to understand what is happening and what can happen" in the context of a climate emergency.

"Rigor is needed in interpreting decarbonization and offset targets. The Science-Based Targets initiative is built on a commitment to research and evaluation, and is now loosening its founding values".

JOSEP PEÑUELAS, CREAF and CSIC researcher.

In line with this idea, researcher Maurizio Mencuccini clarifies that from the point of view of scientific expertise, "the 34 signatories are not against emissions offsetting schemes, but we demand that their evaluations be based on the best available science. Because many previous schemes have not worked properly". And he points to the risk this poses for greenwashing. Jordi Martínez Vilalta also reinforces the argument that "lowering the criteria for carbon offsets does not help us to solve the climate crisis, but rather the opposite".

“The 34 undersigned scientists do not oppose emissions offsetting schemes, but demand that their assessments be based on the best available science".

MAURIZIO MENCUCCINI, ICREA researcher at CREAF.

Influencing large corporations

The Science-Based Targets initiative is an organisation that advises and guides companies and financial institutions around the world to set greenhouse gas emission reduction targets for the year 2050 at the latest. Its influence lies both in the organisations with which it collaborates and its partners, which are the Carbon Disclosure Project (CDP), the United Nations Global Compact, the We Mean Business coalition, the World Resources Institute (WRI) and the World Wildlife Fund (WWF).

In a short and punchy text, the 34 scientific voices call on the Science-Based Targets initiative to "rescind the statement until concerns around carbon offsets are adequately addressed, and to ensure that future decisions on Scope 3 emissions are approved by scientists and technical advisors". They say that "any other approach would seriously undermine the credibility of the SBTi and jeopardise the mission of the organisation".

"Lowering the criteria for carbon offsets does not help us solve the climate crisis, but rather the opposite".

JORDI MARTÍNEZ-VILALTA, CREAF researcher and UAB associated professor.

The group of 34 experts is calling for Science-Based Targets to disclose its processes for providing evidence on carbon offsets. It also calls for decisions made by the international initiative to be based on "a systematic, public, peer review" of both the evidence on the effectiveness of carbon offsetting by different economic sectors and the offsets included in companies' decarbonization plans and progress.

The proposal for a letter to Nature is being promoted by the researcher William R. L. Anderegg, director of the Wilkes Center for Climate Science and Policy at the University of Utah (USA), who spent a sabbatical year of research at CREAF. In addition to CREAF, representatives from the British universities of Cambridge and Oxford and their scientific platform Oxford Net Zero, the University of Queensland (Australia), the University of Amsterdam (Netherlands), the Center for International Climate Research (Norway) and the ETH Zürich (Switzerland) also signed up. The signatures of specialists from American institutions include the University of California Berkeley, University of New Mexico, University of California Santa Barbara, University of Arkansas, University of California Los Angeles, University of Delaware, US Department of Agriculture Forest Service, Northern Arizona University, Indiana University, University of Clark and West Virginia University.