While most analysis of Brazil's upcoming 4 October election focuses on whether Lula or Flávio Bolsonaro will lead the country, for the EU's climate agenda, however, this is only half the question. Congress is already willing to override the president on environmental law, and is likely to move further to the right. This could undermine the green promises of the EU-Mercosur agreement, regardless of who wins. Brussels should watch the National Congress, especially the Senate, as closely as the presidency.
At the start of April, Brazil's best-known climate champion left the government to run for the Senate. Marina Silva had run Lula's environment ministry for more than three years. She says she wants to protect the government's environmental gains from inside the Senate after Congress rewrote deforestation licensing laws, and her new goal should indicate to Brussels where the main battle for the bloc’s good ties with Brazil lies. Climate change has long been a key part of EU–Brazil relations. A dedicated Climate Change Dialogue was launched in 2011, with new sessions held both in Rio and Brussels since then, and a special two-party think tank forum built for COP30; furthermore, in 2015, the two sides jointly proposed carbon market rules that were later embedded in the Paris Agreement. The EU–Mercosur trade agreement, which has been provisionally applied since 1 May following more than 25 years of negotiation, makes the Paris climate agreement an ‘essential element’ that, if violated, could lead to the deal being suspended, and commits both parties to maintaining environmental standards. However, the deal stalled after 2019, when deforestation in the Amazon climbed under Jair Bolsonaro, and negotiations only resumed again after Lula's return in 2022.
How Brazil's elections work: Brazil is a federal republic with a presidential system: voters elect a president and a two-chamber, or bicameral, National Congress on the same day. The lower house, the 513-seat Chamber of Deputies, is elected by proportional representation for four-year terms, with seats per state roughly tied to population. The upper house, the 81-seat Federal Senate, gives every state and the Federal District three senators regardless of size, elected for eight-year terms in staggered batches of one-third and two-thirds every four years. On 4 October, Brazilians will elect a president, all 513 deputies and 27 of the 54 senators up this cycle, plus state governors and legislatures – a single election day covering both the executive and legislative branches.
Most forecasts follow a simple, but reasonable pattern. If Flávio Bolsonaro, Jair's son, wins, the anti-climate policies of 2019–2022 will be reinstated. If Lula wins, Brazil will continue on a path that has reduced Amazon deforestation to historically low levels. The race is close: in polls from early September, Lula leads the first round, but with a margin of just 2%, and both candidates are still technically tied for a potential runoff on 25 October. However, focusing solely on the presidential numbers can obscure the forces most responsible for turning environmental policy into law: those who can veto decrees, even when the president subscribes to the environmental standards that historically bind the EU and Brazil.
The actor most forecasts miss
One actor that most forecasts miss is the Congress, which has helped build Brazil's climate framework, especially since 2009, including a national climate law and climate fund. However, it is also home to the country's strongest lobby against environmental rules: the agribusiness caucus, which comprises around 340 of Congress's 594 members. Under Workers' Party (or the Portuguese acronym PT) president Dilma Rousseff, it strongly pushed for rewriting the Forest Code in 2012, a law which granted amnesty for illegal deforestation before 2008.
What is the ‘agribusiness caucus’? Alongside political parties, Brazilian lawmakers organise in cross-party ‘parliamentary fronts’, known as ‘bancadas’, built around a shared cause rather than party lines. The largest and most influential is the agribusiness caucus, popularly called the Bancada Ruralista, or ‘Ox Bench’, which groups roughly 340 of Congress's 594 members from dozens of parties and has driven the rollback of environmental and Indigenous rights protections for decades. Other prominent fronts represent evangelical Christians and public security hardliners. Because they cut across party lines, these caucuses can assemble majorities that neither the government nor a single opposition party could muster alone, making them decisive on issues like deforestation, that split parties internally.
In 2025, this caucus went further. Congress passed a general environmental licensing law, known to critics as the ‘Devastation Bill’, which waives or simplifies permits for many projects that damage forests. The Senate voted 54 to 13, while the Chamber of Deputies voted 267 to 116. Lula vetoed 63 provisions. However, in November, just days after Brazil had hosted the UN climate summit in Belém, Congress overturned most of these vetoes.
How a presidential veto is overturned: Brazil's president can veto a bill in whole or, more often, article by article. Congress then has 30 days to consider each veto in a joint session of the Chamber of Deputies and the Senate. Overturning it requires an absolute majority in both houses at once: at least 257 of 513 deputies and 41 of 81 senators voting to reject the president's veto. If either chamber falls short, the veto stands. If both clear the threshold, the vetoed text becomes law regardless of the president's wishes – showing how a determined cross-party majority in Congress can override the executive, even on a law the president has already rejected.
This was not just a victory for the right. In the Chamber of Deputies, 60% of the votes in favour came from parties with ministers in Lula's own government, while the Workers' Party was almost unanimous in its opposition. The decisive force was the ‘Centrão’, a loose bloc of centre-right parties that can side with either the government or the opposition, depending on the issue. For Europe, this is not necessarily an internal dispute. The EU deforestation regulation (EUDR), which prohibits products associated with deforestation, will take effect on 30 December for large companies. The carbon border adjustment mechanism (CBAM), which has been in force since January, imposes a price on the emissions embedded in imports such as steel and fertilizers. Brazil's legislators will help decide how exposed Brazilian exporters will be.
A Congress that leans further right
The Chamber is unlikely to change much. Around 85% of current deputies – 438 out of 513 – are standing for re-election, which usually favours incumbents. The Liberal Party (or the Portuguese acronym PL), led by Flávio Bolsonaro, has the most re-election candidates (77), ahead of Lula's Workers' Party (57).
The shift is sharpest in the Senate, where two thirds of its 81 seats are up for grabs. Poll-based projections published in September suggest that the Liberal Party could gain around 20 seats in the Senate, up from nine today. Meanwhile, the Workers' Party could gain 11 seats and the wider centre-left could gain around 19. An earlier count put the right at around 40 seats, one short of a majority. No group would be able to govern the chamber by itself: the Centrão, with one of its biggest parties alone, the Brazilian Democratic Movement (or the Portuguese acronym MDB), projected to win 11 seats, would hold the balance of power.
These numbers matter because of how Brazilian lawmaking works. Overturning a presidential veto requires the support of 257 deputies and 41 senators. If the Senate leans to the right and is joined by the Centrão and a like-minded Chamber, that threshold can be reached regardless of who wins the presidency. If Lula is re-elected, he could continue to steer ministries, agencies and diplomacy towards common sustainability goals. However, any binding law against deforestation would have to survive the scrutiny of that chamber. A President Flávio Bolsonaro would likely find an ally in it rather than a check.
What Brussels should do
Europe has seen this pattern before. In the European Parliament, the far right holds more than a quarter of the seats, and last year, for the first time, the centre-right European People’s Party backed a major change to corporate sustainability rules with the support of far-right votes rather than with its usual centrist allies. In both instances, the decisive factor was the choice of the centre-right.
Critics of the EU–Mercosur deal in Europe, including the five governments that voted against it, are likely to view every Brazilian rollback as evidence that the deal’s safeguards are ineffective. Brussels should therefore treat the 4 October election as a two-part process and follow the Senate count as closely as the presidential one. It should engage with Brazilian legislators, governors and exporters, not just the presidential palace. The agreement provides Brazilian farmers and industries with a tangible incentive to maintain access to the European market. Brussels should present the deal’s sustainability commitments and deforestation regulation as stable conditions of access, providing those who advocate for climate policy in Congress with something concrete to support.
Marina Silva’s move captures the moment. Brazil’s climate policy was developed in the executive branch, but its future will be decided in the legislature – her own race in São Paulo is close. If Europeans want the green promises of the EU–Mercosur agreement to survive the next four years, they should move beyond asking only who will occupy the presidential palace and start asking who will sit in Congress.
The views and opinions in this article do not necessarily reflect those of the Heinrich-Böll-Stiftung European Union | Global Dialogue.
