The Brazilian Amazon city of Belém will host the UN's 30th annual climate conference from November 10 to 21, with roughly 50,000 delegates converging on the region to negotiate fresh commitments on emissions reductions and forest protection.

Yet the gathering opens against a backdrop of diminishing political consensus and low expectations, underscored by the conspicuous absence of leaders from the world's largest emitters — the US, China, India and Russia.

The conference aims to accelerate implementation of the 2015 Paris Agreement, particularly the goal of limiting global temperature increases to 1.5°C above pre-industrial levels by century's end. However, UN Secretary-General António Guterres delivered a stark assessment on November 6, declaring that "the hard truth is that we have failed to ensure we remain below 1.5 degrees". He denounced the shortfall as "moral failure and deadly negligence".

Current policies are projected to produce warming of approximately 2.7°C, according to the latest UN estimates. Scientists warn the 1.5°C threshold is now virtually certain to be breached, with carbon dioxide concentrations reaching a record 423.9 parts per million last year — the largest annual increase since measurements began in 1957.

The absence of Donald Trump, who has brushed off climate change as "the greatest con job ever perpetrated on the world", cast a long shadow over the proceedings. Without naming the US president directly, Brazil's Luiz Inácio Lula da Silva cautioned against “political extremists” spreading disinformation whilst jeopardising the climate prospects of coming generations.

Chile and Colombia's leaders went further, directly calling Trump a liar. "The science is very clear. It is very important not to falsify the truth," Chile's environment minister Maisa Rojas told journalists.

In sobering remarks, British Prime Minister Sir Keir Starmer acknowledged the erosion of international unity. "It had been a consensus issue internationally and in the UK but today sadly that consensus is gone," he said, whilst insisting that "the UK is all-in" on climate action.

Yet Britain's commitment faced immediate scrutiny when it opted out of Brazil's flagship $125bn Tropical Forests Forever Facility (TFFF) just hours after Starmer's remarks. The fund, designed to channel resources to rainforest protection, had secured only $5.5bn in pledges by the summit's opening, including $3bn from Norway and $1bn from Brazil itself.

Under the proposal, $25bn would come from "sponsor" governments prepared to absorb early risks, whilst another $100bn would be drawn from private investors such as pension and sovereign wealth funds.

The UK's withdrawal stunned observers, given its prominent role in designing the mechanism and launching a global deforestation pledge at the Glasgow summit in 2021.

In contrast, German Chancellor Friedrich Merz is said to be backing the Brazilian initiative, describing the TFFF financing initiative as “interesting” and wanting to “support Brazil and demonstrate Germany’s continued commitment to multilateral climate efforts,” according to sources cited by AFP.

Ambassador André Lago, Brazil's climate envoy and conference president, stated that the summit would demonstrate "that there are already significant responses and solutions to many of the challenges we face". The conference will be split between a Blue Zone for official negotiations and a Green Zone hosting civil society debates, with 15,000 social movement representatives attending a parallel People's Summit.

However, only 143 delegations from the 198 signatory countries have confirmed participation, and a majority of nations have failed to submit updated emissions reduction plans ahead of the gathering.

Despite the diplomatic setbacks, several leaders framed climate action as essential to economic competitiveness and energy security. Finland's President Alexander Stubb declared that "investment for climate change is the growth and prosperity plan for this century", whilst China's Vice Premier Ding Xuexiang touted his country's "green and low carbon development" path.

The conference comes as extreme weather intensifies globally. Hurricane Melissa, which struck the Caribbean last week as a Category 5 storm, killed more than 75 people, with climate change estimated to have increased associated rainfall by 16%.

Stela Herschmann, a climate policy specialist at Brazil's Climate Observatory, said the UN process has been "too slow" to match the pace of environmental deterioration. "The responses have not come at the speed or scale that science indicates are necessary," she said, as quoted by Agencia Brasil.

Since the first Conference of the Parties met in Germany three decades ago, global emissions have accelerated dramatically — with approximately half of all atmospheric CO2 from the industrial age released during this period of climate diplomacy. Fossil fuel combustion still generates 90% of global CO2 emissions, with coal use hitting record highs despite bold transition pledges renewed at every year's climate summit.

Guterres called for immediate action to reverse warming trends. "If we act now, at speed and scale, we can make the overshoot as small, as short, and as safe as possible," he told assembled leaders. "This COP must ignite a decade of acceleration and delivery."

The two-week conference will focus particularly on mobilising finance for countries already experiencing severe climate impacts and negotiating mechanisms to support forest conservation. But the absence of major emitters and the fraying international consensus suggest any agreements may struggle to match the scale of the challenge.