Global tensions, economic uncertainty and a US administration under Donald Trump that is hostile to climate science have snatched political focus away from tackling the fossil fuel pollution and environmental destruction driving warming.
With tepid climate ambition and emissions still rising, UN Secretary-General Antonio Guterres recently acknowledged that crossing 1.5C in the coming years was now inevitable.
But he insisted the world must not give up on the Paris Agreement's safer goal.
"The path to a livable future gets steeper by the day. But this is no reason to surrender," he said this week as countries prepared to meet for the COP30 summit in the Amazon city of Belem.
Scientists say every tenth of a degree over 1.5C magnifies dangerous and costly impacts -- such as drought, heat, fire and floods -- while increasing the risks of passing large-scale tipping points.
Climate scientist Johan Rockstrom, director of the Potsdam Institute for Climate Impact Research, said humanity now faces perhaps 50 to 70 years above 1.5C before possibly dragging temperatures back down.
"It means with essentially a hundred percent certainty that we will have a very rough time before it potentially gets better," he told AFP.
- 'Declare failure' -
The 2015 Paris climate deal aimed to limit global warming to "well below" 2C from pre-industrial (1850-1900) levels -- and 1.5C if possible.
While overshoot -- temperature trajectories that go beyond 1.5C before coming back down -- is not a new concept in science, many leading climate figures have been uneasy talking about it.
"I didn't want to give the impression that it's okay if we overshoot," Patricia Espinosa, the former head of UN Climate Change, told AFP earlier this year.
"I wanted to keep very, very firm."
To minimise or avoid overshoot, the Intergovernmental Panel on Climate Change (IPCC) said emissions needed to peak around 2020 and be essentially halved by 2030.
At the midway point of the decade, emissions continue to rise and so do temperatures, with 2024 the first full year above 1.5C.
So the message is shifting.
"The first thing we need to honestly communicate to humanity, but also to all political leaders in the world gathering in Belem, is that we have to declare failure," said Rockstrom, who was among the scientists consulted by Guterres ahead of COP30 in Brazil.
But this only adds to the urgency for action, he said, with higher warming raising risks for food systems, fresh water and global security.
"There's no evidence that we can adapt to anything beyond two degrees Celsius," Rockstrom said. Beyond 3C would mean "disaster mode" for billions, he added.
The IPCC has warned that crossing 1.5C threatens the widespread melting of mountain glaciers and ice sheets containing enough frozen water to ultimately lift the ocean by metres.
Tropical coral reefs, the nursery for a significant share of marine life and crucial to the livelihoods of some 200 million people, are likely already reaching a tipping point, according to recent research.
But there are still many unknowns, including how long these systems might be able to endure with overshoot.
- Negative emissions -
To turn the situation around, Guterres said the world needed to peak emissions "immediately", speed up the transition to renewable energy, and protect forests and oceans, which play a crucial role in absorbing carbon from the atmosphere.
After reaching net zero by 2050, the world will also need to swiftly deploy strategies to remove carbon from the atmosphere.
Research by Climate Analytics suggests that the huge rollout of cheap green technologies like solar and wind mean fossil fuels could be phased out sooner than expected, with warming ultimately brought back to 1.2C by 2100.
But they said the most ambitious global climate action likely means an overshoot of at least 1.7C for decades.
Lowering temperatures will require the use of controversial technologies -- to capture carbon emissions at source or permanently remove CO2 from the air -- which are not yet operational at scale.
It also relies on forests and the ocean to continue absorbing half of all CO2 pollution.
But that may already be changing.
In October the World Meteorological Organization reported a record jump in the amount of CO2 in the atmosphere and voiced "significant concern" that the land and oceans were becoming less able to soak up carbon dioxide.
"The whole picture points towards an increasing difficulty with relying on the Earth system to take up the carbon," said Bill Hare of Climate Analytics.
"We're now in a very risky space."
'Moral failure': Leaders seek to rally world at Amazon climate talks
Belem, Brazil (AFP) Nov 6, 2025 -
Fears of a fracturing global resolve loomed over climate talks in the Brazilian Amazon on Thursday as world leaders acknowledged their failure to contain global warming to agreed limits.
Heads of state and government met in the city of Belem ahead of the UN COP30 conference, which is set to take place without the United States -- one of the nations most responsible for planet-warming emissions.
Opening the leaders gathering, UN Secretary-General Antonio Guterres set the tone by declaring the world had failed in its promise to hold long-term warming to 1.5 degrees Celsius since the pre-industrial era.
"This is moral failure -- and deadly negligence," he said, adding that to minimize the danger, governments must now act with even more urgency to slash fossil fuel emissions and protect nature.
The UN's weather and climate agency on Thursday said 2025 would be among the hottest years ever recorded.
Brazil hopes COP30, which officially begins on Monday, can reaffirm that climate change remains a global priority despite wars, trade tensions, economic uncertainty and the chilling effect of the Trump administration.
President Trump has dismissed climate science as a "con job" and has sought to torpedo international climate action in other forums, all the while boosting fossil fuels.
America's absence cast a shadow over Thursday's summit, where speakers took turns condemning Trump's climate denialism and lamenting the loss of global momentum.
"The president of the United States in the last UN assembly said that the climate crisis does not exist, and that is a lie," said Chile's Gabriel Boric, while Colombia's Gustavo Petro, whose US visa was canceled by Trump's government, likewise tore into him.
Brazilian president and host Luiz Inacio Lula da Silva referred to "extremist forces (that) fabricate fake news to obtain electoral gains and imprison future generations."
The world's biggest emitter, China, was present at the summit and pledged to double down on its climate action, which has included the vast rollout of renewable energy and green technologies at home and abroad.
"China is a country that honors its commitments," Chinese Vice Premier Ding Xuexiang said pointedly.
He added his country would "accelerate the green transition in all areas of economic and social development" and chided those who would put up trade barriers against its solar panels, batteries and electric cars.
- Uphill battle -
Leaders from other major economies, including the European Union, Britain and France were also in attendance to show that the international community could still pull together.
Britain's Keir Starmer said "the UK is all in" -- framing investment in the energy transition as an economic opportunity, but raised fears that the global climate "consensus is gone."
The choice of Belem, a city of 1.4 million people, half of whom live in working-class neighborhoods known as favelas, has been controversial due to its limited infrastructure, with sky-high hotel fees complicating the participation of small delegations and NGOs.
Brazil's recent approval of oil drilling near the mouth of the Amazon River will sit awkwardly at the conference.
So, too, will the unanswered call for a wave of ambitious new climate pledges ahead of COP30.
- 'Heaviest price' -
Brazil launched a new rainforest conservation fund on Thursday, with a promised contribution from Norway of up to 30 billion kroner ($2.9 billion) in loans.
COP30 will also focus on adaptation, a demand of countries which cannot afford to build defenses against climate disasters.
DR Congo President Felix Tshisekedi on Thursday said that "insufficient" climate finance was helping to drive an inequality crisis.
"Those who have contributed the least to climate change are now paying the heaviest price," he said.
These countries want concrete detail on how climate finance can be substantially boosted to $1.3 trillion a year by 2035 -- the estimated need in the developing world.
The hosts are also under pressure to marshal a response to the 1.5C failure. Even if all commitments are enacted in full, global warming is still set to reach up to 2.5C by century's end.
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