The collapse of Joe Biden’s Build Back Better legislation would have disastrous consequences for the global climate crisis, making it almost impossible for the US to comply with its greenhouse gas reduction pledges made under the Paris accords.

The US president’s sweeping economic recovery and social welfare bill is in serious trouble after the Democratic senator Joe Manchin announced his opposition to the $1.75tn spending package that includes the country’s largest ever climate crisis investment.

The shock move by the fossil fuel-friendly West Virginia lawmaker came after a year of record-breaking fires, floods, hurricanes and droughts devastated families across America, and amid warnings that such deadly extreme weather events will intensify unless there is radical action to curb greenhouse gases.

The Build Back Better (BBB) legislation earmarks $555bn to tackle the US’s largest sources of global heating gasses – energy and transportation – through a variety of grants, tax incentives and other policies to boost jobs and technologies in renewable energy, as well as major investments in sustainable vehicles and public transit services.

It is by far the largest chunk of federal funding for Biden’s climate crisis initiatives, without which experts say it will be impossible to meet the administration’s target of reducing greenhouse gas emissions by at least 50% below 2005 levels by 2030.

Globally, the US is the second-largest emitter of greenhouse gases after China, and scientists warn that even halving emissions by 2030 may not be enough to avoid a catastrophic rise in atmospheric and oceanic temperatures.

But BBB would be a major step forward towards the US meeting the goals laid out by Biden at last month’s UN climate talks in Glasgow, with no time to waste given the regression during the Trump administration. Without it, the Biden administration would be forced to rely on a web of new regulations and standards which could be overturned by future presidents.

Lawmakers, climate experts and labor groups have voiced intense anger and frustration over Manchin’s refusal to support the bill, which would leave the Democrats without the necessary votes to get it through the Senate.

Raúl Grijalva, chair of the House natural resources committee, said the concentration of political power in a few hands had caused nothing but “gridlock and frustration”.

“Our country has serious economic and environmental problems that demand government action. If we don’t take that action, we’ll look back at this moment as a decisive wrong turn in the life of our country,” Grijalva said in a statement.

“Who died and made Joe Manchin king, how is this a democracy?” said Mary Annaïse Heglar, climate writer and co-host of the podcast Hot Take. “There’s been a dereliction of duty by politicians for decades who’ve failed to make the case for climate action … climate math won’t reset just because the political math did.”

Writing on Twitter, Jesse Jenkins, an energy professor at Princeton University who leads a group analysing the potential of BBB, said Manchin’s decision was “devastating” given the high stakes. “Passing #BuildBackBetter would lower energy costs and secure both the US’s climate goals and its global competitiveness in some of the most important industries of the 21st century. Failure would cost Americans dearly.”

BBB would build on a bipartisan infrastructure bill, signed into law last month, which contains important steps towards transforming America’s fossil fuel fired transport system by incentivizing zero emission public transit, a national network of electric vehicle chargers and a renewables energy grid.

But BBB goes much further. For instance, homeowners would get incentives to install rooftop solar systems and insulate their homes.

It also provides significant funding to address a range of environmental injustices which have led to Black, Latino, Indigenous and other marginalized Americans being disproportionately exposed to the harmful effects of fossil fuel pollution, ageing infrastructure like lead pipes, emerging toxins and the climate crisis.

The bill includes billions of dollars in grants and other schemes to clean up pollution and create toxic-free communities, healthy ports and climate-resilient affordable housing, as well as research and development infrastructure at historically Black colleges and universities.

So if Manchin move finally scuppers the BBB act – as is widely feared – frontline communities in the US, and across the world, would bear the brunt of the inaction.

“Build Back Better is our once-in-a-generation opportunity to combat the climate crisis and advance environmental justice through transformative investments that only the government can provide,” said Abigail Dillen, president of the legal non-profit Earthjustice. “The urgency couldn’t be greater. As communities across our country are displaced by weather disasters and others breathe polluted air and drink poisoned water, political leaders like Senator Manchin cannot continue denying the crisis before us.”

The climate crisis is undeniably causing havoc and misery across the world, with 2021 one of the deadliest ever years for weather disasters in the US. This year’s death toll includes at least 200 people killed by extreme heat in the Pacific north-west over the summer and 125 deaths caused by the extreme freeze in Texas in February.

After years of scepticism, the majority of Americans now want government action to tackle the climate crisis but the majority of republicans – and a handful of democrats – continue to obstruct meaningful policy initiatives.

Manchin, whose family profits from the coal industry in West Virginia, has already pushed out key climate policies during the BBB negotiations including a program to incentivize electricity utilities to use renewable power sources.

Yet even some of Manchin’s core supporters are urging him to reconsider his opposition to the current bill, which includes several policies that would directly benefit large numbers of West Virginians including the state’s struggling coal miners.

In a statement, the United Mine Workers of America (UMWA), which named Manchin as an honorary member last year, warned that benefits to coalminers suffering from black lung disease will expire at the end of this year unless BBB is passed. The union also supports the bill’s tax incentives that encourage manufacturers to build facilities on abandoned coalfields that would employ thousands of unemployed miners.

Cecil Roberts, the union’s president, said: “We urge Senator Manchin to revisit his opposition to this legislation and work with his colleagues to pass something that will help keep coalminers working, and have a meaningful impact on our members, their families, and their communities.”