On the campaign trail, Joe Biden quoted the following words of his favourite poet, Seamus Heaney: “Hope for a great sea change / on the far side of revenge.” As the US president-elect finally takes the oath of office in Washington DC, the rest of the world desperately needs him to effect a sea change. If his first task is to reunite a divided America, his second is to end American isolationism: to show Americans that they need the world, and show the world that we still need America. Given the intertwined triple threats of the pandemic, economic collapse and climate catastrophe, his presidency will be defined not by the previous benchmarks of 100 days, but rather by its first 10 or 20 days. The Trump impeachment trial notwithstanding, day one will see Biden delivering on his plans to roll out mass vaccination and to reboot the ailing US economy by forcing the biggest fiscal stimulus in history through Congress. Given that body’s new political makeup and Biden’s own inclinations, his multi-trillion-dollar plan will be greener than anything ever contemplated by US lawmakers. But Biden must then go global. His presidency will be forged or broken on the anvil of those existential crises, and the internationalist in him knows that not one of these three domestic objectives – a virus-free, an economically resilient and a pollution-free US – can be fully realised without multilateral cooperation. Yet this is something that economic nationalists in both the US’s main political parties have not just rejected but scorned. Once, in the unipolar world immediately after the cold war, the US acted multilaterally (think of the global coalition that ousted Iraq from Kuwait 30 years ago). Recently, in a multipolar world, it has been acting unilaterally. Breaking with the aggressive populist nationalism of the Trump years will not be easy. So we should not expect a rerun of the lofty “go anywhere, pay any price” internationalism of the past. This thinking was once so dominant that John F Kennedy’s inaugural address in 1961 made scarcely any mention of domestic concerns. Nor should we expect any attempt by Biden to repeat Bill Clinton’s global Third Way of the 1990s – an over-triumphalist attempt, at a time of undisputed American hegemony, to lock every country into an updated “Washington consensus”. Now, in a world where there are many competing centres of power, and two and a half centuries after its Declaration of Independence, the United States needs a more modest “declaration of interdependence”. In language that will, on first hearing, seem protectionist, Biden will repeat his campaign statements that American foreign policy must now be determined by its domestic priorities. But because eliminating the virus, rebuilding commerce and trade and dealing with the climate crisis all depend on working more closely with other countries, the new president will abandon the walls, the tariffs and the xenophobia of the Trump years for a policy more “alliances first” than “America first”. And the Biden I came to know from working with him during the global financial crisis will not only be the most Atlanticist of recent presidents, but will make the most of his reputation as the great conciliator. Biden should immediately telephone the Italian prime minister – the current chairman of the G20 group of nations – and propose he urgently convene a summit of world leaders to coordinate emergency global action on each of the health, economic and environmental crises. The president-elect knows that immunising the US will not be enough to protect its citizens as long as poor countries cannot afford vaccinations and the virus continues to mutate and potentially reinfect those previously immunised. The US and Europe should lead a consortium of G20 countries to cover the estimated $30bn (£22bn) shortfall in funds needed to vaccinate the entire world. This is a bargain compared with the trillions in economic activity that will be lost if the pandemic rages on or, once contained, returns. Even before Covid, the US, like all advanced economies, was facing a high-unemployment low-growth decade, and no major economy – or developing-world nation – will fully recover the reduced output and lost jobs of 2020 unless and until there is a synchronised global plan that lifts growth. In today’s low-inflation and low-interest-rate environment, there is a global surplus of savings waiting to be invested, and public investment that boosts productivity will pay for itself by creating a virtuous circle of consumer demand, growth and rising tax revenues. I know from my experience during the global financial crisis that if the US, Europe and Asia agree to coordinate their fiscal stimuli, the multiplier effect – the spillover from increased trade and consumption – will be twice as effective in delivering growth as if each bloc acts on its own. The dividend from heightened cooperation could be upwards of 20 million much-needed jobs – and that boost could be even bigger if President Biden overturned President Trump’s objections to emergency aid for Africa and the developing world. What could become a 21st-century Marshall plan could include debt relief; the creation of $1.2tn of new international money through what are called special drawing rights; and matching funds for health, education and poverty reduction from the IMF and World Bank. Biden, who will rejoin the Paris climate accords this week, should also announce that he will attend this December’s Cop26 climate conference in Glasgow. He has already said that the 2020s may be our last chance to avoid catastrophic global warming. His domestic energy initiatives will be welcome, but not enough. The transition to a net-zero carbon economy is the greatest international endeavour of our times, and the US and Europe must now lead, persuading all countries, rich and poor, to implement a global green new deal and agree carbon reduction targets for 2030. Trump’s abject failures and his legacy, a more insecure world, present Biden with another historic opportunity. The Joe Biden I know will signal his determination to stand up to Chinese illiberalism and Russian opportunism. He will act quickly to secure a revamped Iranian treaty that not only constrains Tehran’s nuclear ambitions but also tackles its sponsorship of terrorism. But underpinning these immediate imperatives is a profound generational challenge. Since the 1980s, when Biden went to Moscow to help Ronald Reagan secure his nuclear weapons reductions deal with President Gorbachev, he has been in the forefront of demands for nuclear disarmament. I believe Biden could be the first president of the nuclear age to declare and deliver a “no first use” policy on nuclear weapons. By also negotiating global bans on both nuclear testing and the enrichment of uranium, his presidency could usher in a decade of disarmament. These historic steps would pave the way for the renunciation by Saudi Arabia, the UAE, Egypt and Turkey of any nuclear aspirations, the further isolation of North Korea, and the downgrading of the role of nuclear weapons on the road to their eventual elimination. Not since Franklin Roosevelt, nearly 90 years ago, has a US president come to office amid so many pressing crises and so loud a clamour for change. FDR’s words on his inaugural day, a powerful call to “action and action now”, apply with equal force to these perilous days. And President Biden knows it. His task is no less than, as Seamus Heaney put it, to “make hope and history rhyme”. • Gordon Brown was UK prime minister from 2007 to 2010. His latest book, Seven Ways to Change the World, will be published by Simon & Schuster this summer