Nuclear arms proliferation and climate change are abiding threats to global security. US President Joe Biden reversed predecessor Donald Trump’s stance on both in his first few days in office. After Biden rejoined the international Paris Agreement on fighting climate change, nuclear arms control prompted his first call to Russian President Vladimir Putin. The New Strategic Arms Reduction Treaty (New START), a five-year deal that caps the US and Russian arsenals of nuclear warheads and provides for verification of compliance, expires on Friday. Renewal has been jeopardised by Trump’s demands for Chinese involvement, a one-year extension and tougher verification of Russian compliance. It is an example of the difference between Biden and Trump on multilateralism, including disarmament pacts. Many other issues divide the Biden administration and the Kremlin. Relations are fraught amid the massive cyberattack targeting federal agencies, interference in US elections, “aggression” against Ukraine and human rights. The latter includes the treatment of opposition leaders and the alleged poisoning of the now jailed Alexei Navalny. But, thankfully, the two showed they could still cooperate on nuclear issues. Biden reciprocated Putin’s offer of a five-year extension of START and the two aim to wrap it up this week. New START, which provides for regular site inspections of the other side’s arsenal, is considered an insurance policy against a full-blown arms race. A Pentagon spokesman said the US could not afford to lose the treaty’s intrusive inspection and notification tools. Failing to extend it swiftly would weaken America’s understanding of Russia’s long-range nuclear forces. Moscow obviously concurs, in reverse. That is why it offered to renew the treaty for five years unconditionally. Hopefully Biden’s proposal that the two sides explore new verifiable arms control agreements leads to further safeguards against proliferation and miscalculation that could raise the nuclear threat. Biden calls on Putin to release Kremlin critic Navalny Trump had already left two treaties with Russia, one on overflights and the other on intermediate-range nuclear forces. He withdrew the US from the Iran nuclear deal in 2018, despite international weapons inspectors insisting that the agreement struck with seven nations in 2015 was working. China, with an expanding nuclear programme but far fewer arms, has repeatedly rejected American pressure to participate in START. Meanwhile, Beijing has agreed to join the United Nations’ Arms Trade Treaty, which Trump announced last year he would withdraw from – a multilateral pact aimed at regulating cross-border sales of several categories of conventional arms that prohibits their transfer under certain circumstances.