After the United Nations conference in Scotland drew a mix of supportive and scathing reviews from observers, any work in tandem on climate and easing of tensions on Taiwan and other security issues would be welcome.
In statements this month, both leaders appeared to recognise the need to better manage the great power rivalry.
"From tackling the Covid-19 pandemic to addressing the existential threat of the climate crisis, the relationship between the United States and China has global significance," Biden said. And Xi acknowledged: "Both countries will gain from co-operation and lose from confrontation. Co-operation is the only right choice".
At COP26 the two countries announced a plan to work together on cutting greenhouse gases in the next decade, including reducing methane, and transport, energy and industry emissions.
If the world is to have any hope of staying under the 1.5C warming goal, that needs to happen.
The COP26 deal by near 200 countries included weak language on coal power, the source of 20 per cent of emissions. A change pushed by India referred to a "phase down" rather than "phase out".
Greenpeace executive director Jennifer Morgan said: "It's meek, it's weak and the 1.5C goal is only just alive, but a signal has been sent that the era of coal is ending. And that matters."
Renewable energy is becoming economically cheaper and widespread. "Coal is dead. Coal is being phased out," said Helen Mountford of the World Resources Institute think-tank. "It's a shame that they watered it down."
For instance, a floating solar farm with 145,000 panels, that's thought to be the world's largest hydro solar hybrid system, has this month begun generating power in Thailand.
Austria, Belgium and Sweden have closed their last coal plants. But hugely populous countries China and India are among the biggest coal consumers.
Big carbon-polluting nations have been told to make stronger emission-cutting pledges next year at the next climate conference in Egypt and rules for a global carbon market were approved.
Countries agreed to increase funding for climate adaptation but wealthy nations have failed to provide developing ones with a previously promised US$100 billion a year. No compensation fund for damage was agreed.
There have also been deals during the conference on deforestation, electric vehicles and finance for measures against climate change.
Overall there's a widening gap between the plodding advances countries are pledging and the radical action some increasingly frustrated officials, scientists and campaigners say is needed.
Former Irish President Mary Robinson, a member of a group of retired leaders called The Elders, said the deal involved "some progress, but nowhere near enough to avoid climate disaster ... People will see this as a historically shameful dereliction of duty".
The conference is part of an attempt to gradually increase heat on decision makers but the slow pace of change is playing with fire.
More urgency is needed from the US and China in particular.
Activists will see COP26 as more evidence that protests and pressure will have to be stepped up.
