The surest way for that to happen is to forge a constructive relationship between our two countries. Absent that, it is imperative that we put our differences aside to tackle these two existential challenges.

As the two largest economies, the United States and China can set the tone for a global effort against climate change by investing in clean-energy technology, adopting strict environmental rules and encouraging their trading partners to do the same. (Of course, the current administration does not accept the reality of climate change, but future administrations will hopefully recognize the urgency of action.)

Cooperation is also needed to address the spread or possible use of nuclear weapons. North Korea’s continued development of fissile materials and missiles is an apparent contravention of its recent agreement with the United States. And North Korea isn’t the only concern. Pakistan, for example, has a weak government and uncertain controls over its nuclear arsenal.

The arc of human history is one of frequent conflict. Unless you believe human nature is likely to change, that suggests a serious risk that nuclear arms will be used at some point by state or nonstate actors. United States-China cooperation to limit nuclear proliferation among states, the diversion of nuclear material to terrorists and other risks would make us all safer.

The most promising prospect for tackling these challenges is to put our countries’ economic relationship back on steady footing. The tenor of the relationship gets set at the top, so it’s time for Presidents Trump and Xi Jinping to work out their current trade disputes within a framework that prioritizes cooperation.