When all is said and done at the UN climate talks, and the ink on the COP26 agreement is dry, one awkward question will remain: how enforceable will the deal be anyway?

In the last year, countries have announced a flurry of net-zero emissions pledges. The United States promised net zero by 2050, China and Saudi Arabia targeted 2060, and India 2070.

Many other countries submitted formal pledges - known as "nationally determined contributions" or NDCs - to cut emissions this decade, ahead of this month's UN climate conference in Glasgow.

Whether those goals are legally binding...