[contingencies]

I'm no expert, there is an entire field here. However, basically, anything people agree to value can function as an asset to be traded as nationally issued fiat-currency (debt) is today. There's essentially no difference, though the latter has the historical benefit of being demanded as tax and supporting by a large army, theoretically though the governments cannot wield these against the hippy next door for, you know, growing trees (environmental credits) or sharing spliffs (social credits).

People wanting the currency (debt) is based upon trust; ie. the trust that the debt society owes you, symbolized in the form of your possession of the asset in question, will be redeemed at some future point by someone else for something you want. (Note that due to inflation and the creation of money in current era systems this debt notion is flipped; typical money must be repaid - with interest, at speed - or forfeited. But that's a tangent.)

A path forward will probably include convincing one or more governments to adopt some alternate assets and begin to effectively provide rates of exchange through government tax incentives or similar. This could kickstart a modern renaissance in multi-asset accounting and localized economies. Not holding my breath on speed, but anything's possible. Part of the challenge here is that social and environmental concerns typically cross borders and election terms, and developed countries' political decisionmaking is heavily blinkered against these two classes of issue.

Recommended reading: Debt: The First 5000 Years.