World Government "United Nations Multocracy"

Maintaining a viable economy during Climate Collapse:
The joining of all nations into 1 "Multocracy" United Nations Government.
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Currency issues & solves:
No Currency exchange fees within the coalition government.
All businesses accept the new currencies also. ie Canadian & USD.

Regarding Immigration problems:
Work permits required for the coalition government, except when the currencies reach 1-to-1. (at that time 1 of the currencies is absorbed into the other. ie., USD only instead of Canadian & USD. also reduces costs.)

Gov. Code: simple add ons, and amendments per new nation added to the US, Constitution, and tweaks happen with each ruling as normal.
The UN Guide would be: to remain Democratic.

Advantage:
Reduced military, reduced taxations, reduced government size, ability to implement more energy towards climate disasters, etc.