They warned it could happen: a world of surging nationalism, stalling economic development and the unravelling of decades of international cooperation on climate change and other global challenges.

Long before Donald Trump lurched away from diplomatic norms and the international rules-based order, scientists mapped out different potential futures to understand the possible implications for greenhouse gas emissions.

Developed a decade ago, five of these "pathways" became crucial to the work of the United Nations' IPCC climate expert panel.

These are not predictions for the 21st century. Rather, they envision what could happen with various societal changes including for trade, economic development, technological innovation and global population.

The most optimistic narrative foresees sus

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