Discussion paper

The third degree: evidence and implications for Australia of existential climate-related security risk

Climate change Global environmental change Global warming Scenario planning Australia

Since the Paris climate conference in 2015, much time has been spent talking about and researching 1.5°C to 2°C of climate warming. But there has been relatively little focus on where the climate system is actually heading, given the lack of political commitment to climate action on a global scale: which is 3°C of warming, and possibly much more.

In May 2019, Breakthrough published a policy paper Existential Climate-related Security Risk: A scenario approach, which included a brief 3°C scenario. Understanding scenarios is important because of the role they can play in “thinking the unthinkable”, sensitizing and broadening mindsets to critical global developments, especially the unexpected, and adjusting strategy accordingly. Scenario planning does not forecast, predict or express preferences for the future; rather it is story-telling, painting internally-consistent pictures of alternative worlds which might emerge, given certain assumptions that are credible in the light of both known and lesser known factors.

This paper provides detailed supporting evidence for the brief 3°C scenario. Some contentious aspects are explored, including the possibility that perhaps a billion people could be displaced by 3°C or warming, that some regions may become too hot for human habitation for part of the year, and that critical thresholds, consistent with the “Hothouse Earth” scenario, may be passed.

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