Behind that headline is a question that goes to the heart of climate policy-making and advocacy: given that climate system tipping points are tumbling today, is limiting warming to 1.5°C safe for humanity?

Highlights

• Major elements of Earth’s climate system are now increasingly influenced by self-reinforcing warming processes — or positive feedbacks — due to climate change caused by human greenhouse gas emissions, mainly from burning fossil fuels. A “tipping point” or critical threshold may be reached, such that a small change causes a larger, more critical change to be initiated, taking components of the Earth system from one state to a discreetly different state.
• Feedbacks can drive abrupt, non-linear change that is difficult to model and forecast, with the Earth moving to dramatically different conditions. Such changes may be irreversible on relevant time frames, such as the span of a few human generations. Major tipping points are interrelated and may cascade, so that interactions between them lower the critical temperature thresholds at which each tipping point is passed
• Research released in December 2021 has provided new evidence that West Antarctica’s Thwaites Glacier has passed a tipping point for abrupt change, likely triggering a cascade of similar events on the peninsula. The Arctic, warming at four times the planetary average, is undergoing abrupt change, including on the Greenland Ice Sheet, which has passed a point of system stability.
• These events at both poles are not properly incorporated into current climate models. The evidence suggests that sea-level rises this century will be greater than currently considered feasible by policymakers. Evidence from climate history suggests the current global average temperature increase is enough for 5–9 metres of sea-level rise in the longer term, inundating small island states, agriculturally rich alluvial deltas and vulnerable coastal cities.
• The land-based carbon stores are reaching a critical point, after which their efficiency decreases. There is considerable evidence that eastern Amazonia has “tipped” and is now a net source of carbon.
• Coral reefs are now bleaching so frequently that there is no longer sufficient natural recovery time between bleaching events so that they have entered a death cycle.
• A number of other climate systems, including some ocean and atmospheric circulatory systems, and northern hemisphere permafrost stores, are undergoing significant change, but there is not the knowledge to determine how close to “tipping” they may be.
• Tipping points thresholds identified for the Arctic, Greenland, West Antarctica and coral systems, and for land sinks such as easterm Amazonia, have been reached before or at the current level of warming of 1.2°C.
• The 1.5–2°C target range of the 2015 Paris climate agreement is demonstrably not a safe or appropriate goal for policymakers and advocates concerned about protecting the most climate vulnerable, and requires a major rethink about advocacy goals and what is possible and necessary to achieve them.

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