Prospect of Catastrophe

The Timing of Climate Change Policy

The Prospect of Catastrophe

Most depictions of climate change impacts are linear and gradual, meaning that incremental changes in the environment are assumed to occur with incremental changes in climate. In most simulations of the problem, CO₂ concentrations in the atmosphere slowly rise over time; the climate system is assumed to respond like a dial that is being slowly turned up over time. This gradual change in temperature presumably yields gradual shifts in ecosystems, increases in sea levels, etc.

However, there is evidence that certain aspects of the climate system work more like a switch than a dial, and that a threshold level of warming could trigger sudden changes in the planet that would have dramatic, catastrophic consequences.⁴ One example of such a change is the potential weakening or collapse of the North Atlantic Ocean’s “thermohaline circulation,” the ocean circulation that produces the Gulf Stream current and allows temperatures in Western Europe to rise to higher levels than those of other places of comparable latitude. This process is stable as long as sea surface temperatures remain below a critical threshold. However, climate change could gradually raise sea-surface temperatures above this threshold, resulting in the rapid destabalization of thermohaline circulation, with significant consequences to climate in the North Atlantic region. Another example of a catastrophic event that could be triggered by climate change is the potential break-up of the West Antarctic ice sheet, which would take centuries to occur but could result in catastrophic sea-level rise.

The possibility of these non-linear catastrophic events defies the way computer models traditionally have depicted climate change. Assuming these events are possible, as described in the IPCC’s Third Assessment Report,⁵ the benefits associated with immediate action are far greater than models using “smooth” or linear damage functions would suggest. Immediate action offers us the best chance of avoiding the possibility of catastrophic changes in the world’s climate.

NEXT: Addressing Uncertainty

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