Scoping study: Modelling the interaction between mitigation and adaptation for decision making

Greenhouse gas emissions to date have put the planet on a pathway to at least some warming, perhaps some 1.5°C above pre-industrial levels. This will require adaptation measures. At the same time, it is crucial to curb emissions to avoid more dangerous levels of climate change. Hence, combinations of mitigation and adaptation will be needed to prevent the worst climate change impacts.

In exploring these combinations, the question has been posed as to whether adaptation in a +3°C world, say, could reduce impacts to the level that would have been incurred in a +2°C world (which may or may not already have implemented some adaptation measures). This report explores that notion and argues that adaptation cannot substitute for mitigation – not in a predictable and reliably quantifiable way.

Adaptation occurs on different levels than mitigation, usually at the local or national scale; its feasibility and costs differ greatly across sectors and regions; and there are limits to adaptation – both immutable, physical limits and more mutable financial or societal limits that are inherently difficult to quantify.

Given that adaptation is already built into the assumptions of widely used integrated assessment models (IAMs) of climate economics, however, this report explores how that modelling is done, noting problems not only with how adaptation is modelled, but also how climate change damages are quantified.

The report also explores how these problems might be addressed in an IAM, looking at how the PAGE09 model, developed by co-author Chris Hope, has been adjusted to better reflect uncertainty about climate change impacts and about future adaptation.

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