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Extreme Outcomes

Multiple Authors
Key Messages
  • Extreme outcomes refer to near-catastrophic events and processes that would push the climate system into undesirable states. While highly uncertain, major discontinuities of this nature are poorly represented in most assessments of the economics of climate change.
  • The understanding of extreme outcomes related to climate change is rapidly increasing. Earth systems and sustainability science have brought new insight into the nature of coupled socio-ecological systems, as well as the domains of resilience and surprises. ClimateCost has explored this new evidence and emerging science, considering two central policy questions: What impacts of climate change would make a significant difference to the global cost of climate change? What are the globally significant limits to adaptation?
  • Biogeophysical tipping elements in the Earth system include a number of events that could have serious consequences within 50 to 100 years: melting of the Greenland and West Antarctic ice caps and the Hindu Kush-Himalaya-Tibetan glaciers; changes in the Atlantic thermohaline circulation (THC) and El Niño/Southern Oscillation (ENSO); drought in the Amazon; and shifts in the Indian summer monsoon and rainfall in southwestern North America. ClimateCost has explored the consequences of some of these events.
  • The study has first assessed major sea level rise. Over 600 million people currently live in the low elevation coastal zone (areas below 10 metres of elevation that are hydrologically connected to the sea). Economic activity in this zone is over $2 trillion GDP, slightly less than 3% of global GDP. Asia and the Asia-Pacific account for the majority of the exposed population and a third of the exposed economic activity
  • New scenarios of sea level rise (SLR) highlight the possibility of more extreme changes than Intergovernmental Panel on Climate Change (IPCC) AR4 projections. ClimateCost has used such projections to assess the potential impacts and economic costs of major sea level rise. A high-end scenario of 1.65 m of SLR by the 2080s is estimated to result in nearly a 60% loss of global wetlands and to put over 30 million additional people / year at risk from coastal flooding when the effects of sea level rise and socio-economic change are considered. The economic costs of this high end SLR scenario could be in the region of $ 1 trillion per year (assuming no upgrades or adaptation, current prices, undiscounted, with 90% of this occurring due to climate induced sea level rise). However, such extreme scenarios are uncertain, with a low probability of occurrence.
  • There are already over 30 million migrants that have been caused (at least partially) from environmental forcing (including weather-related disasters). While estimates of future migration from climate change vary considerably, a growing consensus estimate is that over 100 million people could seek to move due to climatic risks (acting with or on top of other factors), possibly as soon as the 2050s.
  • A case study in South Asia has shown that security, conflict and the physical impacts of climate change could contribute to a socially contingent tipping point. South Asia is a major concern given the instability of the Indian monsoon and potential drought risk that might limit agricultural adaptation options.
  • However, projecting these effects is challenging. Climate change, and in particular extreme outcomes, is an example of a ‘wicked’ environmental problem. The ability to predict the future is limited; the chains of causal factors cannot be easily disentangled; and a strong path-dependence means there are many plausible responses.
  • Complex problems, such as tipping elements and extreme outcomes, can only be addressed through multiple lines of evidence. The ClimateCost project has explored a range of approaches, from qualitative narratives and case studies,to integrated assessment models and formal models of behavior based on actor-network approaches.

  • The science base for understanding extreme outcomes and planning adaptive responses requires international cooperation and is an area where European policymakers have a leading role. This is obvious for international water resources, trans-boundary health threats, migration and security. Further science-policy dialogues are warranted, linking across thematic areas.


Downing, TE and Butterfield, RE (2012). Extreme Outcomes: Prospects for major tipping and socially contingent events and associated economic and social costs. Summary of cross-sectoral results from the ClimateCost project funded by the European Community’s Seventh Framework Programme. Technical Policy Briefing Note 7. Oxford: Stockholm Environment Institute.

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