Understanding Climate Risk

Science, policy and decision-making

Full IPCC SREX Report Released

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The full IPCC Special Report Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX) has been released. The download of the entire report (44 Mb) is here, the Summary for Policymakers is here, the press release is here and slide presentation (pdf) here. Also on the site are individual chapters for download, review comments, process information, graphics and the grey literature library.

As I posted late last year with the release of the SPM, the great benefit of this special report is the coming together of the climate change and disaster management expert communities. A marriage, which I’m told, got a bit rocky at times. The report emphasises the need to address both biophysical and social-economic aspects of changing climate extremes and the systems exposed to those changes.

The interactions between changing hazards and system exposure are often difficult to sort out and remain a source of debate. Extremes are often infrequent, so the places they effect often change between events. This makes it very difficult to attribute impacts to the hazards themselves, modifications to the environment or to the number of people and value of development  exposed to those hazards.

One reasons for this is that the underlying statistical analysis assumes that the anthropogenic influence on changing climate hazards is linear with respect to the atmospheric forcing. This makes it very difficult to distinguish a climate signal from the noise of variability.

Increasing exposure of people and economic assets has been the major cause of the long-term increases in economic losses from weather- and climate-related disasters (high confidence). Long-term trends in economic disaster losses adjusted for wealth and population increases have not been attributed to climate change, but a role for climate change has not been excluded (medium evidence, high agreement). These conclusions are subject to a number of limitations in studies to date. Vulnerability is a key factor in disaster losses, yet it is not well accounted for. Other limitations are: (i) data availability, as most data are available for standard economic sectors in developed countries; and (ii) type of hazards studied, as most studies focus on cyclones, where confidence in observed trends and attribution of changes to human influence is low. The second conclusion is subject to additional limitations: (iii) the processes used to adjust loss data over time, and (iv) record length.

This doesn’t satisfy those who demand ‘proof’ of climate-related disasters before they will endorse expert warnings that disasters may occur.  This, of course, is stupid. The proof demand is to counter advocacy for climate change mitigation policy based on evidence of changing extremes. It is part of saying it isn’t happening and it won’t happen.

One way to view the potential for current and future extreme events is to think about where the energy from greenhouse gas forcing is going. Most heat is going into the ocean, delaying atmospheric warming. So observed warming is only part of what we will experience over the long term. There is a heap of evidence for this process from past climate change, in addition to models (backed by theory) and observations. The atmospheric warming process is therefore largely driven by energy from the ocean in the form of both sensible and latent heat. The latter is transferred from ocean to land through evaporation of seawater and rainfall on land.

This transfer is non-linear. Warming occurs in bursts than can be measured statistically as step changes. The linear statistics used for attribution tend to average these out, losing the non-linear component of the warming signal in the process. There is some evidence that rainfall may do this too, but the statistics are much more difficult to attribute. While some of the signals for extreme events such as tropical cyclones may take a long time to emerge in any case, non-linear behaviour in temperature and possibly rainfall (including drought) will be easier to identify and attribute. We are close to being able to do this for SE Australia. If non-linear changes in sea surface temperatures can be linked to storm strength, then tropical cyclones with fall into line as well. My prediction is that by 2020, most extremes on land will be routinely attributed to climate change and variability with moderate to high confidence.

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Written by Roger Jones

March 30, 2012 at 10:49 am

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