Climate Change, Extreme Weather Linked(?) at Last

by Judith Curry

The title for this post comes from a post at Pew Climate, highlighting a big three-part series featured on ScientificAmerican.com  to explain the link between climate change extreme weather.

The series is characterized on the Pew web site as follows:

In a new three-part series featured on Scientific American.com, award-winning science journalist John Carey dissects the science, impacts, and actions to take regarding the record-breaking floods, heat waves, droughts, storms, and wildfires experienced across the United States and the world in the past year. 

Here are the links to the three articles:

• Part 1 Storm Warnings: Extreme Weather is a Product of Climate Change
• Part 2  Global Warming and the Science of Extreme Weather
• Part 3  Our Extreme Future: Predicting and Coping

This is probably the best one-stop shop I’ve seen for the argument that global warming is causing the wide ranging recent spate of extreme events.  It is well written and comprehensive, with plenty of examples of recent weather disasters and authoritative comments from many experts.  The punchline (drum roll . . .) is this statement:

The evidence is in: global warming has caused severe floods, droughts and storms.

So is anyone convinced by these articles?  Below are some deeper perspectives on this issue.

Recent WMO Workshop

The status of our knowledge on attributing extreme events to global warming is summarized by these recommendations from a recent WMO Workshop on Metrics and Methods for Estimation of Extreme Climate Events.

5. General recommendations of the Workshop

The final discussion summarized the recommendations of the BOGs and delivered consolidated general Workshop recommendations as follows:

• WCRP, through its core projects, should enhance efforts to develop improved, high temporal resolution (sub-daily) datasets that can be used to assess changes in extreme rainfall, drought, heat waves, floods, and storms.

• WCRP and in particular, the Working Group on Coupled Modelling, should include in the agenda of model evaluation the focus on the model’s ability to replicate extremes and to better compare model output with observations.

• WCRP core projects (foremost GEWEX and CLIVAR) should place high priority on determining the main phenomena responsible for extremes and improving understanding of the relevant physical processes.

• Special action is required on the development of robust statistical methods for assessing extremes and their uncertainties and on making these tools available for wide-spread use.

• An activity on analysis of extremes utilizing data archived by the WCRP Coupled Model Intercomparison Project should be planned and launched in the near future.

JC’s statement for the Yale360 Forum

And finally, in case you missed it the first time around, here is the statement that I provided to the recent Yale360 Forum on this topic:

Judith Curry, chair of Georgia Institute of Technology’s School of Earth and Atmospheric Sciences.
The substantial interest in attributing extreme weather events to global warming seems rooted in the perceived need for some sort of a disaster to drive public opinion and the political process in the direction of taking action on climate change. However, attempts to attribute individual extreme weather events, or collections of extreme weather events, may be fundamentally ill-posed in the context of the complex climate system, which is characterized by spatiotemporal chaos. There are substantial difficulties and problems associated with attributing changes in the average climate to natural variability versus anthropogenic forcing, which I have argued are oversimplified by the IPCC assessments. Attribution of extreme weather events is further complicated by their dependence on weather regimes and internal multi-decadal oscillations that are simulated poorly by climate models.

I am unconvinced by any of the arguments that I have seen that attributes a single extreme weather event, a cluster of extreme weather events, or statistics of extreme weather events to anthropogenic forcing. Improved analysis of the attribution of extreme weather events requires a substantially improved and longer database of the events. Interpretation of these events in connection with natural climate regimes such as El Nino is needed to increase our understanding of the role of natural climate variability in determining their frequency and intensity. Improved methods of evaluating climate model simulations of distributions of extreme event intensity and frequency in the context of natural variability is needed before any confidence can be placed in inferences about the impact of anthropogenic influences on extreme weather events.

Gavin Schmidt’s take

Note, mine is not just a “skeptics” view; it pretty much agrees with Gavin Schmidt’s RC post last Feb entitled “Going to Extremes.”  An excerpt:

Let’s start with some very basic, but oft-confused points:

• Not all extremes are the same. Discussions of ‘changes in extremes’ in general without specifying exactly what is being discussed are meaningless. A tornado is an extreme event, but one whose causes, sensitivity to change and impacts have nothing to do with those related to an ice storm, or a heat wave or cold air outbreak or a drought.
• There is no theory or result that indicates that climate change increases extremes in general. This is a corollary of the previous statement – each kind of extreme needs to be looked at specifically – and often regionally as well.
• Some extremes will become more common in future (and some less so). We will discuss the specifics below.
• Attribution of extremes is hard. There are limited observational data to start with, insufficient testing of climate model simulations of extremes, and (so far) limited assessment of model projections.