Climate Committee Takes Aim at Extreme Climatic Events

Network News Fall 2004, Vol. 17 No. 2

Recent activities of the climate committee have focused on a new research initiative to study the effects of extreme climatic events. The Extreme Events Working Group (XEWG) formed as a result of a climate committee-sponsored workshop held at the 2003 All-Scientist's meeting in Seattle. The extreme events project is intended as a follow up to the highly successful Climate Variability Ecosystem Response (CVER) project headed by David Greenland during his tenure as Climate Committee chair. The XEWG project borrows many concepts and ideas from CVER, including a cross-perspective and use of a series of guiding framework questions. However, we hope to enhance the cross-site synthesis component of the project. Ultimately, our goal is to create a "typology” of LTER sites according to their response to various types of climatic extremes. We believe that this initiative will provide insight into how various ecosystems might respond to the changes in type, magnitude, and frequency of extreme climate events that are hypothesized to occur under various global climate change scenarios.

In June, XEWG held a two-day workshop at Portland State University to outline the project and formulate synthesis questions to guide the research. The meeting was attended by Tony Brazel (CAP), Andrew Fountain (MCM), Doug Goodin (KNZ), Julian Hadley (HFR), Glenn Juday (BNZ), Brian Kloeppel (CWT), Alan Knapp (SGS & KNZ), Mark Losleben (NWT), and Melinda Smith (KNZ). Early in the discussion, we realized that we needed to consider both extreme climate events (as drivers) and extreme ecological responses in order to address our research objectives. Much of the workshop was spent defining and refining definitions of these two types of extremes. For climate extremes, we came up with two broad definitional characteristics:

  1. Extremes exceed some sort of limit in terms of magnitude, duration, and frequency
  2. Extremes are sensitive to the context in which they occur (i.e. the local climate) relative to some predefined time horizon (e.g. 30-500 years). Based on these two characteristics, we agreed on the following definition:

Extreme climatic events are statistically rare in frequency, magnitude, and/or duration for a single climate parameter or combination of parameters for a particular ecosystem. The ability to recognize and categorize extreme events is dependent upon the length of reliable observational records. An extreme climatic event may or may not induce an ecological response.

This definition conforms fairly well to existing definitions, but extends them by explicitly acknowledging the link between climate extremes and ecological responses.  The definition also “works” from a climatological, as opposed to a meteorological perspective—which is especially important for us because most of the specific research goals we laid out assumed that we would search LTER and other climate databases for longer-term anomalies. 

Defining an extreme ecological response turned out to be a bit more complicated than defining climatic extremes. We considered a number of definitional concepts, most of which seemed to be framed in terms of ecosystem composition, process, or structure. Like the climatological definition, the definition of ecological response seemed to hinge on the idea of limits, but the complexity of ecological systems and their responses necessitated a more complex consideration of the concept of limits. Thus, extreme ecological effects might exceed limits at single or multiple hierarchical levels. Changes might be transient or persistent, and they may or may not affect the future response of the ecosystem of its components. We also discussed directional change and the reestablishment of baselines. We reached a consensus that new baselines could result from a climatic disturbance, but that baseline change was not required for an ecological response to be considered important or significant. Thus:

A extreme ecological response is a change in ecological attributes that is statistically rare in frequency, magnitude, and/or duration, or a persistent alteration of ecological properties at any level of organization.

We spent the rest of the workshop refining the definitions and devising a set of framework questions to guide the research. We summarized the guiding framework in a diagram proposed by Smith and modified by the group during the discussion (Figure 1):

Figure 1:

Much of our analysis will focus on unearthing the nature of the contextual “switch” that determines whether a system reacts in an extreme or non-extreme manner. Figure XX also lists some possible factors in this response. Once it is determined that an extreme response has occurred, other questions concern the nature of that response:

  • Does an ecological impact involve the disruption of existing relationships or completion of a threshold change?
  • Does successional stage or community age effect the conditions for or consequences of an extreme climatic event?
  • What is the time scale of the response (to complete response cycle)?
  • Is response mediated by organisms?
  • Is effect direct or cascading?
  • What antecedent conditions are required for a response to occur and must effects occur in a certain sequence?
  • What is the role of biota (browsers, grazers, etc.) in conditioning the system?
  • What weather/climate variables are associated with the highest productivity and lowest productivity in a system?
  • Are there any extreme climatic events associated with the elimination of species and/or the establishment of new species?
  • Is there a seasonal component of ecological response?
  • What weather/climate variables are most important (precipitation, thermal, wind, mixture, etc.)?
  • Does the ecological response result from novel combinations of climate extremes?
  • What ecosystem variable(s) respond(s)?
  • What limits or thresholds must be exceeded in order for the response to occur?

Trying to initiate this program at all LTER sites and including all possible climate extremes would be very difficult to pull off, so the group decided to begin with a limited pilot program consisting of just two types of climate extremes--temperature and precipitation--for a selected subset of LTER sites. Currently, we are in the process of gathering data and determining which sites will be part of this pilot project. Our goal is to complete this pilot analysis by next spring. Although members of XEWG are mostly associated with the climate committee, we invite comments, suggestions, and participation from all interested LTER researchers.

Douglas G. Goodin
Konza LTER, Committee Chair