Communicating the uncertainties of internal climate variability to the general public

Internal climate variability describes the natural random fluctuation of the climate system, which arise from non-linear dynamic processes in the atmosphere and ocean and are intrinsic to the climate system. It is one of the major sources of uncertainty in climate projections, besides model error and scenario uncertainty. The research branch of initial-condition large ensembles (SMILEs) investigates internal climate variability by employing large ensembles of dozens of climate simulations that are generated using the same model and scenario but slightly different initial conditions. With this, SMILEs enable to statistically capture the spread of internal variability of the climate system.

Regarding science communication with the general public, internal climate variability is an especially challenging topic. This is for one thing due to the large ensembles involved, which call for an adequate presentation format; for another, the possibilities to capture the concept of internal climate variability with real-life experiences are limited since observations represent only one realization of the climate state and, in the case of extreme events, deliver only a limited number of events that are insufficient to cover the spread of internal climate variability.

Here, we present three approaches to encounter the challenges in climate communication with respect to internal climate variability. The first approach involves a study on the extreme event of meteorological droughts in Europe and uses the intuitive drought index “percent-of-normal” to prepare the results of a regional SMILE over Europe for the purpose of science communication. “Drying stripes”, an illustration form inspired by the “warming stripes” by Ed Hawkins, are used to tailor the obtained results in an appealing way for the media (press releases, television and newspapers). The second study approach uses several global SMILEs from the Coupled Intercomparison Project 6 (CMIP6) to investigate climate change effects and the range of internal climate variability for important temperature- and precipitation-based climate indices. The concepts of time of emergence and global warming levels are used to derive concise statements about the degree of global warming at which the analyzed climate indices exceed the noise of internal climate variability. The third approach targets at the preparation of the results from the ClimEx project (“Climate Change and Hydrological Extremes”), which deals with internal climate variability over the study area of Bavaria. The results are presented in form of a flyer and a hydrological atlas, which has been used for communication purposes in cooperation with the Bavarian State Office for the Environment.

These three approaches are initiatives to facilitate a condensed and comprehensible communication of the uncertainty of internal climate variability in climate projections to the general public. The presented formats include analysis, figures, statements and flyers that are targeted for media presentation and agency-based science communication.