Natural and human systems tend to be at least somewhat adapted to local, historical variations in climate. Stormwater infrastructure, for instance, is designed to accommodate a certain amount of water based on a 24-hour, 100-year event. Therefore, when climate change causes local conditions to significantly diverge from what was experienced historically -- and what our local systems are accustomed to -- ecological and societal disruptions may occur.

The time of emergence of the climate change signal is likely to be different for different climate change-related factors (such as precipitation and temperature), as well as locations. Climate change may not be noticeable for many decades for some variables because the projected change is small compared to historic variability. In other cases, the influence of climate change may emerge much earlier. For example, preliminary research suggests the signal emerges earlier in mean Pacific Northwest temperature compared with extreme precipitation events. Understanding when the climate change signal is likely to be “louder” than historical variations on the local level can help decision makers prioritize among many adaptation actions and efforts.

Additionally, time of emergence can be computed not only for average climate but also for management-relevant parameters, such as frequency of precipitation events or stream temperature exceeding a certain threshold. These are critical thresholds used to trigger emergency response.

Photo credit: Julie Morse, Nature Conservancy

Through a combination of climate statistics, engagement with policy and management entities, and data delivery platform development, we developed a new approach to climate change decision support based on the time of emergence concept for the Puget Sound basin in the Pacific Northwest.

The Time of Emergence analysis and prototype online tool were designed to help users explore the basic question: when and where could climate change matter across the Pacific Northwest? Federal, state, and local decision-makers identified dozens of temperature-, precipitation-, hydrologic-, and streamflow-related variables relevant to drought, energy, fish, floods, human health, infrastructure, streamflow, and water quality to be used for time of emergence computation. Additionally, a web-based interaction system enabled users to visualize how the time of emergence of the climate change signal varies geographically for different climate change-related parameters across the Pacific Northwest.

This is a new approach to delivery of climate change information that (1) focuses on identifying the time when climate change causes local conditions to deviate significantly from the past, which we call the Time of Emergence of climate change and (2) provides this information in the context of a wide range of scientifically credible future potential conditions, in order to stimulate and support user understanding of the implications of scientific uncertainty for decisions and priority setting.