The project SMURPHS (Securing Multidisciplinary UndeRstanding and Prediction of Hiatus and Surge events) aims to better understand the causes of periods where the rate of global-mean surface temperature is increased or decreased at decadal time-scales (hereafter referred to as "surge" or "hiatus" events, or collectively as "H/S events") compared with long term (multi-decadal) trends. The focus is to understand the slowdown in the rate of warming since the late 1990s but earlier H/S events will also be considered. Previous investigations have largely focused on single mechanisms contributing to the current hiatus. Our approach advanceed current understanding and improve prediction of hiatus and surge decades by considering multiple mechanisms and their interactions.
A novel, inter-disciplinary framework was applied to three primary research objectives.
Objective 1: Developing a conceptual framework for characterising hiatus and surge events. There is currently no established framework for quantifying H/S events and their main causes. SMURPHS aims to understand the morphology of past events and develop new ways of comparing observations and models to understand interactions between different components of the climate system (atmosphere, land and ocean), forced response and internal variability. Specific objectives are; O1a. To create a suitable conceptual global framework to understand the role of interactions between forced response and internal variability. The framework would concentrate on how different processes can cause H/S events in global-mean surface temperature. O1b. To determine multivariate fingerprints of H/S events and their spatial structure in observations and models. There was a focus on the spatial structure of process variables relating to the flow of energy through the climate system.
Objective 2: Assess the key processes in past hiatus and surge events. The project considered multiple potential mechanisms involved in driving, amplifying and extending H/S events with particular focus on four key processes and their interactions, that have been implicated in past events but have so far been poorly quantified. Specific objectives are; O2a. To understand the role of changing patterns of anthropogenic tropospheric aerosol emissions in driving and influencing the evolution of H/S events. O2b. To determine the influence of volcanic aerosol on H/S events for both large and small eruptions, quiet and active periods. O2c. To identify ocean dynamical mechanisms that alter ocean heat uptake (from the upper ocean, of about 100 m depth, which may be regarded as part of the surface climate system on interannual timescales, into the ocean beneath). O2d. To identify possible cloud feedback changes that alter the Earth's energy imbalance during H/S events. O2e. To understand how these possible drivers interact and may be linked.
Objective 3: Determine the predictability of hiatus and surge events. The extent to which the recent hiatus was predictable is debated. Most hind-casts exhibit too much warming. This may be because the event was inherently unpredictable, or because model biases or inadequate observations preclude the ability to predict it. Specific objectives are: O3a. To assess the potential predictability of H/S events and to determine which processes are essential for predictability. A specific focus was on the role of volcanic eruptions. O3b. To assess the role of H/S events in near term future trends. This was aided by participation in international coordination efforts on decadal prediction. O3c. To quantify the contributions of forcing and internally generated variability to past H/S events O3d. To determine how H/S events affect estimates of transient climate response and equilibrium climate sensitivity.