The Polar Amplification Model Intercomparison Project (PAMIP) contribution to CMIP6: investigating the causes and consequences of polar amplification

Abstract

Abstract. Polar amplification – the phenomenon that external radiative forcing produces a larger change in surface temperature at high latitudes than the global average – is a key aspect of anthropogenic climate change, but its causes and consequences are not fully understood. The Polar Amplification Model Intercomparison Project (PAMIP) contribution to the Sixth Coupled Model Intercomparison Project (CMIP6, Eyring et al. 2016) seeks to improve our understanding of this phenomenon through a coordinated set of numerical model experiments documented here. In particular, PAMIP will address the following primary questions: 1. What are the relative roles of local sea ice and remote sea surface temperature changes in driving polar amplification? 2. How does the global climate system respond to changes in Arctic and Antarctic sea ice? These issues will be addressed with multi-model simulations that are forced with different combinations of sea ice and/or sea surface temperatures representing present day, pre-industrial and future conditions. The use of three time periods allows the signals of interest to be diagnosed in multiple ways. Lower priority tier experiments are proposed to investigate additional aspects and provide further understanding of the physical processes. These experiments will address the following specific questions: What role does ocean-atmosphere coupling play in the response to sea ice? How and why does the atmospheric response to Arctic sea ice depend on the pattern of sea ice forcing? How and why does the atmospheric response to Arctic sea ice depend on the model background state? What are the roles of local sea ice and remote sea surface temperature in polar amplification, and the response to sea ice, over the recent period since 1979? How does the response to sea ice evolve on decadal and longer timescales? A key goal of PAMIP is to determine the real world situation using imperfect climate models. Although the experiments proposed here form a coordinated set, we anticipate a large spread across models. However, this spread will be exploited by seeking emergent constraints in which model uncertainty may be reduced by using an observable quantity that physically explains the inter-model spread. In summary, PAMIP will improve our understanding of the physical processes that drive polar amplification and its global climate impacts, thereby reducing the uncertainties in future projections and predictions of climate change and variability.

Ural Blocking as a Driver of Early‐Winter Stratospheric Warmings

“…It cannot be ruled out that SC‐WACCM is particularly insensitive to present‐day BK sea ice anomalies and that in the real world the feedback they exert onto the atmosphere is larger than suggested in this study. Coordinated multimodel experiments with various sea ice forcings, including BK sea ice anomalies (Smith et al, ), will help clarifying the role of sea ice on atmospheric variability. In the meantime, the present study further questions causality between BK sea ice, the UB, and the warm Arctic/cold Siberia pattern (Sorokina et al, ).…”

Ural Blocking Driving Extreme Arctic Sea Ice Loss, Cold Eurasia, and Stratospheric Vortex Weakening in Autumn and Early Winter 2016–2017

“…It is still an open question, whether the sea ice loss over the BKS exerts any positive feedback forcing that favored the recurrence of the UB events as an upper‐level manifestation of the WACS/WACE pattern (Honda et al, ; Mori et al, , ; Sun et al, ). The Polar Amplification MIP (PAMIP; Smith et al, ) is expected to bring progress on this question. Multimodel simulations that are forced with various combinations of sea ice representing present‐day, preindustrial, and future conditions will be analyzed to investigate whether the sea ice changes over the BKS can influence UB activity and the WACS pattern.…”

Global Coupled Climate Response to Polar Sea Ice Loss: Evaluating the Effectiveness of Different Ice‐Constraining Approaches

“…The extent to which these discrepancies arise from structural differences across models (i.e., model physics and resolution) or from differences in experimental design (location of sea ice loss and methodology) has not been documented. Thus, a coordinated experimental protocol is needed to properly compare model simulations (Smith et al, ).…”

“…A coordinated set of coupled ocean‐atmosphere model experiments has been proposed as part of the Polar Amplification Model Intercomparison Project (PAMIP) to investigate the global climate response to Arctic and Antarctic sea ice loss on decadal and centennial timescales (Smith et al, ). In these experiments, polar sea ice will be artificially decreased without altering greenhouse gas (GHG) concentrations so as to differentiate its effect on the global climate system from other aspects of anthropogenic climate change.…”