NERC-NSF-GEO Assessing Decadal Variability of sea Ice (ADVIce)
Lead Research Organisation:
UNIVERSITY OF EXETER
Abstract
The climate is unequivocally warming as has been predicted for decades, but sea ice at both poles continues to surprise. Arctic sea-ice cover has remained relatively steady for the past ~20 years. This slowdown was unexpected, coming after three decades of rapid decline. Even with the benefit of hindsight, the slowdown is puzzling given that the global average temperature has continued to rise. In the Antarctic, sea-ice cover remained stable, or even slightly increased, from 1979 to 2015. However, Antarctic sea ice has dropped dramatically since 2016.
On decadal timescales, sea ice evolution is likely controlled by both internal climate variability and responses to volcanic eruptions and human emissions (greenhouse gases and aerosols), but their relative contributions and the mechanisms involved are poorly known. ADVIce addresses this research gap. To explain the recent slowdown in Arctic sea-ice loss and surge in Antarctic sea-ice loss, and to avoid future surprises, a deeper understanding of decadal sea-ice variability is needed. The overarching aim of ADVIce is to provide this information, through 3 interconnected objectives:
Identify the mechanisms and forcings of decadal sea-ice variability and their representation in climate models.
Diagnose the likelihood, characteristics and drivers of SSEs in past, current and future climates.
Provide more precise near-term projections of Arctic and Antarctic sea ice.
To address objective 1, observed and reconstructed sea-ice variability over the past century will be examined using innovative statistical methods to diagnose modes of decadal sea-ice variability and their atmospheric and oceanic drivers. This will provide a fundamental understanding of the mechanisms of decadal sea-ice variability. The same methods will be applied to climate models to evaluate their ability to simulate these observed modes and their drivers. New simulations will be performed to extend the large ensembles of CMIP6 historical simulations to near-present, to cover the time periods of the recent Arctic slowdown and Antarctic surge. Building on this foundation, we will quantify the roles of natural and anthropogenic forcings using newly available single-forcing large ensemble simulations. In parallel and complementary to the analysis of modes of decadal sea-ice variability, for objective 2, we will identify surge and slowdown events (SSEs) in climate models and explore their characteristics, focussing on their frequency, predictability, longevity, oceanic and atmospheric precursors, and changing likelihood and character in a warming climate. Finally, in objective 3, the improved knowledge of mechanisms of decadal sea-ice variability and their fidelity in climate models will guide a reassessment of near-term climate projections of sea ice at both poles. We will develop methods to adjust projections to account for different phasing (and potentially magnitudes) of decadal variability, which our pilot work suggests will significantly alter near-term projections, including the time of emergence of ice-free Arctic summers. This is important for guiding future decision-making on environmental change at the two poles over the coming decades.
There are timely and important research questions that need answering in both hemispheres (e.g., recent unexplained trends) and, since the same methods can be applied to both, an opportunity exists to address these in an integrated and efficient manner. ADVIce will inform model development by identifying processes that are deficient in models, which will be of benefit to the producers and users of climate models and their projections, through close partnership with the Met Office.
On decadal timescales, sea ice evolution is likely controlled by both internal climate variability and responses to volcanic eruptions and human emissions (greenhouse gases and aerosols), but their relative contributions and the mechanisms involved are poorly known. ADVIce addresses this research gap. To explain the recent slowdown in Arctic sea-ice loss and surge in Antarctic sea-ice loss, and to avoid future surprises, a deeper understanding of decadal sea-ice variability is needed. The overarching aim of ADVIce is to provide this information, through 3 interconnected objectives:
Identify the mechanisms and forcings of decadal sea-ice variability and their representation in climate models.
Diagnose the likelihood, characteristics and drivers of SSEs in past, current and future climates.
Provide more precise near-term projections of Arctic and Antarctic sea ice.
To address objective 1, observed and reconstructed sea-ice variability over the past century will be examined using innovative statistical methods to diagnose modes of decadal sea-ice variability and their atmospheric and oceanic drivers. This will provide a fundamental understanding of the mechanisms of decadal sea-ice variability. The same methods will be applied to climate models to evaluate their ability to simulate these observed modes and their drivers. New simulations will be performed to extend the large ensembles of CMIP6 historical simulations to near-present, to cover the time periods of the recent Arctic slowdown and Antarctic surge. Building on this foundation, we will quantify the roles of natural and anthropogenic forcings using newly available single-forcing large ensemble simulations. In parallel and complementary to the analysis of modes of decadal sea-ice variability, for objective 2, we will identify surge and slowdown events (SSEs) in climate models and explore their characteristics, focussing on their frequency, predictability, longevity, oceanic and atmospheric precursors, and changing likelihood and character in a warming climate. Finally, in objective 3, the improved knowledge of mechanisms of decadal sea-ice variability and their fidelity in climate models will guide a reassessment of near-term climate projections of sea ice at both poles. We will develop methods to adjust projections to account for different phasing (and potentially magnitudes) of decadal variability, which our pilot work suggests will significantly alter near-term projections, including the time of emergence of ice-free Arctic summers. This is important for guiding future decision-making on environmental change at the two poles over the coming decades.
There are timely and important research questions that need answering in both hemispheres (e.g., recent unexplained trends) and, since the same methods can be applied to both, an opportunity exists to address these in an integrated and efficient manner. ADVIce will inform model development by identifying processes that are deficient in models, which will be of benefit to the producers and users of climate models and their projections, through close partnership with the Met Office.