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James A. Screen
,
Clara Deser
, and
Lantao Sun

Abstract

In early January 2014, an Arctic air outbreak brought extreme cold and heavy snowfall to central and eastern North America, causing widespread disruption and monetary losses. The media extensively reported the cold snap, including debate on whether human-induced climate change was partly responsible. Related to this, one particular hypothesis garnered considerable attention: that rapid Arctic sea ice loss may be increasing the risk of cold extremes in the midlatitudes. Here we use large ensembles of model simulations to explore how the risk of North American daily cold extremes is anticipated to change in the future, in response to increases in greenhouse gases and the component of that response solely due to Arctic sea ice loss. Specifically, we examine the changing probability of daily cold extremes as (un)common as the 7 January 2014 event. Projected increases in greenhouse gases decrease the likelihood of North American cold extremes in the future. Days as cold or colder than 7 January 2014 are still projected to occur in the mid-twenty-first century (2030–49), albeit less frequently than in the late twentieth century (1980–99). However, such events will cease to occur by the late twenty-first century (2080–99), assuming greenhouse gas emissions continue unabated. Continued Arctic sea ice loss is a major driver of decreased—not increased—North America cold extremes. Projected Arctic sea ice loss alone reduces the odds of such an event by one-quarter to one-third by the mid-twenty-first century, and to zero (or near zero) by the late twenty-first century.

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Dillon J. Amaya
,
Michael A. Alexander
,
Antonietta Capotondi
,
Clara Deser
,
Kristopher B. Karnauskas
,
Arthur J. Miller
, and
Nathan J. Mantua
Open access
Sarah M. Kang
,
Matt Hawcroft
,
Baoqiang Xiang
,
Yen-Ting Hwang
,
Gabriel Cazes
,
Francis Codron
,
Traute Crueger
,
Clara Deser
,
Øivind Hodnebrog
,
Hanjun Kim
,
Jiyeong Kim
,
Yu Kosaka
,
Teresa Losada
,
Carlos R. Mechoso
,
Gunnar Myhre
,
Øyvind Seland
,
Bjorn Stevens
,
Masahiro Watanabe
, and
Sungduk Yu

Abstract

This article introduces the Extratropical–Tropical Interaction Model Intercomparison Project (ETIN-MIP), where a set of fully coupled model experiments are designed to examine the sources of longstanding tropical precipitation biases in climate models. In particular, we reduce insolation over three targeted latitudinal bands of persistent model biases: the southern extratropics, the southern tropics, and the northern extratropics. To address the effect of regional energy bias corrections on the mean distribution of tropical precipitation, such as the double intertropical convergence zone problem, we evaluate the quasi-equilibrium response of the climate system corresponding to a 50-yr period after the 100 years of prescribed energy perturbation. Initial results show that, despite a large intermodel spread in each perturbation experiment due to differences in ocean heat uptake response and climate feedbacks across models, the southern tropics is most efficient at driving a meridional shift of tropical precipitation. In contrast, the extratropical energy perturbations are effectively damped by anomalous heat uptake over the subpolar oceans, thereby inducing a smaller meridional shift of tropical precipitation compared with the tropical energy perturbations. The ETIN-MIP experiments allow us to investigate the global implications of regional energy bias corrections, providing a route to guide the practice of model development, with implications for understanding dynamical responses to anthropogenic climate change and geoengineering.

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Amy Solomon
,
Lisa Goddard
,
Arun Kumar
,
James Carton
,
Clara Deser
,
Ichiro Fukumori
,
Arthur M. Greene
,
Gabriele Hegerl
,
Ben Kirtman
,
Yochanan Kushnir
,
Matthew Newman
,
Doug Smith
,
Dan Vimont
,
Tom Delworth
,
Gerald A. Meehl
, and
Timothy Stockdale

Abstract

Given that over the course of the next 10–30 years the magnitude of natural decadal variations may rival that of anthropogenically forced climate change on regional scales, it is envisioned that initialized decadal predictions will provide important information for climate-related management and adaptation decisions. Such predictions are presently one of the grand challenges for the climate community. This requires identifying those physical phenomena—and their model equivalents—that may provide additional predictability on decadal time scales, including an assessment of the physical processes through which anthropogenic forcing may interact with or project upon natural variability. Such a physical framework is necessary to provide a consistent assessment (and insight into potential improvement) of the decadal prediction experiments planned to be assessed as part of the IPCC's Fifth Assessment Report.

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