Arctic decadal variability in a warming world

Natural decadal variability of surface air temperature might obscure Arctic temperature trends induced by anthropogenic forcing. It is therefore imperative to know how Arctic decadal variability (ADV) will change as the climate warms. In this study, we evaluate ADV characteristics in three equilibrium climates with present-day, double, and quadrupled atmospheric CO2 forcing. The dominant region of variability, which is located over the Barents and Greenland Sea at present, shifts to the central Arctic and Siberian regions as the climate warms. The maximum variability in sea ice cover and surface air temperature occurs in the CO2 doubling climate when sea ice becomes more vulnerable to melt over vast stretches of the Arctic. Furthermore, the links between dominant atmospheric circulation modes and Arctic surface climate characteristics vary strongly with climate change. For instance, a positive Arctic Oscillation index is associated with a colder Arctic in warmer climates, instead of a warmer Arctic at present. Such changing relationships are partly related to the retreat of sea ice because altered wind patterns influence the sea ice distribution and hence the associated local surface fluxes. The atmospheric pressure distributions governing ADV and the associated large-scale dynamics also change with climate warming. The changing character of the ADV shows that it is vital to consider (changes in) ADV when addressing Arctic warming in climate model projections

Seasonal and regional contrasts of future trends in interannual arctic climate variability

Future changes in interannual variability (IAV) of Arctic climate indicators such as sea ice and precipitation are still fairly uncertain. Alongside global warming-induced changes in means, a thorough understanding of IAV is needed to more accurately predict sea ice variability, distinguish trends and natural variability, as well as to reduce uncertainty around the likelihood of extreme events. In this study we rank and select CMIP6 models based on their ability to replicate observations, and quantify simulated IAV trends (1981–2100) of Arctic surface air temperature, evaporation, precipitation, and sea ice concentration under continued global warming. We argue that calculating IAV on grid points before area-averaging allows for a more realistic picture of Arctic-wide changes. Large model ensembles suggest that on shorter time scales (30 years), IAV of all variables is strongly dominated by natural variability (e.g. 93% for sea ice area in March). Long-term trends of IAV are more robust, and reveal strong seasonal and regional differences in their magnitude or even sign. For example, IAV of surface temperature increases in the Central Arctic, but decreases in lower latitudes. Arctic precipitation variability increases more in summer than in winter; especially over land, where in the future it will dominantly fall as rain. Our results emphasize the need to address such seasonal and regional differences when portraying future trends of Arctic climate variability.</p

Oceanic heat transport into the Arctic under high and low CO2 forcing

Enhanced ocean heat transport into the Arctic is linked to stronger future Arctic warming and polar amplification. To quantify the impact of ocean heat transport on Arctic climate, it is imperative to understand how its magnitude and the associated mechanisms change in other climate states. This paper therefore assesses the ocean heat transport into the Arctic at 70∘N for climates forced with a broad range of carbon dioxide concentration levels, ranging from one-fourth to four times modern values. We focused on ocean heat transports through the Arctic entrances (Bering Strait, Canadian Archipelago, and Nordic Seas) and identified relative contributions of volume and temperature to these changes. The results show that ocean heat transport differences across the five climate states are dominated by heat transport changes in the Nordic Seas, although in the warmest climate state heat transport through the Bering Strait plays an almost equally important role. This is primarily caused by changes in horizontal currents owing to anomalous wind responses and to differential advection of thermal anomalies. Changes in sea ice cover play a prominent role by modulating the surface heat fluxes and the impact of wind stresses on ocean currents. The Atlantic meridional overturning circulation and its associated heat transport play a more modest role in the ocean heat transport into the Arctic. The net effect of these changes is that the poleward ocean heat transport at 70∘N strongly increases from the coldest climate to the warmest climate state

Calibration of basal melt on past ice discharge lowers projections of Antarctica’s sea level contribution

Abstract. Antarctic mass loss is the largest contributor to uncertainties in sea level projections on centennial timescales. In this study the contribution of Antarctica’s ice discharge to future sea level changes is computed with ocean thermal forcing from 14 earth system models and linear response functions from 16 ice sheet models for three greenhouse gas emission scenarios. Different than in previous studies, basal melt was calibrated on observed Antarctic ice discharge rather than on basal melt itself with an iterative approach. For each model combination, a linear and quadratic melt dependency were calibrated both regionally (in five Antarctic sectors) and at the continental scale. Projections using all model combinations show that the variation in basal melt computation methods affect the projected sea level more than the scenario variations (SSP1-2.6 to SSP5-8.5). After calibration, a high number of model pairs still underestimated ice discharge in hindcasts over 1979–2017. Therefore top 10 % best-performing model combinations were selected for each method. A comparison between these model selections shows that the quadratic melt parameterisation with Antarctic-wide calibration performs best in reproducing past ice discharge. We conclude that calibration of basal melt on past ice discharge combined with model selection makes projections of Antarctic ice discharge (more) consistent with observations over the past four decades. Moreover, calibration of basal melt on past ice discharge results in lower basal melt sensitivities and thus lower projections of Antarctica’s sea level contribution than estimates of previous multi-model studies

Ophthalmological findings in infants with microcephaly and presumable intra-uterus Zika virus infection

ABSTRACT Purpose: In 2015, a twenty-fold increase in the prevalence of microcephaly in Brazil was reported, and the Ministry of Health associated this abnormal prevalence with the maternal-fetal Zika virus (ZIKV) transmission. Methods: We assessed the ophthalmological findings of ten mothers and their infants that had been clinically diagnosed with ZIKV-related microcephaly and presented ocular abnormalities, born from May to December 2015. Results: Seven mothers (70.0%) referred symptoms during pregnancy (malaise, rash and arthralgia), of which six (85.7%) were in the first trimester. At the time of exam, no ophthalmological abnormalities were identified in the mothers and they did not report ocular symptoms during pregnancy. Serology was negative in all infants for Toxoplasmosis, Rubella, Cytomegalovirus, Syphilis and Human Immunodeficiency Viruses. Ocular findings included macular alterations (gross pigment mottling and/or chorioretinal atrophy) in fifteen eyes (75.0%), and optic nerve abnormalities (hypoplasia with double-ring sign, pallor, and/or increased cup-to-disk ratio) in nine eyes (45.0%). Conclusions: Patients presented normal anterior segment and important macular and optic nerve abnormalities. Further studies will assess the visual significance of these alterations

Arctic climate change and decadal variability

High northern latitudes exhibit enhanced near-surface warming in a climate with increasing greenhouse gases compared to other parts of the globe, indicating an amplified climate response to external forcing. Decadal to multidecadal variability sometimes enhances and at other times reduces the long-term trends. Therefore, the influence of internal variability should be taken into account when externally forced climate signals are assessed. This thesis contributes to our understanding of Arctic climate projections by clarifying the role of coupled ocean-sea-ice-atmosphere processes on the long-term trends and decadal variability of the Arctic climate system. Important mechanisms linked to the location of the sea ice margin and ocean heat transports into the Arctic have been identified and were shown to have a substantial effect on the Arctic's response to climate change

Arctic decadal variability in a warming world

Natural decadal variability of surface air temperature might obscure Arctic temperature trends induced by anthropogenic forcing. It is therefore imperative to know how Arctic decadal variability (ADV) will change as the climate warms. In this study, we evaluate ADV characteristics in three equilibrium climates with present-day, double, and quadrupled atmospheric CO2 forcing. The dominant region of variability, which is located over the Barents and Greenland Sea at present, shifts to the central Arctic and Siberian regions as the climate warms. The maximum variability in sea ice cover and surface air temperature occurs in the CO2 doubling climate when sea ice becomes more vulnerable to melt over vast stretches of the Arctic. Furthermore, the links between dominant atmospheric circulation modes and Arctic surface climate characteristics vary strongly with climate change. For instance, a positive Arctic Oscillation index is associated with a colder Arctic in warmer climates, instead of a warmer Arctic at present. Such changing relationships are partly related to the retreat of sea ice because altered wind patterns influence the sea ice distribution and hence the associated local surface fluxes. The atmospheric pressure distributions governing ADV and the associated large-scale dynamics also change with climate warming. The changing character of the ADV shows that it is vital to consider (changes in) ADV when addressing Arctic warming in climate model projections

Low-frequency variability of surface air temperature over the Barents Sea : causes and mechanisms

The predominant decadal to multidecadal variability in the Arctic region is a feature that is not yet well-understood. It is shown that the Barents Sea is a key region for Arctic-wide variability. This is an important topic because low-frequency changes in the ocean might lead to large variations in the sea-ice cover, which then cause massive changes in the ocean-atmosphere heat exchanges. Here we describe the mechanism driving surface temperatures and heat fluxes in the Barents Sea based primarily on analyzes of one global coupled climate model. It is found that the ocean drives the low-frequency changes in surface temperature, whereas the atmosphere compensates the oceanic transport anomalies. The seasonal dependence and the role of individual components of the ocean-atmosphere energy budget are analyzed in detail, showing that seasonally-varying climate mechanisms play an important role. Herein, sea ice is governing the seasonal response, by acting as a lid that opens and closes during warm and cold periods, respectively, thereby modulating the surface heat fluxes.</p