Polar Amplification and Ice Free Conditions under 1.5, 2 and 3 °C of Global Warming as Simulated by CMIP5 and CMIP6 Models

One of the most visible signs of global warming is the fast change in the polar regions. The increase in Arctic temperatures, for instance, is almost twice as large as the global average in recent decades. This phenomenon is known as the Arctic Amplification and reflects several mutually supporting processes. An equivalent albeit less studied phenomenon occurs in Antarctica. Here, we used numerical climate simulations obtained from CMIP5 and CMIP6 to investigate the effects of +1.5, 2 and 3 °C warming thresholds for sea ice changes and polar amplification. Our results show robust patterns of near-surface air-temperature response to global warming at high latitudes. The year in which the average air temperatures brought from CMIP5 and CMIP6 models rises by 1.5 °C is 2024. An average rise of 2 °C (3 °C) global warming occurs in 2042 (2063). The equivalent warming at northern (southern) high latitudes under scenarios of 1.5 °C global warming is about 3 °C (1.8 °C). In scenarios of 3 °C global warming, the equivalent warming in the Arctic (Antarctica) is close to 7 °C (3.5 °C). Ice-free conditions are found in all warming thresholds for both the Arctic and Antarctica, especially from the year 2030 onwards.

Response of Northern Hemisphere weather and climate to Arctic sea ice decline: Resolution independence in Polar Amplification Model Intercomparison Project (PAMIP) simulations

The impact of Arctic sea ice decline on the weather and climate in mid-latitudes is still much debated, with observation suggesting a strong and models a much weaker link. In this study, we use the atmospheric model OpenIFS, in a set of model experiments following the protocol outlined in the Polar Amplification Model Intercomparison Project (PAMIP), to investigate whether the simulated atmospheric response to future changes in Arctic sea ice fundamentally depends on model resolution. More specifically, we increase the horizontal resolution of the model from 125km to 39km with 91 vertical levels; in a second step resolution is further increased to 16km with 137 levels in the vertical. The model does produce a response to sea ice decline with a weaker mid latitude Atlantic jet and increased blocking in the high latitude Atlantic, but no sensitivity to resolution can be detected with 100 members. Furthermore we find that the ensemble convergence toward the mean is not impacted by the model resolutions considered here.

Precipitation associated with extra-tropical cyclones: response to uniform global warming and to polar amplification

<p>Extra-tropical cyclones constitute a large part of the circulation in the mid-latitudes and can lead to high impact weather. Therefore, it is beneficial to society to determine how these storms and their associated weather may change in the future. We focus on precipitation associated with extra-tropical cyclones (ETCs) and first aim to determine how the relationship between dynamical measures (e.g. maximum relative vorticity) of cyclone intensity and ETC related precipitation will response to climate change. Secondly, because not all ETCs are the same, we investigate whether the relationship between ETC precipitation and ETC intensity depends on the type of cyclone. Finally, we examine whether certain types of ETCs, in terms of their precipitation patterns, are likely to become more or less common in the future. We address these questions using aqua-planet simulations performed using an atmosphere-only model (OpenIFS) with fixed sea surface temperatures (SSTs). The simulations are run at T255 resolution (~ 80 km) and are 10 years long which generates a very large sample size of ETCs (> 14,000). The three simulations differ only in terms of the specific SST distribution: a control simulation is performed with the well-known “QObs” SST distributions, the second simulation has a uniform warming of 4K applied everywhere, and the third simulation is a polar amplification experiment with a 5K warming poleward of 45 degrees. In each experiment, all ETCs are objectively identified and tracked. Different types of cyclones are identified by applying k-means clustering to the precipitation pattern within a 12-degree radius of the cyclone centre. In all three experiments, more dynamically intense ETCs have more precipitation associated with them but there is considerable spread. Uniform warming strengthens this relationship and hence a ETC of a certain dynamical intensity will have more precipitation associated with it in a warmer climate. Clustering identifies 4 distinct types of ETCs in terms of their precipitation patterns: ETCs with most precipitation associated with the warm front; ETCs dominated by cold front precipitation; ETCs dominated by cyclone-centred precipitation; ETCs with very little precipitation. All 4 cyclone types appear in each experiment. Uniform warming causes a notable increase in the number of ETCs with precipitation concentrated on the warm front and a decrease in the number of ETCs with weak precipitation. In contrast, polar warming causes a large increase in the number of ETCs with weak precipitation and ETCs dominated by cold front precipitation decrease in number. These results, and others, will be presented along with dynamical interpretations.</p>

CAS FGOALS-f3-L Large-ensemble Simulations for the CMIP6 Polar Amplification Model Intercomparison Project

Large-ensemble simulations of the atmosphere-only time-slice experiments for the Polar Amplification Model Intercomparison Project (PAMIP) were carried out by the model group of the Chinese Academy of Sciences (CAS) Flexible Global Ocean-Atmosphere-Land System (FGOALS-f3-L). Eight groups of experiments forced by different combinations of the sea surface temperature (SST) and sea ice concentration (SIC) for pre-industrial, present-day, and future conditions were performed and published. The time-lag method was used to generate the 100 ensemble members, with each member integrating from 1 April 2000 to 30 June 2001 and the first two months as the spin-up period. The basic model responses of the surface air temperature (SAT) and precipitation were documented. The results indicate that Arctic amplification is mainly caused by Arctic SIC forcing changes. The SAT responses to the Arctic SIC decrease alone show an obvious increase over high latitudes, which is similar to the results from the combined forcing of SST and SIC. However, the change in global precipitation is dominated by the changes in the global SST rather than SIC, partly because tropical precipitation is mainly driven by local SST changes. The uncertainty of the model responses was also investigated through the analysis of the large-ensemble members. The relative roles of SST and SIC, together with their combined influence on Arctic amplification, are also discussed. All of these model datasets will contribute to PAMIP multi-model analysis and improve the understanding of polar amplification.

Middle and Late Jurassic climatic, oceanographic and environmental trends along the Viking Corridor

<p><strong>Keywords: Late Jurassic; palaeoclimate; Greenland; carbon cycling; Viking Corridor; belemnite stable isotopes</strong></p><p>The “polar amplification” effect, whereby the poles experience greater changes in temperature compared to the low latitudes for a given global average temperature change, makes high-latitude isotope records ideally suited to investigate fluctuations in palaeoclimate. The present study investigates palaeoclimatic and oceanographic changes along the Viking Corridor – the narrow seaway that connected the Tethys to the Arctic Boreal Realm during the Middle and Late Jurassic.</p><p>Stable-isotope data obtained from belemnites from East Greenland, originating from along the western margin of the Viking Corridor, show a M. Bathonian warming trend, which may indicate the reopening of the corridor after North Sea doming. We also discuss various controls on the carbon-isotope record that may dampen or amplify global signals. Changes in local depositional settings caused partial overprinting of the δ<sup>13</sup>C record during the Late Jurassic VOICE event.</p>

Response of Northern Hemisphere weather and climate to Arctic sea ice decline: The role of resolution in Polar Amplification Model Intercomparison Project (PAMIP) simulations

<p>The impact of Arctic sea ice decline on the weather and climate in mid-latitudes is still much debated, with observation suggesting a strong and models a much weaker link. In this study, we use the atmospheric model OpenIFS, in a set of model experiments following the protocol outlined in the Polar Amplification Model Intercomparison Project (PAMIP), to investigate whether the simulated atmospheric response to future changes in Arctic sea ice fundamentally depends on model resolution. More specifically, we increase the horizontal resolution of the model from 125km to 39km with 91 vertical levels; in a second step resolution is further increased to 16km with 137 levels in the vertical. We find that neither the mean atmospheric response nor the ensemble convergence toward the mean are strongly impacted by the model resolutions considered here.</p>