Arctic Sea Ice: Decadal Simulations and Future Scenarios Using BESM-OA

Abstract

Important international reports and a significant number of scientific publications have reported on the abrupt decline of Arctic sea ice and its impact on the Global Climate System. In this paper, we evaluated the ability of the newly implemented Brazilian Earth System Model (BESM-OA) to represent Arctic sea ice and sensitivity to CO 2 forcing, using decadal simulations (1980-2012) and future scenarios (2006-2100). We validated our results with satellite observations and compared them to Coupled Model Intercomparison Project, Phase 5 (CMIP5) for the same numerical experiment. BESM results for the seasonal cycle are consistent with CMIP5 models and observations. However, almost all models tend to overestimate sea ice extent in March compared to observations. The correct evaluation of minimum record of sea ice, in terms of time, spatial and area remains a limitation in Coupled Global Climate Models. Looking to spatial patterns, we found a systematic model error in September sea ice cover between the Beaufort Sea and East Siberia for most models. Future scenarios show a decrease in sea ice extent in response to an increase in radiative forcing for all models. From the year 2045 onwards, all models show a dramatic shrinking in sea ice and ice free conditions at the end of the melting season. The projected future sea ice loss is explained by the combined effects of the amplified warming in northern hemisphere high latitudes and feedbacks processes. KeywordsArctic Sea Ice, Climate Models, Brazilian Earth System Model F. Casagrande et al. 352

Overview of climate change in the BESM-OA2.5 climate model

“…(shortwave plus longwave) radiation closure at TOA, it shows deficiency in representing shortwave radiation over the Arctic and the ocean near the Antarctic (Casagrande et al, 2016).…”

“…More than that, BESM has the objective of being an additional climate model with ability of reproduce changes that are physically understood in order to study the global climate system. In this sense, a new version of BESM is under development in order to overcome the present extra-tropical and tropical climate simulation deficiencies, as reported in Casagrande et al (2016) and Veiga et al (2018), respectively. Notwithstanding, the inter-model spread in climate sensitivity discussed here, mainly that regarding the cloud feedback, remains a scientific challenge for the future.…”

“…CC BY 4.0 License.shortwave component response over both the Arctic and the Southern Ocean near Antarctica. Even though BESM presents an acceptable radiation closure at TOA (less than 2 W m −2 bias), it is deficient in representing shortwave radiation over the Arctic and the Southern Ocean, as a result of negative biases of middle and high clouds in the extratropics as shown byCasagrande et al (2016). Therefore, it is plausible that such a deficiency in cloud representation could cause the high positive values in SW cloud feedback.…”

Inter-hemispheric seasonal comparison of Polar Amplification using radiative forcing of quadrupling CO<sub>2</sub> experiment

“…Similar result was found for the sea ice simulation from BESM model (See in Figure 2). Additionally, Casagrande et al,(2016), using BESM-OA V2.3 model, showed that the sea 200 ice spatial pattern could vary largely between CMIP5 models, especially in frontiers areas.…”

Exploring Opportunities for Performance Improvement in a Global Climate Model

“…An ice model, called Sea Ice Simulator (SIS), is included in MOM5. SIS acts as an interface between the atmospheric and oceanic models, being responsible for calculating the fluxes ocean/ice and ice/atmosphere, and for communicating ocean/atmosphere fluxes on regions where there is no real ice [Casagrande et al 2016].…”