Rising global temperatures change Caspian Sea's ice regime, study finds

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The ice regime of the Caspian Sea, Earth's largest inland body of water, has changed over past decades and a new study has revealed why.

An annual warming of 1.1 C and 1.3 C for the cold period since 1990 has negatively influenced the ice regime of the Caspian Sea, located between Europe and Asia. The obtained results indicated frequent moderate and warm winters and reduced occurrence of very severe winters. As changes occurred in the ice regime, the occurrence of the first ice events has been delayed and the establishment of stable ice in the last decade occurred later. The disappearance of ice is observed to occur earlier.

"Winter severity, which is closely linked to ice thickness has clearly decreased since the cold winters in 1950s and 1960s. Milder winters have changed ice conditions in the northernmost part of the Caspian Sea," says a recent study published by the Central Asian Journal of Water Research.

The authors analyzed changes in air temperature as the main indicator of climate change, and a potential ice regime shift. The study focused on the northeast part of the coast of Kazakhstan, where ice conditions are peculiarly sever and used temperature anomalies in late autumn and winter to explain variations in sea ice.

The authors note that a trend of increasing air temperatures could be detected since the middle of the last century to the present times.

"An analysis of 15 north Caspian meteorological stations shows that the mean annual temperature has increased compared to the base period taken from the beginning of observations to 1989. The temperature rise during the period 1990-2015 compared to the base period was on average of 1.1 C, and the temperature rise for 2000-2015 on average of 1.4 C. For the cold period (November-March), the air temperature increased by 1.3 C for 1990-2015 and by 1.6 C for 2000-2015."

"The temperature increase during the cold period by more than the annual air temperature indicates that the recent warming might, especially, influence sea ice conditions," reads the report.

The study of the trends in air temperature during a winter period from 1961 to 2016 , showed that frequency of very severe and severe winters has decreased, and consequently during the last decades the frequency of moderate and mild winters has increased. Winters in the 60s and 70s were more severe with the amount of negative temperature sum closer to the maximum value observed.

"Ice thickness analysis for the period 1980-2016 reveals a large year to year variation in ice thickness and a steady trend of reduced ice thickness from 1981 to 2016," the authors noted.

A detailed comparison of these winters shows that in sever winters, steady ice formation starts in November in the northern part of the Caspian Sea and in the third week of January in the middle part of the Caspian Sea. In mild winters, ice was established in the northern regions in December, but in the middle part a stable ice cover was not observed.

The thickness of ice during a severe winter reached 58 cm in the northern part of the sea and 22 cm in the middle part and during a mild winter ice thickness does not exceed 20 cm in the northern part. Melting and disappearance of sea ice in the severe winter of 2011-2012 was observed later than in the mild winter of 2015-2016. Duration of the ice period of 2011-2012 was 156 days and the duration of the ice period of 2015-2016 was 98 days (almost two months shorter).

The authors note that further impacts of climate change on sea ice could be large and need to be further studied.

"Ice cracks and splits increase with warmer climate. Lack of ice cohesion could disrupt a habitat of Caspian species, such as the Caspian seal," the report reads.

The authors say other consequences and potential loss of the Caspian ecosystem are needed to be analyzed to assess mitigation measures for climate change impact.

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