River ice, also known as river ice, is one of the many components of the Earth’s cryosphere. Also, tracking how they evolve as the Earth warms is an important topic. As such, innovative results were obtained in a study published on January 1.
Due to the seasonal cycle, more than half of the world’s rivers freeze for part of the year. A characteristic which influences both socio-economic life and the functioning of ecosystems at the latitudes concerned. However, observations show that the average extent of river ice is decreasing. A coherent and expected evolution in the context of the current global warming.
An innovative study on the evolution of river ice
However, until very recently, no systematic quantification of trends had been established on a global scale. As a result, many questions remained unanswered. These include problems related to seasonality, duration of freeze-up and modalities for future changes.
A new study published in Nature on January 1, 2020 fills this gap. To do this, the authors took advantage of more than 405,000 satellite images over the period 1984-2018 in order to assess past developments on a global scale. Over 7.5 million rivers have been analyzed in this way. In addition, scientists have developed an empirical model calibrated on these observations in order to anticipate future developments.
“We have detected widespread declines in monthly river ice cover. And the trend predicted for future losses is likely to cause economic challenges for residents and industries along these rivers, “said Xiao Yang, lead author of the paper. In addition, he recalls that these changes risk “modifying the seasonal trends in greenhouse gas emissions from rivers”.
Eastern Europe: one of the most affected regions
The results show that the average extent of river ice has decreased by about 2.5% in the past 34 years. As for the future, declines ranging from 9 to 15% in winter and from 12 to 68% in the intermediate seasons are projected. The spectrum of possible values depends on the location and the scenario of greenhouse gas emissions considered. It should be noted that the sectors most affected by the past and future setback are Alaska, Eastern Europe and the Tibetan plateau.
Finally, the authors note that the average freezing time is shortened by up to 6 days per degree of global warming. In a pessimistic scenario, this would lead us to an additional 16-day decrease by the end of the century. The positive is that this scenario seems less and less likely. With a more realistic scenario, an average decline of only 7 additional days is expected.
“Our results show that on a global scale, river ice is decreasing in a measurable way and will continue to decline in a linear fashion with the forecast increase in surface air temperature (…)” we can read in the summary of the study. These changes will at least require a review of the socio-economic organization at high latitudes (transport, housing, etc.).