Ice albedo feedback

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Proportion of sunlight of different surface textures reflected into space
Albedo change in Greenland. The picture shows the difference in the reflected radiation in 2011 compared to the mean value for the years 2000–2006 in false colors . The image was taken with the help of the satellite MODIS added

Ice-albedo feedback is the interaction between the cryosphere (snow- and ice-covered earth's surface ) and global climate . According to the terms of control engineering , this is a positive feedback , which further amplifies the active cause. Water and soil absorb approx. 90% of the radiated energy and heat up, which leads to the melting of further snow and ice surfaces. Conversely, a cooling leads to an expansion of snow and ice surfaces, thus to an increased reflection and further cooling.

Snow and ice have a high albedo (reflectivity of sunlight); only a small part of the incident solar energy is absorbed. Snow-covered ice has the highest reflectivity with an albedo of 0.9. In contrast, the albedo of water is only about 0.06, i.e. That is, 94% of the incident solar energy is absorbed, only 6% is reflected.

James Croll was the first scientist to recognize the importance of ice albedo feedback in explaining the formation of the ice ages.

The strength of the ice-albedo feedback can be seen, for example, from the fact that in polar latitudes there are also low temperatures in summer, although the amount of energy radiated in over 24 hours is greater than at the equator. In addition to the melting enthalpy of the ice, this is primarily due to the strong albedo of the snow and ice surfaces.

development

The phenomenon is also relevant to global warming : there it intensifies the effect of greenhouse gases and is the main factor in the so-called polar amplification . The first model calculations go back to the Russian climatologist Michail Budyko in the 1960s; Researchers there had already suspected that a decline in sea ice in the Arctic would lead to a decrease in albedo.

As a result of global warming in the Arctic , increasing glacier melt and the disappearance of Arctic polar ice can be seen: based on satellite measurements , data from 35 years are now (2014) available for the Arctic ; they show that the sea ice cover there has decreased by 40 percent during the summer months.

The influence of the ice-albedo feedback is taken into account in climate models . A study published in 2011 indicates, however, that all models used for the IPCC report published in 2007 underestimated the effect; Although the measured values ​​are certainly faulty due to the relatively short observation period of only one normal period , the difference to the feedback assumed in the climate models is too pronounced to be entirely attributable to a measurement error. According to the study, the additional radiative forcing that resulted from a reduction in ice albedo feedback over the past 30 years amounts to approx. 0.45 W / m² or 30% of the radiative forcing of the CO 2 emitted by humans since industrialization and is therefore twice as high as is assumed in current climate models. The causes are unclear and not necessarily to be found in global warming. This was confirmed in another study that was published in early 2014; Using satellite measurements, it was found that the Arctic ice albedo has decreased by a factor of two to three more than previous studies had suggested; If the additional energy absorbed according to these data were distributed evenly across the globe, it would correspond to 25 percent of the warming that is directly attributable to the increase in carbon dioxide in the atmosphere. This finding is not yet found in current climate development models.

To explain the unexpectedly strong drop in albedo, the effects of human immissions and cryoflora are currently being investigated. A study from 2015 came to the conclusion that the darkening of snow and ice surfaces by biofilms , in particular by the bloom of red snow algae , has been underestimated in climate models.

Individual evidence

  1. ↑ Jürgen Beetz : Feedback: How feedback determines our lives and dominates nature, technology, society and the economy. Springer Spectrum, Heidelberg 2015, ISBN 978-3-662-47089-3 , p. 108.
  2. ^ Walter Roedel: Physics of our environment - The atmosphere . 3. Edition. Springer, Heidelberg 2000, ISBN 3-540-67180-3 , 1.2 The solar radiation, p. 21 , Table 1.3 (some values ​​for the backscattering power - albedo - of the earth's surface) .
  3. ^ Thermodynamics: Albedo ( English ) In: All About Sea Ice . National Snow and Ice Data Center. Retrieved July 5, 2016.
  4. ↑ James Croll: Climate and Time in Their Geological Relations. A Theory of Secular Changes of the Earth's Climate. Appleton, New York 1885 ( books.google.de ).
  5. ↑ Wolfgang Weischert: Introduction to General Climatology. Physical and meteorological basics. Verlag Borntraeger Gebrueder, ISBN 978-3-443-07142-4 .
  6. ^ Climate and Earth's Energy Budget , article on earthobservatory.nasa.gov.
  7. ↑ a b Deutschlandfunk , Research News. February 18, 2014, Monika Seynsche : The Arctic is absorbing more and more heat on deutschlandfunk.de (February 20, 2014)
  8. ^ Loss of reflectivity in the Arctic doubles estimate of climate models. In: ScienceDaily. January 18, 2011, accessed January 21, 2011
  9. ^ K. Pistone, I. Eisenman, Veerabhadran Ramanathan : Observational determination of albedo decrease caused by vanishing Arctic sea ice . In: Proceedings of the National Academy of Sciences . tape 111 , no. 9 , March 4, 2014, ISSN  0027-8424 , p. 3322-3326 , doi : 10.1073 / pnas.1318201111 .
  10. ↑ Kristina Pistone, Ian Eisenman, Veerabhadran Ramanathan: Radiative Heating of an Ice-Free Arctic Ocean . In: Geophysical Research Letters . tape 0 , no. 0 , ISSN  1944-8007 , doi : 10.1029 / 2019GL082914 ( wiley.com [accessed July 16, 2019]).
  11. ↑ The biogeography of red snow microbiomes and their role in melting arctic glaciers. Retrieved July 15, 2017 .

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