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On the recent Arctic Warming
Stockholm University, Faculty of Science, Department of Meteorology.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Arctic region attracts considerable scientific interest in these years. Some of the Earth's most pronounced signs of the recent climate change are found here. The summer sea-ice cover is shrinking at an alarming rate. At the same time the region warms faster than the rest of the globe.

The sea-ice reduction implies an increase of solar-radiation absorption at the surface leading to warming which is expected to be larger at higher than at lower latitudes. It is therefore often assumed that the sea-ice reduction is a major cause of the observed Arctic temperature amplification. However, results presented in this thesis suggest that the snow and ice-albedo feedbacks are a contributing but not dominating mechanism behind the Arctic amplification. A coupled climate-model experiment with a doubling of the atmospheric CO2 concentration reveals a considerable Arctic surface-air-temperature amplification in a world without surface-albedo feedback. The amplification is only 8 % larger when this feedback is included. Instead the greenhouse effect associated with an increase of humidity and cloud cover over the Arctic seems to play a major role for the amplification.

Reanalysis data, which are partly based on observations, show Arctic temperature amplification well above the surface in the troposphere. In the summer season, the amplification has its maximum at ~ 2 km height. These trends cannot be explained by the snow- and ice-albedo feedbacks which are expected to induce the largest amplification near the surface. Instead, a considerable part of the trends aloft can be linked to an increase of the atmospheric energy transport into the Arctic.

A major topic of this thesis is the linkage between the mid-latitude circulation and the Arctic warming. It is suggested that the atmospheric meridional energy transport is an efficient indicator of this linkage.

Place, publisher, year, edition, pages
Stockholm: Meteorologiska institutionen (MISU) , 2008. , 107 p.
Keyword [en]
Climate change, atmospheric energy transport
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences
Identifiers
URN: urn:nbn:se:su:diva-7473ISBN: 978-91-7155-618-9 (print)OAI: oai:DiVA.org:su-7473DiVA: diva2:198363
Public defence
2008-04-25, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 10:00
Opponent
Supervisors
Available from: 2008-04-03 Created: 2008-04-03Bibliographically approved
List of papers
1. Do Changes in the Midlatitude Circulation Have Any Impact on the Arctic Surface Air Temperature Trend?
Open this publication in new window or tab >>Do Changes in the Midlatitude Circulation Have Any Impact on the Arctic Surface Air Temperature Trend?
2006 In: Journal of Climate, ISSN 0894-8755, Vol. 19, no 20, 5422-5437 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24812 (URN)
Note
Part of urn:nbn:se:su:diva-7473Available from: 2008-04-03 Created: 2008-04-03Bibliographically approved
2. Atmospheric mass-transport inconsistencies in the ERA-40 reanalysis
Open this publication in new window or tab >>Atmospheric mass-transport inconsistencies in the ERA-40 reanalysis
2007 In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, Vol. 133, no 624, 673-680 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24813 (URN)000247221400011 ()
Note
Part of urn:nbn:se:su:diva-7473Available from: 2008-04-03 Created: 2008-04-03Bibliographically approved
3. Vertical structure of recent Arctic warming
Open this publication in new window or tab >>Vertical structure of recent Arctic warming
Show others...
2008 (English)In: Nature, ISSN 0028-0836, Vol. 451, no 7174, 53-56 p.Article in journal (Refereed) Published
Abstract [en]

Near-surface warming in the Arctic has been almost twice as large as the global average over recent decades1, 2, 3, 4, 5—a phenomenon that is known as the 'Arctic amplification'. The underlying causes of this temperature amplification remain uncertain. The reduction in snow and ice cover that has occurred over recent decades6, 7 may have played a role5, 8. Climate model experiments indicate that when global temperature rises, Arctic snow and ice cover retreats, causing excessive polar warming9, 10, 11. Reduction of the snow and ice cover causes albedo changes, and increased refreezing of sea ice during the cold season and decreases in sea-ice thickness both increase heat flux from the ocean to the atmosphere. Changes in oceanic and atmospheric circulation, as well as cloud cover, have also been proposed to cause Arctic temperature amplification12, 13, 14, 15, 16, 17. Here we examine the vertical structure of temperature change in the Arctic during the late twentieth century using reanalysis data. We find evidence for temperature amplification well above the surface. Snow and ice feedbacks cannot be the main cause of the warming aloft during the greater part of the year, because these feedbacks are expected to primarily affect temperatures in the lowermost part of the atmosphere, resulting in a pattern of warming that we only observe in spring. A significant proportion of the observed temperature amplification must therefore be explained by mechanisms that induce warming above the lowermost part of the atmosphere. We regress the Arctic temperature field on the atmospheric energy transport into the Arctic and find that, in the summer half-year, a significant proportion of the vertical structure of warming can be explained by changes in this variable. We conclude that changes in atmospheric heat transport may be an important cause of the recent Arctic temperature amplification.

National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:su:diva-24814 (URN)10.1038/nature06502 (DOI)000252079300031 ()
Note
Part of urn:nbn:se:su:diva-7473Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2010-01-21Bibliographically approved
4. Polar amplification in a coupled climate model with locked albedo
Open this publication in new window or tab >>Polar amplification in a coupled climate model with locked albedo
2009 (English)In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 33, no 5, 629-643 p.Article in journal (Refereed) Published
Abstract [en]

In recent years, a substantial reduction of the sea ice in the Arctic has been observed. At the same time, the near-surface air in this region is warming at a rate almost twice as large as the global average—this phenomenon is known as the Arctic amplification. The role of the ice-albedo feedback for the Arctic amplification is still a matter of debate. Here the effect of the surface-albedo feedback (SAF) was studied using a coupled climate model CCSM3 from the National Center for Atmospheric Research. Experiments, where the SAF was suppressed by locking the surface albedo in the entire coupled model system, were conducted. The results reveal polar temperature amplification when this model, with suppressed albedo, is forced by a doubling of the atmospheric CO2 content. Comparisons with variable albedo experiments show that SAF amplifies the surface-temperature response in the Arctic area by about 33%, whereas the corresponding value for the global-mean surface temperature is about 15%. Even though SAF is an important process underlying excessive warming at high latitudes, the Arctic amplification is only 15% larger in the variable than in the locked-albedo experiments. It is found that an increase of water vapour and total cloud cover lead to a greenhouse effect, which is larger in the Arctic than at lower latitudes. This is expected to explain a part of the Arctic surface–air-temperature amplification.

Place, publisher, year, edition, pages
Springer, 2009
Keyword
Albedo feedback, Polar amplification, Greenhouse effect, Climate-model experiment
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-24815 (URN)10.1007/s00382-009-0535-6 (DOI)000269188800004 ()
Note
Part of urn:nbn:se:su:diva-7473Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2017-12-13Bibliographically approved

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