Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Pristine aerosol concentrations, cloud droplet size and early Holocene climate
KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
Stockholm University.
KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
Stockholm University.
Show others and affiliations
(English)Manuscript (preprint) (Other academic)
Abstract [en]

This work investigates how the simulated early Holocene climate is influenced by the representation of aerosols and their effect on the climate. The representations of the direct and first indirect aerosol effects in the Community Earth System Model, version1 (CESM1) are modified in two sensitivity experiments.

In the first sensitivity experiment (CESM 9k R14), the first indirect effect on the simulated climate is modified by setting the cloud droplet effective radius, (Reff ) in the model to a constant value. This value is chosen to be representative for pristine conditions. In the second sensitivity experiment (CESM 9k CAMO), the representation of both the direct and first indirect effects is modified. An atmosphere-only model with interactive aerosols is used to simulate the early Holocene aerosol loading and the change in Reff due to the decrease in atmospheric aerosols.

The changes in aerosol effects introduced in the two sensitivity experiments differ both in magnitude and spatial pattern. We find that despite the difference in the spatial pattern of the changes in the aerosol effects, the warming patterns in the two sensitivity experiments are similar; the surface temperature increases in both simulations, with an enhanced warming in the Arctic region. The warming is approximately twice as large in the CESM 9k R14 simulation than in the CESM 9k CAMO simulation.

National Category
Climate Research
Identifiers
URN: urn:nbn:se:kth:diva-127918OAI: oai:DiVA.org:kth-127918DiVA: diva2:646655
Note

QS 2013

Available from: 2013-09-09 Created: 2013-09-09 Last updated: 2013-09-10Bibliographically approved
In thesis
1. Modelling the early to mid-Holocene Arctic climate
Open this publication in new window or tab >>Modelling the early to mid-Holocene Arctic climate
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In the recent past it has become evident that the Earth's climate is changing, and that human activity play a significant role in these changes. One of the regions where the ongoing climate change has been most evident is in the Arctic: the surface temperature has increased twice as much in this region as compared to the global average, in addition, a significant decline in the Arctic sea-ice extent has been observed in the past decades. Climate model studies of past climates are important tools to understand the ongoing climate change and how the Earth's climate may respond to changes in the forcing.

This thesis includes studies of the Arctic climate in simulations of the early and mid-Holocene, 9 000 and 6 000 years before present. Changes in the Earth's orbital parameters resulted in increased summer insolation as compared to present day, especially at high northern latitudes. Geological data imply that the surface temperatures in the early to mid Holocene were similar to those projected for the near future. In addition, the geological data implies that the Arctic sea ice cover was significantly reduced in this period. This makes the early to mid-Holocene an interesting period to study with respect to the changes observed in the region at present.

Several model studies of the mid-Holocene have been performed through the Paleoclimate Modeling Intercomparison Project (PMIP1 to PMIP3). The simulations have been performed with climate models of varying complexity, from atmosphere-only models in the first phase to fully coupled models with the same resolution as used for future climate simulations in the third phase. The first part of this thesis investigates the simulated sea ice in the pre-industrial and mid-Holocene simulations included in the PMIP2 and PMIP3 ensemble. As the complexity of the models increases, the models simulate smaller extents and thinner sea ice in the Arctic; the sea-ice extent suggested by the proxy data for the mid-Holocene is however not reproduced by the majority of the models.

One possible explanation for the discrepancy between the simulated and reconstructed Arctic sea ice extent is missing or inadequate representations of important processes. The representation of atmospheric aerosol direct and indirect effects in past climates is a candidate process. Previous studies of deeper time periods have concluded that the representation of the direct and indirect effects of the atmospheric aerosols can influence the simulated climates, and reduce the equator to pole temperature gradient in past warm climates, in better agreement with reconstructions. The second part of the thesis investigates the influence of aerosol on the early Holocene climate. The indirect effect of reduced aerosol concentrations as compared to the present day is found to cause an amplification of the warming, especially in the Arctic region. A better agreement with reconstructed Arctic sea ice extent is thus achieved.

Abstract [sv]

Under senare tid har det blivit uppenbart att jordens klimat håller på att förändras, och att mänsklig aktivitet spelar en viktig roll för dessa ändringar. Ett av de områden där den pägäende klimatfärändringen har varit tydligast är Arktis: temperaturen vid ytan har ökat dubbelt så mycket här jämfört med det globala genomsnittet. Dessutom har man observerat en betydande nedgång i havsisens utbredning i Arktis de senaste decennierna. Simuleringar gjorda med klimatmodeller av forntida klimat är viktiga verktyg för att förstå de pågående klimatförändringarna och hur jordens klimat påverkas av ändringar i klimatsystemets drivningar.

Denna avhandling består av studier av det arktiska klimatet i modellsimuleringar av tidig och mid-holocen, ca. 9 000 och 6 000 år före nutid. Förändringar i jordens bana kring solen resulterade i en ökad sommar-solinstrålning jämfört med nutid, särskilt vid höga nordliga breddgrader. Geologiska data antyder att jordens temperatur vid ytan under denna period kan jämföras med dem vi förväntar för den närmaste framtiden. Vidare indikerar geologiska data att havsisen i Arktisk var kraftigt reducerad under denna period. Detta gör tidig till mid-holocen till en intressant period att studera, med avseende på de förändringar som för närvarande har observerats i området.

Flera modellstudier av mitt-holocen har utförts i de olika faserna av Paleoclimate Modeling Intercomparison Project (PMIP1 till PMIP3). Simuleringarna har utförts med klimatmodeller av varierande komplexitet, från atmosfärsmodeller i den första fasen, till fullt kopplade modeller med hög rumslig upplösning i den tredje fasen. I den första delen av denna avhandling undersöks den simulerade havsisen i de förindustriella och mid-holocen simuleringar som ingår i PMIP2 och PMIP3 ensemblerna. Modellerna simulerar mindre utbredning och tunnare havsis i Arktis i den senare PMIP ensemblen, men fortfarande återskapar inte modellerna generelt den havsisutbredning som de geologiska data indikerar.

En möjlig förklaring till skillnaderna mellan den simulerade och rekonstruerade havsisutsträckningen kan vara att viktiga processer i klimatsystemet saknas eller inte är tillräckligt väl beskrivna i modellerna. Beskrivningen av atmosfäriska aerosoler och dess effekter på klimatet är en möjlig kandidatprocess. Från studier av forntida varma tidsperioder har man dragit slutsatsen att beskrivningen av aerosoleffekterna påverkar det simulerade klimatet. Bland annat kan man minska temperaturgradienten mellan ekvator och polerna i tidigare varma klimat, vilket bättre överensstämmer med temperaturrekonstruktioner. Den andra delen av avhandlingen undersöker påverkan av aerosoler på klimatet under tidig holocen. Den indirekta effekten som följer av lägre aerosolkoncentrationer i tidig holocen jämfört med i dag, visar sig orsaka en förstärkning av uppvärmningen, särskilt i det arktiska områet, vilket stämmer bättre med havsisrekonstruktioner från denna period.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. x, 27 p.
Series
Trita-MEK, ISSN 0348-467X ; 2013:16
Keyword
Arctic, early Holocene, mid-Holocene, climate modelling, paleoclimate, sea ice, climate change
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-127870 (URN)978-91-7501-860-7 (ISBN)
Presentation
2013-09-27, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20130910

Available from: 2013-09-10 Created: 2013-09-09 Last updated: 2013-09-10Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Berger, MaritBrandefelt, JennyWei, Liang
By organisation
TurbulenceLinné Flow Center, FLOW
Climate Research

Search outside of DiVA

GoogleGoogle Scholar

urn-nbn

Altmetric score

urn-nbn
Total: 128 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf