Browsing by Subject "CMIP5"

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  • Räisänen, Jouni (2017)
    An energy balance decomposition of temperature changes is conducted for idealized transient CO2-only simulations in the fifth phase of the Coupled Model Intercomparison Project. The multimodel global mean warming is dominated by enhanced clear-sky greenhouse effect due to increased CO2 and water vapour, but other components of the energy balance substantially modify the geographical and seasonal patterns of the change. Changes in the net surface energy flux are important over the oceans, being especially crucial for the muted warming over the northern North Atlantic and for the seasonal cycle of warming over the Arctic Ocean. Changes in atmospheric energy flux convergence tend to smooth the gradients of temperature change and reduce its land-sea contrast, but they also amplify the seasonal cycle of warming in northern North America and Eurasia. The three most important terms for intermodel differences in warming are the changes in the clear-sky greenhouse effect, clouds, and the net surface energy flux, making the largest contribution to the standard deviation of annual mean temperature change in 34, 29 and 20 % of the world, respectively. Changes in atmospheric energy flux convergence mostly damp intermodel variations of temperature change especially over the oceans. However, the opposite is true for example in Greenland and Antarctica, where the warming appears to be substantially controlled by heat transport from the surrounding sea areas.
  • Guan, Yanlong; Lu, Hongwei; Jiang, Yelin; Tian, Peipei; Qiu, Lihua; Heiskanen, Janne; Pellikka, Petri (2021)
    Variations in climate types are commonly used to describe changes in natural vegetation cover in response to global climate change. However, few attempts have been made to quantify the heterogeneous dynamics of climate types. In this study, based on the Coupled Model Intercomparison Project phase 5 (CMIP5) historical and representative concentration pathway (RCP) runs from 18 global climate models, we used Shannon's Diversity Index (SHDI) and Simpson's Diversity Index (SIDI) to characterise of global climate heterogeneity from a morphological perspective. Our results show that global climate heterogeneity calculated by the SHDI/SIDI indices decreased from 1901 to 2095 at a significance level of 0.01. As radiative forcing intensified from RCP 2.6 to 8.5, the SHDI/SIDI decreased significantly. Furthermore, we observed that the spatial distribution of global climate heterogeneity was significantly reduced, with a pronounced latitudinal trend. Sensitivity analysis indicated that the temperature increase played a more significant role in reducing global climate heterogeneity than precipitation under the three warming scenarios, which is possibly attributed to anthropogenic forcing. Our findings suggest that the dynamics of global climate heterogeneity can be an effective means of quantifying global biodiversity loss.
  • Karjalainen, Olli; Aalto, Juha; Luoto, Miska; Westermann, Sebastian; Romanovsky, Vladimir E.; Nelson, Frederick E.; Etzelmueller, Bernd; Hjort, Jan (2019)
    Ongoing climate change is causing fundamental changes in the Arctic, some of which can be hazardous to nature and human activity. In the context of Earth surface systems, warming climate may lead to rising ground temperatures and thaw of permafrost. This Data Descriptor presents circumpolar permafrost maps and geohazard indices depicting zones of varying potential for development of hazards related to near-surface permafrost degradation, such as ground subsidence. Statistical models were used to predict ground temperature and the thickness of the seasonally thawed (active) layer using geospatial data on environmental conditions at 30 arc-second resolution. These predictions, together with data on factors (ground ice content, soil grain size and slope gradient) affecting permafrost stability, were used to formulate geohazard indices. Using climate-forcing scenarios (Representative Concentration Pathways 2.6, 4.5 and 8.5), permafrost extent and hazard potential were projected for the 2041-2060 and 2061-2080 time periods. The resulting data (seven permafrost and 24 geohazard maps) are relevant to near-future infrastructure risk assessments and for targeting localized geohazard analyses.
  • Räisänen, Jouni (2019)
    The effect of atmospheric circulation on temperature variability and trends in Finland in 1979–2018 is studied using a trajectory-based method. On the average 81% of the detrended interannual variance of monthly mean temperatures is explained by the start points of the three-dimensional trajectories, with the best performance in autumn and winter. Atmospheric circulation change is only found to have had a small impact on the observed annual mean temperature trends, but it has considerably modified the trends in individual months. In particular, changes in circulation explain the lack of observed warming in June, the very modest warming in October in southern Finland, and about a half of the very large warming in December. The residual trends obtained by subtracting the circulation-related change from observations are robustly positive in all months of the year, exhibit a smoother seasonal cycle, and agree better with the multi-model mean temperature trends from models in the 5th Coupled Model Intercomparison Project (CMIP5). Nevertheless, some differences between the residual trends and the average CMIP5 trends are also found.
  • Kim, Sol; Sinclair, Victoria A.; Räisänen, Jouni; Ruuhela, Reija (2018)
    The number and intensity of individual hot days affecting Finland in the current and future climate is investigated together with the circulation patterns associated with the hot days. In addition, the number, length and intensity of heat waves lasting at least 3 days is also considered. ERA-Interim reanalysis data and both direct model output and bias-corrected data for historical and future climate [representative concentration pathway 4.5 (RCP4.5) scenario] simulations from 17 global climate models are analysed. Three intensities of heat waves and hot days are defined based on daily mean temperature thresholds of 20, 24 and 28 °C. The percentage of summertime days which exceed these temperature thresholds is shown to increase in the future. In ERA-Interim, 24% of summertime days in southern Finland exceed the lowest temperature threshold while none exceed the highest temperature threshold. Under the RCP4.5 scenario these values increase to 47 and 1%, respectively. Larger relative changes occur in northern Finland. Heat waves are also longer in the RCP4.5 simulations than in the historical simulations. In southern Finland, the mean length of a heat wave where the 20 °C daily mean temperature is exceeded is 6.1 days in the historical simulations but increases to 9.4 days in the RCP4.5 simulations. The hot days in both northern and southern Finland are associated with a statistically significant positive pressure anomaly over Finland and to the east to Finland and a statistically significant negative pressure anomaly over Russia between 90 and 120°E. These pressure anomalies were evident for all intensities of hot days in the current climate and the future climate. The magnitude of the pressure anomalies increases as the daily mean temperature threshold increases. However, for hot days which exceed the same daily mean temperature threshold, the pressure anomalies are weaker in the RCP4.5 simulations than in the historical or ERA-Interim data.
  • Guan, Yanlong; Lu, Hongwei; He, Li; Adhikari, Hari; Pellikka, Petri; Maeda, Eduardo; Heiskanen, Janne (2020)
    Increases and decreases in the areas of climatic types have become one of the most important responses to climate warming. However, few attempts have been made to quantify the complementary relationship between different climate types or to further assess changes in the spatial morphology. In this study, we used different observed datasets to reveal a dispersion phenomenon between major global climate types in 1950-2010, which is significantly consistent with the increasing trend of global temperatures. As the standard deviation of the area of major climate zones strengthened in 1950-2010, the global climatic landscape underwent notable changes. Not only did the area change, but the shape of the overall boundary became regular, the aggregation of climatic patches strengthened, and the climatic diversity declined substantially. However, changes in the global climatic landscapes are not at equilibrium with those on the continental scale. Interpreting these climatic morphological indices can deepen our understanding of the redistribution response mechanisms of species to climate change and help predict how they will be impacted by long-term future climate change.
  • Pouta, Pekka (Helsingin yliopisto, 2020)
    Hallitustenvälinen ilmastonmuutospaneeli IPCC määrittelee Pohjois-Atlantin subpolaaripyörteen ilmaston käänne-elementiksi, joka voi joutua ilmaston muutoksen seurauksena toiseen tilaan. Tässä työssä tarkastellaan ensin tieteellisten artikkelien pohjalta subpolaaripyörrettä ja sen vuorovaikutusta muun meren, sekä ilmakehän kiertoliikkeen kanssa. Sen jälkeen muodostetaan CMIP5-projektin (Coupled Model Intercomparison Project 5) ilmastomallien pohjalta kaksi malliryhmää. Toisessa on kolme mallia, joissa subpolaaripyörteen syvänveden muodostus romahtaa, toinen on vertailuryhmä. Subpolaaripyörteen romahdus näyttää todennäköisemmältä kuin CMIP5-malliryhmien kokoa vertailemalla voisi päätellä ja romahdus voi tapahtua jo pienimmällä RCP2.6-skenaariolla. Suunnilleen yhtä todennäköistä, kuin yksi romahdus, on useampi nopea subpolaaripyörteen heikkeneminen, joiden välissä subpolaaripyörre voimistuu uudelleen. Tämä ilmiö voi lisätä tulevaisuuden ilmastossa vaikeasti ennakoitavaa vuosikymmenten välistä vaihtelua. Subpolaaripyörteen romahduksen ilmastovaikutukset ovat suurimmat arktisella alueella, Pohjois-Atlantilla ja Euroopassa. Se heikentäisi pohjoisen napa-alueen lämpenemistä, joka muuten on paljon voimakkaampaa kuin maapallon keskimääräinen lämpeneminen. Euroopassa ilmiö hillitsee ilmastonmuutoksen aiheuttamaa lämpenemistä ja voi muuttaa ilmakehän keskimääräistä kiertoliikettä. Suurimmat vaikutukset keskittyvät kuitenkin subpolaaripyörteen alueelle.