| 1. |
- Barcikowska, M. J., et al.
(author)
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Chances in the future summer Mediterranean climate: contribution of teleconnections and local factors
- 2020
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In: Earth System Dynamics. - : Copernicus GmbH. - 2190-4979 .- 2190-4987. ; 11:1, s. 161-181
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Journal article (peer-reviewed)abstract
- This study analyzes future climate for the Mediterranean region projected with the high-resolution coupled CM2.5 model, which incorporates a new and improved land model (LM3). The simulated climate changes suggest pronounced warming and drying over most of the region. However, the changes are distinctly smaller than those of the CMIP5 multi-model ensemble. In addition, the changes over much of southeast and central Europe indicate very modest warming compared to the CMIP5 projections and also a tendency toward wetter conditions. These differences indicate a possible role of factors such as land surface-atmospheric interactions in these regions. Our analysis also highlights the importance of correctly projecting the magnitude of changes in the summer North Atlantic Oscillation, which has the capacity to partly offset anthropogenic warming and drying over the western and central Mediterranean. Nevertheless, the projections suggest a decreasing influence of local atmospheric dynamics and teleconnections in maintaining the regional temperature and precipitation balance, in particular over arid regions like the eastern and southern Mediterranean, which show a local maximum of warming and drying. The intensification of the heat low in these regions rather suggests an increasing influence of warming land surface on the local surface atmospheric circulation and progressing desertification.
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| 2. |
- Chylek, P., et al.
(author)
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Annual Mean Arctic Amplification 1970-2020: Observed and Simulated by CMIP6 Climate Models
- 2022
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 49:13
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Journal article (peer-reviewed)abstract
- While the annual mean Arctic Amplification (AA) index varied between two and three during the 1970-2000 period, it reached values exceeding four during the first two decades of the 21st century. The AA did not change in a continuous fashion but rather in two sharp increases around 1986 and 1999. During those steps the mean global surface air temperature trend remained almost constant, while the Arctic trend increased. Although the "best" CMIP6 models reproduce the increasing trend of the AA in 1980s they do not capture the sharply increasing trend of the AA after 1999 including its rapid step-like increase. We propose that the first sharp AA increase around 1986 is due to external forcing, while the second step close to 1999 is due to internal climate variability, which models cannot reproduce in the observed time.
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| 3. |
- Chylek, Petr, et al.
(author)
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Arctic Amplification in the Community Earth System Models (CESM1 and CESM2)
- 2023
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In: Atmosphere. - 2073-4433. ; 14:5
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Journal article (other academic/artistic)abstract
- We compare the Arctic amplification (AA) produced by the two Community Earth System Models CESM1 and CESM2, members of the CEMIP5 (Coupled Models Intercomparison Project phase 5) and CEMIP6 collections, respectively. We find that the CESM1 model reproduces the recent high values of the AA deduced from the observed temperature much better than the CESM2. The correlation coefficient within the 1970–2012 time period between CESM1-simulated AA and the observed one is 0.47, while the CESM2 simulation leads to an anticorrelation of r = −0.53. Even the more successful model (CESM1) is not able to reproduce recent high AA values of 4–5. The main cause of this failure is the model’s overestimate of the rate of increase in the mean global temperature in years post 1990. When the CESM1 model’s simulated trend of the mean global temperature is replaced in the expression for the AA by the observed temperature trend, the correlation coefficient increases from 0.47 to 0.75. The CESM1 model is among the best north American models in AA simulation while the CESM2 model is among the least successful.
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| 4. |
- Chylek, P., et al.
(author)
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CMIP5 Climate Models Overestimate Cooling by Volcanic Aerosols
- 2020
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 47:3
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Journal article (peer-reviewed)abstract
- We compare projections of the observed hemispherical mean surface temperature (HadCRUT4.6.0.0) and the ensemble mean of CMIP5 climate models' simulations on a set of standard regression model forcing variables. We find that the volcanic aerosol regression coefficients of the CMIP5 simulations are consistently significantly larger (by 40-49%) than the volcanic aerosol coefficients of the observed temperature. The probability that the observed differences are caused just by chance is much less than 0.01. The overestimate is due to the climate models' response to volcanic aerosol radiative forcing. The largest overestimate occurs in the winter season of each hemisphere. We hypothesize that the models' parameterization of aerosol-cloud interactions within ice and mixed phase clouds is a likely source of this discrepancy. Furthermore, the models significantly underestimate the effect of solar variability on temperature for both hemispheres. Plain Language Summary We compare the observed and climate models' simulated hemispherical mean temperature projections on a set of influencing factors. The influencing factors include the man-made greenhouse gases and aerosols as well as natural solar variability, volcanic eruptions, and internal climate variability. If the observed and model-simulated temperatures were the same, the projections would be very similar. We find that the projections are not similar. The climate models overestimate the cooling effect of volcanic activity and underestimate the effect of the variability of solar radiation. Our results point out that future models should improve the treatment of volcanic aerosols and solar variability to increase the reliability of climate change projections.
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| 5. |
- Chylek, Petr, et al.
(author)
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High Values of the Arctic Amplification in the Early Decades of the 21st Century: Causes of Discrepancy by CMIP6 Models Between Observation and Simulation
- 2023
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In: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES. - 2169-897X .- 2169-8996. ; 128:23
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Journal article (peer-reviewed)abstract
- Arctic Amplification (AA) in the first decade of the 21st century has reached values between 4 and 5, with a subsequent decrease to current values of about 3.6, while the value was from 2 to 3 during the twentieth century. The ensemble mean of the CMIP6 models has difficulty in reproducing the recently observed high values of the AA. In this report, we identify the main reason for this difficulty to be the CMIP6 models overestimate of the mean global temperature trend since about 1990. The largest values of the AA are observed in winter and spring. A sharp AA peak in 1987 spring was caused by a peak in the Arctic temperature trend occurring at the same time as a dip in the trend of mean global temperature. The winter AA has increased almost monotonically since 1990. Dividing the AA between the Arctic land and ocean areas shows that the ocean area makes a larger contribution to the AA. Our future projection of the AA suggests an increasing AA for about the next decade, followed by a slow decrease to about 3.5 in the 2050s. The Arctic is warming faster than the average warming of the whole earth. The Arctic Amplification (AA) is defined as the ratio of the Arctic to global mean warming rates. Thus, the AA increases when the rate of Arctic warming increases, when the rate of global warming decreases, or when both happen at the same time. For most of the twentieth century, the AA was between 2 and 3. However, during the first few years of the 21st century, the AA has reached over four. The current climate models are not able to reproduce the observed early 21st-century high values of AA. We find that the main reason for this difficulty is the models' overestimate of the global warming rates after 1990. The early 21st century high values of the AA are caused by a higher temperature trend over the Arctic and a lower global temperature trendThe CMIP6 models' difficulty in reproducing the observed AA is due to the models' overestimate of the rate of mean global warming after 1990The future projection of the AA suggests an increasing AA for about the next decade with a slowly decreasing trend after that
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| 7. |
- Folland, Chris K., et al.
(author)
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Pen portraits of Presidents - Sir Basil John Mason, CB, DSc, FRS
- 2020
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In: Weather. - : Wiley. - 0043-1656 .- 1477-8696. ; 75:1, s. 26-29
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Journal article (peer-reviewed)abstract
- We present a short biography of Sir John Mason, part of Weather's series of pen portraits of Past Presidents of the Royal Meteorological Society. This biography is longer than a normal pen portrait to reflect Sir John Mason's exceptional and wide-ranging achievements and to show how he contributed to the debate about climate change. We include a discussion of his early years, particularly his pioneering work in cloud physics. We particularly review the key activities of the Met Office with which he was closely involved in his years as Director General, followed by his activities after retirement and his main awards.
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