AGW Observer

Observations of anthropogenic global warming

New research from last week 9/2012

Posted by Ari Jokimäki on March 5, 2012

This week’s scientists are from Estonia, Finland, France, Germany, India, Italy, Netherlands, Portugal, Spain, Switzerland, United Kingdom, and United States. It seems that we have lot of European studies this week. Oh, the studies themselves? Well, they are amazingly interesting as usual. They have studied cold spells, aerosols, clouds, maximum temperatures, water vapor, meteorological measurements, lake sediments, winter precipitation, trees, and even crop prices. And you should have seen the studies that got away!


Where exactly model simulations of clouds go wrong?

Exposing global cloud biases in the Community Atmosphere Model (CAM) using satellite observations and their corresponding instrument simulators – Kay et al. (2012)

Abstract: “Satellite observations and their corresponding instrument simulators are used to document global cloud biases in the Community Atmosphere Model (CAM) versions 4 and 5. The model-observation comparisons show that despite having nearly identical cloud radiative forcing, CAM5 has a much more realistic representation of cloud properties than CAM4. In particular, CAM5 exhibits substantial improvement in three long-standing climate model cloud biases: 1) the underestimation of total cloud, 2) the overestimation of optically thick cloud, and 3) the underestimation of mid-level cloud. While the increased total cloud and decreased optically thick cloud in CAM5 result from improved physical process representation, the increased mid-level cloud in CAM5 results from the addition of radiatively active snow. Despite these improvements, both CAM versions have cloud deficiencies. Of particular concern, both models exhibit large but differing biases in the subtropical marine boundary layer cloud regimes that are known to explain inter-model differences in cloud feedbacks and climate sensitivity. More generally, this study demonstrates that simulator-facilitated evaluation of cloud properties, such as amount by vertical level and optical depth, can robustly expose large and at times radiatively compensating climate model cloud biases.”

Citation: J. E. Kay, B. R. Hillman, S. A. Klein, Y. Zhang, B. Medeiros, R. Pincus, A. Gettelman, B. Eaton, J. Boyle, R. Marchand, and T. P. Ackerman, Journal of Climate 2012.


Possibly positive feedback from cirrostratus and cirrus clouds in warmer climate

Convection-climate feedbacks in the ECHAM5 general circulation model: Evaluation of cirrus cloud life cycles with ISCCP satellite data from a Lagrangian trajectory perspective – Gehlot & Quaas (2012)

Abstract: “A process-oriented climate model evaluation is presented, applying the International Satellite Cloud Climatology Project (ISCCP) simulator to pinpoint deficiencies related to the cloud processes in the ECHAM5 general circulation model. A Lagrangian trajectory analysis is performed to track the transitions of anvil cirrus originating from deep-convective detrainment to cirrostratus and thin cirrus, comparing ISCCP observations and the ECHAM5 model. Trajectories of cloudy air parcels originating from deep convection are computed for both, the ISCCP observations and the model, over which the ISCCP joint histograms are used for analyzing the cirrus life cycle over 5 days. The clouds originating from detrainment from deep-convection decay and gradually thin-out after the convective event over 3 to 4 days. The effect of the convection-cirrus transitions in a warmer climate is analyzed, in order to understand the climate feedbacks due to deep-convective cloud transitions. An idealized climate change simulation is performed using a +2K Sea Surface Temperature (SST) perturbation. The Lagrangian trajectory analysis over perturbed climate suggests that more and thicker cirrostratus and cirrus clouds occur in the warmer climate compared to the present day climate. Stronger convection is noticed in the perturbed climate which leads to an increased precipitation, especially on day-2 and -3 after the individual convective events. The shortwave and the longwave cloud forcings both increase in the warmer climate, with an increase of net cloud radiative forcing (NCRF), leading to an overall positive feedback of the increased cirrostratus and cirrus clouds from a Lagrangian transition perspective.”

Citation: Swati Gehlot and Johannes Quaas, Journal of Climate 2012.


Temperature was related to crop prices in 19th century Sweden

Climatic signatures in crops and grain prices in 19th-century Sweden – Holopainen et al. (2012)

Abstract: “Climate and weather variation affect agricultural productivity, with consequences for both overall food availability and the wider economy. Knowledge of these processes has implications for understanding historical demography and predicting effects of climate change on societies. We studied the relationships between ambient temperature and the yields and prices of principle grains (wheat, rye, barley oats) in Sweden from 1803 to 1914. We found that the annual general crop index (a measure of overall crop yield) correlated negatively with the annual average price of the four grains. Overall temperature during the period of crop growth was related positively to general crop index and negatively to average crop price. At the level of month of crop growth, when the relationship between temperature and general crop index was most positive, that between temperature and average crop price was most negative. This strong structured relationship was found to be consistent when yields of each crop were considered separately, and indicates that the relationships between crop yield and crop price were to a large extent due to the influence of ambient temperature. Price correlations between pairs of crop species were in all cases greater than the correlation of yields. Within individual crops, correlations between price and yield were stronger for those crops for which imports were not available, and which were therefore subject to the weakest influence from rising globalisation. Our analyses demonstrate the sensitivity of historical agriculture to climatic factors, and the extent to which this affected the wider economy. It is likely that the susceptibility of agriculture to climatic risks was ascended by the concomitant climate regime, the ‘Little Ice Age’. Moreover, our study period spans the period of rising globalisation, and suggests a weakening influence of prevailing weather on crop prices.”

Citation: Jari Holopainen, Ian J Rickard, Samuli Helama, The Holocene March 1, 2012 0959683611434220, doi: 10.1177/0959683611434220.


The trees that grow on glaciers

The influence of glacier surface processes on the short-term evolution of supraglacial tree vegetation: A case study of the Miage Glacier, Italian Alps – Pelfini et al. (2012)

Abstract: “Supraglacial debris cover allows vegetation to colonize glacier surface, and whenever it is enough stable and thick, also shrubs and trees can germinate and grow. Supraglacial tree growth and distribution patterns on the glacier are closely connected with the debris-covered glacier dynamics and evolution. The aim of the research reported here was to evaluate the tree age and tree distribution patterns on the glacier tongue and the influence of ice-cliff backwasting, close to glacier terminus, on tree loss. We analysed the fragile and fast-changing environment that is present on the lower ablation sector of the Miage Glacier (Mont Blanc Massif, Italian Alps) where some ice cliffs are present and backwasting and downwasting phenomena occur. Tree features and short-term evolution were analysed with respect to glacier variations (mainly surface displacements and ice ablation) and geometry changes of the two most representative ice cliffs. The supraglacial trees’ life time resulted to be mainly controlled by glacier surface displacements and by the occurrence of backwasting and downwasting processes, whereas tree germination was associated with fine debris presence. These factors, controlling plants’ life and growth on the glacier, are an actual limit when supraglacial trees are analysed to reconstruct past environmental changes occurred on the glacier tongue. Moreover, we found that a large number of trees die under conditions of dominating backwasting inducing the loss of debris substrate (condition met especially on the northern glacier lobe). Instead, in the case of prevalence of downwasting (condition mainly observed on the southern glacier lobe), trees more easily survive and flow downvalley transported by the glacier flux.”

Citation: Manuela Pelfini, Guglielmina Diolaiuti, Giovanni Leonelli, Mauro Bozzoni, Nicoletta Bressan, Daniele Brioschi, Anna Riccardi, The Holocene March 2, 2012 0959683611434222, doi: 10.1177/0959683611434222.


Extreme winter precipitation events projected to increase significantly in western United States

Changes in winter precipitation extremes for the Western United States under a warmer climate as simulated by regional climate models – Dominguez et al. (2012)

Abstract: “We find a consistent and statistically significant increase in the intensity of future extreme winter precipitation events over the western United States, as simulated by an ensemble of regional climate models (RCMs) driven by IPCC AR4 global climate models (GCMs). All eight simulations analyzed in this work consistently show an increase in the intensity of extreme winter precipitation with the multi-model mean projecting an area-averaged 12.6% increase in 20-year return period and 14.4% increase in 50-year return period daily precipitation. In contrast with extreme precipitation, the multi-model ensemble shows a decrease in mean winter precipitation of approximately 7.5% in the southwestern US, while the interior west shows less statistically robust increases.”

Citation: Dominguez, F., E. R. Rivera, D. P. Lettenmaier, and C. L. Castro (2012), Changes in winter precipitation extremes for the Western United States under a warmer climate as simulated by regional climate models, Geophys. Res. Lett., doi:10.1029/2011GL050762, in press.


Greenland lake sediments show Norse agriculture only weakly but modern agriculture markedly

A paleoecological perspective on 1450 years of human impacts from a lake in southern Greenland – Perren et al. (2012)

Abstract: “A multiproxy sedimentary record from Lake Igaliku in southern Greenland documents 1450 years of human impacts on the landscape. Diatoms, scaled chrysophytes, and C and N geochemistry show perturbations consistent with recent agricultural activities (post-AD 1980), superimposed upon long-term environmental variability. While the response to Norse agriculture (~AD 986–1450) is weak, the biological response to the last 30 years of modern sheep farming is marked, with drastic changes in diatom taxa, δ13C and δ15N isotopic ratios, and a sharp increase in scaled chrysophytes. Indeed, current conditions in the lake during the last 30 years are unprecedented in the context of the last 1450 years. The dominant driver for recent changes is likely an intensification of agricultural practices combined with warming summer temperatures. Warm temperatures and agricultural disturbance together during Norse Landnám did not lead to the marked changes seen in the modern lake environment over the last 30 years. The synergistic response between increased climate warming and agriculture will likely have unanticipated effects. These findings confirm the sensitivity of Arctic lakes to external anthropogenic forcing and are the first analyses of their kind for the effects of agriculture in Greenland.”

Citation: Bianca B Perren, Charly Massa, Vincent Bichet, Émilie Gauthier, Olivier Mathieu, Christophe Petit, Hervé Richard, The Holocene March 1, 2012 0959683612437865, doi: 10.1177/0959683612437865.


Calibrating lake sediment records with meteorological data

Calibrating biogeochemical and physical climate proxies from non-varved lake sediments with meteorological data: methods and case studies – von Gunten et al. (2012)

Abstract: “Lake sediment records are underrepresented in comprehensive, quantitative, high-resolution (sub-decadal), multi-proxy climate reconstructions for the past millennium. This is largely a consequence of the difficulty of calibrating biogeochemical lake sediment proxies to meteorological time series (calibration-in-time). Thanks to recent methodological advances, it is now possible. This paper outlines a step-by-step, specifically tailored methodology, with practical suggestions for calibrating and validating biogeochemical proxies from lake sediments to meteorological data. This approach includes: (1) regional climate data; (2) site selection; (3) coring and core selection; (4) core chronology; (5) data acquisition; and (6) data analysis and statistical methods. We present three case studies that used non-varved lake sediments from remote areas in the Central Chilean Andes, where little a priori information was available on the local climate and lakes, or their responses to climate variability. These case studies illustrate the potential value and application of a calibration-in-time approach to non-varved lake sediments for developing quantitative, high-resolution climate reconstructions.”

Citation: Lucien von Gunten, Martin Grosjean, Christian Kamenik, Marian Fujak and Roberto Urrutia, Journal of Paleolimnology, DOI: 10.1007/s10933-012-9582-9.


Portuguese meteorological measurements from 18th century

Early Portuguese meteorological measurements (18th century) – Alcoforado et al. (2012) [FULL TEXT]

Abstract: “Natural proxies, documentary evidence and instrumental data are the only sources used to reconstruct past climates. In this paper, we present the 18th century meteorologists (either Portuguese or foreigners) who made the first observations at several sites in Continental Portugal, Madeira Island and Rio de Janeiro (Brazil), from 1749 until 1802. Information is given concerning observation site, variables observed, measurement period, methods of measurements and sources (both manuscript and printed). Some examples from the data usefulness are given: rainfall variability in Madeira (1749–1753) and in continental Portugal (1781–1793) was reconstructed, allowing to extend towards the late 18th century the well known negative correlation between the NAO index and seasonal rainfall. Furthermore, previously unpublished data for 1783–1784 have allowed analysing the consequences of the Lakagígar eruption in Portugal: foggy and haze days are referred to in summer 1783, but unlike the hot summer observed in northern and central Europe, temperatures in Portugal were lower than average. Additionally, observations from Rio de Janeiro in Brazil show that the Lakagígar consequences may well have spread to sectors of the Southern Hemisphere. Although the series are short, the data have been used for climate reconstruction studies and may also be useful to improve the quality of large scale reconstruction datasets.”

Citation: Alcoforado, M. J., Vaquero, J. M., Trigo, R. M., and Taborda, J. P.: Early Portuguese meteorological measurements (18th century), Clim. Past, 8, 353-371, doi:10.5194/cp-8-353-2012, 2012.


High altitude water vapor feedback analysis

Using satellites to investigate the sensitivity of longwave downward radiation to water vapor at high elevations – Naud et al. (2012)

Abstract: “Many studies suggest that high-elevation regions may be among the most sensitive to future climate change. However, in situ observations in these often remote locations are too sparse to determine the feedbacks responsible for enhanced warming rates. One of these feedbacks is associated with the sensitivity of longwave downward radiation (LDR) to changes in water vapor, with the sensitivity being particularly large in many high-elevation regions where the average water vapor is often low. We show that satellite retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth’s Radiant Energy System (CERES) can be used to expand the current ground-based observational database and that the monthly averaged clear-sky satellite estimates of humidity and LDR are in good agreement with the well-instrumented Center for Snow and Avalanche Studies ground-based site in the southwestern Colorado Rocky Mountains. The relationship between MODIS-retrieved precipitable water vapor and surface specific humidity across the contiguous United States was found to be similar to that previously found for the Alps. More important, we show that satellites capture the nonlinear relationship between LDR and water vapor and confirm that LDR is especially sensitive to changes in water vapor at high elevations in several midlatitude mountain ranges. Because the global population depends on adequate fresh water, much of which has its source in high mountains, it is critically important to understand how climate will change there. We demonstrate that satellites can be used to investigate these feedbacks in high-elevation regions where the coverage of surface-based observations is insufficient to do so.”

Citation: Naud, C. M., J. R. Miller, and C. Landry (2012), Using satellites to investigate the sensitivity of longwave downward radiation to water vapor at high elevations, J. Geophys. Res., 117, D05101, doi:10.1029/2011JD016917.


Maximum temperatures have increased faster than minimum temperatures in Spain

Recent trends in mean maximum and minimum air temperatures over Spain (1961–2006) – del Río et al. (2012)

Abstract: “This study analyzes the mean maximum and minimum temperature trends on a monthly, seasonal, and annual timescale by applying various statistical tools to data from 476 Spanish weather stations during the period between 1961 and 2006. The magnitude of the trends was derived from the slopes of the regression lines using the least squares method, and the nonparametric Mann–Kendall test was used to determine the statistical significance of the trends. Temperature significantly increased in over 60% of the country in March, June, spring, and summer in the case of maximum temperatures and in March, May, June, August, spring, and summer for minimum temperatures. At the annual resolution, temperatures significantly increased in over 90% of Spain with a rise of around 0.3°C/decade. The maximum temperature increased at a higher rate than the minimum temperature from midsummer to early winter as well as in winter, spring, and summer and also on an annual basis.”

Citation: S. del Río, A. Cano-Ortiz, L. Herrero and A. Penas, Theoretical and Applied Climatology, DOI: 10.1007/s00704-012-0593-2.


Analysis of aerosol and cloud forcing over India

Aerosol and cloud feedbacks on surface energy balance over selected regions of the Indian subcontinent – Urankar et al. (2012)

Abstract: “We investigate aerosol and cloud forcing on the surface energy balance over selected regions in India. Four regions were selected with different surface characteristics and have considerable differences in the long-term trends and seasonal distribution of clouds and aerosols. These regions are described as (1) northern semiarid, (2) humid subtropical, (3) populated central peninsula, and (4) northeast monsoon impacted. Modern Era Retrospective-analysis for Research and Applications (MERRA) data and Climate Forecast System Reanalysis version 2 (CFSR) data are used in this study. An intercomparison of cloud fractions from both data sets shows that CFSR systematically underestimates high-cloud fraction during premonsoon and monsoon seasons. However, there are fewer low-cloud fraction biases. The positive temporal trend over 31 years (1979–2009) from MERRA in high clouds is greater than that of low clouds. This is due to positive anomalies in the cloud ice and supercooled liquid water content in MERRA. Biases in the radiative fluxes and surface fluxes show a strong relationship (correlations exceeding 0.8) with cloud fraction biases, more so for the high clouds. During the premonsoon season, aerosol forcing causes a change in surface shortwave radiation of −24.5, −25, −19, and −16 W m−2 over regions 1 −4, respectively. The corresponding longwave radiation decrease is −9.8, −6.8, −4.5, and −1.9 W m−2 over these same regions, respectively. The maximum surface shortwave reduction due to clouds, which is observed during the monsoon season, is −86, −113, −101, and −97 W m−2 for these same regions, respectively. A decreasing trend in the boundary layer height is noticed both in MERRA and CFSR. The variation in the Bowen ratio and its relation to aerosol and cloud effect anomalies are also discussed.”

Citation: Urankar, G., T. V. Prabha, G. Pandithurai, P. Pallavi, D. Achuthavarier, and B. N. Goswami (2012), Aerosol and cloud feedbacks on surface energy balance over selected regions of the Indian subcontinent, J. Geophys. Res., 117, D04210, doi:10.1029/2011JD016363.


Western European cold spells are projected to become warmer

Western European cold spells in current and future climate – de Vries et al. (2012)

Abstract: “This paper discusses western European cold spells (where temperature falls below the 10% quantile of the winter temperature distribution) in current and future climate. It is demonstrated that many of the projected future changes in cold-spell statistics (duration, return period, intensity) can be explained by changes in the mean (increase) and variance (decrease) of the winter temperature distribution. After correcting for these changes (by subtracting the mean temperature and by dividing by the standard deviation), future cold-spell statistics display no major changes outside estimated error bounds. In absolute terms however, the future cold spells are projected to become ∼5°C warmer (and remain above freezing point), thus having a significant climatic impact. An important contributor to the projected future decrease of temperature variance is shown to be the reduction of the mean zonal temperature gradient (land-sea contrast). These results have been obtained using a 17-member ensemble of climate-model simulations with current and future concentration of greenhouse gases.”

Citation: de Vries, H., R. J. Haarsma, and W. Hazeleger (2012), Western European cold spells in current and future climate, Geophys. Res. Lett., 39, L04706, doi:10.1029/2011GL050665.


CLASSIC OF THE WEEK: Kirde (1938)

Change of climate in the northern hemisphere – Kirde (1938) [FULL TEXT]

Abstract: No abstract. Opening sentences: “An attempt is made in this paper to analyze the variations of climate in the Northern Hemisphere. For this purpose we have used the temperature observations of meteorological stations whose period of observation extends at least from 45 to 50 years beginning with 1860 – 1870.”

Citation: Kirde, Kaarel, Äratrükk: Acta et commentationes Universitatis Tartuensis (Dorpatensis), A XXXIII. 5.


When each paper is published, it is notified in AGW Observer Facebook page and Twitter page. Here’s the archive for the research papers of previous weeks. If this sort of thing interests you, be sure to check out A Few Things Illconsidered. They also have a weekly posting containing lots of links to new research and other climate related news.

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