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Papers on snow cover changes

Posted by Ari Jokimäki on February 19, 2013

This is a list of papers on snow cover changes with an emphasis on hemispheric and global observational analyses. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

UPDATE (October 19, 2014): Armstrong & Brodzik (2001) added. Regional section with a few papers added.

Change in snow phenology and its potential feedback to temperature in the Northern Hemisphere over the last three decades – Peng et al. (2013) “Trends in the duration or extent of snow cover are expected to feedback to temperature trends. We analyzed trends in dates of onset and termination of snow cover in relation to temperature over the past 27 years (1980–2006) from over 636 meteorological stations in the Northern Hemisphere. Different trends in snow duration are observed over North America and Eurasia. Over North America, the termination date of snow cover remained stable during the 27 years, whereas over Eurasia it has advanced by 2.6 ± 5.6 d decade−1. Earlier snow cover termination is systematically correlated on a year-to-year basis with a positive temperature anomaly during the snowmelt month with a sensitivity of −0.077 °C d−1. These snow feedbacks to air temperature are more important in spring, because high net radiation is coupled with thin snow cover. Shushi Peng et al 2013 Environ. Res. Lett. 8 014008 doi:10.1088/1748-9326/8/1/014008. [Full text]

Northern Hemisphere spring snow cover variability and change over 1922–2010 including an assessment of uncertainty – Brown & Robinson (2011) “An update is provided of Northern Hemisphere (NH) spring (March, April) snow cover extent (SCE) over the 1922–2010 period incorporating the new climate data record (CDR) version of the NOAA weekly SCE dataset, with annual 95% confidence intervals estimated from regression analysis and intercomparison of multiple datasets. The uncertainty analysis indicates a 95% confidence interval in NH spring SCE of ±5–10% over the pre-satellite period and ±3–5% over the satellite era. The multi-dataset analysis shows larger uncertainties monitoring spring SCE over Eurasia (EUR) than North America (NA) due to the more complex regional character of the snow cover variability and larger between-dataset variability over northern Europe and north-central Russia. Trend analysis of the updated SCE series provides evidence that NH spring snow cover extent has undergone significant reductions over the past ~90 yr and that the rate of decrease has accelerated over the past 40 yr. The rate of decrease in March and April NH SCE over the 1970–2010 period is ~0.8 million km2 per decade corresponding to a 7% and 11% decrease in NH March and April SCE respectively from pre-1970 values. In March, most of the change is being driven by Eurasia (NA trends are not significant) but both continents exhibit significant SCE reductions in April. The observed trends in SCE are being mainly driven by warmer air temperatures, with NH mid-latitude air temperatures explaining ~50% of the variance in NH spring snow cover over the 89-yr period analyzed. However, there is also evidence that changes in atmospheric circulation around 1980 involving the North Atlantic Oscillation and Scandinavian pattern have contributed to reductions in March SCE over Eurasia. Brown, R. D. and Robinson, D. A.: Northern Hemisphere spring snow cover variability and change over 1922–2010 including an assessment of uncertainty, The Cryosphere, 5, 219-229, doi:10.5194/tc-5-219-2011, 2011. [Full text]

Long-term variability in Northern Hemisphere snow cover and associations with warmer winters – McCabe & Wolock (2010) “A monthly snow accumulation and melt model is used with gridded monthly temperature and precipitation data for the Northern Hemisphere to generate time series of March snow-covered area (SCA) for the period 1905 through 2002. The time series of estimated SCA for March is verified by comparison with previously published time series of SCA for the Northern Hemisphere. The time series of estimated Northern Hemisphere March SCA shows a substantial decrease since about 1970, and this decrease corresponds to an increase in mean winter Northern Hemisphere temperature. The increase in winter temperature has caused a decrease in the fraction of precipitation that occurs as snow and an increase in snowmelt for some parts of the Northern Hemisphere, particularly the mid-latitudes, thus reducing snow packs and March SCA. In addition, the increase in winter temperature and the decreases in SCA appear to be associated with a contraction of the circumpolar vortex and a poleward movement of storm tracks, resulting in decreased precipitation (and snow) in the low- to mid-latitudes and an increase in precipitation (and snow) in high latitudes. If Northern Hemisphere winter temperatures continue to warm as they have since the 1970s, then March SCA will likely continue to decrease. Gregory J. McCabe, David M. Wolock, Climatic Change, March 2010, Volume 99, Issue 1-2, pp 141-153, DOI: 10.1007/s10584-009-9675-2.

Changing Northern Hemisphere Snow Seasons – Choi et al. (2010) “Spatial and temporal patterns in the onset, offset, and length of the snow season across Northern Hemisphere continents are examined for the period from 1967 to 2008. Full snow seasons (FSS) and core snow seasons (CSS) are defined based on the consistency of snow cover within a location over the course of the cold season. Climatologically, the seasonal onsets of FSS and CSS progress more rapidly across the continents than the slower spring northward offset. Average Northern Hemisphere FSS duration has decreased at a rate of 0.8 week decade−1 (5.3 days decade−1) between the winters of 1972/73 and 2007/08, while there is no significant hemispheric change in CSS duration. Changes in the FSS duration are attributed primarily to a progressively earlier offset, which has advanced poleward at a rate of 5.5 days decade−1. A major change in the trends of FSS offset and duration occurred in the late 1980s. Earlier FSS offsets, ranging from 5 to 25 days, and resultant abbreviated durations are observed in western Europe, central and East Asia, and the mountainous western United States. Where regional changes in CSS were observed, most commonly there were shifts in both onset and offset dates toward earlier dates. Results indicate that it is important to pay close attention to spring snowmelt as an indicator of hemispheric climate variability and change. Choi, Gwangyong, David A. Robinson, Sinkyu Kang, 2010: Changing Northern Hemisphere Snow Seasons. J. Climate, 23, 5305–5310. doi: [Full text]

Recent Northern Hemisphere snow cover extent trends and implications for the snow-albedo feedback – Déry & Brown (2007) “Monotonic trend analysis of Northern Hemisphere snow cover extent (SCE) over the period 1972–2006 with the Mann-Kendall test reveals significant declines in SCE during spring over North America and Eurasia, with lesser declines during winter and some increases in fall SCE. The weekly mean trend attains −1.28, −0.78, and −0.48 × 106 km2 (35 years)−1 over the Northern Hemisphere, North America, and Eurasia, respectively. The standardized SCE time series vary and trend coherently over Eurasia and North America, with evidence of a poleward amplification of decreasing SCE trends during spring. Multiple linear regression analyses reveal a significant dependence of the retreat of the spring continental SCE on latitude and elevation. The poleward amplification is consistent with an enhanced snow-albedo feedback over northern latitudes that acts to reinforce an initial anomaly in the cryospheric system. Stephen J. Déry, Ross D. Brown, Geophysical Research Letters, Volume 34, Issue 22, November 2007, DOI: 10.1029/2007GL031474. [Full text]

Variability and trends in the annual snow-cover cycle in Northern Hemisphere land areas, 1972–2000 – Dye (2002) “This study investigated variability and trends in the annual snow-cover cycle in regions covering high-latitude and high-elevation land areas in the Northern Hemisphere. The annual snow-cover cycle was examined with respect to the week of the last-observed snow cover in spring (WLS), the week of the first-observed snow cover in autumn (WFS), and the duration of the snow-free period (DSF). The analysis used a 29-year time-series (1972–2000) of weekly, visible-band satellite observations of Northern Hemisphere snow cover from NOAA with corrections applied by D. Robinson of Rutgers University Climate Laboratory. Substantial interannual variability was observed in WLS, WFS and DSF (standard deviations of 0·8–1·1, 0·7–0·9 and 1·0–1·4 weeks, respectively), which is related directly to interannual variability in snow-cover area in the regions and time periods of snow-cover transition. Over the nearly three-decade study period, WLS shifted earlier by 3–5 days/decade as determined by linear regression analysis. The observed shifts in the annual snow-cover cycle underlie a significant trend toward a longer annual snow-free period. The DSF increased by 5–6 days/decade over the study period, primarily as a result of earlier snow cover disappearance in spring. The observed trends are consistent with reported trends in the timing and length of the active growing season as determined from satellite observations of vegetation greenness and the atmospheric CO2 record. Dennis G. Dye, Hydrological Processes, Volume 16, Issue 15, pages 3065–3077, 30 October 2002, DOI: 10.1002/hyp.1089.

Recent northern hemisphere snow extent: A comparison of data derived from visible and microwave satellite sensors – Armstrong & Brodzik (2001)
Abstract: “During the past four decades much important information on Northern Hemisphere snow extent has been provided by the NOAA weekly snow extent charts derived from visible-band satellite imagery. Passive microwave satellite remote sensing can enhance snow measurements based on visible data alone because of the ability to penetrate clouds, provide data during darkness and the potential to provide an index of snow depth or water equivalent. We compare the fluctuation of Northern Hemisphere snow cover over the past twenty years using these two satellite remote sensing techniques. Results show comparable inter-annual variability with similar long-term hemispheric-scale trends indicating decreases in snow extent of approximately 0.2 percent per year. The passive microwave snow algorithm applied in this study indicates less snow-covered area than the visible data during fall and early winter when the snow is shallow. New algorithms designed to reduce this apparent error are being developed and tested.”
R. L. Armstrong, M. J. Brodzik (2001), Recent northern hemisphere snow extent: A comparison of data derived from visible and microwave satellite sensors. Geophysical Research Letters, 28: 3673–3676. doi: 10.1029/2000GL012556. [FULL TEXT]

Northern Hemisphere Snow Cover Variability and Change, 1915–97 – Brown (2000) “Historical and reconstructed snow cover data from stations in Canada, the United States, the former Soviet Union, and the People’s Republic of China were used to reconstruct monthly snow cover extent (SCE) fluctuations over midlatitudinal (40°–60°N) regions of North America (NA) and Eurasia back to the early 1900s using an areal snow index approach. The station distribution over NA allowed SCE to be reconstructed back to 1915 for 6 months (November–April), along with estimates of monthly mean snow water equivalent (SWE) from gridded daily snow depth data. Over Eurasia, SCE was able to be reconstructed back to 1922, but major gaps in the station network limited the approach to 3 months (October, March, and April). The reconstruction provided evidence of a general twentieth century increase in NA SCE, with significant increases in winter (December–February) SWE averaging 3.9% per decade. The results are consistent with an observed increasing trend in winter snow depth over Russia and provide further evidence for systematic increases in precipitation over NH midlatitudes. North American spring snow cover was characterized by rapid decreases during the 1980s and early 1990s with a significant long-term decrease in April SWE averaging 4.4% per decade. Eurasia was characterized by a significant reduction in April SCE over the 1922–97 period associated with a significant spring warming. The snow cover reduction was significant at the hemispheric scale with an estimated average NH SCE loss of 3.1 × 106 km2 (100 yr)−1 associated with significant warming of 1.26°C (100 yr)−1 over NH midlatitudinal land areas (40°–60°N). The computed temperature sensitivity of NH April SCE was −2.04 × 106 km2 °C−1. Since 1950, March SCE decreases have become more important than those in April with significant reductions over both continents averaging 8.5 × 106 km2 (100 yr)−1. March was also observed to have experienced the largest warming during the November–April snow season with significant post-1950 warming trends in both continents averaging 4.1°C (100 yr)−1. The hemisphere-wide elevated March snow cover–temperature response is consistent with the position of the snowline over continental grassland vegetation zones where snow cover is relatively shallow and the potential snow cover area–albedo feedback is large.” Brown, Ross D., 2000: Northern Hemisphere Snow Cover Variability and Change, 1915–97. J. Climate, 13, 2339–2355. doi:;2. [Full text]

Northern Hemisphere snow extent: regional variability 1972–1994 – Frei & Robinson (1999) “Snow cover is an important hydrologic and climatic variable due to its effects on water supplies, and on energy and mass exchanges at the surface. We investigate the kinematics and climatology of Northern Hemisphere snow extent between 1972 and 1994, and associated circulation patterns. Interannual fluctuations of North American and Eurasian snow extents are driven by both hemispheric scale signals, as well as signals from smaller ‘coherent’ regions, within which interannual fluctuations of snow extent are highly correlated. These regions cover only 2–6% of the continental land area north of 20°N, yet during many months they explain more than 60% of the variance in continental snow extent. They are identified using Principal Components Analysis (PCA) of digitized snow extent charts obtained from the National Oceanic and Atmospheric Administration (NOAA). Significant month-to-month persistence is found over western North America and Europe during winter and spring. Geographically and seasonally dependent associations are identified between North American snow extent and atmospheric circulation patterns, surface air temperature, and snowfall. Over western North America, snow extent is associated with the longitudinal position of the North American ridge. Over eastern North America, snow extent is associated with a meridional oscillation in the 500-mb geopotential height field. These teleconnection patterns, derived using composite analyses, are associated with secondary modes of tropospheric variability during autumn and winter. During spring, snow extent becomes effectively decoupled from tropospheric dynamics. These results are useful for understanding the natural variability of the climate system, reconstructing pre-satellite era climate variability, evaluating climate models, and detecting climate change. Allan Frei, David A. Robinson, International Journal of Climatology, Volume 19, Issue 14, pages 1535–1560, 30 November 1999, DOI: 10.1002/(SICI)1097-0088(19991130)19:143.0.CO;2-J. [Full text]

Recent variations and regional relationships in Northern Hemisphere snow cover – Robinson et al. (1995) Abstract doesn’t seem to be available online. Robinson, David A.; Frei, Allan; Serreze, Mark C., Annals of Glaciology, vol.21, pp.71-76.

Changes of Snow Cover, Temperature, and Radiative Heat Balance over the Northern Hemisphere – Groisman et al. (1994) “Contemporary large-scale changes in satellite-derived snow cover were examined over the Northern Hemisphere extratropical land (NEL) areas. These areas encompass 55% of the land in the Northern Hemisphere. Snow cover (S) transient regions, the “centers of action” relative to interannual variations of snow cover, were identified for the years 1972–1992. During these years a global retreat in snow cover extent (SE) occurred in the second half of the hydrologic year (April–September). Mean annual SE has decreased by 10% (2.3 × 106 km2). Negative trends account for one-third to one-half of the interannual continental variance of SE. The historical influence of S on the planetary albedo and outgoing longwave radiation (OLR) is investigated. The mean annual response of the S feedback on the radiative balance (RB) is negative and suggests a large-scale heat redistribution. During autumn and early winter (up to January), however, the feedback of S on the planetary RB may he positive. Only by February does the cooling effect of S (due to albedo increase) dominate the planetary warming due to reduced OLR over the S. Despite a wintertime maximum in SF, the feedback in spring has the greatest magnitude. The global retreat of spring SE should lead to a positive feedback on temperature. Based on observed records of S, changes in RB are calculated that parallel an observed increase of spring temperature during the past 20 years. The results provide a partial explanation of the significant increase in spring surface air temperature observed over the land areas of the Northern Hemisphere during the past century. The mean SE in years with an El Niño and La Niña were also evaluated. El Niño events are generally accompanied by increased SE over the NEL during the first half of the hydrological year. In the second half of the hydrologic year (spring and summer), the El Niño events are accompanied by a global retreat of SE. Groisman, Pavel Ya, Thomas R. Karl, Richard W. Knight, Georgiy L. Stenchikov, 1994: Changes of Snow Cover, Temperature, and Radiative Heat Balance over the Northern Hemisphere. J. Climate, 7, 1633–1656. doi:;2. [Full text]

Global Snow Cover Monitoring: An Update – Robinson et al. (1993) “Accurate monitoring of the large-scale dimensions of global snow cover is essential for understanding details of climate dynamics and climate change. Presently, such information is gathered individually from ground station networks and satellite platforms. Efforts are in progress to consolidate and analyze long-term station records from a number of countries. To gain truly global coverage, however, satellite-based monitoring techniques must be employed. A 27-year record of Northern Hemisphere continental snow cover produced by the National Oceanic and Atmospheric Administration (NOAA) is the longest such environmental record available. Records of Southern Hemisphere continental cover and snow on top of Arctic sea ice have been produced by similar means for a portion of this interval. The visible imagery charting technique used to generate these data provides information on snow extent but not on snow volume. Satellite microwave analyses over Northern Hemisphere lands show some promise in this regard, however, large-scale monitoring of snow extent with microwave data remains less accurate than visible charting. This paper updates the status of global snow cover monitoring, concentrating on the weekly snow charts prepared by NOAA and discussing a new and consistent record of monthly snow cover generated from these weekly charts. The NOAA charts show a reduction of hemispheric snow cover over the past five years, particularly in spring. Snow areas from the NOAA product are then compared with values derived using passive microwave data. The latter consistently reports less snow cover than the more accurate visible product. Finally, future snow monitoring initiatives are recommended. These include continuing the consistent NOAA product until an all-weather all-surface product is developed. The latter would use multiple data sources and geographic information systems techniques. Such an integrative product would need extensive comparisons with the NOAA product to ensure the continued utility of the lengthy NOAA observations in studies of climate change. In a retrospective sense, satellite charts from the middle 1960s to early 1970s need reevaluation and techniques to merge satellite products with historic station time series must be developed. Robinson, David A., Kenneth F. Dewey, Richard R. Heim, 1993: Global Snow Cover Monitoring: An Update. Bull. Amer. Meteor. Soc., 74, 1689–1696. doi:;2. [Full text]

Interannual Variability of Wintertime Snow Cover across the Northern Hemisphere – Gutzler & Rosen (1992) “Digitized maps of Northern Hemisphere snow cover derived from visible satellite imagery are examined to assess the interannual variability of snow cover in winter months for years 1972–90. The secular trend of winter snow cover over the landmasses of Eurasia and North America during this period is extremely small in December and January. A decreasing trend of somewhat larger magnitude is observed in Eurasian snow cover in February. Fluctuations of detrended interannual snow-cover anomalies averaged over the Eurasian and North American continents are positively correlated. By subdividing the continents into longitudinal sectors it is determined that this intercontinental relationship is due to high correlations between European and North American sectors. The relationship of snow-cover fluctuations to large-scale circulation anomalies is described using lime series of teleconnection pattern indices derived from monthly mean geopotential height fields. A pattern of height anomalies resembling the North Atlantic Oscillation is correlated with snow-cover anomalies in North America and Europe. The Pacific-North American teleconnection pattern is highly correlated with snow-cover anomalies in western North America but has limited influence on intercontinental snow-cover fluctuations.” Gutzler, David S., Richard D. Rosen, 1992: Interannual Variability of Wintertime Snow Cover across the Northern Hemisphere. J. Climate, 5, 1441–1447. doi:;2. [Full text]

Recent secular variations in the extent of Northern Hemisphere snow cover – Robinson & Dewey (1990) “Northern hemisphere snow cover during 1988 and 1989 was at its lowest extent since the advent of reliable satellite snow-cover monitoring in 1972; running some 8–10% below the eighteen-year annual mean of 25.7 million km2. Monthly minima for the period of record occurred six times during these two years. In general, the last nine years of the satellite record had less extensive cover than the 1972–80 interval. Negative anomalies during the 1980s were largest over Eurasia in all seasons, and in the Spring over North America. Hemispheric seasonal means for the most recent nine years were 3.7% to 8.4% lower than those between 1972 and 1980. Results are based on analyses of National Oceanic and Atmospheric Administration weekly snow charts, which are produced from visible satellite imagery.” David A. Robinson, Kenneth F. Dewey, Geophysical Research Letters, Volume 17, Issue 10, pages 1557–1560, September 1990, DOI: 10.1029/GL017i010p01557. [Full text]

A Digital Archive of Northern Hemisphere Snow Cover, November 1966 through December 1980 – Dewey & Heim (1982) “The purpose of this article is to acquaint the research community with a new data base—a digitized archive of Northern Hemisphere snow cover. Historically, those researchers who needed snow cover data for climatic and atmospheric boundary layer studies have had to rely on the irregularly spaced (and in some regions, sparse)grid of point observations. Northern Hemisphere Weekly Snow and Ice Cover Charts, which are created from analyzed satellite imagery at the National Earth Satellite Service (NESS), have been available on an operational basis since late 1966. Each of these weekly charts for the period November 1966 through December 1980 was digitized and stored in a new data archive. Snow cover area and snow cover frequency climatologies were created and examples are presented. The significance of this unique data archive is examined by comparing the 14-year mean annual snow cover frequency climatology with several published snow cover climatologies. The potential uses for this data archive in meteorological and climatological studies also are reviewed. Dewey, Kenneth F., Richard Heim, 1982: A Digital Archive of Northern Hemisphere Snow Cover, November 1966 through December 1980. Bull. Amer. Meteor. Soc., 63, 1132–1141. doi:;2. [Full text]

Regional analyses





North America


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Papers on 2003 heat wave in Europe

Posted by Ari Jokimäki on February 8, 2013

This is a list of papers on 2003 heat wave in Europe. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

Heat-related mortality in the Florentine area (Italy) before and after the exceptional 2003 heat wave in Europe: an improved public health response? – Morabito et al. (2012) “High ambient temperatures have been associated with increased mortality across the world. Several studies suggest that timely preventive measures may reduce heat-related excess mortality. The main aim of this study was to detect the temporal modification of heat-related mortality, in older adults (aged 65–74) and in elderly ≥75 years old, in the Florentine area by comparing previous (1999–2002) and subsequent (2004–2007) periods to the summer of 2003, when a regional Heat-Health Warning System (HHWS) was set up. Mortality data from 1999 to 2007 (May–September) were provided by the Mortality Registry of the Tuscany Region (n = 21,092). Weather data were used to assess daily apparent temperatures (AT). Case-crossover time-stratified designs and constrained segmented distributed lag models were applied. No significant heat-related mortality odds ratio (OR) variations were observed among the sub-periods. Nevertheless, a general OR decrease dating from 1999–2002 (OR 1.23; lack of HHWS) to 2004–2005 (OR 1.21; experimental HHWS running only for Florence) and to 2006–2007 (OR 1.12; official HHWS extended to the whole Florentine area) was observed when the maximum AT was considered. This modification was only evident in subjects ≥75 years old. The heat effect was higher and sustained for more days (until lag 9) during the period 1999–2002 than 2004–2007. The decrease of the excessive heat effect on mortality between periods with the absence and existence of a HHWS is also probably due to the mitigation of preventive measures and the implementation of a HHWS with specific interventions for safeguarding the health of the “frail elderly”.” Marco Morabito, Francesco Profili, Alfonso Crisci, Paolo Francesconi, Gian Franco Gensini, Simone Orlandini, International Journal of Biometeorology, September 2012, Volume 56, Issue 5, pp 801-810, DOI: 10.1007/s00484-011-0481-y.

Influence of sea surface temperature on the European heat wave of 2003 summer. Part I: an observational study – Feudale & Shukla (2011) “The heat wave affecting Europe during summer of 2003 is analyzed in detail with observational and reanalysis data. Surface, middle and upper troposphere analysis reveal particular circulation patterns related to an atmospheric blocking condition. In general seasonal anomalies, like this intense heat wave, are strongly related to boundary conditions. Composites and empirical orthogonal functions analysis provide evidence for an organized structure in the sea surface temperature (SST) anomaly field: high SSTs in the Mediterranean basin, the North Sea and further north toward the Arctic Circle were observed mainly in the months of June and August. The outcome of this analysis on observational data shows the SST as one of the possible factors in enhancing the heat wave in the European area.” Laura Feudale, Jagadish Shukla, Climate Dynamics, May 2011, Volume 36, Issue 9-10, pp 1691-1703, DOI: 10.1007/s00382-010-0788-0. [Full text]

Influence of sea surface temperature on the European heat wave of 2003 summer. Part II: a modeling study – Feudale & Shukla (2011) “The Center for Ocean–Land–Atmosphere Studies Atmospheric General Circulation Model is used to investigate the role of global boundary conditions of sea surface temperature (SST) in the establishment and maintenance of the European heat wave of 2003 summer. It is found that the global SST anomalies can explain many major features of the European heat wave during the summer of 2003. A further experiment has investigated the role of SST outside the Mediterranean area. This supplements the results of a previous study where the role of warm Mediterranean SST was analyzed. The results suggest that the SST anomalies had an additional effect of reducing the baroclinicity in the European area reinforcing the blocking circulation and helping to create ideal conditions for the establishment of the heat wave.” Laura Feudale, Jagadish Shukla, Climate Dynamics, May 2011, Volume 36, Issue 9-10, pp 1705-1715, DOI: 10.1007/s00382-010-0789-z.

Impact of aerosol direct radiative forcing on the radiative budget, surface heat fluxes, and atmospheric dynamics during the heat wave of summer 2003 over western Europe: A modeling study – Péré et al. (2011) “In this work, an off-line coupling between the chemistry-transport model CHIMERE (associated with an aerosol optical module) and the meteorological model Weather Research and Forecasting (WRF) is used to study (1) the direct radiative forcing of pollution aerosols during the heat wave of summer 2003 over western Europe and (2) the possible feedbacks of this direct radiative forcing on the surface-atmosphere system. Simulations performed for the period 7–15 August 2003 reveal a significant decrease of daily mean solar radiation reaching the surface (ΔFBOA = −(10–30) W/m2) because of back scattering at the top of the atmosphere (ΔFTOA = −(1–12) W/m2) and also absorption of solar radiation by polluted particles (ΔFatm = + (5–23) W/m2). During daytime, the aerosol surface dimming induces a mean reduction of both sensible (16 W/m2) and latent (21 W/m2) heat fluxes emitted by the terrestrial surface, resulting in a radiative cooling of the air near the surface (up to 2.9 K/d at noon). Simultaneously, the absorption of solar energy by aerosols causes an atmospheric radiative heating within the planetary boundary layer reaching 1.20 K/d at noon. As a consequence, the direct radiative effect of aerosols is shown to reduce both the planetary boundary layer height (up to 30%) and the horizontal wind speed (up to 6%); that may have contributed to favor the particulate pollution during the heat wave of summer 2003.” J. C. Péré, M. Mallet, V. Pont, B. Bessagnet, Journal of Geophysical Research: Atmospheres (1984–2012), Volume 116, Issue D23, December 2011, DOI: 10.1029/2011JD016240.

A Review of the European Summer Heat Wave of 2003 – García-Herrera et al. (2010) “This paper reviews the European summer heat wave of 2003, with special emphasis on the first half of August 2003, jointly with its significant societal and environmental impact across Western and Central Europe. We show the pattern of record-breaking temperature anomalies, discuss it in the context of the past, and address the role of the main contributing factors responsible for the occurrence and persistence of this event: blocking episodes, soil moisture deficit, and sea surface temperatures. We show that the anticyclonic pattern corresponds more to an anomalous northern displacement of the North Atlantic subtropical high than a canonical blocking structure, and that soil moisture deficit was a key factor to reach unprecedented temperature anomalies. There are indications that the anomalous Mediterranean Sea surface temperatures (SSTs) have contributed to the heat wave of 2003, whereas the role of SST anomalies in other oceanic regions is still under debate. There are methodological limitations to evaluate excess mortality due to excessive temperatures; however, the different studies available in the literature allow us to estimate that around 40,000 deaths were registered in Europe during the heat wave, mostly elderly persons. Despite previous efforts undertaken by a few cities to implement warning systems, this dramatic episode has highlighted the widespread un-preparedness of most civil and health authorities to cope with such large events. Therefore, the implementation of early warning systems in most European cities to mitigate the impact of extreme heat is the main consequence to diminish the impact of future similar events. In addition to mortality (by far the most dramatic impact), we have also analyzed the record-breaking forest fires in Portugal and the evidence of other relevant impacts, including agriculture and air pollution.” R. García-Herrera, J. Díaz, R. M. Trigo, J. Luterbacher & E. M. Fischer, Critical Reviews in Environmental Science and Technology, Volume 40, Issue 4, 2010, DOI:10.1080/10643380802238137.

Increase in out-of-hospital cardiac arrest attended by the medical mobile intensive care units, but not myocardial infarction, during the 2003 heat wave in Paris, France – Empana et al. (2009) “Objectives: To address the association between the 2003 heat wave in Paris (France) and the occurrence of out-of-hospital cardiac arrest. Design: An analysis of the interventions of the medical mobile intensive care units of the City of Paris for out-of-hospital cardiac arrest and prehospital myocardial infarctions, which were routinely and prospectively computerized from January 1, 2000, to December 31, 2005. Setting: City of Paris, France. Patients: Participants were consecutive victims of witnessed out-of-hospital cardiac arrest due to heart disease and of ST-segment elevation myocardial infarction (STEMI) aged ≥18 yrs, who were attended by the medical mobile intensive care units (MICUs) of the City of Paris from January 1, 2000, to December 31, 2005. Interventions: None. Measurements and Main Results: The numbers of out-of-hospital cardiac arrests and of STEMIs during the 2003 heat wave period (August 1 to August 14) were compared (Poisson regression analysis) with the respective average numbers during the same period in reference years 2000–2002 and 2004–2005 when there was no heat wave. Mean ages of the 3049 patients experiencing out-of-hospital cardiac arrest and the 2767 patients experiencing STEMI attended by the MICUs during the study period were 64.3 ± 18.0 and 65.2 ± 15.4, respectively, and two thirds were males. During the heat wave period, the number of out-of-hospital cardiac arrests (n = 40) increased 2.5-fold compared with the reference periods (n = 81 for 5 yrs; p < .001); this corresponded to an estimated relative rates of out-of-hospital cardiac arrests of 2.34 (95% confidence interval, 1.60–3.41), after adjustment for age and for gender. This increase was observed in both genders (p for interaction with gender = .48) but only in those who were aged ≥60 yrs (p for interaction with age = .005). No variation was found for myocardial infarctions during heat wave. Conclusions: These data suggest that a heat wave may be associated with an increased risk of sudden cardiac death in the population.” Empana, Jean-Philippe MD, PhD; Sauval, Patrick MD; Ducimetiere, Pierre PhD†; Tafflet, Muriel MPH; Carli, Pierre MD; Jouven, Xavier MD, PhD, Critical Care Medicine: December 2009 – Volume 37 – Issue 12 – pp 3079-3084, doi: 10.1097/CCM.0b013e3181b0868f.

Air pollution during the 2003 European heat wave as seen by MOZAIC airliners – Tressol et al. (2008) “This study presents an analysis of both MOZAIC profiles above Frankfurt and Lagrangian dispersion model simulations for the 2003 European heat wave. The comparison of MOZAIC measurements in summer 2003 with the 11-year MOZAIC climatology reflects strong temperature anomalies (exceeding 4°C) throughout the lower troposphere. Higher positive anomalies of temperature and negative anomalies of both wind speed and relative humidity are found for the period defined here as the heat wave (2–14 August 2003), compared to the periods before (16–31 July 2003) and after (16–31 August 2003) the heat wave. In addition, Lagrangian model simulations in backward mode indicate the suppressed long-range transport in the mid- to lower troposphere and the enhanced southern origin of air masses for all tropospheric levels during the heat wave. Ozone and carbon monoxide also present strong anomalies (both ~+40 ppbv) during the heat wave, with a maximum vertical extension reaching 6 km altitude around 11 August 2003. Pollution in the planetary boundary layer (PBL) is enhanced during the day, with ozone mixing ratios two times higher than climatological values. This is due to a combination of factors, such as high temperature and radiation, stagnation of air masses and weak dry deposition, which favour the accumulation of ozone precursors and the build-up of ozone. A negligible role of a stratospheric-origin ozone tracer has been found for the lower troposphere in this study. From 29 July to 15 August 2003 forest fires burnt around 0.3×106 ha in Portugal and added to atmospheric pollution in Europe. Layers with enhanced CO and NOy mixing ratios, advected from Portugal, were crossed by the MOZAIC aircraft in the free troposphere over Frankfurt. A series of forward and backward Lagrangian model simulations have been performed to investigate the origin of anomalies during the whole heat wave. European anthropogenic emissions present the strongest contribution to the measured CO levels in the lower troposphere (near 30%). This source is followed by Portuguese forest fires which affect the lower troposphere after 6 August 2003 and even the PBL around 10 August 2003. The averaged biomass burning contribution reaches 35% during the affected period. Anthropogenic CO of North American origin only marginally influences CO levels over Europe during that period.” Tressol, M., Ordonez, C., Zbinden, R., Brioude, J., Thouret, V., Mari, C., Nedelec, P., Cammas, J.-P., Smit, H., Patz, H.-W., and Volz-Thomas, A.: Air pollution during the 2003 European heat wave as seen by MOZAIC airliners, Atmos. Chem. Phys., 8, 2133-2150, doi:10.5194/acp-8-2133-2008, 2008. [Full text]

General and specific mortality among the elderly during the 2003 heat wave in Genoa (Italy) – Conti et al. (2007) “The effects of heat waves on health can be serious for elderly persons, especially those in urban areas. We investigated in-depth the mortality excess during the 2003 heat wave among elderly persons (>74 years) in the City of Genoa (Italy). The excess in general mortality was calculated for the period July 16–August 31, as the ratio of observed to expected deaths. To evaluate “harvesting”, we compared observed and expected mortality in the period September 2003–April 2004. We also studied the relationship between mortality and climatic conditions considering daily maximum temperature and Humidex discomfort degrees, as well as “lag-time”. For cause-specific mortality, we considered all pathologies reported on the death certificate. The excess in general mortality was significant and was greatest in the first half of August. During Summer 2003, in Genoa the climatic conditions (described in terms of maximum temperature and Humidex Index) were extremely hot; regarding lag-time, the greatest correlation between the number of observed deaths and the maximum temperature values was observed for the three preceding days (ρ=0.568; significance level <0.01). The prominent causes of death, for which an excess was observed, were cerebrovascular diseases, severe respiratory diseases, severe renal diseases, dementia; moreover, certain pathologic conditions and symptoms, usually not lethal, were also frequent causes of death (e.g., hypovolemia, hyperpyrexia, decubitus ulcers and immobilization syndrome). The results of this study confirm the relationship between the heat waves and death among elderly, stressing that, because of their poorer physical health and the prevalence of cognitive disturbances that hinder risk perception, it is necessary to properly care for them during heat waves.” Susanna Conti, Maria Masocco, Paola Meli, Giada Minelli, Ernesto Palummeri, Renata Solimini, Virgilia Toccaceli, Monica Vichi, Environmental Research, Volume 103, Issue 2, February 2007, Pages 267–274,

Excess mortality related to the August 2003 heat wave in France – Fouillet et al. (2006) “Objectives: From August 1st to 20th, 2003, the mean maximum temperature in France exceeded the seasonal norm by 11–12°C on nine consecutive days. A major increase in mortality was then observed, which main epidemiological features are described herein. Methods: The number of deaths observed from August to November 2003 in France was compared to those expected on the basis of the mortality rates observed from 2000 to 2002 and the 2003 population estimates. Results: From August 1st to 20th, 2003, 15,000 excess deaths were observed. From 35 years age, the excess mortality was marked and increased with age. It was 15% higher in women than in men of comparable age as of age 45 years. Excess mortality at home and in retirement institutions was greater than that in hospitals. The mortality of widowed, single and divorced subjects was greater than that of married people. Deaths directly related to heat, heatstroke, hyperthermia and dehydration increased massively. Cardiovascular diseases, ill-defined morbid disorders, respiratory diseases and nervous system diseases also markedly contributed to the excess mortality. The geographic variations in mortality showed a clear age-dependent relationship with the number of very hot days. No harvesting effect was observed. Conclusions: Heat waves must be considered as a threat to European populations living in climates that are currently temperate. While the elderly and people living alone are particularly vulnerable to heat waves, no segment of the population may be considered protected from the risks associated with heat waves.” A. Fouillet, G. Rey, F. Laurent, G. Pavillon, S. Bellec, C. Guihenneuc-Jouyaux, J. Clavel, E. Jougla and Denis Hémon, International Archives of Occupational and Environmental Health, Volume 80, Number 1, 16-24, DOI: 10.1007/s00420-006-0089-4. [Full text]

The 2003 Heat Wave in France: Dangerous Climate Change Here and Now – Poumadère et al. (2005) “In an analysis of the French episode of heat wave in 2003, this article highlights how heat wave dangers result from the intricate association of natural and social factors. Unusually high temperatures, as well as socioeconomic vulnerability, along with social attenuation of hazards, in a general context where the anthropogenic contribution to climate change is becoming more plausible, led to an excess of 14,947 deaths in France, between August 4 and 18, 2003. The greatest increase in mortality was due to causes directly attributable to heat: dehydration, hyperthermia, heat stroke. In addition to age and gender, combinatorial factors included preexisting disease, medication, urban residence, isolation, poverty, and, probably, air pollution. Although diversely impacted or reported, many parts of Europe suffered human and other losses, such as farming and forestry through drought and fires. Summer 2003 was the hottest in Europe since 1500, very likely due in part to anthropogenic climate change. The French experience confirms research establishing that heat waves are a major mortal risk, number one among so-called natural hazards in postindustrial societies. Yet France had no policy in place, as if dangerous climate were restricted to a distant or uncertain future of climate change, or to preindustrial countries. We analyze the heat wave’s profile as a strongly attenuated risk in the French context, as well as the causes and the effects of its sudden shift into amplification. Research and preparedness needs are highlighted.” Marc Poumadère, Claire Mays, Sophie Le Mer, Russell Blong, Risk Analysis
Volume 25, Issue 6, pages 1483–1494, December 2005, DOI: 10.1111/j.1539-6924.2005.00694.x.
[Full text]

The impact of the summer 2003 heat waves on mortality in four Italian cities – Michelozzi et al. (2005) “This study evaluates the impact of the 2003 heat wave on cause-specific mortality and the role of demographic characteristics and socioeconomic conditions that may have increased the risk of mortality in four Italian cities: Bologna, Milan, Rome and Turin. Daily mortality counts, for the resident population by age, sex and cause of death were considered. Daily excess mortality was calculated as the difference between the number of deaths observed and the smoothed average. The impact of heat on health is measured in terms of maximum apparent temperature. The greatest excess in mortality was observed in the north west of Italy (Turin, +23% and Milan, +23%). The old (75-84 years) and the very old (85+ years) were the age groups most affected, and when stratifying by sex, the increase in mortality seemed to be greater among females. The greatest excess in mortality was registered in those with low socioeconomic status in Rome (+17.8%) and in those with lower education levels in Turin (+43%). The analysis of cause-specific mortality not only confirms results from previous studies of an increase in heat-related mortality by respiratory and cardiovascular diseases, but also shows a significant excess in mortality for diseases of the central nervous system and for metabolic/endocrine disorders. Results from 2003 highlight the necessity of targeting future prevention programmes at the susceptible sub-groups identified. The introduction of warning systems alongside efficient preventive plans and the monitoring of mortality during heat waves may represent a valid tool for the reduction of heat-related deaths.” Michelozzi P, de Donato F, Bisanti L, Russo A, Cadum E, DeMaria M, D’Ovidio M, Costa G, Perucci CA, Euro Surveillance : Bulletin Europeen sur les Maladies Transmissibles = European Communicable Disease, Bulletin [2005, 10(7):161-5].

Summary of the mortality impact assessment of the 2003 heat wave in France – Pirard et al. (2005) “France experienced a record-breaking heat wave between 2 and 15 August 2003. All the French regions were affected by this heat wave, which resulted in an excess of 14 800 deaths between 1 and 20 August. The increase in the number of excess deaths followed the same pattern as the increase in temperatures. No deviance from the normal death rate was observed in the month of August during the last third of the month, nor during the following three months. There was a clear discrepancy in the impact of the heat wave from city to city. If the effect of duration of consecutive days with high minimal temperatures and deviance with the seasonal normal temperature was patent, this could not explain all of the observed variability of the death incidence. The victims were mainly elderly women older than 75 years. In terms of relative risk and contribution to the global toll, deaths linked to heat were the most important. Based on these results, the French government developed a Heat Health Watch Warning System and set up a preventive action plan for each region in 2004.” Pirard P, Vandentorren S, Pascal M, Laaidi K, Le Tertre A, Cassadou S, Ledrans M, Euro Surveillance : Bulletin Europeen sur les Maladies Transmissibles = European Communicable Disease Bulletin [2005, 10(7):153-6].

Epidemiologic study of mortality during the Summer 2003 heat wave in Italy – Conti et al. (2005) “Introduction: It is widely recognized that extreme climatic conditions during summer months may constitute a major public health threat. Owing to what is called the “urban heat island effect,” as well as to the consequences of heat waves on health, individuals living in cities have an elevated risk of death when temperature and humidity are high compared to those living in suburban and rural areas. Studies on heat wave-related mortality have further demonstrated that the greatest increases in mortality occur in the elderly. Following the unusually hot summer of 2003 and the dramatic news from neighboring countries such as France, the Italian Minister of Health requested the Istituto Superiore di Sanità-Bureau of Statistics to undertake an epidemiologic study of mortality in Italy during Summer 2003 to investigate whether there had been an excess of deaths, with a particular focus on the elderly population. Materials and methods: Communal offices, which maintain vital statistics, were asked for the individual records of death of residents registered daily during the period 1 June–31 August 2003 and during the same period of 2002 for each of the 21 capitals of the Italian regions. As it was necessary to obtain mortality data quickly from many municipalities and to make the analysis as soon as possible, the method adopted was comparison of mortality counts during the heat wave with figures observed during the same period of the previous year. Results: Compared with 2002, between 1 June and 31 August 2003, there was an overall increase in mortality of 3134 (from 20,564 to 23,698). The greatest increase was among the elderly; 2876 deaths (92%) occurred among people aged 75 years and older, a more than one-fifth increase (21.3%, from 13.517 to 16.393%). The highest increases were observed in the northwestern cities, which are generally characterized by cold weather, and in individuals 75 years and older: Turin (44.9%), Trento (35.2%), Milan (30.6%), and Genoa (22.2%). Of note are also the increases observed in two southern cities, L’Aquila (24.7%) and Potenza (25.4%), which are located, respectively, at 700 and 800 m above see level. For Bari and Campobasso, both in the South, with a typically hot summer climate, the increase during the last 15 days of August was 186.2 and 450%, respectively. Conclusions: The relationship between mortality and discomfort due to climatic conditions as well as the short lag time give a clear public health message: preventive, social, and health care actions must be administered to the elderly and the frail to avoid excess deaths during heat waves.” Susanna Conti, Paola Meli, Giada Minelli, Renata Solimini, Virgilia Toccaceli, Monica Vichi, Carmen Beltrano, Luigi Perini, Environmental Research, Volume 98, Issue 3, July 2005, Pages 390–399,

The 2003 heat wave as an example of summers in a greenhouse climate? Observations and climate model simulations for Basel, Switzerland – Beniston & Diaz (2004) “The heat wave that affected many parts of Europe during the course of summer 2003 may be a harbinger of summers that could occur more regularly in a future climate, under enhanced greenhouse gas concentrations. Switzerland was not exempt from the 2003 heat wave and, indeed, the previous absolute maximum temperature record dating back to the middle of the 20th century was exceeded by over 2 °C. Regional climate simulations undertaken for the European region emphasize the fact that summers will become progressively as hot as the 2003 event, such that, in the latter part of the 21st century, it is likely to become the norm. On the basis of this study, the 2003 event should be considered as a “shape of things to come” and thereby prompt timely decision making in terms of appropriate adaptation and mitigation strategies.” Martin Beniston, Henry F. Diaz, Global and Planetary Change, Volume 44, Issues 1–4, December 2004, Pages 73–81, [Full text]

The 2003 heat wave in Europe: A shape of things to come? An analysis based on Swiss climatological data and model simulations – Beniston (2004) “The 2003 heat wave that affected much of Europe from June to September bears a close resemblance to what many regional climate models are projecting for summers in the latter part of the 21st century. Model results suggest that under enhanced atmospheric greenhouse-gas concentrations, summer temperatures are likely to increase by over 4°C on average, with a corresponding increase in the frequency of severe heat waves. Statistical features of the 2003 heat wave for the Swiss site of Basel are investigated and compared to both past, 20th century events and possible future extreme temperatures based on model simulations of climatic change. For many purposes, the 2003 event can be used as an analog of future summers in coming decades in climate impacts and policy studies.” Beniston, M. (2004), The 2003 heat wave in Europe: A shape of things to come? An analysis based on Swiss climatological data and model simulations, Geophys. Res. Lett., 31, L02202, doi:10.1029/2003GL018857. [Full text]

Mortality in 13 French Cities During the August 2003 Heat Wave – Vandentorren et al. (2004) “We observed the daily trend in mortality rates during the 2003 heat wave in 13 of France’s largest cities. Mortality data were collected from July 25 to September 15 each year from 1999 through 2003. The conjunction of a maximum temperature of 35°C and a minimum temperature of 20°C was exceptional in 7 cities. An excess mortality rate was observed in the 13 towns, with disparities from +4% (Lille) to +142% (Paris).” Stéphanie Vandentorren, Florence Suzan, Sylvia Medina, Mathilde Pascal, Adeline Maulpoix, Jean-Claude Cohen, and Martine Ledrans Mortality in 13 French Cities During the August 2003 Heat Wave. American Journal of Public Health: September 2004, Vol. 94, No. 9, pp. 1518-1520, doi: 10.2105/AJPH.94.9.1518. [Full text]

Air pollution related deaths during the 2003 heat wave in the Netherlands – Fischer et al. (2004) “In the Netherlands an excess of 1000–1400 deaths was estimated due to the hot temperatures that occurred during the 2003 summer period. We estimated the number of deaths attributable to the ozone and Particular Matter (PM10) concentrations in the summer period June–August 2003. Our calculations show that an excess of around 400–600 air pollution-related deaths may have occurred compared to an ‘average’ summer. These calculations suggest that in the Netherlands, a significant proportion of the deaths now being attributed to the hot summer weather can reasonably be expected to have been caused by air pollution.” Paul H. Fischer, Bert Brunekreef, Erik Lebret, Atmospheric Environment, Volume 38, Issue 8, March 2004, Pages 1083–1085,

The role of increasing temperature variability in European summer heatwaves – Schär et al. (2004) “Instrumental observations and reconstructions of global and hemispheric temperature evolution reveal a pronounced warming during the past 150 years. One expression of this warming is the observed increase in the occurrence of heatwaves. Conceptually this increase is understood as a shift of the statistical distribution towards warmer temperatures, while changes in the width of the distribution are often considered small. Here we show that this framework fails to explain the record-breaking central European summer temperatures in 2003, although it is consistent with observations from previous years. We find that an event like that of summer 2003 is statistically extremely unlikely, even when the observed warming is taken into account. We propose that a regime with an increased variability of temperatures (in addition to increases in mean temperature) may be able to account for summer 2003. To test this proposal, we simulate possible future European climate with a regional climate model in a scenario with increased atmospheric greenhouse-gas concentrations, and find that temperature variability increases by up to 100%, with maximum changes in central and eastern Europe.” Christoph Schär, Pier Luigi Vidale, Daniel Lüthi, Christoph Frei, Christian Häberli, Mark A. Liniger & Christof Appenzeller, Nature 427, 332-336 (22 January 2004) | doi:10.1038/nature02300. [Full text]

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Simplistic explanations of climate related issues

Posted by Ari Jokimäki on February 1, 2013

There’s a page that lists texts written by people trying to describe complex scientific issues by using only the thousand most used words in English language. To go with this, there’s an online editor that warns you if you have used a word outside of the thousand most used words. The Way Things Break had a good go at this.

There, and I also seen it mentioned in private communication, it was said that this is a bad communications tool. It is that. The things explained with only 1000 words are sometimes hard to read and understand because descriptions have to take quite strange routes to explain things. But I don’t think the point of this excercise is to provide a good communications tool. I think it’s a good way to get you thinking how to describe things in a more simple manner, but most importantly, I think it’s just fun word game.

So, I did a couple of short ones with the editor. Here’s the first:

Some type of light can be seen and some type of light can not be seen. In this rock ball where we live, air does not let all types of light go through. Light that can be seen goes through the air well but some of the light that can not be seen does not go through the air that well.

Light that can be seen from the sun goes through the air and hits the ground, which warms and sends warm type of light, which can not be seen, to the air. Air does not let all the warm type light through. Air stops some of it and sends it again to all directions, so some of it also goes back to ground. That makes ground warm even more.

And the second one:

This word I can not write here tells the mean situation of the air around you. It tells how warm it has been as 30 year mean, so short time changes are not what this word is about. It also tells how much rain there has been during long time. White soft looking things in the sky can change how warm or how much rain there is in the air around you. Another important thing for that is the sun. Also how the air and water go around in the world can change the situation with the air around you. There are also some other things that can cause changes to the air situation, such as small matter pieces in the air, different types of air that stop some types of light, and high rock things that send fire and hot rocks to the sky with loud sound.

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