R. Bradley - Academia.edu (original) (raw)

Papers by R. Bradley

Research paper thumbnail of Diatom and stable isotope record of Late Holecene lake ontogeny at Indrepollen, Lofoten, NW Norway: a response to isostacy and neoglacial cooling

Research paper thumbnail of MRI Newsletter 3: Understanding Climate Change in Mountains

Mountain Research and Development, 2004

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Research paper thumbnail of The Need for a Global Paleoclimate Observing System

Research paper thumbnail of Working Group 1: Observations

Developments in Atmospheric Science, 1991

Research paper thumbnail of JOUZEL J, LORIUS C and REYNAUD D (2013) The white planet: the evolution and future of our frozen world.(English translation, adapted and revised) Princeton University Press, Princeton, NJ. 306pp. ISBN-10: 0-691144-99-0, ISBN-13: 978-0-691-14499-3, hardback, $ US29. 95

Research paper thumbnail of Holocene paleoclimatology of the Queen Elizabeth Islands, Canadian High Arctic

Quaternary Science Reviews, 1990

Research paper thumbnail of Past and present glaciological responses to climate in eastern Baffin Island

Much of Baffin Island is close to the modern glaciation limit and climatic changes within the las... more Much of Baffin Island is close to the modern glaciation limit and climatic changes within the last decade are already being reflected in snow cover extent. Statistical analysis of glacierized and ice-free corries indicates that changes in direct solar radiation due to astronomical factors are inadequate to account for glacierization of those at present ice-free. These and other sources of evidence demonstrate the need for augmented winter snowfall in order to increase the extent of glacierization. The pattern of glacial history in this area is for maximum ice extent during the early glacial phase (>68,000, <137,000 BP), followed by a reduction in ice volume during the cold pleniglacial (>24,000, < 68,000 BP) and then a limited late glacial advance (the Cockburn Stade, ca. 8,000 BP) due to increased precipitation. The Barnes Ice Cap did not disappear in the Holocene as it did in the last interglacial. The area is highly suitable for long-term monitoring of climatic change and glacial response.

Research paper thumbnail of Secular climatic fluctuations in southwestern Colorado

Research paper thumbnail of Environmental change and cultural change in the eastern Canadian Arctic during the last 5000 years

Arctic and Alpine …, 1977

Research paper thumbnail of Synoptic climatology of the western United States in relation to climatic fluctuations during the twentieth century

An objectively derived catalogue of daily pressure patterns for 11199-1974 has been prepared for ... more An objectively derived catalogue of daily pressure patterns for 11199-1974 has been prepared for the western Uoited States. The temperature and precipitation characteristics of the major types are described and a more detailed analysis for Colorado in extreme cold and warm months shows that the sign of the anomalies for each type is generally consistent with expectation hased Oil the prohable airflow patterns. A regression analysis of type frequencies versus temperature and precipitation anomalies for 1899-1970 at stations east and west of the Continental Divide in the Rocky Mountain states shows that useful explanation of variance is obtained only for temperatures in the transition seasons and for precipitation west of the Divide in winter and east of the Divide in spring. Within-type variahility of the climatic characteristics is one source of the discrepancy. The results underline the problems encountered in trying to. link climatic anomalies with atmospheric circulation characteristics. KEY WORDS Synoptic ciimatology Western United States Recent climatic fluctuations Climatic anomalies * The time take on the University of Colorado CDC 6400 for the 60-month sample was approximately 122 min. compared with only 60 min. for classification of the 75 years.

Research paper thumbnail of ENSO signal in continental temperature and precipitation records

Research paper thumbnail of Little Ice Age'summer temperature variations: their nature and relevance to recent global warming trends

Research paper thumbnail of Recent Changes In the North American Arctic Boundary Layer In Winter

Journal of Geophysical Research, 1993

Research paper thumbnail of Variability of Freezing Levels, Melting Season Indicators, and Snow Cover for Selected High-Elevation and Continental Regions In the Last 50 Years

Climatic Change, 2003

We have used NCEP/NCAR Reanalysis data and a Northern Hemisphere snow cover data set to analyze c... more We have used NCEP/NCAR Reanalysis data and a Northern Hemisphere snow cover data set to analyze changes in freezing level heights and snow cover for the past three to five decades. All the major continental mountain chains exhibit upward shifts in the height of the freezing level surface. The pattern of these changes is generally consistent with changes in snow cover, both over the course of the year and spatially. We examined different free-air temperature parameters (dry bulb temperature, virtual temperature, and 700-500 hPa thickness) using the Reanalysis grid point values located over the different mountain areas as defined in this study. The different trend values were in reasonably good agreement with each other, particularly over the second half of the record. Freezing level changes in the American Cordillera are strongly modulated by the El Niño/Southern Oscillation (ENSO) phenomenon and the freezing level heights (FLH) respond to both interannual and decadal-scale change in tropical Pacific sea surface temperature (SST). The ∼0.5 • C increase in SST recorded in the tropical Pacific since the 1950s accounts for approximately half of the increase in FLH in tropical and subtropical latitudes of the Cordilleran region during that same time.

Research paper thumbnail of Climatology of Surface-Based Inversions In the North American Arctic

Journal of Geophysical Research, 1992

Research paper thumbnail of Projected Temperature Changes Along the American Cordillera and the Planned GCOS Network

Geophysical Research Letters, 2004

shows large and statistically significant free air temperature 8 changes (compared to controls) a... more shows large and statistically significant free air temperature 8 changes (compared to controls) along the axis of the 9 American Cordillera (from Alaska to southern Chile). At all 10 latitudes, the modeled change in temperature increases with 11 elevation. Temperature increases are especially large in 12 boreal summer months from $35-50°N, and year-round in 13 the high mountains of Peru, Bolivia and northern Chile. If 14 these models are correct, mountain ranges that extend high 15 into the lower troposphere are likely to experience 16 significant warming, with implications for glacier mass 17 balance and water resources, montane ecosystems and high 18 elevation agricultural activities. There are few high 19 elevation meteorological stations to validate the model 20 projections, or to monitor future changes. The planned 21 GCOS (Global Climate Observing System) network is not 22 adequate to address the critical issues raised by these model 23 simulations; additional high elevation observing stations are 24 needed.

Research paper thumbnail of The Recent Climate Record: What It Can and Cannot Tell Us

Research paper thumbnail of Climate Change: Climate In Medieval Time

Science, 2003

Many papers have referred to a &a... more Many papers have referred to a "Medieval Warm Period." But how well defined is climate in this period, and was it as warm as or warmer than it is today? In their Perspective, Bradley et al. review the evidence and conclude that although the High Medieval (1100 to 1200 A.D.) was warmer than subsequent centuries, it was not warmer than the late 20th century. Moreover, the warmest Medieval temperatures were not synchronous around the globe. Large changes in precipitation patterns are a particular characteristic of "High Medieval" time. The underlying mechanisms for such changes must be elucidated further to inform the ongoing debate on natural climate variability and anthropogenic climate change.

Research paper thumbnail of Temperature Variations During the Last Century at High Elevation Sites

Climatic Change, 1997

Differential temperature changes with altitude can shed light on the relative importance of natur... more Differential temperature changes with altitude can shed light on the relative importance of natural versus anthropogenic climatic change. There has been heightened interest in this subject recently due to the finding that high-elevation tropical glaciers have been retreating and that significant melting from even the highest alpine regions has occurred in some areas during the past 20 years or so, as recorded in ice core records, which do not reveal any similar period during previous centuries to millennia. In this paper we find evidence for appreciable differences in mean temperature changes with elevation during the last several decades of instrumental records. The signal appears to be more closely related to increases in daily minimum temperature than changes in the daily maximum. The changes in surface temperature vary spatially, with Europe (particularly western Europe), and parts of Asia displaying the strongest high altitude warming during the period of record. High-elevation climate records of long standing taken at a number of mountain tops throughout the world, but primarily in Europe, are available from a number of countries. In some cases, meteorological observations at these unique mountain sites have been discontinued for a variety of reasons, usually budgetary. It is hoped that the papers published in this special issue of Climatic Change can contribute to a reassessment of the value of continuing climate measurements at these mountain observatories by the appropriate entities, so that we may continue to have access to climate information from the 'tops of the world'.

Research paper thumbnail of Precipitation Fluctuations Over Global Land Areas Since the Late 1800s

Research paper thumbnail of Diatom and stable isotope record of Late Holecene lake ontogeny at Indrepollen, Lofoten, NW Norway: a response to isostacy and neoglacial cooling

Research paper thumbnail of MRI Newsletter 3: Understanding Climate Change in Mountains

Mountain Research and Development, 2004

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Research paper thumbnail of The Need for a Global Paleoclimate Observing System

Research paper thumbnail of Working Group 1: Observations

Developments in Atmospheric Science, 1991

Research paper thumbnail of JOUZEL J, LORIUS C and REYNAUD D (2013) The white planet: the evolution and future of our frozen world.(English translation, adapted and revised) Princeton University Press, Princeton, NJ. 306pp. ISBN-10: 0-691144-99-0, ISBN-13: 978-0-691-14499-3, hardback, $ US29. 95

Research paper thumbnail of Holocene paleoclimatology of the Queen Elizabeth Islands, Canadian High Arctic

Quaternary Science Reviews, 1990

Research paper thumbnail of Past and present glaciological responses to climate in eastern Baffin Island

Much of Baffin Island is close to the modern glaciation limit and climatic changes within the las... more Much of Baffin Island is close to the modern glaciation limit and climatic changes within the last decade are already being reflected in snow cover extent. Statistical analysis of glacierized and ice-free corries indicates that changes in direct solar radiation due to astronomical factors are inadequate to account for glacierization of those at present ice-free. These and other sources of evidence demonstrate the need for augmented winter snowfall in order to increase the extent of glacierization. The pattern of glacial history in this area is for maximum ice extent during the early glacial phase (>68,000, <137,000 BP), followed by a reduction in ice volume during the cold pleniglacial (>24,000, < 68,000 BP) and then a limited late glacial advance (the Cockburn Stade, ca. 8,000 BP) due to increased precipitation. The Barnes Ice Cap did not disappear in the Holocene as it did in the last interglacial. The area is highly suitable for long-term monitoring of climatic change and glacial response.

Research paper thumbnail of Secular climatic fluctuations in southwestern Colorado

Research paper thumbnail of Environmental change and cultural change in the eastern Canadian Arctic during the last 5000 years

Arctic and Alpine …, 1977

Research paper thumbnail of Synoptic climatology of the western United States in relation to climatic fluctuations during the twentieth century

An objectively derived catalogue of daily pressure patterns for 11199-1974 has been prepared for ... more An objectively derived catalogue of daily pressure patterns for 11199-1974 has been prepared for the western Uoited States. The temperature and precipitation characteristics of the major types are described and a more detailed analysis for Colorado in extreme cold and warm months shows that the sign of the anomalies for each type is generally consistent with expectation hased Oil the prohable airflow patterns. A regression analysis of type frequencies versus temperature and precipitation anomalies for 1899-1970 at stations east and west of the Continental Divide in the Rocky Mountain states shows that useful explanation of variance is obtained only for temperatures in the transition seasons and for precipitation west of the Divide in winter and east of the Divide in spring. Within-type variahility of the climatic characteristics is one source of the discrepancy. The results underline the problems encountered in trying to. link climatic anomalies with atmospheric circulation characteristics. KEY WORDS Synoptic ciimatology Western United States Recent climatic fluctuations Climatic anomalies * The time take on the University of Colorado CDC 6400 for the 60-month sample was approximately 122 min. compared with only 60 min. for classification of the 75 years.

Research paper thumbnail of ENSO signal in continental temperature and precipitation records

Research paper thumbnail of Little Ice Age'summer temperature variations: their nature and relevance to recent global warming trends

Research paper thumbnail of Recent Changes In the North American Arctic Boundary Layer In Winter

Journal of Geophysical Research, 1993

Research paper thumbnail of Variability of Freezing Levels, Melting Season Indicators, and Snow Cover for Selected High-Elevation and Continental Regions In the Last 50 Years

Climatic Change, 2003

We have used NCEP/NCAR Reanalysis data and a Northern Hemisphere snow cover data set to analyze c... more We have used NCEP/NCAR Reanalysis data and a Northern Hemisphere snow cover data set to analyze changes in freezing level heights and snow cover for the past three to five decades. All the major continental mountain chains exhibit upward shifts in the height of the freezing level surface. The pattern of these changes is generally consistent with changes in snow cover, both over the course of the year and spatially. We examined different free-air temperature parameters (dry bulb temperature, virtual temperature, and 700-500 hPa thickness) using the Reanalysis grid point values located over the different mountain areas as defined in this study. The different trend values were in reasonably good agreement with each other, particularly over the second half of the record. Freezing level changes in the American Cordillera are strongly modulated by the El Niño/Southern Oscillation (ENSO) phenomenon and the freezing level heights (FLH) respond to both interannual and decadal-scale change in tropical Pacific sea surface temperature (SST). The ∼0.5 • C increase in SST recorded in the tropical Pacific since the 1950s accounts for approximately half of the increase in FLH in tropical and subtropical latitudes of the Cordilleran region during that same time.

Research paper thumbnail of Climatology of Surface-Based Inversions In the North American Arctic

Journal of Geophysical Research, 1992

Research paper thumbnail of Projected Temperature Changes Along the American Cordillera and the Planned GCOS Network

Geophysical Research Letters, 2004

shows large and statistically significant free air temperature 8 changes (compared to controls) a... more shows large and statistically significant free air temperature 8 changes (compared to controls) along the axis of the 9 American Cordillera (from Alaska to southern Chile). At all 10 latitudes, the modeled change in temperature increases with 11 elevation. Temperature increases are especially large in 12 boreal summer months from $35-50°N, and year-round in 13 the high mountains of Peru, Bolivia and northern Chile. If 14 these models are correct, mountain ranges that extend high 15 into the lower troposphere are likely to experience 16 significant warming, with implications for glacier mass 17 balance and water resources, montane ecosystems and high 18 elevation agricultural activities. There are few high 19 elevation meteorological stations to validate the model 20 projections, or to monitor future changes. The planned 21 GCOS (Global Climate Observing System) network is not 22 adequate to address the critical issues raised by these model 23 simulations; additional high elevation observing stations are 24 needed.

Research paper thumbnail of The Recent Climate Record: What It Can and Cannot Tell Us

Research paper thumbnail of Climate Change: Climate In Medieval Time

Science, 2003

Many papers have referred to a &a... more Many papers have referred to a "Medieval Warm Period." But how well defined is climate in this period, and was it as warm as or warmer than it is today? In their Perspective, Bradley et al. review the evidence and conclude that although the High Medieval (1100 to 1200 A.D.) was warmer than subsequent centuries, it was not warmer than the late 20th century. Moreover, the warmest Medieval temperatures were not synchronous around the globe. Large changes in precipitation patterns are a particular characteristic of "High Medieval" time. The underlying mechanisms for such changes must be elucidated further to inform the ongoing debate on natural climate variability and anthropogenic climate change.

Research paper thumbnail of Temperature Variations During the Last Century at High Elevation Sites

Climatic Change, 1997

Differential temperature changes with altitude can shed light on the relative importance of natur... more Differential temperature changes with altitude can shed light on the relative importance of natural versus anthropogenic climatic change. There has been heightened interest in this subject recently due to the finding that high-elevation tropical glaciers have been retreating and that significant melting from even the highest alpine regions has occurred in some areas during the past 20 years or so, as recorded in ice core records, which do not reveal any similar period during previous centuries to millennia. In this paper we find evidence for appreciable differences in mean temperature changes with elevation during the last several decades of instrumental records. The signal appears to be more closely related to increases in daily minimum temperature than changes in the daily maximum. The changes in surface temperature vary spatially, with Europe (particularly western Europe), and parts of Asia displaying the strongest high altitude warming during the period of record. High-elevation climate records of long standing taken at a number of mountain tops throughout the world, but primarily in Europe, are available from a number of countries. In some cases, meteorological observations at these unique mountain sites have been discontinued for a variety of reasons, usually budgetary. It is hoped that the papers published in this special issue of Climatic Change can contribute to a reassessment of the value of continuing climate measurements at these mountain observatories by the appropriate entities, so that we may continue to have access to climate information from the 'tops of the world'.

Research paper thumbnail of Precipitation Fluctuations Over Global Land Areas Since the Late 1800s