Thomas Crowley - Academia.edu (original) (raw)
Personal by Thomas Crowley
A pdf version of Tom Crowleys last web-page, then run at U of Edinburgh; links to the activities ... more A pdf version of Tom Crowleys last web-page, then run at U of Edinburgh; links to the activities in Edingburgh have been deleted.
Later, the links on this page will be updated to links at academia.edu
Obituary in Guardian, in 2014, by John Abraham and Dana Nutticelli
Full version of Tom Crowley's CV
Papers by Thomas Crowley
Abstract Stable global temperatures of the last 10–15 years have been a topic of considerable dis... more Abstract Stable global temperatures of the last 10–15 years have been a topic of considerable discussion.
A new proxy extension of the global temperature record enables better placement of this feature in
a longer historical perspective. The fixed-grid composite covers the interval 1801–1984, with an extension
to 1782, and anchors the global temperature record in the last major cold interval of the Little Ice
Age, when carbon dioxide concentration was at preanthropogenic levels. Except for greater and longer
cooling (approximately twice the length of Pinatubo) associated with the Tambora eruption, the proxy
agrees with the most widely cited previous assessment of global temperature over this interval, lending
more confidence to a centennial extension of the global temperature record. The proxy correlation is as
high as 0.83 for the interval 1907–1984 (df=8, p=0.001), with the 21st century 1.0∘C±0.2∘C warmer
than the nonvolcanic base state. This remarkable linearity requires a clear theoretical understanding as to
how an exceedingly complex system can, on the global average, behave in such a simple way. Removal of
the linear radiatively forced component from the global temperature record yields an estimate of natural
variability for the last 230 years and indicates no unusual natural variability during the recent 10–15 years.
Based on the estimate of unforced variability over the last 170 years, there is about a 40% chance of continued
“natural cooling” over the next few years, with about a 10% chance of cooling persisting into the
next decade
Journal of Climate, 1989
The sensitivity of a linear two dimensional Energy Balance Model (EBM) to altered surface albedo ... more The sensitivity of a linear two dimensional Energy Balance Model (EBM) to altered surface albedo and insolation over the last 18 000 years is compared to simulations made with the NCAR Community Climate Model (CCM). The two-dimensional EBM is a more general form of that described in North {ital et} {ital al}. and allows for regionally varying albedos of ice
Journal of Geophysical Research, 1990
Paleoceanography, 1999
AbstractGeochemical analyses of coral skeletons are increasingly used to estimate past sea surfac... more AbstractGeochemical analyses of coral skeletons are increasingly used to estimate past sea surface temperatures (SSTs). In this paper we suggest that the standard method of calibrating geochemical time series against a (usually short) local time series requires modification. In order to draw large-scale inferences about climate from coral proxy data it is also necessary to (1) calibrate against larger fields such as the local gridded data sets and (2) validate results against an independent data set (e.g., early 20th century). This approach has been applied in a pilot study to a coral record from New Caledonia. Despite a high δ18O correlation (r=−0.88) with the in situ and gridded SST data sets, estimated early 20th-century temperatures are more than 1.5°C colder than observed if the standard seasonal calibration is used. Regression against mean annual temperatures, which has a different slope relation, yields better estimates of early 20th-century SSTs. However, testing of a Sr/Ca record from New Caledonia yields better agreement with early 20th century SSTs. Routine validation exercises for other coral sites are necessary to clarify the robustness of geochemical coral proxies as estimators of past environmental change.
Geophysical Research Letters, 2003
Abstract[1] Observational studies show a significant increase in ocean heat content over the last... more Abstract[1] Observational studies show a significant increase in ocean heat content over the last half century. Herein we estimate heat content changes during the last millennium with a climate model whose forcing terms have been best-fit to surface proxy data. The model simulates the observed late 20th century ocean heat content increase and a comparable Little Ice Age minimum. When glacial advances are factored in, these results imply a sea level fall after the Middle Ages that is consistent with some geologic data. The present ocean heat content increase can be traced back to the mid-19th century, with a near-linear rate of change during the 20th century.
Journal of Geophysical Research, 1991
Three different levels of sensitivity experiments were conducted to examine the effect of Gondwan... more Three different levels of sensitivity experiments were conducted to examine the effect of Gondwanaland landmass on the magnitude of summer warming over ice sheets: (1) simulations with present solar luminosity and present orbital forcing resulted in summer temperatures over the Gondwanan Ice Sheet 12 - 17 C greater than over the Pleistocene Laurentide Ice Sheet; (2) lowering the solar constant 3 percent or modifying the seasonal insolation cycle to a 'cold summer orbit' reduced the warming but still led to significant differences between Gondwanan and Pleistocene simulations; and (3) the combined effect of lowering the solar constant and modifying the seasonal insolation cycle to a cold summer orbit resulted in temperature patterns over the Gondwanan Ice Sheet similar to the Pleistocene. Model simulations also predict tropical sea surface temperatures about 4 C less than at present as a result of reduced solar luminosity.
Journal of Climate, 2000
... Corresponding author address: Dr. William T. Hyde, Department of Oceanography, Texas A&M ... more ... Corresponding author address: Dr. William T. Hyde, Department of Oceanography, Texas A&M University, College Station, TX 77843-3146. ... Self 1982) provides volcanologic estimates of eruptions from ejecta data; for example, Pinatubo (1991) has a VEI of 6, Agung (1963) one ...
Geophysical Research Letters, 1992
Geophysical Research Letters, 2001
SCIENCE 280, 728-730, May 1, 1998
During the last interglacial, Antarctic climate changed before that of the Northern Hemisphere. L... more During the last interglacial, Antarctic climate changed before that of the Northern Hemisphere. Large local changes in precession forcing could have produced this pattern if there were a rectified response in sea ice cover. Results from a coupled sea ice–ocean general circulation model supported this hypothesis when it was tested for three intervals around the last interglacial. Such a mechanism may play an important role in contributing to phase offsets between Northern and Southern Hemisphere climate change for other time intervals.
Nature 405, 425-429, May 25, 2000
Ice sheets may have reached the Equator in the late Proterozoic era (600±800 Myr ago), according ... more Ice sheets may have reached the Equator in the late Proterozoic era (600±800 Myr ago), according to geological and palaeomagnetic studies, possibly resulting in a `snowball Earth'. But this period was a critical time in the evolution of multicellular animals, posing the question of how early life survived under such environmental stress. Here we present computer simulations of this unusual climate stage with a coupled climate/ice-sheet model. To simulate a snowball Earth, we use only a reduction in the solar constant compared to present-day conditions and we keep atmospheric CO2 concentrations near present levels. We ®nd rapid transitions into and out of full glaciation that are consistent with the geological evidence. When we combine these results with a general circulation model, some of the simulations result in an equatorial belt of open water that may have provided a refugium for multicellular animals.
Science 289,270-277, 2000
Recent reconstructions of Northern Hemisphere temperatures and climate forcing over the past 1000... more Recent reconstructions of Northern Hemisphere temperatures and climate forcing over the past 1000 years allow the warming of the 20th century to be placed within a historical context and various mechanisms of climate change to be tested. Comparisons of observations with simulations from an energy balance climate model indicate that as much as 41 to 64% of preanthropogenic ( pre-1850) decadal-scale temperature variations was due to changes in solar irradiance and volcanism. Removal of the forced response from reconstructed temperature time series yields residuals that show similar variability to those of control runs of coupled models, thereby lending support to the models’ value as estimates of low-frequency variability in the climate system. Removal of all forcing except greenhouse gases from the #1000-year time series results in a residual with a very large late-20th-century warming that closely agrees with the response predicted from greenhouse gas forcing. The combination of a unique level of temperature increase in the late 20th century and improved constraints on the role of natural variability provides further evidence that the greenhouse effect has already established itself above the level of natural variability in the climate system. A 21st-century global warming projection far exceeds the natural variability of the past 1000 years and is greater than the best estimate of global temperature change for the last interglacial.
Geology; v. 34; no. 6; p. 421–424; doi: 10.1130/G22108.1, Jun 2006
Reconstructions of Phanerozoic CO2 levels have generally relied on geochemical modelin or proxy d... more Reconstructions of Phanerozoic CO2 levels have generally relied on geochemical modelin or proxy data. Because the uncertainty inherent in such reconstructions is large
enough to be climatically significant, inverse climate modeling may help to constrain paleo- CO2 estimates. In particular, we test the plausibility of this technique by focusing on the climate from 360 to 260 Ma, a time in which the Siberian landmass was in middle to high latitudes, yet had little or no permanent land ice. Our climate model simulations predict a lower limit for CO2—the value beneath which Siberia acquires ‘‘excess’’ ice. Simulations provide little new information for the period in which Siberia was at a relatively low paleoaltitude (360–340 Ma), but model results imply that paleo-CO2 levels had to be greater than 2–4! modern values to be consistent with an apparently ice-free Siberia in the late Permian. These results for the later period in general agree with soil CO2 proxies and the timing of Gondwanan deglaciation, thus providing support for a significant CO2 increase before the end-Permian boundary event. Our technique may be applicable to other time intervals of unipolar glaciation.
Geophys. Res. Lett., 33, L18404, doi:10.1029/ 2006GL027445, 2006
Researchers and coastal managers are pondering how accelerated sea-level rise and possibly intens... more Researchers and coastal managers are pondering how accelerated sea-level rise and possibly intensified storms will affect shorelines. These issues are most often investigated in a cross-shore profile framework, fostering the implicit assumption that coastline responses will be approximately uniform in the alongshore direction. However, experiments with a recently developed numerical model of coastline change on a large spatial domain suggest that the shoreline responses to climate change could be highly variable. As storm and wave climates change, large-scale coastline shapes are likely to shift—causing areas of greatly accelerated coastal erosion to alternate with areas of considerable shoreline accretion. On complex-shaped coastlines, including cuspate-cape and spit coastlines, the alongshore variation in shoreline retreat rates could be an order of
magnitude higher than the baseline retreat rate expected from sea-level rise alone.
A pdf version of Tom Crowleys last web-page, then run at U of Edinburgh; links to the activities ... more A pdf version of Tom Crowleys last web-page, then run at U of Edinburgh; links to the activities in Edingburgh have been deleted.
Later, the links on this page will be updated to links at academia.edu
Obituary in Guardian, in 2014, by John Abraham and Dana Nutticelli
Full version of Tom Crowley's CV
Abstract Stable global temperatures of the last 10–15 years have been a topic of considerable dis... more Abstract Stable global temperatures of the last 10–15 years have been a topic of considerable discussion.
A new proxy extension of the global temperature record enables better placement of this feature in
a longer historical perspective. The fixed-grid composite covers the interval 1801–1984, with an extension
to 1782, and anchors the global temperature record in the last major cold interval of the Little Ice
Age, when carbon dioxide concentration was at preanthropogenic levels. Except for greater and longer
cooling (approximately twice the length of Pinatubo) associated with the Tambora eruption, the proxy
agrees with the most widely cited previous assessment of global temperature over this interval, lending
more confidence to a centennial extension of the global temperature record. The proxy correlation is as
high as 0.83 for the interval 1907–1984 (df=8, p=0.001), with the 21st century 1.0∘C±0.2∘C warmer
than the nonvolcanic base state. This remarkable linearity requires a clear theoretical understanding as to
how an exceedingly complex system can, on the global average, behave in such a simple way. Removal of
the linear radiatively forced component from the global temperature record yields an estimate of natural
variability for the last 230 years and indicates no unusual natural variability during the recent 10–15 years.
Based on the estimate of unforced variability over the last 170 years, there is about a 40% chance of continued
“natural cooling” over the next few years, with about a 10% chance of cooling persisting into the
next decade
Journal of Climate, 1989
The sensitivity of a linear two dimensional Energy Balance Model (EBM) to altered surface albedo ... more The sensitivity of a linear two dimensional Energy Balance Model (EBM) to altered surface albedo and insolation over the last 18 000 years is compared to simulations made with the NCAR Community Climate Model (CCM). The two-dimensional EBM is a more general form of that described in North {ital et} {ital al}. and allows for regionally varying albedos of ice
Journal of Geophysical Research, 1990
Paleoceanography, 1999
AbstractGeochemical analyses of coral skeletons are increasingly used to estimate past sea surfac... more AbstractGeochemical analyses of coral skeletons are increasingly used to estimate past sea surface temperatures (SSTs). In this paper we suggest that the standard method of calibrating geochemical time series against a (usually short) local time series requires modification. In order to draw large-scale inferences about climate from coral proxy data it is also necessary to (1) calibrate against larger fields such as the local gridded data sets and (2) validate results against an independent data set (e.g., early 20th century). This approach has been applied in a pilot study to a coral record from New Caledonia. Despite a high δ18O correlation (r=−0.88) with the in situ and gridded SST data sets, estimated early 20th-century temperatures are more than 1.5°C colder than observed if the standard seasonal calibration is used. Regression against mean annual temperatures, which has a different slope relation, yields better estimates of early 20th-century SSTs. However, testing of a Sr/Ca record from New Caledonia yields better agreement with early 20th century SSTs. Routine validation exercises for other coral sites are necessary to clarify the robustness of geochemical coral proxies as estimators of past environmental change.
Geophysical Research Letters, 2003
Abstract[1] Observational studies show a significant increase in ocean heat content over the last... more Abstract[1] Observational studies show a significant increase in ocean heat content over the last half century. Herein we estimate heat content changes during the last millennium with a climate model whose forcing terms have been best-fit to surface proxy data. The model simulates the observed late 20th century ocean heat content increase and a comparable Little Ice Age minimum. When glacial advances are factored in, these results imply a sea level fall after the Middle Ages that is consistent with some geologic data. The present ocean heat content increase can be traced back to the mid-19th century, with a near-linear rate of change during the 20th century.
Journal of Geophysical Research, 1991
Three different levels of sensitivity experiments were conducted to examine the effect of Gondwan... more Three different levels of sensitivity experiments were conducted to examine the effect of Gondwanaland landmass on the magnitude of summer warming over ice sheets: (1) simulations with present solar luminosity and present orbital forcing resulted in summer temperatures over the Gondwanan Ice Sheet 12 - 17 C greater than over the Pleistocene Laurentide Ice Sheet; (2) lowering the solar constant 3 percent or modifying the seasonal insolation cycle to a 'cold summer orbit' reduced the warming but still led to significant differences between Gondwanan and Pleistocene simulations; and (3) the combined effect of lowering the solar constant and modifying the seasonal insolation cycle to a cold summer orbit resulted in temperature patterns over the Gondwanan Ice Sheet similar to the Pleistocene. Model simulations also predict tropical sea surface temperatures about 4 C less than at present as a result of reduced solar luminosity.
Journal of Climate, 2000
... Corresponding author address: Dr. William T. Hyde, Department of Oceanography, Texas A&M ... more ... Corresponding author address: Dr. William T. Hyde, Department of Oceanography, Texas A&M University, College Station, TX 77843-3146. ... Self 1982) provides volcanologic estimates of eruptions from ejecta data; for example, Pinatubo (1991) has a VEI of 6, Agung (1963) one ...
Geophysical Research Letters, 1992
Geophysical Research Letters, 2001
SCIENCE 280, 728-730, May 1, 1998
During the last interglacial, Antarctic climate changed before that of the Northern Hemisphere. L... more During the last interglacial, Antarctic climate changed before that of the Northern Hemisphere. Large local changes in precession forcing could have produced this pattern if there were a rectified response in sea ice cover. Results from a coupled sea ice–ocean general circulation model supported this hypothesis when it was tested for three intervals around the last interglacial. Such a mechanism may play an important role in contributing to phase offsets between Northern and Southern Hemisphere climate change for other time intervals.
Nature 405, 425-429, May 25, 2000
Ice sheets may have reached the Equator in the late Proterozoic era (600±800 Myr ago), according ... more Ice sheets may have reached the Equator in the late Proterozoic era (600±800 Myr ago), according to geological and palaeomagnetic studies, possibly resulting in a `snowball Earth'. But this period was a critical time in the evolution of multicellular animals, posing the question of how early life survived under such environmental stress. Here we present computer simulations of this unusual climate stage with a coupled climate/ice-sheet model. To simulate a snowball Earth, we use only a reduction in the solar constant compared to present-day conditions and we keep atmospheric CO2 concentrations near present levels. We ®nd rapid transitions into and out of full glaciation that are consistent with the geological evidence. When we combine these results with a general circulation model, some of the simulations result in an equatorial belt of open water that may have provided a refugium for multicellular animals.
Science 289,270-277, 2000
Recent reconstructions of Northern Hemisphere temperatures and climate forcing over the past 1000... more Recent reconstructions of Northern Hemisphere temperatures and climate forcing over the past 1000 years allow the warming of the 20th century to be placed within a historical context and various mechanisms of climate change to be tested. Comparisons of observations with simulations from an energy balance climate model indicate that as much as 41 to 64% of preanthropogenic ( pre-1850) decadal-scale temperature variations was due to changes in solar irradiance and volcanism. Removal of the forced response from reconstructed temperature time series yields residuals that show similar variability to those of control runs of coupled models, thereby lending support to the models’ value as estimates of low-frequency variability in the climate system. Removal of all forcing except greenhouse gases from the #1000-year time series results in a residual with a very large late-20th-century warming that closely agrees with the response predicted from greenhouse gas forcing. The combination of a unique level of temperature increase in the late 20th century and improved constraints on the role of natural variability provides further evidence that the greenhouse effect has already established itself above the level of natural variability in the climate system. A 21st-century global warming projection far exceeds the natural variability of the past 1000 years and is greater than the best estimate of global temperature change for the last interglacial.
Geology; v. 34; no. 6; p. 421–424; doi: 10.1130/G22108.1, Jun 2006
Reconstructions of Phanerozoic CO2 levels have generally relied on geochemical modelin or proxy d... more Reconstructions of Phanerozoic CO2 levels have generally relied on geochemical modelin or proxy data. Because the uncertainty inherent in such reconstructions is large
enough to be climatically significant, inverse climate modeling may help to constrain paleo- CO2 estimates. In particular, we test the plausibility of this technique by focusing on the climate from 360 to 260 Ma, a time in which the Siberian landmass was in middle to high latitudes, yet had little or no permanent land ice. Our climate model simulations predict a lower limit for CO2—the value beneath which Siberia acquires ‘‘excess’’ ice. Simulations provide little new information for the period in which Siberia was at a relatively low paleoaltitude (360–340 Ma), but model results imply that paleo-CO2 levels had to be greater than 2–4! modern values to be consistent with an apparently ice-free Siberia in the late Permian. These results for the later period in general agree with soil CO2 proxies and the timing of Gondwanan deglaciation, thus providing support for a significant CO2 increase before the end-Permian boundary event. Our technique may be applicable to other time intervals of unipolar glaciation.
Geophys. Res. Lett., 33, L18404, doi:10.1029/ 2006GL027445, 2006
Researchers and coastal managers are pondering how accelerated sea-level rise and possibly intens... more Researchers and coastal managers are pondering how accelerated sea-level rise and possibly intensified storms will affect shorelines. These issues are most often investigated in a cross-shore profile framework, fostering the implicit assumption that coastline responses will be approximately uniform in the alongshore direction. However, experiments with a recently developed numerical model of coastline change on a large spatial domain suggest that the shoreline responses to climate change could be highly variable. As storm and wave climates change, large-scale coastline shapes are likely to shift—causing areas of greatly accelerated coastal erosion to alternate with areas of considerable shoreline accretion. On complex-shaped coastlines, including cuspate-cape and spit coastlines, the alongshore variation in shoreline retreat rates could be an order of
magnitude higher than the baseline retreat rate expected from sea-level rise alone.
nature 45, 226-230; doi:10.1038/nature07365, Nov 13, 2008
Climate in the early Pleistocene varied with a period of 41 kyr and was related to variations in ... more Climate in the early Pleistocene varied with a period of 41 kyr and was related to variations in Earth’s obliquity. About 900 kyr ago, variability increased and oscillated primarily at a period of ~100 kyr, suggesting that the link was then with the eccentricity of Earth’s orbit. This transition has often been attributed to a nonlinear response to small changes in external boundary conditions. Here we propose that increasing variablility within the past million years may indicate that the climate system was approaching a second climate bifurcation point, after which it would transition again to a new stable state characterized by permanentmid-latitude Northern Hemisphere glaciation. From this perspective the pastmillion years can be viewed as a transient interval in the evolution of Earth’s climate. We support our hypothesis using a coupled energybalance/ice-sheetmodel, which furthermore predicts that the future
transition would involve a large expansion of the Eurasian ice sheet. The process responsible for the abrupt change seems to be the albedo discontinuity at the snow–ice edge. The best-fit model run, which explains almost 60% of the variance in global ice volume during the past 400 kyr, predicts a rapid transition in the geologically near future to the proposed glacial state. Should it be attained, this state would be more ‘symmetric’ than the present climate, with comparable areas of ice/sea-ice cover in each hemisphere, and would represent the culmination of 50 million years of evolution from bipolar nonglacial climates to bipolar glacial climates.
Journal of Geophysical Research, 1993