scholarly journals Comparing Twentieth- and Twenty-First-Century Patterns of Interannual Precipitation Variability over the Western United States and Northern Mexico*

2012 ◽  
Vol 13 (1) ◽  
pp. 366-378 ◽  
Author(s):  
Tyler W. Ruff ◽  
Yochanan Kushnir ◽  
Richard Seager
Keyword(s):  
United States ◽  
Twentieth Century ◽  
Interannual Variability ◽  
Climate Models ◽  
Precipitation Variability ◽  
First Century ◽  
Western United States ◽  
Spatial Structures ◽  
Northern Mexico ◽  
Twenty First Century

Abstract The ability of coupled climate models to simulate the patterns of interannual precipitation variability over the western half of the United States and northern Mexico is investigated by applying principal component analysis to observations and model output. Global Precipitation Climatology Centre (GPCC) observations are compared to the pooled twentieth-century warm- and cold-season precipitation averages simulated by five coupled global climate models included in the Intergovernmental Panel on Climate Change Fourth Assessment Report. The pooled model spatial structures (EOFs) closely match those of the GPCC observations for both halves of the year. Additionally, the twenty-first-century model pooled EOFs are almost identical in spatial extent and amplitude to their twentieth-century counterparts. Thus, the spatial characteristics of large-scale precipitation variability in the western United States are not projected to change in the twenty-first century. When global observed and modeled seasonally averaged sea surface temperature anomalies are correlated with the time series corresponding to the three leading EOFs to discern sources of each mode of precipitation variability, a pattern reminiscent of El Niño is found to be the only significant association. The spatial structures of variability also appear independent of the model-predicted precipitation trend over the twenty-first century, indicating that the mechanisms responsible for the trend are different from those associated with interannual variability. The results of this study lend confidence in the pooled model predictions of seasonal precipitation patterns, and they suggest that future changes will primarily result from the contribution of the mean trend over which statistically stationary interannual variability is superimposed.

Great Plains Precipitation and Its SST Links in Twentieth-Century Climate Simulations, and Twenty-First- and Twenty-Second-Century Climate Projections

2010 ◽  
Vol 23 (23) ◽  
pp. 6409-6429 ◽  
Author(s):  
Alfredo Ruiz-Barradas ◽  
Sumant Nigam
Keyword(s):  
United States ◽  
Twentieth Century ◽  
Great Plains ◽  
Summer Precipitation ◽  
Precipitation Variability ◽  
Second Century ◽  
First Century ◽  
Climate Simulations ◽  
Central United States ◽  
Twenty First Century

Abstract The present work assesses spring and summer precipitation over North America as well as summer precipitation variability over the central United States and its SST links in simulations of the twentieth-century climate and projections of the twenty-first- and twenty-second-century climates for the A1B scenario. The observed spatial structure of spring and summer precipitation poses a challenge for models, particularly over the western and central United States. Tendencies in spring precipitation in the twenty-first century agree with the observed ones at the end of the twentieth century over a wetter north-central and a drier southwestern United States, and a drier southeastern Mexico. Projected wetter springs over the Great Plains in the twenty-first and twenty-second centuries are associated with an increase in the number of extreme springs. In contrast, projected summer tendencies have demonstrated little consistency. The associated observed changes in SSTs bear the global warming footprint, which is not well captured in the twentieth-century climate simulations. Precipitation variability over the Great Plains presents a coherent picture in spring but not in summer. Models project an increase in springtime precipitation variability owing to an increased number of extreme springs. The number of extreme droughty (pluvial) events during the spring–fall part of the year is under(over)estimated in the twentieth century without consistent projections. Summer precipitation variability over the Great Plains is linked to SSTs over the Pacific and Atlantic Oceans, with no apparent ENSO link in spite of the exaggerated variability in the equatorial Pacific in climate simulations; this has been identified already in observations and atmospheric models forced with historical SSTs. This link is concealed due to the increased warming in the twenty-first century. Deficiencies in land surface–atmosphere interactions and global teleconnections in the climate models prevent them from a better portrayal of summer precipitation variability in the central United States.

Rewriting the Captivity Narrative for Contemporary Children: Speare, Bruchac, and the French and Indian War

2011 ◽  
Vol 84 (2) ◽  
pp. 318-346 ◽  
Author(s):  
Sara L. Schwebel
Keyword(s):  
United States ◽  
Twentieth Century ◽  
First Century ◽  
Captivity Narratives ◽  
French And Indian War ◽  
Captivity Narrative ◽  
Twenty First Century ◽  
Anglo American ◽  
Indian War ◽  
War Stories

Juxtaposing the French and Indian War stories of Elizabeth George Speare, a mid-twentieth- century Anglo-American children's author, against those of Joseph Bruchac, a twenty-first- century Abenaki children's author, reveals how flexible and powerful captivity narratives have been in shaping arguments about gender, nationhood, citizenship, and land in the postwar United States.

scholarly journals What Caused the Observed Twentieth-Century Weakening of the Walker Circulation?

2011 ◽  
Vol 24 (24) ◽  
pp. 6501-6514 ◽  
Author(s):  
Scott B. Power ◽  
Greg Kociuba
Keyword(s):  
Twentieth Century ◽  
Climate Models ◽  
Southern Oscillation ◽  
Walker Circulation ◽  
Natural Variability ◽  
First Century ◽  
External Forcing ◽  
Wide Range ◽  
Twenty First Century ◽  
The Walker Circulation

Abstract The Walker circulation (WC) is one of the world’s most prominent and important atmospheric systems. The WC weakened during the twentieth century, reaching record low levels in recent decades. This weakening is thought to be partly due to global warming and partly due to internally generated natural variability. There is, however, no consensus in the literature on the relative contribution of external forcing and natural variability to the observed weakening of the WC. This paper examines changes in the strength of the WC using an index called BoxΔP, which is equal to the difference in mean sea level pressure across the equatorial Pacific. Change in both the observations and in World Climate Research Programme (WCRP) Coupled Model Intercomparison Project phase 3 (CMIP3) climate models are examined. The annual average BoxΔP declines in the observations and in 15 out of 23 models during the twentieth century (results that are significant at or above the 95% level), consistent with earlier work. However, the magnitude of the multimodel ensemble mean (MMEM) 1901–99 trend (−0.10 Pa yr−1) is much smaller than the magnitude of the observed trend (−0.52 Pa yr−1). While a wide range of trends is evident in the models with approximately 90% of the model trends in the range (−0.25 to +0.1 Pa yr−1), even this range is too narrow to encompass the magnitude of the observed trend. Twenty-first-century changes in BoxΔP under the Special Report on Emissions Scenarios (SRES) A1B and A2 are also examined. Negative trends (i.e., weaker WCs) are evident in all seasons. However, the MMEM trends for the A1B and A2 scenarios are smaller in magnitude than the magnitude of the observed trend. Given that external forcing linked to greenhouse gases is much larger in the twenty-first-century scenarios than twentieth-century forcing, this, together with the twentieth-century results mentioned above, would seem to suggest that external forcing has not been the primary driver of the observed weakening of the WC. However, 9 of the 23 models are unable to account for the observed change unless the internally generated component of the trend is very large. But indicators of observed variability linked to El Niño–Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation have modest trends, suggesting that internally variability has been modest. Furthermore, many of the nine “inconsistent” models tend to have poorer simulations of climatic features linked to ENSO. In addition, the externally forced component of the trend tends to be larger in magnitude and more closely matches the observed trend in the models that are better able to reproduce ENSO-related variability. The “best” four models, for example, have a MMEM of −0.2 Pa yr−1 (i.e., approximately 40% of the observed change), suggesting a greater role for external forcing in driving the observed trend. These and other considerations outlined below lead the authors to conclude that (i) both external forcing and internally generated variability contributed to the observed weakening of the WC over the twentieth century and (ii) external forcing accounts for approximately 30%–70% of the observed weakening with internally generated climate variability making up the rest.

scholarly journals More Frequent, Longer, and Hotter Heat Waves for Australia in the Twenty-First Century

2014 ◽  
Vol 27 (15) ◽  
pp. 5851-5871 ◽  
Author(s):  
Tim Cowan ◽  
Ariaan Purich ◽  
Sarah Perkins ◽  
Alexandre Pezza ◽  
Ghyslaine Boschat ◽  
...  
Keyword(s):  
Twentieth Century ◽  
Climate Models ◽  
Heat Waves ◽  
First Century ◽  
Maximum Temperature ◽  
Historical Period ◽  
Tropical Regions ◽  
Summer Heat ◽  
Ensemble Mean ◽  
Twenty First Century

Abstract Extremes such as summer heat waves and winter warm spells have a significant impact on the climate of Australia, with many regions experiencing an increase in the frequency and duration of these events since the mid-twentieth century. With the availability of Coupled Model Intercomparison Project phase 5 (CMIP5) climate models, projected changes in heat waves and warm spells are investigated across Australia for two future emission scenarios. For the historical period encompassing the late twentieth century (1950–2005) an ensemble mean of 15 models is able to broadly capture the observed spatial distribution in the frequency and duration of summer heat waves, despite overestimating these metrics along coastal regions. The models achieve a better comparison to observations in their simulation of the temperature anomaly of the hottest heat waves. By the end of the twenty-first century, the model ensemble mean projects the largest increase in summer heat wave frequency and duration to occur across northern tropical regions, while projecting an increase of ~3°C in the maximum temperature of the hottest southern Australian heat waves. Model consensus suggests that future winter warm spells will increase in frequency and duration at a greater rate than summer heat waves, and that the hottest events will become increasingly hotter for both seasons by century’s end. Even when referenced to a warming mean state, increases in the temperature of the hottest events are projected for southern Australia. Results also suggest that following a strong mitigation pathway in the future is more effective in reducing the frequency and duration of heat waves and warm spells in the southern regions compared to the northern tropical regions.

America's Pragmatic Role?

2020 ◽  
Author(s):  
Deborah Avant
Keyword(s):  
United States ◽  
Twentieth Century ◽  
International Relations ◽  
The United States ◽  
Global Leadership ◽  
First Century ◽  
Global Leader ◽  
The Future ◽  
Twenty First Century

Abstract What has made the United States a global leader? Though analysts often attribute American success to a combination of resources and ideas, a subtle undercurrent in these arguments points to pragmatism and the creativity it often generates as an important part of the story. First theorized by American philosophers in the nineteenth and early twentieth centuries, pragmatism emphasizes that creativity can reshape how we see norms and interests to make cooperation more likely. After discussing the basic elements of pragmatism and its intersection with prominent international relations arguments, I show how the creativity that pragmatism envisions appears in each of these books. Though the collected authors do not label themselves as pragmatists, piecing these pragmatic elements together demonstrates the importance of creativity for key global leadership moments in the twentieth century, as well as important, if under-appreciated, governance innovations in the twenty-first century. It also offers insights into how the United States might move into the future.

CLIMATE CHANGE SCENARIOS FOR THE U.S. NATIONAL ASSESSMENT

2003 ◽  
Vol 84 (12) ◽  
pp. 1711-1724 ◽  
Author(s):  
Michael C. MacCracken ◽  
Eric J. Barron ◽  
David R. Easterling ◽  
Benjamin S. Felzer ◽  
Thomas R. Karl
Keyword(s):  
Climate Change ◽  
Twentieth Century ◽  
Climate Models ◽  
Climatic Conditions ◽  
First Century ◽  
Climate Change Scenarios ◽  
Climate Scenarios ◽  
National Assessment ◽  
Twenty First Century ◽  
The U.S

In support of the U.S. National Assessment of the Potential Consequences of Climate Variability and Change, climate scenarios were prepared to serve as the basis for evaluating the vulnerability of environmental and societal systems to changes projected for the twenty-first century. Since publication of the results of the assessment at the end of 2000, the National Research Council's report Climate Change Science: An Analysis of Some Key Questions, and the U.S. government's U.S. Climate Action Report—2002 have both relied on the assessment's findings. Because of the importance of these findings, it is important to directly address questions regarding the representativeness and usefulness of the model-based projections on which the findings were based. In particular, criticisms have focused on whether the climate models that were relied upon adequately represented twentieth-century conditions and whether their projections of conditions for the twenty-first century were outliers. Reexamination of the approach used in developing and evaluating the climate scenarios indicates that the results from the two primary climate modeling groups that were relied upon allowed the generation of climate scenarios that span much of the range of possible future climatic conditions projected by the larger set of model simulations, which was compiled for the IPCCs Third Assessment Report. With the set of models showing increasing agreement in their simulations of twentieth-century trends in climate and of projected changes in climate on subcontinental to continental scales, the climate scenarios that were generated seem likely to provide a plausible representation of the types of climatic conditions that could be experienced during the twenty-first century. Warming, reduced snow cover, and more intense heavy precipitation events were projected by all models, suggesting such changes are quite likely. However, significant differences remain in the projection of changes in precipitation and of the regional departures in climate from the larger-scale patterns. For this reason, evaluating potential impacts using climate scenarios based on models exhibiting different regional responses is a necessary step to ensuring a representative analysis. Utilizing an even more encompassing set of scenarios in the future could help move from mainly qualitative toward more certain and quantitative conclusions.

scholarly journals Explaining the Spread in Global Mean Thermosteric Sea Level Rise in CMIP5 Climate Models*

2015 ◽  
Vol 28 (24) ◽  
pp. 9918-9940 ◽  
Author(s):  
Angélique Melet ◽  
Benoit Meyssignac
Keyword(s):  
Twentieth Century ◽  
Sea Level ◽  
Radiative Forcing ◽  
Climate Models ◽  
First Century ◽  
Model Ensemble ◽  
Ocean Heat Uptake ◽  
Feedback Parameter ◽  
Twenty First Century ◽  
Global Mean

Abstract The ocean stores more than 90% of the energy excess associated with anthropogenic climate change. The resulting ocean warming and thermal expansion are leading contributors to global mean sea level (GMSL) rise. Confidence in projections of GMSL rise therefore depends on the ability of climate models to reproduce global mean thermosteric sea level (GMTSL) rise over the twentieth century. This study first compares the GMTSL of the climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to observations over 1961–2005. Although the model ensemble mean is within the uncertainty of observations, the model ensemble exhibits a large spread. The authors then aim to explain the spread in CMIP5 climate model GMTSL over the twentieth and twenty-first centuries. It is shown that the climate models’ GMTSL rise depends linearly on the time-integrated radiative forcing F (under continuously increasing radiative forcing). The constant of proportionality μ expresses the transient thermosteric sea level response of the climate system, and it depends on the fraction of excess heat stored in the ocean, the expansion efficiency of heat, the climate feedback parameter, and the ocean heat uptake efficiency. The across-model spread in μ explains most (>70%) of the across-model spread in GMTSL rise over the twentieth and twenty-first centuries, while the across-model spread in time-integrated F explains the rest. The time-integrated F explains less variance in the across-model GMTSL rise in twenty-first-century than in twentieth-century simulations, as the spread in F is reduced over the twenty-first century because the anthropogenic aerosol forcing, which is a large source of uncertainty in F, becomes relatively smaller.

A Comparative Study of Precipitation and Evaporation between CMIP3 and CMIP5 Climate Model Ensembles in Semiarid Regions

2014 ◽  
Vol 27 (10) ◽  
pp. 3731-3749 ◽  
Author(s):  
Noel C. Baker ◽  
Huei-Ping Huang
Keyword(s):  
United States ◽  
Twentieth Century ◽  
Negative Trend ◽  
First Century ◽  
Positive Trend ◽  
Southwestern United States ◽  
Semiarid Regions ◽  
Drying Trend ◽  
Twenty First Century ◽  
Model Ensembles

Abstract The twentieth-century climatology and twenty-first-century trend in precipitation P, evaporation E, and P − E for selected semiarid U.S. Southwest and Mediterranean regions are compared between ensembles from phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). The twentieth-century simulations are validated with precipitation from observation and evaporation from reanalysis. It is found that the Special Report on Emissions Scenarios (SRES) A1B simulations in CMIP3 and the simulations with representative concentration pathways (RCPs) 4.5 and 8.5 in CMIP5 produce qualitatively similar seasonal cycles of the twenty-first-century trend in P − E for both semiarid regions. For the southwestern United States, it is characterized by a strong drying trend in spring, a weak moistening trend in summer, a weak drying trend in winter, and an overall drying trend for the annual mean. For the Mediterranean region, a drying trend is simulated for all seasons with an October maximum and July minimum. The consistency between CMIP3 and CMIP5 scenarios indicates that the simulated trend is robust; however, while the trend in P − E is negative in spring for the southwestern United States for all CMIP ensembles, CMIP3 predicts a strongly negative trend in P and minor negative trend in E whereas both CMIP5 scenarios predict a nearly zero trend in P and positive trend in E. For the twentieth-century simulations, the P, E, and P − E of the two model ensembles are statistically indistinguishable for most seasons. This “stagnation” of the simulated climatology from CMIP3 to CMIP5 implies that the hydroclimatic variable biases have not decreased in the newer generation of models. Notably, over the southwestern United States the CMIP3 models produce too much precipitation in the cold season. This bias remains almost unchanged in CMIP5.

The Effect of Global Warming on Severe Thunderstorms in the United States

2015 ◽  
Vol 28 (6) ◽  
pp. 2443-2458 ◽  
Author(s):  
Jacob T. Seeley ◽  
David M. Romps
Keyword(s):  
United States ◽  
Wind Shear ◽  
Large Scale ◽  
Climate Models ◽  
Relative Weight ◽  
The United States ◽  
First Century ◽  
High Performing ◽  
Severe Thunderstorms ◽  
Twenty First Century

Abstract How will warming temperatures influence thunderstorm severity? This question can be explored by using climate models to diagnose changes in large-scale convective instability (CAPE) and wind shear, conditions that are known to be conducive to the formation of severe thunderstorms. First, an ensemble of climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) is evaluated on its ability to reproduce a radiosonde climatology of such storm-favorable conditions in the current climate’s spring and summer seasons, focusing on the contiguous United States (CONUS). Of the 11 climate models evaluated, a high-performing subset of four (GFDL CM3, GFDL-ESM2M, MRI-CGCM3, and NorESM1-M) is identified. Second, the twenty-first-century changes in the frequency of environments favorable to severe thunderstorms are calculated in these high-performing models as they are forced by the RCP4.5 and RCP8.5 emissions pathways. For the RCP8.5 scenario, the models predict consistent CONUS-mean fractional springtime increases in the range of 50%–180% by the end of the twenty-first century; for the summer, three of the four models predict increases in the range of 40%–120% and one model predicts a small decrease. This disagreement between the models is traced to divergent projections for future CAPE and boundary layer humidity in the Great Plains. This paper also explores the sensitivity of the results to the relative weight given to wind shear in determining how “favorable” a large-scale environment is for the development of severe thunderstorms, and it is found that this weighting is not the dominant source of uncertainty in projections of future thunderstorm severity.

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