Climate Change and...
- Climate Variability
- Climate Models
Effects of Climate Change
Sea Surface Temperatures
ABSTRACT: An analysis of historical sea surface temperatures provides evidence for global warming since 1900, in line with land-based analyses of global temperature trends, and also shows that over the same period, the eastern equatorial Pacific cooled and the zonal sea surface temperature gradient strengthened. Recent theoretical studies have predicted such a pattern as a response of the coupled ocean-atmosphere system to an exogenous heating of the tropical atmosphere. This pattern, however, is not reproduced by the complex ocean-atmosphere circulation models currently used to simulate the climatic response to increased greenhouse gases. Its presence is likely to lessen the mean 20th-century global temperature change in model simulations.
ABSTRACT: The mid-summer rainfall singularity of the Southwest United States (principally Arizona) exhibits marked variations on interannual and decadal time scales. Examination of the synoptic mechanisms involved in these variations is undertaken here. In particular, associations between the rainfall, the dominant latitude of the summertime mid-tropospheric subtropical ridge (STR) over the southwest United States, and the sea surface temperatures (SSTs) of the equatorial and North Pacific region are documented. The analysis utilizes a composite approach for sets of extreme years chosen on the basis of the rainfall and circulation anomalies.
It is found that northward (southward) displaced seasonal STR is associated with wetter (drier) summers in Arizona. Further, these extremes have tended to follow winters characterized by positive (negative) phases of the Pacific-North America (PNA) teleconnection pattern. The latter association arises, at least in part from the “memory” imparted to the atmosphere by the accompanying anomalies of Pacific SSTs. However, during the summer season, more localized anomalies of SST appear important for Arizona rainfall variations. In wet (but not dry) summers, an enhanced longitudinal gradient of SST exists between the west coast of the United States, Baja California, and the Gulf of California. This is accompanied by a steeper gradient of lower tropospheric heights (and implied stronger geostrophic flow) and also a reversal in both the total (850–500 mb) and partial (850–700 mb) thickness gradients across the region compared with dry summers. These results seem to confirm the importance of lower-level southwesterly flow for moisture transport into the deserts.
Recent decadal variations in the singularity involve particularly runs of wetter (drier) summers in the 1950s (1970s). Preliminary analysis of these variations for years that were non-ENSO suggests that they may result from the operation of mechanisms similar to those attending the interannual variability of Arizona summer rainfall (viz., the STR and Pacific SSTs). A contributory mechanism in the longer-term trend of STR between these decades appears to be a change in the tropical–extratropical gradient of Pacific SSTs during the summer and antecedent spring. The gradient evidently strengthened during the period, helping to explain the shift to more frequent southward displacements of STR over the Southwest and, accordingly, reduced summer rainfall in Arizona.
ABSTRACT: Paleoclimatic data are increasingly showing that abrupt change is present in wide regions of the globe. Here a mechanism for abrupt climate change with global implications is presented. Results from a tropical coupled ocean–atmosphere model show that, under certain orbital configurations of the past, variability associated with El Niño–Southern Oscillation (ENSO) physics can abruptly lock to the seasonal cycle for several centuries, producing a mean sea surface temperature (SST) change in the tropical Pacific that resembles a La Niña. It is suggested that this change in SST would have a global impact and that abrupt events such as the Younger Dryas may be the outcome of orbitally driven changes in the tropical Pacific.
Cortese, G., A. Abelmann, R. Gersonde (2007). The last five glacial-interglacial transitions: A high-resolution 450,000-year record from the subantarctic Atlantic. Paleoceanography 22 (PA4203): doi:10.1029/2007PA001457
ABSTRACT: A submillennial resolution, radiolarian-based record of summer sea surface temperature (SST) documents the last five glacial to interglacial transitions at the subtropical front, southern Atlantic Ocean. Rapid fluctuations occur both during glacial and interglacial intervals, and sudden cooling episodes at glacial terminations are recurrent. Surface hydrography and global ice volume proxies from the same core suggest that summer SST increases prior to terminations lead global ice-volume decreases by 4.7 ± 3.7 ka (in the eccentricity band), 6.9 ± 2.5 ka (obliquity), and 2.7 ± 0.9 ka (precession). A comparison between SST and benthicd13 C suggests a decoupling in the response of northern subantarctic surface, intermediate, and deep water masses to cold events in the North Atlantic. The matching features between our SST record and the one from core MD97-2120 (southwest Pacific) suggests that the super-regional expression of climatic events is substantially affected by a single climatic agent: the Subtropical Front, amplifier and vehicle for the transfer of climatic change. The direct correlation between warmerDTsite at Vostok and warmer SST at ODP Site 1089 suggests that warmer oceanic/atmospheric conditions imply a more southward placed frontal system, weaker gradients, and therefore stronger Agulhas input to the Atlantic Ocean.
ABSTRACT: Tropical cyclone activity has long been understood to respond to changing properties of the large-scale atmospheric and oceanic environment. In this essay, evidence for changing tropical cyclone activity is reviewed, and the controversy surrounding the quality of the data itself and the attribution of these environmental changes to various natural and anthropogenic causes, is discussed. At the same time, there is growing evidence that global tropical cyclone activity may itself affect climate in such a way as to mitigate tropical climate change but amplify climate change at higher latitudes. This evidence is reviewed, and possible routes forward in exploring these effects are suggested.
A. Kaplan, M. A. Cane, Y. Kushnir, A. C. Clement, M. B. Blumenthal, B. Rajagopalan (1998). Analyses of global sea surface temperature 1856–1991. Journal of Geophysical Research 103 (C9): 18,567–18,589
ABSTRACT: Global analyses of monthly sea surface temperature (SST) anomalies from 1856 to 1991 are produced using three statistically based methods: optimal smoothing (OS), the Kaiman filter (KF) and optimal interpolation (OI). Each of these is accompanied by estimates of the error covariance of the analyzed fields. The spatial covariance function these methods require is estimated from the available data; the timemarching model is a first-order autoregressive model again estimated from data. The data input for the analyses are monthly anomalies from the United Kingdom Meteorological Office historical sea surface temperature data set (MOHSST5) [Parker et al., 1994] of the Global Ocean Surface Temperature Atlas (GOSTA) [Bottomley et al., 1990].
These analyses are compared with each other, with GOSTA, and with an analysis generated by projection (P) onto a set of empirical orthogonal functions (as in Smith et al. ). In theory, the quality of the analyses should rank in the order OS, KF, OI, P, and GOSTA. It is found that the first four give comparable results in the data-rich periods (1951–1991), but at times when data is sparse the first three differ significantly from P and GOSTA. At these times the latter two often have extreme and fluctuating values, prima facie evidence of error. The statistical schemes are also verified against data not used in any of the analyses (proxy records derived from corals and air temperature records from coastal and island stations). We also present evidence that the analysis error estimates are indeed indicative of the quality of the products. At most times the OS and KF products are close to the OI product, but at times of especially poor coverage their use of information from other times is advantageous.
The methods appear to reconstruct the major features of the global SST field from very sparse data. Comparison with other indications of the El Niño – Southern Oscillation cycle show that the analyses provide usable information on interannual variability as far back as the 1860s.
ABSTRACT: Interannual and interdecadal variability in the summertime mean North Pacific storm track is examined in relation to summertime mean sea surface temperature (SST), nimbostratus, and marine stratiform cloudiness (MSC) (stratus, stratocumulus, fog). The storm track is diagnosed by root-mean-squared daily vertical velocity at 500 mb during the summer season (rmsω) obtained from the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis. The cloud and SST data are obtained from surface observations. Year-to-year variations in the storm track exhibit significant coupling to variations in cloudiness and SST across the North Pacific. These correspond to coincident latitudinal shifts in the storm track, SST gradient, and MSC gradient. Moreover, both rmsω and nimbostratus show that the storm track moved equatorward and intensified between 1952 and 1995, consistent with the previously documented upward trend in MSC and downward trend in SST. Lead–lag relationships suggest variability in the storm track has a large role in forcing variability in SST. Boundary layer cloudiness responds to and adds a positive feedback to variability in SST.
Weak relationships are observed with the summertime mean large-scale circulation, as diagnosed by sea level pressure. This suggests summertime North Pacific atmosphere–ocean interaction is dominated by local processes operating in the storm track and over the SST gradient, unlike the situation during winter.
ABSTRACT: We present global fields of decadal annual surface temperature anomalies, referred to the period 1951–1980, for each decade from 1881–1890 to 1981–1990 and for 1984–1993. In addition, we show decadal calendar-seasonal anomaly fields for the warm decades 1936–1945 and 1981–1990. The fields are based on sea surface temperature (SST) and land surface air temperature data. The SSTs are corrected for the pre-World War II use of uninsulated sea temperature buckets and incorporate adjusted satellite-based SSTs from 1982 onward. Our results extend those published in the 1990 Intergovernmental Panel on Climate Change Scientific Assessment and its 1992 supplement. We assess the impact of various sources of error in the fields. Despite poor data coverage initially and around the two World Wars the generally cold end of the nineteenth century and start to the twentieth century are confirmed, together with the substantial warming between about 1920 and 1940. Slight cooling of the northern hemisphere took place between the 1950s and the mid-1970s, although slight warming continued south of the equator. Recent warmth has been most marked over the northern continents in winter and spring, but the 1980s were warm almost everywhere apart from Greenland, the northwestern Atlantic and the midlatitude North Pacific. Parts of the middle- to high-latitude southern ocean may also have been cool in the 1980s, but in this area the 1951–1980 climatology is unreliable.
The impact of the satellite data is reduced because the record of blended satellite and in situ SST is still too short to yield a climatology from which to calculate representative anomalies reflecting climatic change in the southern ocean. However, we propose a method of using existing satellite data in a step toward this target. The maps are condensed into global and hemispheric decadal surface temperature anomalies. We show the sensitivity of these estimated anomalies to alternative methods of compositing the spatially incomplete fields. Renning decadal zonal means and annual global and hemispheric time series are also shown. Finally, we discuss some salient features in terms of observed atmospheric circulation changes and of the results of climate model integrations with increasing atmospheric greenhouse gases.
A. L. Sabin, N. G. Pisias (1996). Sea surface temperature changes in the northeastern Pacific Ocean during the past 20,000 years and their relationship to climate change in northwestern North America. Quaternary Research 46 (1): 48-61
ABSTRACT: Modern ocean–atmosphere interactions in the northeastern Pacific Ocean have a significant effect on the climate of the west coast of North America. We present radiolarian microfossil-based temperature reconstructions for the eastern North Pacific spanning the past 20,000 yr to examine possible correlations and linkages between continental climate change and changes in sea surface temperature (SST) in the northeastern Pacific Ocean on millennial time scales. The reconstructions indicate that the regional pattern of ocean circulation off the west coast of North America was further south 15,000 cal yr B.P. than it is today, and reached its present location 13,000 cal yr B.P. The North Pacific Drift and Transition Zone were further south as a result of a more southerly North Pacific high pressure cell prior to 13,000 cal yr B.P. While two continental paleoclimate records from northwestern North America show regional differences, they also can be correlated to the SST changes. A coastal site at 48°N shows similar patterns in summer temperatures, as observed in offshore marine records of SSTs. However, an inland continental record seems to reflect more-regional-scale changes in sea surface conditions showing a thermal maximum centered at 10,000 cal yr B.P which is observed in the marine transect south of 42°N. We conclude, based on the pattern of oceanographic change as reflected in radiolarian assemblages, that changes in the past latitudinal position of the North Pacific Drift played a significant role in controlling continental climate immediately to its east, as it does in the present environment. We also conclude that during the past 20,000 yr much of the evolution of oceanographic change is related to the migration of the atmospheric pressure cells (the North Pacific high and Aleutian low) of the northeastern Pacific.
Thunell, R., E. Tappa, E. Kincaid, C. Pride (1999). Sea-surface temperature anomalies associated with the 1997–1998 El Niño recorded in the oxygen isotope composition of planktonic foraminifera. Geology 27 (9): 843-846
ABSTRACT: Anomalously warm sea-surface temperatures and associated high rainfall propagated northward from the eastern equatorial Pacific along the western margin of North America during the 1997–1998 El Niño. We present data from the Guaymas Basin (Gulf of California) and the Santa Barbara Basin (Southern California Borderlands) that clearly demonstrate that the oxygen isotope composition of planktonic foraminifera accurately records the local sea-surface temperature changes related to the El Niño phenomenon. On the basis of this observation, the varved sediments accumulating in these basins should contain a detailed history of both the occurrence and intensity of past El Niño events.
ABSTRACT: Warm-season (April–September) temperature models based on a network of coastal ring-width and maximum latewood density tree-ring chronologies are the first reconstructions for coastal stations along the Gulf of Alaska and the Pacific Northwest. These well-verified temperature models are consistent with long climatic series from coastal stations and other proxy data from the Pacific coast. Cool summers during the 1850s and late 1800s in the Gulf of Alaska correspond to general glacier advance from the region. The Pacific Northwest reconstruction shows summer temperatures cooling in the early 1800s, coincident with a maximum of glacier activity in the coastal Olympic Mountains, Washington. The two warm-season temperature records show intervals when anomalies are opposite in sign, most notably during the 1850s, when cooling is inferred for the Gulf and warming is inferred for the Pacific Northwest. The records are coherent, however, during other intervals, with both showing cooling in the early 1800s and warming around 1870. The phase of these two records may reflect decadal changes in large-scale circulation in the northeastern Pacific. These land temperature reconstructions are strongly correlated with nearby sea surface temperatures, indicating large-scale oceanic–atmospheric influences.
ABSTRACT: Regional climate trends are of interest both for understanding natural climate processes and as tests of anthropogenic climate change signatures. Relative to global trends, however, their detection is hampered by smaller datasets and the influence of regional climate processes such as the Southern Oscillation. Regional trends are often presented by authors without demonstration of statistical significance. In this paper, regional-average annual series of air temperature and sea surface temperature for the New Zealand region are analyzed using a systematic statistical approach that selects the optimum statistical model (with respect to serial correlation, linearity, etc.), explicitly models the interannual variability associated with observable regional climate processes, and tests significance. It is found that the residuals are stationary and are a red noise process [ARMA(1,0)] for all the series examined. The SOI and a meridional circulation anomaly index (both high-pass filtered) are “explanatory variables” for interannual variability. For national-average air temperature (AT), linear and exponential trend models are equally valid but for simplicity the linear model is preferred. Failure to model the serial correlation in AT would result in an estimated confidence interval for trend that is too small by 36%. The use of the explanatory variables tightens the confidence interval by 15%.
Significant trends were detected. The trend in AT for 1896–1994 is 0.11 ± 0.035°C decade−1 (95% confidence interval). This is about double the trend reported for global data, which may be due to the relative absence of sulfate aerosols in the South Pacific region. The trends in maximum and minimum temperature over this period are not statistically different. However, for the later period of 1951–90, the trend in maximum temperature reduces to an insignificant value, while the trend in minimum temperature remains high, resulting in a significant downward trend in diurnal range of 0.10°C decade−1 . Similar diurnal range behavior in other regions has been tentatively attributed to increasing cloudiness. The trend in a regional SST series for 1928–94, 0.07°C decade−1 , is about half the trend in AT for the same period. The trend in the difference, SST–AT, −0.06°C decade−1 , is statistically significant. This implies the existence of an atmospheric warming source for the additional air temperature trend, and may mean that the heat fluxes between the atmosphere and ocean in the New Zealand region are subject to a large trend, with the direction of flux change being toward the ocean. The results of the study are consistent with the IPCC predictions of climate change.