scholarly journals Tropical Pacific spatial trend patterns in observed sea level: internal variability and/or anthropogenic signature?

2012 ◽  
Vol 8 (1) ◽  
pp. 349-389 ◽  
Author(s):  
B. Meyssignac ◽  
D. Salas y Melia ◽  
M. Becker ◽  
W. Llovel ◽  
A. Cazenave
Keyword(s):  
Sea Level ◽  
20Th Century ◽  
Characteristic Time ◽  
Climate Models ◽  
Tropical Pacific ◽  
External Forcing ◽  
Spatial Trend ◽  
Anthropogenic Forcing ◽  
Coupled Climate Models ◽  
Sea Level Trend

Abstract. We investigate the spatio-temporal variability of sea level trend patterns observed by satellite altimetry since 1993, focusing on the Tropical Pacific. The objective of this study is two fold. On the basis of a 2-D past sea level reconstruction (over 1950–2009) – based on a combination of observations and ocean modelling – and multi-century control runs (i.e. with constant, preindustrial external forcing) from eight coupled climate models, we investigate how these sea level trend patterns evolved during the last decades and centuries, and what their characteristic time scales are. Using 20th century coupled climate model runs, we also examine whether observed trend patterns are driven by external forcing factors (i.e. solar plus volcanic variability and changes in anthropogenic forcing) or if they essentially result from natural climate variability. For this analysis, we computed sea level trend patterns over successive 17 yr windows (i.e. the length of the altimetry record) both for the reconstructed sea level and model runs. We compared them to altimetry-based observed trends. The 2-D sea level reconstruction shows similar spatial trend patterns to those observed during the altimetry era. The patterns appear to have fluctuated with time with a characteristic time scale of the order of 25–30 yr. Similar behaviour is found in multi-centennial control runs of the coupled climate models. The same analysis, performed on 20th century model runs does not display significant differences. This suggests that Tropical Pacific sea level trend fluctuations are still dominated by the internal natural variability of the ocean-atmosphere coupled system. While our analysis cannot rule out any influence of anthropogenic forcing, it concludes that the latter effects on the regional sea level patterns are still hardly detectable.

scholarly journals Tropical Pacific spatial trend patterns in observed sea level: internal variability and/or anthropogenic signature?

2012 ◽  
Vol 8 (2) ◽  
pp. 787-802 ◽  
Author(s):  
B. Meyssignac ◽  
D. Salas y Melia ◽  
M. Becker ◽  
W. Llovel ◽  
A. Cazenave
Keyword(s):  
Sea Level ◽  
Climate Models ◽  
Internal Variability ◽  
Tropical Pacific ◽  
External Forcing ◽  
Spatial Trend ◽  
Trend Pattern ◽  
Coupled Climate Models ◽  
Sea Level Trend ◽  
The Tropical Pacific

Abstract. In this study we focus on the sea level trend pattern observed by satellite altimetry in the tropical Pacific over the 1993–2009 time span (i.e. 17 yr). Our objective is to investigate whether this 17-yr-long trend pattern was different before the altimetry era, what was its spatio-temporal variability and what have been its main drivers. We try to discriminate the respective roles of the internal variability of the climate system and of external forcing factors, in particular anthropogenic emissions (greenhouse gases and aerosols). On the basis of a 2-D past sea level reconstruction over 1950–2009 (based on a combination of observations and ocean modelling) and multi-century control runs (i.e. with constant, preindustrial external forcing) from eight coupled climate models, we have investigated how the observed 17-yr sea level trend pattern evolved during the last decades and centuries, and try to estimate the characteristic time scales of its variability. For that purpose, we have computed sea level trend patterns over successive 17-yr windows (i.e. the length of the altimetry record), both for the 60-yr long reconstructed sea level and the model runs. We find that the 2-D sea level reconstruction shows spatial trend patterns similar to the one observed during the altimetry era. The pattern appears to have fluctuated with time with a characteristic time scale of the order of 25–30 yr. The same behaviour is found in multi-centennial control runs of the coupled climate models. A similar analysis is performed with 20th century coupled climate model runs with complete external forcing (i.e. solar plus volcanic variability and changes in anthropogenic forcing). Results suggest that in the tropical Pacific, sea level trend fluctuations are dominated by the internal variability of the ocean–atmosphere coupled system. While our analysis cannot rule out any influence of anthropogenic forcing, it concludes that the latter effect in that particular region is stillhardly detectable.

scholarly journals A Regime Shift in Seasonal Total Antarctic Sea Ice Extent in the 20th Century

2021 ◽  
Author(s):  
Ryan Fogt ◽  
Amanda Sleinkofer ◽  
Marilyn Raphael ◽  
Mark Handcock
Keyword(s):  
Sea Ice ◽  
20Th Century ◽  
Climate Models ◽  
Historical Context ◽  
The Arctic ◽  
Sea Ice Extent ◽  
Antarctic Sea Ice ◽  
Coupled Climate Models ◽  
High Degree ◽  
The Antarctic

Abstract In stark contrast to the Arctic, there have been statistically significant positive trends in total Antarctic sea ice extent since 1979, despite a sudden decline in sea ice in 2016(1–5) and increasing greenhouse gas concentrations. Attributing Antarctic sea ice trends is complicated by the fact that most coupled climate models show negative trends in sea ice extent since 1979, opposite of that observed(6–8). Additionally, the short record of sea ice extent (beginning in 1979), coupled with the high degree of interannual variability, make the record too short to fully understand the historical context of these recent changes(9). Here we show, using new robust observation-based reconstructions, that 1) these observed recent increases in Antarctic sea ice extent are unique in the context of the 20th century and 2) the observed trends are juxtaposed against statistically significant decreases in sea ice extent throughout much of the early and middle 20th century. These reconstructions are the first to provide reliable estimates of total sea ice extent surrounding the continent; previous proxy-based reconstructions are limited(10). Importantly, the reconstructions continue to show the high degree of interannual Antarctic sea ice extent variability that is marked with frequent sudden changes, such as observed in 2016, which stress the importance of a longer historical context when assessing and attributing observed trends in Antarctic climate(9). Our reconstructions are skillful enough to be used in climate models to allow better understanding of the interconnected nature of the Antarctic climate system and to improve predictions of the future state of Antarctic climate.

scholarly journals Network connectivity between the winter Arctic Oscillation and summer sea ice in CMIP6 models and observations

2022 ◽  
Author(s):  
William Gregory ◽  
Julienne Stroeve ◽  
Michel Tsamados
Keyword(s):  
Sea Ice ◽  
Sea Level ◽  
Arctic Oscillation ◽  
Climate Models ◽  
Sea Ice Concentration ◽  
Sea Level Pressure ◽  
The North ◽  
Coupled Climate Models ◽  
Ice Concentration ◽  
Arctic Summer

Abstract. The indirect effect of winter Arctic Oscillation (AO) events on the proceeding summer Arctic sea ice extent suggests an inherent winter-to-summer mechanism for sea ice predictability. On the other hand, operational regional summer sea ice forecasts in a large number of coupled climate models show a considerable drop in predictive skill for forecasts initialised prior to the date of melt onset in spring, suggesting that some drivers of sea ice variability on longer time scales may not be well represented in these models. To this end, we introduce an unsupervised learning approach based on cluster analysis and complex networks to establish how well the latest generation of coupled climate models participating in phase 6 of the World Climate Research Programme Coupled Model Intercomparison Project (CMIP6) are able to reflect the spatio-temporal patterns of variability in northern-hemisphere winter sea-level pressure and Arctic summer sea ice concentration over the period 1979–2020, relative to ERA5 atmospheric reanalysis and satellite-derived sea ice observations respectively. Two specific global metrics are introduced as ways to compare patterns of variability between models and observations/reanalysis: the Adjusted Rand Index – a method for comparing spatial patterns of variability, and a network distance metric – a method for comparing the degree of connectivity between two geographic regions. We find that CMIP6 models generally reflect the spatial pattern of variability of the AO relatively well, although over-estimate the magnitude of sea-level pressure variability over the north-western Pacific Ocean, and under-estimate the variability over the north Africa and southern Europe. They also under-estimate the importance of regions such as the Beaufort, East Siberian and Laptev seas in explaining pan-Arctic summer sea ice area variability, which we hypothesise is due to regional biases in sea ice thickness. Finally, observations show that historically, winter AO events (negatively) covary strongly with summer sea ice concentration in the eastern Pacific sector of the Arctic, although now under a thinning ice regime, both the eastern and western Pacific sectors exhibit similar behaviour. CMIP6 models however do not show this transition on average, which may hinder their ability to make skilful seasonal to inter-annual predictions of summer sea ice.

scholarly journals Assessment of Twentieth-Century Regional Surface Temperature Trends Using the GFDL CM2 Coupled Models

2006 ◽  
Vol 19 (9) ◽  
pp. 1624-1651 ◽  
Author(s):  
T. R. Knutson ◽  
T. L. Delworth ◽  
K. W. Dixon ◽  
I. M. Held ◽  
J. Lu ◽  
...  
Keyword(s):  
Twentieth Century ◽  
Climate Models ◽  
Global Climate Models ◽  
Geophysical Fluid Dynamics Laboratory ◽  
External Forcing ◽  
Tropical Eastern Pacific ◽  
Coupled Models ◽  
Northern Asia ◽  
Anthropogenic Forcing ◽  
Temperature Records

Abstract Historical climate simulations of the period 1861–2000 using two new Geophysical Fluid Dynamics Laboratory (GFDL) global climate models (CM2.0 and CM2.1) are compared with observed surface temperatures. All-forcing runs include the effects of changes in well-mixed greenhouse gases, ozone, sulfates, black and organic carbon, volcanic aerosols, solar flux, and land cover. Indirect effects of tropospheric aerosols on clouds and precipitation processes are not included. Ensembles of size 3 (CM2.0) and 5 (CM2.1) with all forcings are analyzed, along with smaller ensembles of natural-only and anthropogenic-only forcing, and multicentury control runs with no external forcing. Observed warming trends on the global scale and in many regions are simulated more realistically in the all-forcing and anthropogenic-only forcing runs than in experiments using natural-only forcing or no external forcing. In the all-forcing and anthropogenic-only forcing runs, the model shows some tendency for too much twentieth-century warming in lower latitudes and too little warming in higher latitudes. Differences in Arctic Oscillation behavior between models and observations contribute substantially to an underprediction of the observed warming over northern Asia. In the all-forcing and natural-only forcing runs, a temporary global cooling in the models during the 1880s not evident in the observed temperature records is volcanically forced. El Niño interactions complicate comparisons of observed and simulated temperature records for the El Chichón and Mt. Pinatubo eruptions during the early 1980s and early 1990s. The simulations support previous findings that twentieth-century global warming has resulted from a combination of natural and anthropogenic forcing, with anthropogenic forcing being the dominant cause of the pronounced late-twentieth-century warming. The regional results provide evidence for an emergent anthropogenic warming signal over many, if not most, regions of the globe. The warming signal has emerged rather monotonically in the Indian Ocean/western Pacific warm pool during the past half-century. The tropical and subtropical North Atlantic and the tropical eastern Pacific are examples of regions where the anthropogenic warming signal now appears to be emerging from a background of more substantial multidecadal variability.

scholarly journals Model Thermohaline Trends in the Mediterranean Sea during the Last Years: A Change with Respect to the Last Decades?

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
F. Javier Soto-Navarro ◽  
Francisco Criado-Aldeanueva
Keyword(s):  
Mediterranean Sea ◽  
Sea Level ◽  
20Th Century ◽  
The South ◽  
Steric Sea Level ◽  
Eastern Basin ◽  
The Mediterranean ◽  
Sea Level Trend ◽  
Clear Change

Temperature and salinity outputs from ECCO (years 93–09) and GLORYS (years 03–09) models have been used to compute the thermohaline and steric sea level trends in the surface (0–150 m), intermediate (150 m–600 m), and deep (600 m–bottom) layers of the Mediterranean Sea. Some changes with respect to the second half of the 20th century have been observed: the cooling of the upper waters of the entire eastern basin since 1950 seems to have vanished; the warming of WMDW historically reported for the second half of the last century could have reversed, although there is no agreement between both models at this point (trends of different sign are predicted); the salinification of WMDW reported for the previous decades is not observed in the south-westernmost area in the period 93–09, and a clear change from positive to negative in the steric sea level trend with respect to the period 93–05 is detected due to the sharp decreasing steric sea level of years 02–06.

GLOBAL IMPACT AND UNCERTAINTY ASSESSMENT OF SEA LEVEL RISE BASED ON MULTIPLE CLIMATE MODELS

2018 ◽  
Vol 74 (5) ◽  
pp. I_167-I_174 ◽  
Author(s):  
Koujiro TSUCHIDA ◽  
Makoto TAMURA ◽  
Naoko KUMANO ◽  
Eiji MASUNAGA ◽  
Hiromune YOKOKI
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Climate Models ◽  
Uncertainty Assessment ◽  
Global Impact

scholarly journals Reconciling global mean and regional sea level change in projections and observations

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jinping Wang ◽  
John A. Church ◽  
Xuebin Zhang ◽  
Xianyao Chen
Keyword(s):  
Sea Level ◽  
Climate Models ◽  
Tide Gauge ◽  
Sea Level Change ◽  
Global Network ◽  
Weighted Mean ◽  
Level Change ◽  
Regional Sea Level ◽  
Global Mean ◽  
Regional Sea Level Change

AbstractThe ability of climate models to simulate 20th century global mean sea level (GMSL) and regional sea-level change has been demonstrated. However, the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) and Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) sea-level projections have not been rigorously evaluated with observed GMSL and coastal sea level from a global network of tide gauges as the short overlapping period (2007–2018) and natural variability make the detection of trends and accelerations challenging. Here, we critically evaluate these projections with satellite and tide-gauge observations. The observed trends from GMSL and the regional weighted mean at tide-gauge stations confirm the projections under three Representative Concentration Pathway (RCP) scenarios within 90% confidence level during 2007–2018. The central values of the observed GMSL (1993–2018) and regional weighted mean (1970–2018) accelerations are larger than projections for RCP2.6 and lie between (or even above) those for RCP4.5 and RCP8.5 over 2007–2032, but are not yet statistically different from any scenario. While the confirmation of the projection trends gives us confidence in current understanding of near future sea-level change, it leaves open questions concerning late 21st century non-linear accelerations from ice-sheet contributions.

Interannual Variations and Prediction of Spring Precipitation over China

2018 ◽  
Vol 31 (2) ◽  
pp. 655-670 ◽  
Author(s):  
YuJia You ◽  
Xiaojing Jia
Keyword(s):  
Regression Model ◽  
Yangtze River ◽  
Climate Models ◽  
Seasonal Forecast ◽  
Forecast Skill ◽  
Interannual Variations ◽  
The Yangtze River ◽  
Spring Precipitation ◽  
Coupled Climate Models ◽  
Time Variations

The interannual variations and the prediction of the leading two empirical orthogonal function (EOF) modes of spring (April–May) precipitation over China for the period from 1951 to 2014 are investigated using both observational data and the seasonal forecast made by six coupled climate models. The leading EOF mode of spring precipitation over China (EOF1-prec) features a monosign pattern, with the maximum loading located over southern China. The ENSO-related tropical Pacific SST anomalies in the previous winter can serve as a precursor for EOF1-prec. The second EOF mode of spring precipitation (EOF2-prec) over China is characterized by a dipole structure, with one pole near the Yangtze River and the other one with opposite sign over the Pearl River delta. A North Atlantic sea surface temperature (SST) anomaly dipole in the preceding March is found contribute to the prec-EOF2 and can serve as its predictor. A physics-based empirical (P-E) model is then formulated using the two precursors revealed by the observational analysis to forecast the variations of EOF1-prec and EOF2-prec. Compared to coupled climate models, which have little skill in forecasting the time variations of the two EOF modes, this P-E model can significantly improve the forecast skill of their time variations. A linear regression model is further established using the time series forecast by the P-E model to forecast the spring precipitation over China. Results suggest that the seasonal forecast skill of the spring precipitation over southeastern China, especially over the Yangtze River area, can be significantly improved by the regression model.

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