Interdecadal Trends Research Articles

Inter-America meridional circulation and boreal summer climate

Atmospheric convection across the northern inter-Americas is modulated by trade-wind subsidence and subtropical easterly waves from June to October. Northward migration of the equatorial trough is coupled to the meridional circulation (MC) and surface temperatures above 27ºC. Forming a MC index via S-N height sections of total and anomalous streamfunction, statistical relationships are examined which focus on Jun-Oct season when the South American monsoon is quiescent. Both east Pacific and tropical north Atlantic exhibit cool ocean – dry atmosphere response to an intensified MC. During periods of faster MC, composite humidity is depleted over the Caribbean 10–25 N in conjunction with westerly wind shear, thereby limiting atmospheric convection. The ocean response to intensified MC is evaporative cooling and a deep layer of increased salinity in the Caribbean, that may sustain anomalous air-sea interactions. Long-term trends reveal intensification of the MC in boreal summer: rising over the Amazon, subsiding over the Caribbean, inter-connected by lower and upper airflows. The annually pulsed MC conspires with inter-decadal trends to produce many of the features presented.

The role of Arctic sea ice loss in the interdecadal trends of the East Asian summer monsoon in a warming climate

The East Asian summer monsoon precipitation has exhibited a well-known “southern China flood and northern China drought” pattern in recent decades. The increase in aerosols and warming oceans are recognized as two important forcings that control of the precipitation trends over East Asian land. However, in this study, by using large ensemble simulations from the CMIP6 Polar Amplification Model Intercomparison Project (PAMIP), the influence of Arctic amplification, serving as the prominent feature of global warming, is very important in modulating the East Asian summer precipitation pattern, which is comparable to the influence of sea surface temperature (SST). Additionally, the observed “southern China flood and northern China drought” pattern only exists in July and August, whereas a triple pattern with the precipitation positive anomaly center over Middle China occurs in June. These patterns are closely connected with the regional differences in Arctic sea ice loss from June to July, affected through both the Rossby waves propagating in a weaker westerly jet and the decrease in the large-scale meridional thermal contrast in a warming climate.

Modulation Effect of the Annual Cycle on Interdecadal Warming Trends over the Tibetan Plateau during 1998–2020

Abstract The Tibetan Plateau is a sensitive area of global climate change, where few conventional observations exist. Satellite AMSU-A microwave temperature sounding observations of brightness temperature (TB) are located in the absorption band of oxygen, which is well mixed in the atmosphere, and have microwave frequencies varying from 50.3 to 57.6 GHz. Therefore, AMSU-A TB observations at different sounding channels reflect atmospheric temperatures at different altitudes. In this study, AMSU-A TB observations during 1998–2020 from five polar-orbiting environmental meteorological satellites (POESs) are employed to investigate the interdecadal warming/cooling trends over the Tibetan Plateau. A limb correction is first applied to all AMSU-A channels before using TB observations at all fields of view for examining geographic distributions and differences of global warming/cooling trends. It is found that interdecadal trends of upper-tropospheric warming and stratospheric cooling are stronger over the Qinghai Tibetan Plateau than its eastern plain areas. An interdecadal variation of the annual cycle over the Tibetan Plateau is an important factor for the enhanced tropospheric warming trend. We also applied a different approach of significance testing that is based on counting signs of local trends (sign test) and confirmed that the detected significant local trends were not a result of chance. In addition, high-frequency noise in TB observations with periods smaller than annual and semiannual oscillations do not affect the climate trends of TB very much, but significantly reduced the uncertainty of the TB trends over the Tibetan Plateau.

Interannual modulations in sea level rise over tropical Northwest Pacific in satellite altimeter measurements

The sea level rise (SLR) estimates in tropical Pacific are dominantly influenced by interannual and interdecadal variations in limited data sets such as satellite altimeter measurements. The Sea Level Anomaly (SLA) trends during 1993–2012 (extensively reported) and 1993–2020 significantly differ with substantial weakening during 1993–2020 over tropical Northwest Pacific (NWP; 0–15°N; 120°E −170°E). An ensemble empirical mode decomposition (EEMD) approach is employed to derive residual SLA by removing the high-frequency SLA variations including the interannual and interdecadal variations. The linear trends estimated from residual SLA provides a better estimate for the trends in SLA. The residual trends have greatly reduced the observed differences in SLA trends between 1993–2012 and 1993–2020. Our analysis suggests that it is the interdecadal variations in SLA that caused the weakening of overall trend during 1993–2020. In particular, the interdecadal trend in SLA over NWP is ≈ −1.73 mm year−1, whereas the trends in total and the residual SLA are estimated as 4.26 mm year−1 and 6.32 mm year−1, respectively. Furthermore, it is observed that there is an in-phase connection between the interannual and the interdecadal variations of SLA associated with La Niña compared with El Niño. Therefore, the non-occurrence of La Niña after 2012 to 2020 possibly has contributed for the decreasing trend in interdecadal variations due to its in-phase connection. In short, the complexity of variations in SLA at different timescales over NWP and the Pacific significantly influences the SLA trend estimates.

A Fuzzy Weighted Moving Average to Analyze Actual Warming

This article firstly proposes a fuzzy weighted moving average (FWMA) to compute well for the beginning and end parts. Then, the FWMA is applied to both of the annual anomalies and the annual standardized differences (variance adjusted anomalies) of temperature among the six top nations or regions of cumulative CO₂emissions, Canada and the globe to reveal and compare the interdecadal trends. The related topic of ‘land/sea warming contrast’ was re-analyzed with the FWMA. The main findings are somewhat unexpected as follows: (1) The FWMA curves of anomalies showed that all six nations got warming up stronger than the globe except for India. But the sequence order of the nation’s warming extents in the last decade were much different from those of nation’s cumulative CO₂emissions. (2) The FWMA of the annual standardized differences of temperature showed much better than the annual anomalies. The sequence order of nation’s warming up agreed with that of the cumulative CO₂emissions among the seven nations. In contrary, the globe got warming obviously higher than all the seven nations or regions. The direct reason, in statistics, is that the climatologic variance of the globe is much smaller than all the seven nations, in statistics. (3) The related phenomena of ‘land/sea warming contrast’ appeared only in their anomalies, but disappeared all in the standardized differences. The direct reason is depended upon the around 2 times of difference of the climatologic variance between the land and sea. (4) The FWMA curves for the globe actually much closes to that of the sea than the land.

Long-Term Variability on Suspended Particulate Matter Loads From the Tributaries of the World’s Largest Choked Lagoon

Continental freshwater contributions are the main long-term control on the variability of suspended particulate matter (SPM) concentrations in choked lagoons. The current work aims to assess the seasonal to interdecadal variability in SPM concentrations from Patos Lagoon tributaries, as a case study towards the understanding of tributaries contributions to coastal lagoons. Thus, an interdecadal dataset (1984–2020) was collected in the region of the tributaries of Patos Lagoon (southern Brazil), integrating Landsat series (653 scenes) and in situ measurements. SPM concentrations were estimated from the scenes using a semi-analytical multiwavelength algorithm, applied in the regions of the lower course of the tributaries. Results identified SPM concentrations variability in seasonal scales, enhanced by El Niño Southern Oscillation (ENSO) in interannual time scales, also influencing in interdecadal trends. The seasonal SPM concentration variability reached 50 g.m–3 to each tributary. Higher SPM concentration values occurred from winter to spring, enhanced during El Niño periods and frequently reaching annual means higher than 100 g.m–3. Periods from summer to autumn, however, presented lower SPM concentrations, especially during La Niña periods, when the mean annual SPM concentration remained mostly below 50 g.m–3. Seasonal and interannual (ENSO) forcings combined developed configurations of high input periods (HIP) and low input periods (LIP). During the LIP, the river plumes are limited to their tributary zone of influence and the whole lagoon has reduced SPM concentrations. During the HIP, the river plumes spread over the lagoon sub-environments, and the SPM concentrations of all tributaries reach the estuarine zone and the ocean. Thus, the mentioned natural phenomena influence the river plumes spreading, the SPM concentrations in the lagoon, and the export to the Atlantic Ocean in time scales varying from seasonal to interdecadal.

The Variability of Summer Atmospheric Water Cycle over the Tibetan Plateau and Its Response to the Indo-Pacific Warm Pool

The Tibetan Plateau (TP), atmosphere, and Indo-Pacific warm pool (IPWP) together constitute a regional land–atmosphere–ocean water vapor transport system. This study uses remote sensing data, reanalysis data, and observational data to explore the spatiotemporal variations of the summer atmospheric water cycle over the TP and its possible response to the air-sea interaction in the IPWP during the period 1958–2019. The results reveal that the atmospheric water cycle process over the TP presented an interannual and interdecadal strengthening trend. The climatic precipitation recycle ratio (PRR) over the TP was 18%, and the stronger the evapotranspiration, the higher the PRR. On the interdecadal scale, the change in evapotranspiration has a significant negative correlation with the Pacific Decadal Oscillation (PDO) index. The variability of the water vapor transport (WVT) over the TP was controlled by the dynamic and thermal conditions inside the plateau and the external air-sea interaction processes of the IPWP. When the summer monsoon over the TP was strong, there was an anomalous cyclonic WVT, which increased the water vapor budget (WVB) over the TP. The central and eastern tropical Pacific, the maritime continent and the western Indian Ocean together constituted the triple Sea Surface Temperature (SST) anomaly, which enhanced the convective activity over the IPWP and induced a significant easterly wind anomaly in the middle and lower troposphere, and then generated pronounced easterly WVT anomalies from the tropical Pacific to the maritime continent and the Bay of Bengal. Affected by the air-sea changes in the IPWP, the combined effects of the upstream strengthening and the downstream weakening in the water vapor transport process, directly and indirectly, increased the water vapor transport and budget of TP.

Distinct Interdecadal Change Contrasts Between Summer and Autumn in Latitude‐Longitude Covariability of Northwest Pacific Typhoon Genesis Locations

AbstractThis study investigates seasonality of interdecadal changes in latitude‐longitude covariability of the Northwest Pacific (WNP)‐mean tropical cyclogenesis location (TCGL). It is found that the latitude‐longitude covariability in WNP‐mean TCGL of typhoons has experienced seasonally distinct interdecadal shifts since 1998, weakening in summer and strengthening in autumn. Since significant westward shift of WNP‐mean TCGL exists in both summer and autumn, but robust poleward shift is only detected in autumn. The linchpin of such seasonal difference is the subtropical WNP sea‐surface temperature (SST) warming in the key region of 125°–140°E, 15°–30°N, where numbers of typhoons increase in autumn but not in summer. Two main factors are responsible for the SST warming in the key region: the interdecadal trend of local SST and the Central Pacific La Niña‐teleconnected warming. However, neither condition occurs in summer, highlighting the importance of seasonal difference in climatological background when interpreting climatic changes in typhoons.

Climatological variations in aerosol optical depth and aerosol type identification in Liaoning of Northeast China based on MODIS data from 2002 to 2019

The climatological variations of aerosol optical properties are significant in the study of aerosol effect on regional environment. The MODIS level 2 aerosol optical depth (AOD) products (MOD04/MYD04) at 10 km were used to identify the spatial distribution, interdecadal trends, and aerosol types from 2002 to 2019 in Liaoning province over Northeast China. The highest AOD was distributed in central Liaoning, with a peak value of approximately 0.6 and the fine mode fraction (FMF) was higher in eastern Liaoning about 0.8. The overall AOD for Liaoning in summer was significantly higher than that in other seasons, and the higher AOD values were observed in central Liaoning and the area around Bohai Rim (up to approximately 0.7). The frequency of 0.1 ≤ AOD < 0.2 and 0.2 ≤ AOD < 0.3 was highest in 14 cities of Liaoning. For FMF > 0.8, the cities were categorised into those with an increase frequency of 15% to 20%, and those with a decrease frequency of 5% to 10%. During 2014 to 2019, the interannual variation in AOD in Liaoning exhibited a significant downward trend, with a minimum AOD of approximately 0.25 in 2019. The FMF in Liaoning from 2002 to 2019 exhibited a fluctuating trend around 0.5. The AOD in Liaoning showed an increasing trend from 2002 to 2008 with a maximum of approximately 0.02/year and a clear decreasing trend from 2009 to 2019 of approximately −0.02/year. Maritime aerosol mostly occurred in cities in western Liaoning accounted for 20.58% to 36.52%. Dust aerosol had a considerable influence on central Liaoning accounting for 2.95% to 16.18%. In eastern Liaoning, continental background aerosol accounted for 36.69% to 43.30%. These results revealed the influence of AOD and fine particles on aerosol extinction in Northeast China and provided important information for the climate change in Northeast Asia.

Evaluation of interdecadal trends in sea ice, surface winds and ocean waves in the Arctic in 1980--2019

Evaluation of interdecadal trends in sea ice, surface winds and ocean waves in the Arctic in 1980--2019

Trends in the differences between homogenized ground surface temperature and surface air temperature in China during 1961\u20132016 and its possible causes

Based on the latest series of homogenized ground surface temperature (GST) and surface air temperature (SAT) data for China, this study performed a detailed analysis of the trend of the differences between the two homogenized series in 1961–2016. The differences, referred to as surface–air temperature differences (SATDs) in this study, were separately averaged by month, season, and year. The long-term and spatial changes in the trends of SATDs were investigated. Moreover, interdecadal trend breakpoints were identified to understand the characteristics of trends in fluctuation. The possible influences of precipitation, Pacific Decadal Oscillation (PDO), and global warming on SATDs were also analyzed. The results showed that during the 12 months of a year, only three months, March, April, and May, exhibited increasing trends of station-averaged, monthly mean SATDs while the other nine months exhibited decreasing trends. In addition, the station-averaged annual and seasonal mean SATDs of summer, autumn, and winter all showed significant decreasing trends, while the spring mean SATDs showed a significant increasing trend. The spatial distribution pattern of the linear trends of monthly, seasonal, and annual SATDs in meteorological stations indicated that SATDs had more obviously increasing trends in the northern regions than the southern regions of China. The trends of station-averaged monthly mean SATDs (except for April) and station-averaged seasonal and annual mean SATDs experienced interdecadal breakpoints, fully indicative of obvious interdecadal fluctuations with temporal complexity among China’s SATD trends. By the regression analysis of monthly STADs against simultaneous precipitation, as well as the comparative analysis of their linear trends, we found that both amount of precipitation and the change of precipitation type have important influences on SATDs. The results of convergent cross mapping analysis also revealed the causal effect of precipitation on SATDs.

Interdecadal variability of tropical cyclone genesis frequency in western North Pacific and South Pacific ocean basins

Variability of tropical cyclone (TC) genesis frequency in the western North Pacific and South Pacific ocean basins in the interdecadal scale is studied. It is demonstrated that the TC genesis frequency in these ocean basins experienced an abrupt decrease near the end of the 20th century. The decreased occurrence of TC genesis in the two recent decades is mainly located in the low-latitude regions at the eastern side of the two ocean basins. It is also shown that a significant part of the decreased TC genesis occurred during October to December, i.e. the post-peak season in the western North Pacific ocean basin and the pre-peak season in the South Pacific ocean basin. The interdecadal trend of variation in the TC genesis frequency in these adjacent two ocean basins seems to be mainly due to a common mechanism, i.e. the variation in the atmospheric vorticity. In contrast to the decrease in the total TC genesis, the intense typhoon occurrence frequency experienced an interdecadal increase during the same period. This trend for intense typhoons is particularly clear in the western North Pacific ocean basin. The zonal distribution of the increased number in the intense typhoon occurrence shows a similar pattern to the increased value of the sea surface temperature. It is then suggested that the variation in the intense typhoon occurrence frequency in the western North Pacific ocean basin is related to a change in the La Niña-like sea surface warming pattern.

Opposite interdecadal variations of wintertime haze occurrence over North China Plain and Yangtze River Delta regions in 1980–2013

In this study the interdecadal variations of haze pollution during recent 34 years from 1980 to 2013 over eastern China are investigated. It is found that opposite interdecadal variations of wintertime haze days (WHDs) between the North China Plain region (NCP) and the Yangtze River Delta region (YRD) occurred in this period, i.e., a decreased interdecadal trend of anomalous WHDs appeared in NCP and an increased trend in YRD. Meteorological factors driven the opposite interdecadal variations of anomalous WHDs are revealed. In the phase of interdecadal variations with more WHDs in NCP and less in YRD before 1996, there were weaker northerly winds in the lower troposphere over eastern China accompanied with a weakened Siberia High and mid-latitude westerly jet. The decreased northerly winds are conductive to the local accumulation of air pollutants in NCP and inhibition of air pollutants to be transported from North China to YRD. Consequently, more WHDs appeared in YRD and less in NCP. On the contrary, in the phase of interdecadal variations with less WHDs in NCP and more in YRD after 1996, stronger northerly winds associated with strengthened Siberia High and westerly jet, appeared over eastern China. The increased northerly winds are favorable for the dispersion of air pollutants in NCP and transport more pollutants from North China to the downstream area in YRD, resulting in less WHDs in NCP and more in YRD.

Drought-induced tree growth decline in the desert margins of Northwestern China

Water deficiency is the primary limiting factor for tree growth in arid and semi-arid areas. Droughts associated with rising temperatures have increased in severity and frequency globally over the past few decades, making the trees in the drought-prone sites first be affected by water shortages. However, our understanding of tree growth status in these areas, and of their response to drought, is currently insufficient; especially in the context of global warming. Here, we studied 94 Chinese pine (Pinus tabulaeformis) and 86 spruce (Picea crassifolia) trees from different altitudes [2,100–2400 m above sea level (a.s.l.)] distributed at the desert margins of Northwestern China to explore tree growth and drought response from multiple perspectives using dendroecological approaches. Significant growth decline, across all tree species and altitudes, was detected in response to an interdecadal trend towards a drier climate. Moreover, the extent of tree growth decline, the proportion of affected trees, and the degree of moisture dependence have all tended to increase in each sample site, most likely due to enhanced drought severity and duration in recent decades. The more sensitive and susceptible trees were found at lower elevations (drier sites) and may signify a higher vulnerability to heating-induced drought stress. Tree resistance to drought showed strong negative correlation with drought severity across all sample sites. However, the connection between post-drought tree resilience and drought intensity is weak, perhaps because the samples were all collected from living trees, while those that had died were not sampled. The priority for future work should be to combine surviving and dead trees simultaneously, thus achieving a more representative view of tree resilience to drought; this will improve our knowledge of forest dynamics and even ecosystem succession in these vulnerable and sensitive environments.

Reduced European aerosol emissions suppress winter extremes over northern Eurasia

Winter extreme weather events receive major public attention due to their serious impacts1, but the dominant factors regulating their interdecadal trends have not been clearly established2,3. Here, we show that the radiative forcing due to geospatially redistributed anthropogenic aerosols mainly determined the spatial variations of winter extreme weather in the Northern Hemisphere during 1970–2005, a unique transition period for global aerosol forcing4. Over this period, the local Rossby wave activity and extreme events (top 10% in wave amplitude) exhibited marked declining trends at high latitudes, mainly in northern Eurasia. The combination of long-term observational data and a state-of-the-art climate model revealed the unambiguous signature of anthropogenic aerosols on the wintertime jet stream, planetary wave activity and surface temperature variability on interdecadal timescales. In particular, warming due to aerosol reductions in Europe enhanced the meridional temperature gradient on the jet’s poleward flank and strengthened the zonal wind, resulting in significant suppression in extreme events over northern Eurasia. These results exemplify how aerosol forcing can impact large-scale extratropical atmospheric dynamics, and illustrate the importance of anthropogenic aerosols and their spatiotemporal variability in assessing the drivers of extreme weather in historical and future climate. Anthropogenic aerosol emissions decreased over North America and Europe but increased over Asia since the 1970s. This caused jet stream winds to shift poleward over the Atlantic, decreasing planetary wave activity and partially inhibiting extreme winter weather over northern Eurasia.

A comparison of haze pollution variability in China using haze indices based on observations.

Defining the occurrence and degree of haze pollution (HP) in China has been extremely controversial in recent years. This study elaborates on the meanings of ten most frequently used HP indices based on observation and compares their performance in measuring the HP variability in China concerning the annual cycle, interannual variations and interdecadal trends for the period of 1980-2015. It is found that these indices exhibit a high consistency in South China, while apparent discrepancies exist in North Chinam, Sichuan Basin and the Yangtze River Delta. Observed surface PM2.5 concentration is utilized to assess the performance of the ten HP indices. Results show that some of these indices can well capture primary features of the HP in some specific area, only these defined by a daily averaged value or 14:00 single threshold value have relatively good performance in the whole Eastern China. Such four indices (HPI2/HPI3/HPI4/HPI5) exhibit high consistence in depicting spatial-temporal variations (from annual cycle to interannual variability) of surface PM2.5 concentration over China, meaning they can highlight the significance of high aerosol concentration in triggering HP events. Moreover, further analysis suggest that the contributions of weather conditions to the occurrence and degree of the HP is becoming more in China, especially in the NC, SCB, YRD regions. These results provide useful guidance for monitoring variations of the HP in China and for making long-term environmental regulatory and controlling policy.

Spatiotemporal distribution of landing tropical cyclones and disaster impact analysis in coastal China during 1990–2016

To assess the impact of tropical cyclones (hereafter as TCs) along the southeast coast of China, this study analyzed the spatiotemporal variation of TC-induced disasters, interannual variability of disasters and their intensities by using the data during 1990–2016. Economic losses were calculated by using the three disaster indices: based on the area of affected crops, number of collapsed buildings, and direct economic losses. Entropy method was used to improve the comprehensive disaster index impact model for the first time and use it in tropical cyclone disaster assessment. It is found that there was no obvious interannual variation in the total number of TCs affecting China, although low-intensity TCs decreased and high-intensity TCs increased significantly. Conditions in 2015 were used as a reference to convert the loss index. Results show that 1997 was a turning point in the combined disaster index. Moreover, interannual fluctuations were severe in the former period, but lower in the latter and smoother. According to the economic calculations from the three disaster indices, the economic value of collapsed buildings and affected crops tended to decrease over the interdecadal period, whereas there was an obvious increasing interdecadal trend in direct economic losses. This result indicates that the tropical cyclone induced disasters has gradually shifted from primary industry to secondary and tertiary industry. Results from this paper will provide science based support to policy makers to reduce the economic losses in natural disasters.

Long-Term Spatiotemporal Variation in the Juvenile Fish Assemblage of the Tramandaí River Estuary (29°S) and Adjacent Coast in Southern Brazil

Based on a set of intermittent and seasonal data, covering a discontinuous 21-year period (1995 to 2016) and using a standard beach seine with replicates at several collection points inside the Tramandai River estuary (TRE) and outside in the marine adjacent coastal area (MACA), we evaluated connectivity between TRE and MACA and the spatiotemporal variations of fish associations. In the TRE (405 samples; 42,987 individuals) 55 species were captured. In the MACA (297 samples; 54,295 individuals) 41 species were captured. After data standardization the expected richness of the TRE [E(S) = 18.2] was significantly greater (p <0.05) than that of the MACA [E(S) = 14.4]. The fish association structure and distribution patterns in TRE and MACA are dynamic and interconnected but quite different in terms of species composition, especially due to the influence of local salinity. The TRE association is richer in a number of species but numerically dominated by marine estuarine-dependent juveniles. Freshwater species may eventually be carried in by heavy rains, bringing pulses of species richness. The MACA association is represented by a few typical marine species in addition to a couple of estuarine-related transient species who uses the surf-zone as a passageway to enter the estuaries. Even if there is a higher percentage of common species reported (30 out of 66), the monthly average Jaccard Index of similarity (JI = 28%) and the monthly average Percent Similarity Index (PSI=30%) was low, suggesting that the shallow water functional connectivity between MACA and TRE are represented by few species that occur equally in abundance in both environments. Juvenile of two species of mullets (Mugil liza and Mugil curema) add up to more than 70% of the total catches in both environments. The hypothesized signal of decadal diversity and abundance reduction seems to be muffled by seasonal environmental fluctuation revealing that fish assemblage of MACA and TRE are highly resilient through the years. The only observed interdecadal trend was the reduction in abundance of juvenile M. liza that seems to parallel the reduction in abundance of the adults fishing stocks in southern Brazil.

Regional and Seasonal Characteristics of the Recent Expansion of the Tropics

In recent decades, the subtropical edges of Earth’s Hadley circulation have shifted poleward. Some studies have concluded that this observed tropical expansion is occurring more rapidly than predicted by global climate models. However, recent modeling studies have shown that internal variability can account for a large fraction of the observed circulation trends, at least in an annual-mean, zonal-mean framework. This study extends these previous results by examining the seasonal and regional characteristics of the recent poleward expansion of the Hadley circulation using seven reanalysis datasets, sea level pressure observations, and surface wind observations. The circulation has expanded the most poleward during summer and fall in both hemispheres, with more zonally asymmetric circulation trends occurring in the Northern Hemisphere (NH). The seasonal and regional characteristics of these observed trends generally fall within the range of trends predicted by climate models for the late twentieth and early twenty-first centuries, and in most cases, the magnitude of the observed trends does not exceed the range of interdecadal trends in the models’ control runs, which arise exclusively from internal variability. One exception occurs during NH fall when large observed poleward shifts in the atmospheric circulation over the North Atlantic sector exceed nearly all trends projected by models. While most recent NH circulation trends are consistent with a change in phase of the Pacific decadal oscillation (PDO), the observed circulation trends over the North Atlantic instead reflect 1) large natural variability unrelated to the PDO and/or 2) a climate forcing (or the circulation response to that forcing) that is not properly captured by models.

Interdecadal trends in composition, density, size, and mean trophic level of fish species and guilds before and after coastal development in the Mexican Caribbean

This study explores the possible influence of human coastal development (before and after) and protected area status (within and outside a marine protected area, MPA) on composition, density, and maximum size of fish species and guilds, including mean trophic level of the fish community, in four localities of the Yucatan Peninsula, Mexican Caribbean. Reef fish density, maximum length, species composition, and trophic guilds were recorded by SCUBA belt transects and stationary points in fore reef and lagoon reef areas at decadal intervals (1995–1998, 2006–2010, 2014–2015). Mean density of most species and guilds decreased significantly through the years, as also did mean trophic level of the fish community. Some fish species increased in length. Fish density for many species was larger outside than inside the MPA in 1995–1998; however, the difference tended to disappear in the more recent decades, which reflects either a positive effect of the MPA, or a detrimental effect of coastal development in the non-protected area. Nevertheless, the overall negative trends suggest a regional or global rather than a local cause.