Natural Climate Variability Research Articles

Long-term ecological trajectories of a disturbed Mediterranean coastal lagoon (Biguglia lagoon): Ecosystem-based approach and considering its resilience for conservation?

Coastal lagoons are subjected to ever-increasing direct or indirect anthropic pressures and are inexorably deteriorating with serious issues regarding their resilience. In this paper, we assessed the functioning and evolution of the highly disturbed Biguglia coastal lagoon (Mediterranean Sea, Corsica) through an ecosystem-based approach (EBA), using multiple biotic and abiotic proxies (hydro-climatic context and eutrophication), considering its connectivity to sea and watershed and biological compartments (macrophytes, phytoplankton, and invasive species) and taking into account human influence (management actions and fishing activities). The aim of this work is firstly to provide a comprehensive analysis of its long-term (2000–2021) ecological evolution trajectory and then, based on these results, to anticipate management strategies for supporting its conservation and restoration, and the maintenance of ecosystem services it offers. Results revealed that while the lagoon showed these days a good capacity to recover after disturbance and absorb change, it recently exhibited considerable changes in its phytoplankton community composition, developed an increased susceptibility to biological invasion, and experienced a drastic reduction in fish stocks. The major interannual variations of the mean salinity, strongly dependent on management interventions beyond natural climatic variability, summarized this instability. In the future, the lagoon may no longer be able to cope with even small disturbances, which could then be sufficient to reach a breakpoint and tip the system permanently into undesired/degraded states. We demonstrated that local and punctual management actions are not always beneficial for the entire ecosystem or even detrimental in some instances. Such a retrospective ecosystem-based approach is fundamental for producing the holistic insights required to implement efficient integrated ecosystem management. This further helps enhance lagoon resilience and hence preserve its ecosystem services in the context of increasing global changes. Such lessons are useful anywhere for comparable ecosystems.

From Stamps to Parabolas.

I am a child of Sputnik, the satellite launched by the Soviet Union in 1957. That event created opportunities for me to escape the horrors of apartheid by emigrating from South Africa to the United States. There, fortuitously, I was given excellent opportunities to explore how an interplay between the waves and currents influences climate variability, from interannual El Niño events to millennial ice ages. During my career, I also witnessed intriguing facets of the interactions between the profoundly different worlds of science and of human affairs. Up to 1957, El Niño was welcomed as a blessing, but by 1982 it had become a curse-not because it changed, but because our human activities are making us vulnerable to natural climate variability. We have learned to cope admirably with the occasional failures of the Indian monsoons; the resultant famines are not as calamitous as they once were. What guidance does that limited success provide for a response to global warming, a climate change we humans are inducing? This article briefly summarizes how my career as a geoscientist brought me to the conclusion that a strategy to promote responsible stewardship of planet Earth should be based on love rather than fear. We can only love what we know, so warnings of imminent gloom and doom should be complemented with efforts to make everyone aware of the wonders of our amazing planet-the only one in the universe known to be habitable.

Current Siberian heating is unprecedented during the past seven millennia

The Arctic is warming faster than any other region on Earth. Putting this rapid warming into perspective is challenging because instrumental records are often short or incomplete in polar regions and precisely-dated temperature proxies with high temporal resolution are largely lacking. Here, we provide this long-term perspective by reconstructing past summer temperature variability at Yamal Peninsula – a hotspot of recent warming – over the past 7638 years using annually resolved tree-ring records. We demonstrate that the recent anthropogenic warming interrupted a multi-millennial cooling trend. We find the industrial-era warming to be unprecedented in rate and to have elevated the summer temperature to levels above those reconstructed for the past seven millennia (in both 30-year mean and the frequency of extreme summers). This is undoubtedly of concern for the natural and human systems that are being impacted by climatic changes that lie outside the envelope of natural climatic variations for this region.

Influences of El Niño-Southern Oscillation on summertime ozone pollution over central-eastern China during 1950-2014.

Summertime ozone pollution has become increasingly severe over many parts of China in recent years. Due to lack of historical ozone observations, few studies have analyzed the linkage between natural climate variability and ozone levels for a long time series. This study uses the simulation datasets from CMIP6 to explore the effects of El Niño-Southern Oscillation (ENSO) on summertime (June/July/August) surface ozone concentrations in central-eastern China (CEC; 20°N-42°N, 100°E-123°E) during the period of 1950-2014. Our results show that, after excluding the emission-related trend, the detrended summertime daily mean surface ozone concentrations averaged over CEC in El Niño years (30.69ppb) are higher than those in La Niña events (29.34ppb). Compared to the summertime mean ozone of 1950-2014 (30.25ppb), the maximum anomalies in CMIP6 are 2.88ppb (9.52% higher) and - 5.52ppb (18.25% lower) in El Niño and La Niña years, respectively. In addition, the summertime MDA8 ozone of CEC is significantly correlated with the central-eastern equatorial Pacific SST (5°N-5°S, 170°W-120°W) (R = 0.29, P-value = 0.02). Such ozone increases/declines in El Niño/La Niña years are also found in satellite observations of OMI ozone. The results show that the ENSO affects the large-scale circulations over central-eastern China, which regulate the regional atmospheric stability and meteorological conditions (including horizontal wind fields, geopotential height, vertical velocity, surface air temperature, and precipitation) to influence the efficiency of ozone photochemical formation and transport. Our study makes better estimation and attribution of future surface ozone pollution in China.

Unveiling four decades of intensifying precipitation from tropical cyclones using satellite measurements

Increases in precipitation rates and volumes from tropical cyclones (TCs) caused by anthropogenic warming are predicted by climate modeling studies and have been identified in several high intensity storms occurring over the last half decade. However, it has been difficult to detect historical trends in TC precipitation at time scales long enough to overcome natural climate variability because of limitations in existing precipitation observations. We introduce an experimental global high-resolution climate data record of precipitation produced using infrared satellite imagery and corrected at the monthly scale by a gauge-derived product that shows generally good performance during two hurricane case studies but estimates higher mean precipitation rates in the tropics than the evaluation datasets. General increases in mean and extreme rainfall rates during the study period of 1980–2019 are identified, culminating in a 12–18%/40-year increase in global rainfall rates. Overall, all basins have experienced intensification in precipitation rates. Increases in rainfall rates have boosted the mean precipitation volume of global TCs by 7–15%/year, with the starkest rises seen in the North Atlantic, South Indian, and South Pacific basins (maximum 59–64% over 40 years). In terms of inland rainfall totals, year-by-year trends are generally positive due to increasing TC frequency, slower decay over land, and more intense rainfall, with an alarming increase of 81–85% seen from the strongest global TCs. As the global trend in precipitation rates follows expectations from warming sea surface temperatures (11.1%/°C), we hypothesize that the observed trends could be a result of anthropogenic warming creating greater concentrations of water vapor in the atmosphere, though retrospective studies of TC dynamics over the period are needed to confirm.

Livelihood Vulnerability Index: Gender Dimension to Climate Change and Variability in REDD + Piloted Sites, Cross River State, Nigeria

Vulnerability to climate change and variability impacts has been identified as a major cog in the wheel of both livelihood and resilience, particularly in vulnerable groups in rural areas. This study aims to assess genders’ vulnerability dimension to climate change and variability in REDD + (Reducing Emission from Deforestation and Forest Degradation+) piloted site/clusters, Cross River State, Nigeria. Data were proportionately collected from selected 200 respondents on gender disaggregated level using questionnaires. The assessment adopted the sustainable livelihood approach (livelihood vulnerability index) and compared the results with the IPCC vulnerability standard of exposure, sensitivity and adaptive capacity weighted mean. The results revealed a significant difference in the vulnerability dimension of both women and men disaggregated levels (LVI: men 0.509, women 0.618). The women category was more vulnerable to six out of seven major components of LVI assessed: (livelihood strategies (0.646), social networks (0.364), water (0.559), health (0.379), food and nutrition (0.507), and natural hazards and climate variability (0.482), while men only vulnerable to socio-demographic major component (0.346). Vulnerability indices also showed women to be more exposed (0.482), and sensitive (0.489) with the least adaptive capacities (0.462) to the climate change and variability impacts. Overall, on the IPCC-LVI index, women are more vulnerable (0.0098) to climate change and variability impacts than men (−0.0093). The study recommends that the women’s category resilience and adaptive capacity should be empowered in adaptation projects in climate change such as REDD + (Reducing Emissions from Deforestation and Forest Degradation+) to reduce their vulnerability to impacts of climate change and variability in the context of exposure, sensitivity, and adaptive capacities. This will be instrumental in formulating policies to address the specific needs of gender categories in reducing vulnerability to climate change and variability. This pragmatic approach may be used to monitor gender vulnerability dimension, and livelihood enhancement and evaluate potential climate change adaptation programs. Additionally, the introduction of IPCC-LVI as a baseline instrument will enhance information on gender resilience and adaptive capacity for policy effectiveness in a data-scarce region particularly Africa.

Tropical cyclone activity in the Solomon Islands region: Climatology, variability, and trends

AbstractThis study examines the climatology, variability, and trends of tropical cyclones (TCs) affecting the Solomon Islands (SI) territory, in the wider southwest Pacific (SWP), using the South Pacific Enhanced Archive for Tropical Cyclones (SPEArTC) database. During the period 1969/1970–2018/2019, 168 TCs were recorded in the SI territory. A cluster analysis is used to objectively partition these tracks into three clusters of similar TC trajectories to obtain better insights into the effects of natural climate variability, particularly due to the El Niño–Southern Oscillation (ENSO) phenomenon, which otherwise is not very apparent for TCs when considered collectively in the SI region. We find that TCs in clusters 1 and 3 show enhanced activity during El Niño phase, whereas TCs in cluster 2 are enhanced during La Niña and neutral phases. In addition to being modulated by ENSO, TCs in clusters 2 and 3 show statistically significant modulation at an intraseasonal timescale due to the Madden–Julian Oscillation (MJO) phenomenon. There are also some indications through sophisticated Bayesian modelling that TCs in clusters 2 and 3 are slightly influenced by the Interdecadal Pacific Oscillation (IPO). These results can have substantial implications for cluster‐specific development of TC prediction schemes for the SI region.

Volcanic stratospheric sulfur injections and aerosol optical depth during the Holocene (past 11 500 years) from a bipolar ice-core array

Abstract. The injection of sulfur into the stratosphere by volcanic eruptions is the dominant driver of natural climate variability on interannual to multidecadal timescales. Based on a set of continuous sulfate and sulfur records from a suite of ice cores from Greenland and Antarctica, the HolVol v.1.0 database includes estimates of the magnitudes and approximate source latitudes of major volcanic stratospheric sulfur injection (VSSI) events for the Holocene (from 9500 BCE or 11 500 years BP to 1900 CE), constituting an extension of the previous record by 7000 years. The database incorporates new-generation ice-core aerosol records with a sub-annual temporal resolution and a demonstrated sub-decadal dating accuracy and precision. By tightly aligning and stacking the ice-core records on the WD2014 chronology from Antarctica, we resolve long-standing inconsistencies in the dating of ancient volcanic eruptions that arise from biased (i.e., dated too old) ice-core chronologies over the Holocene for Greenland. We reconstruct a total of 850 volcanic eruptions with injections in excess of 1 teragram of sulfur (Tg S); of these eruptions, 329 (39 %) are located in the low latitudes with bipolar sulfate deposition, 426 (50 %) are located in the Northern Hemisphere extratropics (NHET) and 88 (10 %) are located in the Southern Hemisphere extratropics (SHET). The spatial distribution of the reconstructed eruption locations is in agreement with prior reconstructions for the past 2500 years. In total, these eruptions injected 7410 Tg S into the stratosphere: 70 % from tropical eruptions and 25 % from NH extratropical eruptions. A long-term latitudinally and monthly resolved stratospheric aerosol optical depth (SAOD) time series is reconstructed from the HolVol VSSI estimates, representing the first Holocene-scale reconstruction constrained by Greenland and Antarctica ice cores. These new long-term reconstructions of past VSSI and SAOD variability confirm evidence from regional volcanic eruption chronologies (e.g., from Iceland) in showing that the Early Holocene (9500–7000 BCE) experienced a higher number of volcanic eruptions (+16 %) and cumulative VSSI (+86 %) compared with the past 2500 years. This increase coincides with the rapid retreat of ice sheets during deglaciation, providing context for potential future increases in volcanic activity in regions under projected glacier melting in the 21st century. The reconstructed VSSI and SAOD data are available at https://doi.org/10.1594/PANGAEA.928646 (Sigl et al., 2021).

The 852/3 CE Mount Churchill eruption: examining the potential climatic and societal impacts and the timing of the Medieval Climate Anomaly in the North Atlantic region

Abstract. The 852/3 CE eruption of Mount Churchill, Alaska, was one of the largest first-millennium volcanic events, with a magnitude of 6.7 (VEI 6) and a tephra volume of 39.4–61.9 km3 (95 % confidence). The spatial extent of the ash fallout from this event is considerable and the cryptotephra (White River Ash east; WRAe) extends as far as Finland and Poland. Proximal ecosystem and societal disturbances have been linked with this eruption; however, wider eruption impacts on climate and society are unknown. Greenland ice core records show that the eruption occurred in winter 852/3 ± 1 CE and that the eruption is associated with a relatively moderate sulfate aerosol loading but large abundances of volcanic ash and chlorine. Here we assess the potential broader impact of this eruption using palaeoenvironmental reconstructions, historical records and climate model simulations. We also use the fortuitous timing of the 852/3 CE Churchill eruption and its extensively widespread tephra deposition of the White River Ash (east) (WRAe) to examine the climatic expression of the warm Medieval Climate Anomaly period (MCA; ca. 950–1250 CE) from precisely linked peatlands in the North Atlantic region. The reconstructed climate forcing potential of the 852/3 CE Churchill eruption is moderate compared with the eruption magnitude, but tree-ring-inferred temperatures report a significant atmospheric cooling of 0.8 ∘C in summer 853 CE. Modelled climate scenarios also show a cooling in 853 CE, although the average magnitude of cooling is smaller (0.3 ∘C). The simulated spatial patterns of cooling are generally similar to those generated using the tree-ring-inferred temperature reconstructions. Tree-ring-inferred cooling begins prior to the date of the eruption suggesting that natural internal climate variability may have increased the climate system's susceptibility to further cooling. The magnitude of the reconstructed cooling could also suggest that the climate forcing potential of this eruption may be underestimated, thereby highlighting the need for greater insight into, and consideration of, the role of halogens and volcanic ash when estimating eruption climate forcing potential. Precise comparisons of palaeoenvironmental records from peatlands across North America and Europe, facilitated by the presence of the WRAe isochron, reveal no consistent MCA signal. These findings contribute to the growing body of evidence that characterises the MCA hydroclimate as time-transgressive and heterogeneous rather than a well-defined climatic period. The presence of the WRAe isochron also demonstrates that no long-term (multidecadal) climatic or societal impacts from the 852/3 CE Churchill eruption were identified beyond areas proximal to the eruption. Historical evidence in Europe for subsistence crises demonstrate a degree of temporal correspondence on interannual timescales, but similar events were reported outside of the eruption period and were common in the 9th century. The 852/3 CE Churchill eruption exemplifies the difficulties of identifying and confirming volcanic impacts for a single eruption, even when the eruption has a small age uncertainty.

Contributions of internal climate variability in driving global and ocean temperature variations using multi-layer perceptron neural network

Roles of internal climate variabilities regulating global and ocean temperature changes is a hot but complex issue of scientific concern, influencing the comprehensive policy-making in response to global and regional warming. In this study, the time series of monthly global and ocean mean surface temperature (GST and OST, respectively) since 1866 is successfully reconstructed via natural and anthropogenic forcing factors and internal climate variability by using a Multi-Layer Perceptron (MLP) neural network technique. The MLP demonstrates prominent monthly GST and OST reconstruction skills on both interannual and annual time scales. Most of the warming in GST and OST since 1866 is found to be attributable to anthropogenic forcing, while the multidecadal and interannual GST and OST variations are considerably dominated by Atlantic Multidecadal Oscillation (AMO). Internal climate variabilities like Interdecadal Pacific Oscillation (IPO) can amplify the GST and OST changes and explain the global warming slowdown since 1998. Southern Oscillation Index (SOI) performs a similar role as IPO but to a lesser extent. Changes in OST caused by solar forcing are more considerable than those in GST. Moreover, the ‘biased warmth’ during the Second World War is successfully reconstructed in MLP. AMO and IPO can explain most annual and even sub-annual temperature variations during this period, offering an explanation for the existence of this abnormal warm period other than that it was entirely caused by instrumental errors. The generally high accuracy of reconstructions on interannual and annual time scales can enhance the ability to monitor the prompt feedback of specific external radiative forcings and internal variabilities to changes in climate.

Utility of Dendrochronology Crossdating Methods in the Development of Arctic Coralline Red Algae Clathromorphum compactum Growth Increment Chronology for Sea Ice Cover Reconstruction

Paleoclimate and paleoenvironmental reconstructions from increment-yielding archives strongly depend on precise age models. Like bivalves, corals, trees, and speleothems, the coralline alga Clathromorphum compactum produces annual growth increments and shows considerable promise as an environmental archive for arctic and subarctic regions. Though their growth increment widths correlate with temperature and sea ice cover in high Arctic regions, existing timeseries have not been crossdated. In fact, previous studies have shown a lack of inter-sample correlation in non-crossdated timeseries suggesting possible age model dating errors. Here, we use dendrochronology crossdating techniques and COFECHA software to ensure and validate synchrony between C. compactum timeseries (<141 years) from three specimens collected near Beechey Island, Nunavut, Canada. Results showed that non-crossdated timeseries constructed by four coralline red algae researchers using annual increments of the same C. compactum samples were highly variable and showcase the likelihood of dating errors in non-crossdated timeseries. Crossdating improved inter-series correlations, and correlations to sea ice-related records, suggesting that at least three crossdated timeseries are required to isolate paleoclimate signals. Our findings suggest that future reconstructions with C. compactum should employ crossdating techniques to reduce dating errors and allow for more precise climate reconstructions.Lay AbstractLong-term environmental records provide a critical baseline to examine how humans have impacted Earth’s natural climate. An important piece to consider is sea ice’s role in natural climate variability because its brightness limits warming by reflecting solar irradiation back to space. However, instrumental records of sea ice rarely extend beyond the early satellite era (late 1970s), limiting our understanding of how sea ice affects natural climate variability in the preindustrial era. A lack of historical baseline prompted the development of sea ice proxies, including the long-lived marine alga, Clathromorphum compactum. Similar to tree-rings, C. compactum produces a new mineralized layer each year, and layer thicknesses have been shown to respond to sea ice cover, making them useful to record long-term sea ice variability. However, a recent study showed that records had replicability problems, maybe due to dating mistakes. Our study applies tree-ring dating methods (dendrochronology) to match annual algal growth layers across algal specimens. Results showed that these new methods reduced dating errors, allowing for more precise past sea ice cover reconstructions.

Insight into summer drought in southern Italy: palaeohydrological evolution of Lake Pergusa (Sicily) in the last 6700 years

AbstractThe Sicily region (central Mediterranean) is at high risk of drying and desertification caused by current warming and land management. The aim of this study is to place current climatic changes within the past trajectories and natural climatic variability of the Holocene. For this we re‐examine a sediment core retrieved at Lake Pergusa covering the last ca. 6700 years. A multiproxy investigation, and in particular the oxygen isotope composition of lacustrine carbonate (δ18Oc), allowed us to reconstruct decadal‐ to centennial‐scale hydrological changes. The wettest period occurred between ca. 6700 and 6000 cal a bp. The δ18Oc record indicates a new period of wetter conditions between ca. 3700 and 2400 cal a bp. In particular, a δ18Oc minimum between 2850 and 2450 cal a bp overlaps with the period of the ‘Great Solar Minimum’ and corresponds to a dramatic reduction of arboreal pollen (AP%) and to an increase in synanthropic pollen, marking the onset of Greek colonization in the region. The longest driest interval corresponds to the Medieval Climate Anomaly, whereas the highest δ18Oc values are recorded in the last 150 years. The trend of the last 3000 years suggests that, considering future climate projections, the area will experience unprecedented drying exacerbated by human impact.

Perceptions and attitudes towards climate change in fishing communities of the Sudd Wetlands, South Sudan.

The Sudd in South Sudan, formed by the White Nile’s Baḥr al-Jabal section, is one of the largest and most important wetlands in the world. Communities in the region almost exclusively depend on fisheries for food and livelihoods. Although threatened by over-exploitation and habitat changes, fish populations are also affected by climate change. Using semi-structured questionnaires, we assessed fisherfolk’s opinions of how recent variation in climate affected their livelihoods and the environment. Fisherfolk perceived that climate had changed in the past decade and were negatively impacted by this. Interviewees reported average higher temperatures, a greater frequency of floods and droughts, unpredictable timing of seasons, and erratic rainfall. Destruction of fishing villages/camps, loss and damage of fishing equipment, shifts in the fishing calendar, reduction of fish trade, and fish catch declines as well as psycho-social problems were given as the major consequences of climate change. Causes of climate change and variability were perceived to be linked to uncontrolled harvest of forest resources, anger of God and ancestors, and natural variability in climate. Most respondents expressed a desire to adopt more responsible behavior such as planting trees and establishing community nurseries, being educated on climate change risks, and sustainable fisheries management. Our results show that fisherfolk in the Sudd are troubled by climate change impacts on their livelihoods and on fish populations. In South Sudan, climate change has been reported from hydroclimatological data but concrete impacts on people remain largely unknown and of little concern because of recent wars and the poor economy. Our study provides an example of how fisherfolks’ local ecological knowledge (LEK) can be used as an early warning system of the negative impacts on livelihoods and fish populations and support adaptation to the changing climate.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10113-022-01928-w.

Public Policy of the Republic of Guinea

Under the UNFCCC, climate change is defined as climate change that is attributed directly or indirectly to human activity, modifies global atmospheric composition, and adds to the natural variability of climate observed over comparable time periods. This definition is different from that of the IPCC, which says that climate change refers to any change in climate whether it is human or natural. Vulnerability is the degree to which a system is sensitive to the adverse effects of climate change, including climate variability and its extremes. It is a function of the nature, magnitude and rate of the climate change to which the system under consideration is exposed, the sensitivity of this system and its capacity for adaptation.Vulnerability is thus a function of physical and socio-economic characteristics. One of the characteristics of Guinea is the very marked contrast between the different natural regions in terms of socio-economic conditions, population density, rainfall and hydrological regimes, relief, soil distribution, and wildlife. Flora. The populations of these different zones are to varying degrees, exposed to poverty (53% of the population live below the poverty line), to variability and to climate change (droughts, floods, extreme temperatures, disruption of the rainfall regime, etc.).Guinea, as a party, is receiving support so that, like other least developed countries, lacking the capacity to address the proven vulnerability of its resources and socio-economic groups, it is preparing its NAPA. This work falls within this framework and aims to outline urgent and immediate adaptation measures, any delay of which will cause increased vulnerability or increased cost. The document produced is the National Action Plan for Adaptation to Climate Change PANA. The document produced is structured as a foreword by His Excellency the Minister of Agriculture, Livestock, Environment, Waters and Forests, an introduction, five chapters, a conclusion, a list of bibliographical references and appendices.The first chapter provides the national context for NAPA: physical presentation, socio-economic aspects, and environmental constraints, institutional and legal framework.The second chapter deals with the NAPA framework. It outlines the climatic risks identified during the regional public consultation workshops, describes their consequences on means and modes of existence, and indicates their trend in the four natural regions. It establishes the vulnerability of socio-economic groups presents the predictable trends of each climate risk and ranks them in order of sensitivity. It shows the integration of NAPA into sectoral development policies and synergy with other multilateral environmental agreements. Finally, this chapter briefly presents the purpose, objectives and constraints of the implementation of the NAPA.The third chapter deals with basic needs for adaptation. Several options have been proposed by natural region. The in-depth analysis of these has allowed them to be grouped into thirteen adaptation options that have been weighted, prioritized and ranked according to six criteria including adaptability, coherence with local development plans, synergy with multilateral environmental agreements. . Keywords: Public Policy, Republic of Guinea DOI: 10.7176/RHSS/12-11-03 Publication date: June 30 th 2022

Coral‐Based Sea Surface Salinity Reconstructions and the Role of Observational Uncertainties in Inferred Variability and Trends

AbstractClimate observations in much of the tropical oceans are scarce during most of the 20th century, so paleoclimate proxies are needed to understand the full range of natural climate variability. Past proxy studies have focused primarily on sea surface temperatures, but there are comparatively few salinity reconstructions. Such reconstructions can extend our understanding of hydroclimate across the tropical oceans, including variability in precipitation, evaporation, and ocean circulation. Here we compile a network of salinity‐sensitive coral δ18O records, then apply a reduced‐space method based on empirical orthogonal function analysis to reconstruct annual tropical salinity anomalies over the 20th century. A comparison of surface salinity data sets, including reanalyzes (SODA2/3, Ocean ReAnalysis System 5 (ORAS5), Global Ocean Data Assimilation System) and objective analyses (Institute of Atmospheric Physics (IAP), EN4, Delcroix), show large discrepancies in the spatial structure, temporal evolution, and importance of the leading modes of variability. Two salinity data sets, IAP and ORAS5, are retained for climate reconstruction. Our coral‐based salinity reconstructions reveal significant long‐term trends over the 20th century, which are likely associated with hydrological cycle intensification and possibly a weakening of the Walker Circulation. These reconstructions also capture the spatial and temporal patterns of salinity anomalies associated with the El Niño‐Southern Oscillation, Interdecadal Pacific Oscillation, and Atlantic Multidecadal Oscillation. Ultimately, this approach can enhance our understanding of tropical hydroclimate prior to the observational era.

Documenting the Evolution of a Southern California Coastal Lagoon during the Late Holocene

Coastal wetlands are declining globally, and although wetland restoration looks to offset these losses, its success relies on anticipating environmental response to external forces. The purpose of this study is to investigate the sedimentological record of Los Peñasquitos Lagoon to determine the processes that drive environmental transitions in a Southern California coastal wetland. For this project, we analyze three sediment cores from the wetland for grain size, total organic matter, and shell assemblages to reconstruct environmental change over the past ~4000 years. From the results, we find that the lagoon was initially an open embayment that persisted for >2000 years; however, at ~1000 cal yrs BP, a short-lived wet climatic period triggered a fluvial deltaic progradation at the head of the lagoon. As the wet period ended and drier conditions returned, the delta began to retreat, and the lagoon infilled as the estuarine mouth bar was permanently established. The permanent establishment of the mouth bar resulted in a transition to a marsh-dominated environment throughout the wetland. Ultimately, these environmental transitions were driven by climate variability, although evidence of human impacts was observed more recently in the record. Therefore, future restoration efforts must consider both natural climatic variability and anthropogenic influences if they intend to sustain coastal wetlands.

Climatic, weather, and socio-economic conditions corresponding to the mid-17th-century eruption cluster

Abstract. The mid-17th century is characterized by a cluster of explosive volcanic eruptions in the 1630s and 1640s, climatic conditions culminating in the Maunder Minimum, and political instability and famine in regions of western and northern Europe as well as China and Japan. This contribution investigates the sources of the eruptions of the 1630s and 1640s and their possible impact on contemporary climate using ice core, tree-ring, and historical evidence but will also look into the socio-political context in which they occurred and the human responses they may have triggered. Three distinct sulfur peaks are found in the Greenland ice core record in 1637, 1641–1642, and 1646. In Antarctica, only one unambiguous sulfate spike is recorded, peaking in 1642. The resulting bipolar sulfur peak in 1641–1642 can likely be ascribed to the eruption of Mount Parker (6∘ N, Philippines) on 26 December 1640, but sulfate emitted from Komaga-take (42∘ N, Japan) volcano on 31 July 1641 has potentially also contributed to the sulfate concentrations observed in Greenland at this time. The smaller peaks in 1637 and 1646 can be potentially attributed to the eruptions of Hekla (63∘ N, Iceland) and Shiveluch (56∘ N, Russia), respectively. To date, however, none of the candidate volcanoes for the mid-17th century sulfate peaks have been confirmed with tephra preserved in ice cores. Tree-ring and written sources point to cold conditions in the late 1630s and early 1640s in various parts of Europe and to poor harvests. Yet the early 17th century was also characterized by widespread warfare across Europe – and in particular the Thirty Years' War (1618–1648) – rendering any attribution of socio-economic crisis to volcanism challenging. In China and Japan, historical sources point to extreme droughts and famines starting in 1638 (China) and 1640 (Japan), thereby preceding the eruptions of Komaga-take (31 July 1640) and Mount Parker (4 January 1641). The case of the eruption cluster between 1637 and 1646 and the climatic and societal conditions recorded in its aftermath thus offer a textbook example of difficulties in (i) unambiguously distinguishing volcanically induced cooling, wetting, or drying from natural climate variability and (ii) attributing political instability, harvest failure, and famines solely to volcanic climatic impacts. This example shows that while the impacts of past volcanism must always be studied within the contemporary socio-economic contexts, it is also time to move past reductive framings and sometimes reactionary oppositional stances in which climate (and environment more broadly) either is or is not deemed an important contributor to major historical events.

A data-model perspective on the Brazilian margin surface warming from the Last Glacial Maximum to the Holocene

The western South Atlantic along the Brazilian margin is an important region for the Atlantic Meridional Overturning Circulation (AMOC) because surface currents in this area transfer warm and salty waters from the Southern Hemisphere to the North Atlantic. Although the number of sea surface temperature (SST) reconstructions has grown in this region, it has been challenging to explain changes in different and sometimes proximal cores. To understand the SST evolution of the Brazilian margin from the Last Glacial Maximum (LGM) to the late Holocene, we present the first SST stack (BRSST stack) for this region. We compare the BRSST stack with the outputs of the transient climate model simulation TraCE-21ka. The BRSST stack shows an LGM cooling of 1.43 °C (from −1.31 to −1.55 °C, 2σ) relative to the late Holocene, followed by deglacial warming starting at ∼ 18.8 ka. TraCE-21ka simulates this early onset of the last deglaciation. Sensitivity experiments suggest that the input of meltwater from retreating ice sheets in the Northern Hemisphere triggered the post-LGM warming, which was subsequently sustained by increasing atmospheric CO2. Deglacial millennial-scale events of AMOC slowdown produced large-scale warming of the Brazilian margin not clearly distinguished by some previous studies. Analyzing our stack in its segregated components, i.e., the North Brazil Current (NBCSST stack) and Brazil Current (BCSST stack) – we noted in-phase warming at the onset of the last deglaciation, which is not found in TraCE-21ka simulations. We attributed this to underestimating the meltwater influence over the tropical Brazilian margin by the model. BRSST stack also presents episodes of abrupt cooling near periods of fast sea-level rise during the last deglaciation, which may be due to rapid AMOC reinvigoration or freshening of the Southern Ocean. Holocene climate resembles that recorded by other compilations, with no clear Holocene thermal maximum but presenting a cooling trend during the late Holocene possibly related to intensified volcanic activity. Our study indicates that the future human-induced SST change expected for the end of the 21st-century will overcome the background of natural climate variability of the last 22,000 years for the Brazilian margin.

Characterizing Changes in Eastern U.S. Pollution Events in a Warming World

AbstractRisk assessments of air pollution impacts on human health and ecosystems would ideally consider a broad set of climate and emission scenarios, as well as natural internal climate variability. We analyze initial condition chemistry‐climate ensembles to gauge the significance of greenhouse‐gas‐induced air pollution changes relative to internal climate variability, and consider response differences in two models. To quantify the effects of climate change on the frequency and duration of summertime regional‐scale pollution episodes over the Eastern United States (EUS), we apply an Empirical Orthogonal Function (EOF) analysis to a 3‐member GFDL‐CM3 ensemble with prognostic ozone and aerosols and a 12‐member NCAR‐CESM1 ensemble with prognostic aerosols under a 21st century RCP8.5 scenario with air pollutant emissions frozen in 2005. Correlations between GFDL‐CM3 principal components for ozone, PM2.5 and temperature represent spatiotemporal relationships discerned previously from observational analysis. Over the Northeast region, both models simulate summertime surface temperature increases of over 4°C from 2006–2025 to 2081–2100 and PM2.5 of up to 1–4 μg m−3. The ensemble average decadal incidence of upper quartile Northeast PM2.5 events lasting at least three days doubles in GFDL‐CM3 and increases by ∼50% in CESM1. In other EUS regions, inter‐model differences in PM2.5 responses to climate change cannot be explained solely by internal climate variability. Our EOF‐based approach anticipates future opportunities to data‐mine initial condition chemistry‐climate model ensembles for probabilistic assessments of changing regional‐scale pollution and heat event frequency and duration, while obviating the need to bias‐correct concentration‐based thresholds separately in individual models.

Influence of the South American Low‐Level Jet on the Austral Summer Precipitation Trend in Southeastern South America

AbstractAustral summer precipitation increased by 27% from 1902 to 2020 over southeastern South America (SESA), one of the largest centennial precipitation trends observed globally. We assess the influence of the South American low‐level jet on the SESA precipitation trend by analyzing low‐level moisture fluxes into SESA in two reanalysis datasets from 1951 to 2020. Increased moisture flux through the jet accounts for 20%–45% of the observed SESA precipitation trend. While results vary among reanalyzes, both point to increased humidity as a fundamental driver of increased moisture flux and SESA precipitation. Increased humidity within the jet is consistent with warming sea surface temperatures driven by anthropogenic forcing, although additional natural climate variations also may have played a role. The jet's velocity also increased, further enhancing precipitation, but without a clear connection to anthropogenic forcing. Our findings indicate the SESA precipitation trend is partly attributable to jet intensification arising from both natural variability and anthropogenic forcing.