Tropical Climate Change Research Articles

Intensified Western Pacific Convection Increases the Probability of Hot Extremes in the Middle East During the Boreal Spring

AbstractUnder global warming, the convective heating over the western Pacific (WP) has exhibited a significantly intensifying trend during the boreal spring, while the surface air temperatures in the Middle East (ME) have increased more rapidly than those in other tropical regions. Are these climate phenomena of the two regions physically connected? If yes, what are the responsible dynamical mechanisms involved? Utilizing the ERA5 reanalysis data and model simulations, this study reveals a significant seesaw variation in the convection and temperature trends between WP and ME. When convective heating intensifies over the WP, the ME tends to be drier and hotter during the spring, and vice versa. A further investigation indicates that the enhanced WP convective heating can induce anticyclonic circulation anomalies in the upper and middle troposphere over the Iranian and Tibetan plateaus. These anomalous high pressures extend westward, exhibiting a barotropic structure, which leads to stronger sinking motions, reduced cloud cover, and increased surface solar radiation over the ME. Consequently, these conditions result in drier and hotter soils and an increase in heatwave days in the ME. This study provides useful information for enhancing our understanding of the role of tropical WP climate change in influencing the upstream climate conditions with a focus on the ME.

ENSO‐Modulated Variability in Winter Shelf Circulation of the Northern South China Sea

AbstractWe combined long‐term observational data from 1999 to 2021 with numerical simulations to study the seasonal changes in the currents along the continental shelf in the Northern South China Sea (NSCS) during winter and how these changes relate to the El Niño‐Southern Oscillation (ENSO). Our results indicate that during El Niño events, the eastward movement of the warm pool in the tropical Pacific Ocean not only leads to colder sea surface temperatures and a stronger Kuroshio current intrusion but also significantly affects the formation of a high‐pressure system in the subtropics over the NSCS. In El Niño years, an anomalous anticyclonic wind stress curl in the South China Sea weakens the northeast winter monsoon, which in turn weakens the cyclonic shelf circulation. The first principal component from the multivariate empirical orthogonal function decomposition, which accounts for 49.02% of the total variance, shows a significant correlation of 0.64 with the Niño 3.4 index, indicating the circulation's sensitivity to tropical climate changes. Our analysis of the winter shelf circulation, based on the along‐isobath depth‐integrated vorticity equation, reveals that the exchange of water across the isobaths over the shelf is mainly controlled by the nonlinear advection of relative vorticity, with wind stress curl and bottom stress curl playing a less significant role in regulating the structure of these exchanges. The combined effect of baroclinic forces and topography likely governs the dynamics over the slope.

Evidence for a Miocene pulse of diversification of the tropical American clade of the Brazil nut family (Lecythidaceae)

ABSTRACT The tropical American species of the Brazil nut family, Lecythidaceae, are abundant in the tree flora, with some economically important species. Yet, the phylogenetic relationships and pace of diversification within this family are understudied. Here, we used shotgun sequencing data for 86 of the 228 currently accepted species in the exclusively tropical American subfamily Lecythidoideae in a phylogenomic context. For each sampled species, we built the full plastid DNA sequence, and also extracted nuclear DNA for 571 regions using the new bioinformatics pipeline REFMAKER, which we used to produce a time-calibrated phylogenetic hypothesis. Our analysis shows that phylogenetic inference from plastid and nuclear DNA alignments resulted in different topologies. The nuclear DNA topology strongly suggests that genus Lecythis should be split into at least four genera. Samples of the genus Eschweilera formed a monophyletic group, with the exception of one sampled species (Eschweilera amazoniciformis S.A.Mori). The Bertholletia clade, which contains the majority of the Lecythidoideae species, and all Lecythis and Eschweilera species, started diversifying around 27.5 Ma, with an accelerated rate of diversification starting in the middle Miocene (c. 12 Ma). The clade sister to Bertholletia (including Corythophora, Eschweilera, and Corrugata, Chartacea and Poiteaui clades) includes at least 124 species and it has diversified less than 10 Ma. This time frame of diversification coincides with major changes in tropical American landscapes and climate associated with the Andean uplift.

Energy performance of a nZEB urban commercial building under the influence of a tropical climate and climate change

Energy performance of a nZEB urban commercial building under the influence of a tropical climate and climate change

The Transition to Double‐Celled Circulations in Mock‐Walker Simulations

AbstractMock‐Walker simulations have the potential to play a key role in a tropical model hierarchy, bridging small‐scale Radiative‐Convective Equilibrium simulations and global models of tropical circulations. We demonstrate that mock‐Walker simulations transition from single‐ to double‐celled overturning circulations as mean Sea Surface Temperature (SST) is increased, with the transition occurring near 300 K. The transition is robust to domain geometry and microphysical scheme, and is favored by larger SST gradients. The transition is associated with the development of a mid‐tropospheric minimum in the radiative‐subsidence velocity over the cold pool of the simulations, and is likely reinforced by zonal moisture and temperature fluxes between the warm and cold pools. Several methods of suppressing the transition are investigated, but all set‐ups produce a double‐cell at sufficiently warm mean SSTs. The striking dynamical transition of mock‐Walker simulations dominates their response to warming, though its relevance for observed tropical climate change is unclear.

Corals Evidence an Underestimation of the 20th Century Warming in the Eastern Pacific Cold Tongue

AbstractThe trade winds cause strong upwelling in the eastern equatorial Pacific, and create the eastern Pacific Cold Tongue (EPCT) that has far‐reaching impacts on global climate. However, large discrepancies persist in quantifying 20th‐century EPCT sea surface temperature (SST) changes across different instrumental data sets. Here we synthesize four coral Sr/Ca‐SST records from the tropical central‐eastern Pacific to develop a Cold Tongue Index (CTI) reconstruction for 1887–1997. The coral CTI record shows a rapid 20th century warming of the EPCT, suggesting an underestimation of warming trends in instrumental CTI records. The decadal to multidecadal changes in reconstructed EPCT SST show an association with the Walker Circulation. Our reconstruction indicates that recent EPCT cooling during the global warming hiatus is not unusual in the context of the 20th century. Our results provide new evidence for 20th century EPCT SST changes and an observational constraint for predicting future tropical climate changes.

Anthropogenic forcings reverse a simulated multi-century naturally-forced Northern Hemisphere Hadley cell intensification

The Hadley circulation plays a central role in determining the location and intensity of the hydrological cycle in tropical and subtropical latitudes. Thus, the human-induced historical and projected weakening of the Northern Hemisphere Hadley circulation has considerable societal impacts. Yet, it is currently unknown how unparalleled this weakening is relative to the response of the circulation to natural forcings in past centuries. Here, using state-of-the-art climate models, we show that in contrast to the recent and future human-induced Hadley circulation weakening, natural forcings acted to intensify the circulation by cooling the climate over the last millennium. The reversal of a naturally-forced multi-centennial trend by human emissions highlights their unprecedented impacts on the atmospheric circulation. Given the amplifying effect of natural forcings on the Hadley circulation, our analysis stresses the importance of adequately incorporating natural forcings in climate model projections to better constrain future tropical climate changes.

Formal designation of Brazilian indigenous lands linked to small but consistent reductions in deforestation

Indigenous territories in Brazil have existed since the pre-European discovery of the continent. Yet, many of them remain without formal recognition by the state. While numerous studies discuss the social implications of indigenous land (IL) designation, limited empirical evidence exists regarding its role in forest conservation. To address this gap, the present study employs a quasi-experimental design and causal-inference methods to estimate the effects of formal IL designation on deforestation across Brazil and its biomes, from 1986 to 2021. Estimates indicate an average impact of −0.05% on deforestation due to the formal designation of ILs nationwide, with variations ranging from −0.21% to 0.04% across different evaluation periods and biomes. Notably, designated ILs in the Cerrado biome had the highest avoided deforestation impacts (−0.12%, on average). No evidence of deforestation leakage was observed. The findings from this study suggest that while the promotion of formal IL designation can lead to consistent reductions in deforestation, the magnitude of its effect is relatively small to be promoted on the sole basis of an effective strategy to mitigate tropical deforestation and climate change. Nevertheless, the potential positive socioeconomic impacts of formal IL designation on indigenous peoples cannot be undermined.

Ecological adaptation of smallholders to tropical climate change in the highland zone of South Sulawesi, Indonesia

Abstract. Busthanul N, Demmallino EB, Sultani HR, Lampe M, Ismail A, Yassi A, Daris L, Saudi MY, Zainuddin A. 2023. Ecological adaptation of smallholders to tropical climate change in the highland zone of South Sulawesi, Indonesia. Biodiversitas 24: 5328-5335. Climate change has adversely affected the stability of agricultural production and livelihood systems, threatening the well-being of farmers in Indonesia, particularly small-scale farmers with limited resources. To mitigate the impacts of climate change on agricultural production, innovative approaches are required. Ecological adaptation is one of such approaches which addresses the threat of climate change. However, studies on ecological adaptation in Indonesia have mostly been concentrated on food crops, with limited attention to horticultural commodities in mountainous regions. This study aims to explore how horticulture farmers in the mountainous region of Enrekang District, South Sulawesi, adapt to the effects of tropical climate change. This study employs a post-positivistic approach, to a case study of the impact of climate change on the horticulture farming community in Enrekang District. The study uses a household survey method to gather quantitative data, while focus group discussions and key informant interviews were used to collect qualitative data using semi-structured and unstructured questionnaires. The study's findings revealed diverse ecological adaptation patterns among horticulture farmers, which include adjustments in planting timing, management of pests and diseases, crop rotation, and the use of pumping systems. In addition to these scientifically based strategies, local knowledge also played a crucial role in adaptation processes. Furthermore, to ensure the sustainability of these ecological adaptation strategies, there is a need for the government and scientists to support and empower local communities collectively. This recognition and collaboration are vital for ensuring the resilience and effectiveness of adaptation efforts in mitigating climate change.

Predicting the loss of forests, carbon stocks and biodiversity driven by a neotropical ‘gold rush’

The loss of tropical forests represents a major threat to biodiversity. With accelerating deforestation in large parts of the Amazon, the Guiana Shield region, with its large expanse of closed forest cover, has the potential to play a crucial role in both climate change mitigation and biodiversity conservation. However, the region is now facing increasing deforestation pressures, primarily from artisanal gold mining activities concentrated in the nation of Guyana. To identify areas of Guyana at the highest risk of deforestation over the next 25 years, we employed a spatio-temporal modelling approach that accounted for the stochastic and contagious nature of deforestation. Our model predicted a 9 % net decrease in total forest cover by 2043. While the primary drivers of deforestation were mining and human settlements, protected areas were shown to reduce the probability of deforestation. Therefore, we assessed the potential impact of a proposed expansion of the protected area network in Guyana, on forest loss, carbon stocks and habitat loss for the country's most threatened forest vertebrates. Establishing the proposed protected areas would reduce forest loss by 17 %, predicted habitat losses by an average of 1.9 % per vertebrate group, and aboveground carbon emissions by 466,968 t over the next 25 years. These findings highlight the utility of using predictive models to identify areas at risk of future deforestation, which can contribute to the development of effective strategies against tropical forest loss, biodiversity loss and climate change.

Rainfall and Salinity Effects on Future Pacific Climate Change

AbstractMost climate models simulate an intensified eastern equatorial Pacific warming in response to increasing greenhouse gas concentrations. So far, the proposed mechanisms have focused on thermodynamic aspects such as the spatial inhomogeneity of evaporative feedbacks, and future increases in upper ocean thermal stratification, partly intensified by projected Walker circulation weakening. Here we show, using earth system model freshwater perturbation experiments, that the simulated future rainfall intensification along the equator plays an important role in tropical climate change. Associated negative equatorial salinity anomalies of about −0.6 permil, which are very similar to the projected late 21st century salinity anomalies in CMIP6 SSP585 scenario, strengthen upper ocean stratification in the Pacific which leads to a flattening of the thermocline, shoaling of the equatorial undercurrent, and major shifts in tropical ocean dynamics. The resulting eastern basin equatorial warming also contributes to a marked weakening of the Pacific Walker circulation. Our analysis illustrates the importance of rainfall and salinity changes in the tropical climate system with relevance for understanding both, patterns of future climate change as well as the El Niño Southern Oscillation phenomenon.

Strengthening atmospheric circulation and trade winds slowed tropical Pacific surface warming

The globally averaged sea-surface temperature (SST) has steadily increased in the last four decades, consistent with the rising atmospheric greenhouse gas concentrations. Parts of the tropical Pacific exhibited less warming than the global average or even cooling, which is not captured by state-of-the-art climate models and the reasons are poorly understood. Here we show that the last four decades featured a strengthening atmospheric circulation and stronger trade winds over the tropical Pacific, which counteracted externally-forced SST warming. Climate models do not simulate the trends in the atmospheric circulation irrespective of whether an external forcing is applied or not and model bias is the likely reason. This study raises questions about model-based tropical Pacific climate change projections and emphasizes the need to enhance understanding of tropical Pacific climate dynamics and response to external forcing in order to project with confidence future climate changes in the tropical Pacific sector and beyond.

Tropical climate change and its impact on horticultural plants in Enrekang District, South Sulawesi, Indonesia

Abstract.Yassi A, Demmallino EB, Sultani HR. 2023. Tropical climate change and its impact on horticultural plants in Enrekang District, South Sulawesi, Indonesia. Biodiversitas 24: 3073-3079. Global, regional, and local changes in climate are phenomenologically different and have distinct impacts on the horticultural and agricultural sectors. Therefore, this research aims to examine tropical climate change in South Sulawesi, Indonesia and analyze its impact on horticultural crops. Apost-positivistic interpretation framework of the case study tradition was used, while the location was determined by purposive sampling followed by comprehensive data collection. Data were analyzed using integrated techniques, and validity tests were carried outto assess thecredibility and reliability. The results indicated a local climate change marked by a differencein the pattern of distribution and intensity of extreme rainfall between 2015 and 2018. This was due toan increase in air temperature, which on average reached ±0.03731°C from the lowest of 22.50°C in 2011 to the highest of 23.12°C in 2020. In other words, it can be stated that the air temperature had increased by ±0.63°C in the last decade. The impact on various types of horticultural crops was marked by a decrease in the production of several kinds of Chinese cabbage,carrots, and green beans in 2015 as well asa very drastic reductionin potato crop production in 2018, while cabbage plants experienced a peak in production in 2018. Some types of horticultural crops such as shallots, cabbage and red chili began to stabilize and even increased their production in the aftermath of climate changeduring said period.

Tropical Cyclones and Climate Change: Global Landfall Frequency Projections Derived from Knutson et al.

Abstract Projections of changes in tropical cyclone (TC) characteristics under climate change are of great interest to those affected by TCs. In a recent paper, Knutson et al. combined a large number of previous results to produce projections consisting of distributions of possible future TC frequencies, intensities, and rainfall rates. These distributions provide a great resource for users of TC information. However, to apply the distributions to impacts models may require the user to solve a number of technical challenges including modeling correlations, fitting distributions, interpolation, and converting the projections to properties at landfall. I consider the frequency and intensity changes, and implement solutions for each of these challenges using a combination of recently published research and a new methodology. This allows me to produce a dataset of TC projections that give frequency changes as a function of landfall region and intensity. Mean intensity changes can then be derived from frequency changes. The projections are presented in a format that allows them to be used in impacts models without further processing. The interpolation and landfall adjustments tend to increase the frequency changes. As a result, my projections give increasing mean frequencies of hurricane-strength landfalling TCs in four out of six global basins, with mean frequencies increasing by up to 16% for a 2°C increase in global mean surface temperature. My projections are highly uncertain, but include uncertainty estimates. They are designed to be a useful resource for anyone interested in possible future TC frequencies and intensities.

Human-induced weakening of the Northern Hemisphere tropical circulation.

By accounting for most of the poleward atmospheric heat and moisture transport in the tropics, the Hadley circulation largely affects the latitudinal patterns of precipitation and temperature at low latitudes. To increase our preparednesses for human-induced climate change, it is thus critical to accurately assess the response of the Hadley circulation to anthropogenic emissions1-3. However, at present, there is a large uncertainty in recent Northern Hemisphere Hadley circulation strength changes4. Not only do climate models simulate a weakening of the circulation5, whereas atmospheric reanalyses mostly show an intensification of the circulation4-8, but atmospheric reanalyses were found to have artificial biases in the strength of the circulation5, resulting in unknown impacts of human emissions on recent Hadley circulation changes. Here we constrain the recent changes in the Hadley circulation using sea-level pressure measurements and show that, in agreement with the latest suite of climate models, the circulation has considerably weakened over recent decades. We further show that the weakening of the circulation is attributable to anthropogenic emissions, which increases our confidence in human-induced tropical climate change projections. Given the large climate impacts of the circulation at low latitudes, the recent human-induced weakening of the flow suggests wider consequences for the regional tropical-subtropical climate.

Sources of Uncertainty in the Time of Emergence of Tropical Pacific Climate Change Signal: Role of Internal Variability

Abstract Determining the time of emergence of anthropogenic climate change signals from natural variability, for both the tropical Pacific mean state and El Niño–Southern Oscillation (ENSO), are critical for early climate warning and adaptation planning. However, there remains considerable uncertainty in estimating those times of emergence in state-of-the-art climate models. In this study, the role of internal variability in the uncertainty of the times of emergence of tropical Pacific annual-mean sea surface temperature (SST) and rainfall, and ENSO-related SST and rainfall are investigated by using three large ensembles of model simulations under the historical and RCP8.5 emission scenarios, as well as the multimodel ensemble from phase 6 of the Coupled Model Intercomparison Project under the historical and SSP5–8.5 emission scenarios. Specific attention is paid to the eastern equatorial Pacific. It is found that internal variability contributes to less than half of the total uncertainty in both the times of emergence of annual-mean SST and rainfall in all the three large ensembles, with more contribution to the latter than to the former. Hence, model differences dominate. Conversely, internal variability contributes to a major part of the total uncertainty in the times of emergence of ENSO-related SST and rainfall in one large ensemble that has sufficient members to show emergent signals. These results imply that we could have a relatively high confidence in claiming that anthropogenic climate change has impacted the annual-mean state, if an emergent annual-mean signal is observed in the real world. However, in claiming changes in ENSO variability, the signal is easily obscured by internal variability.

RECONSTRUCTING KUNGURIAN (CISURALIAN, PERMIAN) TERRESTRIAL ENVIRONMENTS WITHIN A MEGACALDERA IN THE SOUTHERN ALPS (N-ITALY) USING LITHOFACIES ANALYSIS, PALYNOLOGY AND STABLE CARBON ISOTOPES

During the Permian, climate experienced a change from icehouse to greenhouse conditions. Few multidisciplinary studies have investigated Kungurian (late Cisuralian) tropical terrestrial ecosystem and climate changes. Here, we apply an interdisciplinary approach to two alluvial-lacustrine successions of the Athesian Volcanic Group (Southern Alps, northern Italy) deposited in a Kungurian megacaldera during periods of volcanic quiescence. Sedimentological analysis combined with palynofacies studies allowed the reconstruction of the depositional environments. The study of sporomorph assemblages and stable organic carbon isotopes provided information on plant communities and the climate context. Two different depositional environments were present in the megacaldera: one proximal and one more distal with respect to the source, distinguished by a slightly different composition of the sediments, palynofacies and organic carbon isotopes. The plant community in the area was dominated by xeromorphic-hygromorphic taxa. The δ13Corgvalues are comparable to those of other Cisuralian continental organic matter and plants. The stable carbon isotope values show a small variability, which correlates weakly, but significantly, with the abundance of xeromorphic elements. All observations support deposition during semiarid to arid climate conditions, typical of the mid-late Cisuralian in the area.

Variability of thermocline temperature in the Bay of Bengal and its response to solar insolation and Indian monsoon over the last 15 kyr

Surface seawater stratification shows a sensitive response to solar insolation and large-scale ocean current, further playing an important role in the air-sea interactions at different time scales. However, the variation of surface seawater structure and its driving mechanism in the tropical Indian Ocean is poorly understood. We present a new record of thermocline temperature (TWT) obtained using oxygen isotope and Mg/Ca-temperature of the planktonic foraminifer Pulleniatina obliquiloculata (P. obliquiloculata) from core BoB-24 in the central Bay of Bengal (BoB). The results indicate that TWT rose rapidly from the Younger Dryas (YD) and persisted at a peak temperature value of 22.5 °C between 10 and 7 cal ka BP, and subsequently reduced by 1.5 °C in the middle Holocene period. The temporal variability of TWT occurred following the boreal summer insolation, associated with tropical climate changes such as the movement of the Inter-tropical Convergence Zone (ITCZ) as well as relevant changes of seasonal Indian monsoons. During the YD period, the southward movement of ITCZ and strengthened Indian winter monsoon (IWM) influenced the deepening of pycnocline, which caused subsurface warming and decreased stratification. During the middle Holocene, the northward return of ITCZ and strengthening of Indian summer monsoon (ISM) led to a stronger surface water stratification and present cooling trend of optimum TWT (10–7 cal ka BP). Furthermore, the millennial TWT changes presented in this study revealed a close link with North Atlantic climate changes, indicating a dynamic action of Atlantic meridional overturning circulation (AMOC).

Integrated fire management in tropical forests and open landscapes

This article provides a basis for understanding fireinduced processes, and for the need to develop adequate fire management concepts and implementation strategies, highlighting basic processes, phenomena and solutions. These are challenges for decision makers, while the complexity of interactions between land use and other human activities, tropical vegetation characteristics, climate and climate change may also mean that decision makers require expert assistance in capacity building for fire management at local and national levels.

Soil erosion risk under climate change scenarios: A case study in rural area with varying land uses

Soil erosion is one of the major issues in the tropics. The erosion is highly affected by the changes in climate and land cover. Future changes in tropical climate, particularly precipitation are expected to influence the potential risks of soil erosion. In the face of rapid changes in rural land cover for agricultural purposes, the combined forcings of land cover and climate changes have been to be a major threat to the soil conservation due to soil erosion. In this study, climate change scenarios at the northern part of Borneo were developed based on the RCP 4.5 and RCP 8.5 climate scenarios using Weather Research Forecast Model (WRF). The future climate projection scenarios of the total precipitation were used to simulate the potential erosion risks in varying land covers in a rural area of Sabah, Malaysia. The RUSLE model was used for soil erosion modelling, which was integrated with IDRISI Selva that allow the analysis and assessment of erosion risk. The variability of future total precipitations in the area of varying land cover types have resulted in varying degree of potential soil erosion risk The average soil loss at the studied area has increased by 262 t/ha/yr with 35.94 % increment in annual precipitation under RCP 8.5 emission scenario. However, under RCP 4.5, 26.65 % decrement in precipitation has reduced the soil loss by 315.1 t/ha/yr. In this rural area, exceptionally high soil erosion was found at steep slopes and thin vegetation covers. Therefore, an appropriate land use planning, soil conservation practices, and strategic adaptation options plan should be created and developed to ensure the sustainability of the soil conservation and enhance rural agricultural productivity.