Psychiatry Research

Abstract Global warming, landscape alterations and population growth have dramatically altered the three pillars of natural disasters – hazard, vulnerability and exposure, increasing the risk of destructive and deadly natural disasters. In this perspective we breakdown how these factors played out to shape the Brazil’s 2024 floods, one of the most destructive natural hazards in recent history, resulting in over 180 deaths. This short essay explores a newly proposed evidence-based conceptual model supported by data analysis expanding the IPCC climate risk framework. It examines the extreme precipitation and the compounded climate extreme event, including its association with heatwave, atmospheric rivers from the Amazon and El Niño and assesses changes in land cover, population and the death toll of the event. We discuss how this flood event is a heads up to global decision-makers that increases in hazard, vulnerability and exposure are changing the nature of natural disasters, making these destructive events the new norm.

Abstract A quarter of the deforested Amazon has regrown as secondary tropical forest and yet the climatic importance of these complex regenerating landscapes is only beginning to be recognised. Advances in satellite remote-sensing have transformed our ability to detect and map changes in forest cover, while detailed ground-based measurements from permanent monitoring plots and eddy-covariance flux towers are providing new insights into the role of secondary forests in the climate system. This review summarises how progress in data availability on Amazonian secondary forests has led to better understanding of their influence on global, regional and local climate through carbon and non-carbon climate benefits. We discuss the climate implications of secondary forest disturbance and the progress in representing forest regrowth in climate models. Much remains to be learned about how secondary forests function and interact with climate, how these processes change with forest age, and the resilience of secondary forest ecosystems faced with increasing anthropogenic disturbance. Secondary forests face numerous threats: half of secondary forests in the Brazilian legal Amazon were 11 years old or younger in 2023. On average, 1%–2% of Amazon secondary forests burn each year, threatening the permanence of sequestered carbon. The forests that burn are predominantly young (in 2023, 55% of burned secondary forests were <6 years old, <4% were over 30 years old). In the context of legally binding international climate treaties and a rapidly changing political backdrop, we discuss the opportunities and challenges of encouraging tropical forest restoration to mitigate anthropogenic climate change. Amazon secondary forests could make a valuable contribution to Brazil’s Nationally Determined Contribution provided there are robust systems in place to ensure permanence. We consider how to improve communication between scientists and decision-makers and identify pressing areas of future research.

Abstract The Arctic is warming faster than the rest of the globe, posing risks to climate tipping elements such as the collapse of the Greenland Ice Sheet, winter Arctic sea ice loss, weakening of the Atlantic Meridional Overturning Circulation, and permafrost collapse. Stratospheric Aerosol Injection (SAI) has shown potential to ameliorate these effects by reducing surface temperatures. Due to the potential for an asymmetric hemispheric response in precipitation, Arctic-only SAI is not recommended. Given the challenges associated with an Antarctic SAI program, including the lack of nearby large airports, however, we designed and simulated an Arctic-only logistically constrained SAI scenario, considering limitations imposed by factors affecting the planning, execution, and management of operations. Our scenario is constrained by aircraft development and delivery timelines. SAI deployment begins in 2032 and increases to a maximum annual injection of 6.7 TgSO2 by 2053 through 2070. The scenario is simulated in a modified version of the Energy Exascale Earth System Model (E3SMv2). Results indicate that Arctic-only SAI can reduce Northern Hemisphere temperatures and slow sea ice loss, though the early years of deployment may show limited cooling due to low ramp-in injection magnitudes. The Arctic-only SAI introduces minimal impact on Southern Hemisphere temperatures but significant shifts in the hydrologic cycle, particularly around the equator. Southern Hemisphere changes are low within the first two decades, suggesting that asymmetries in Arctic-only SAI deployment could be sustained without severe adverse climate impacts for the first couple of decades. These asymmetries matter given the challenges associated with an Antarctic SAI program. Our findings underscore the necessity of incorporating logistical constraints on deployment and the need for multi-model assessments in the evaluation of polar SAI scenarios. This approach would ensure a strong scientific understanding of polar SAI and facilitates policy and decision-maker understanding of the risks and benefits of SAI.

Abstract Rising greenhouse gas concentrations and declining global aerosol emissions are causing energy to accumulate in Earth’s climate system at an increasing rate. Incomplete understanding of increases in Earth’s energy imbalance and ocean warming reduces the capability to accurately prepare for near term climate change and associated impacts. Here, satellite-based observations of Earth’s energy budget and ocean surface temperature are combined with the ERA5 atmospheric reanalysis over 1985–2024 to improve physical understanding of changes in Earth’s net energy imbalance and resulting ocean surface warming. A doubling of Earth’s energy imbalance from 0.6±0.2 Wm−2 in 2001–2014 to 1.2±0.2 Wm−2 in 2015–2023 is primarily explained by increases in absorbed sunlight related to cloud-radiative effects over the oceans. Observed increases in absorbed sunlight are not fully captured by ERA5 and determined by widespread decreases in reflected sunlight by cloud over the global ocean. Strongly contributing to reduced reflection of sunlight are the Californian and Namibian stratocumulus cloud regimes, but also recent Antarctic sea ice decline in the Weddell Sea and Ross Sea. An observed increase in near-global ocean annual warming by 0.1 ∘ C y r − 1 for each 1 Wm−2 increase in Earth’s energy imbalance is identified over an interannual time-scale (2000–2023). This is understood in terms of a simple ocean mixed layer energy budget only when assuming no concurrent response in heat flux below the mixed layer. Based on this simple energy balance approach and observational evidence, the large observed near-global ocean surface warming of 0.27  ∘ C from 2022 to 2023 is found to be physically consistent with the large energy imbalance of 1.85±0.2 Wm−2 from August 2022 to July 2023 but only if (1) a reduced depth of the mixed layer is experiencing the heating or (2) there is a reversal in the direction of heat flux beneath the mixed layer associated with the transition from La Niña to El Niño conditions. This new interpretation of the drivers of Earth’s energy budget changes and their links to ocean warming can improve confidence in near term warming and climate projections.

Abstract Greenhouse gas accounting conventions were first devised in the 1990’s to assess and compare emissions. Several assumptions were made when framing conventions that remain in practice, however recent advances offer potentially more consistent and inclusive accounting of greenhouse gases. We apply these advances, namely: consistent gross accounting of CO2 sources; linking land use emissions with sectors; using emissions-based effective radiative forcing (ERF) rather than global warming potentials to compare emissions; including both warming and cooling emissions, and including loss of additional sink capacity. We compare these results with conventional accounting and find that this approach boosts perceived carbon emissions from deforestation, and finds agriculture, the most extensive land user, to be the leading emissions sector and to have caused 60% (32%–87%) of ERF change since 1750. We also find that fossil fuels are responsible for 18% of ERF, a reduced contribution due to masking from cooling co-emissions. We test the validity of this accounting and find it useful for determining sector responsibility for present-day warming and for framing policy responses, while recognising the dangers of assigning value to cooling emissions, due to health impacts and future warming.

Abstract A deeper understanding of land use land cover (LULC) dynamics is essential for the sustainable management of the environment and its natural resources, and importantly how the changes affect the provision of ecosystem services and community livelihoods. This study examined the spatio-temporal LULC dynamics around the Budongo Central Forest from 1995 to 2022 and the implications these changes have on the provision of ecosystem services and the livelihoods of local communities. Data were collected using a hybrid approach involving satellite image classification, post-classification change detection, interviews with 156 respondents and 17 key informants. Survey data were subjected to descriptive statistics, Mann-Whitney U tests and Ordinary Least Squares (OLS) regressions. The study results reveal a decline in areas covered by wetlands, forests and grasslands due to the expansion of commercial sugarcane plantations, compounded by an increase in the population emanating from migrant workers. While the area under subsistence agriculture had a marginal expansion, local communities perceived that the changes in LULC resulted in a decline in households’ food availability, water availability and soil fertility. The study concludes that changes in LULC are associated with significant losses in natural assets and ecosystems. These loses in natural assets have significant effects on the livelihoods of community members. Therefore, there is a need for instituting a participatory land use planning approach in the affected communities to mitigate the effects of the LULC changes. This will also help in fostering sustainable natural resource management within the affected communities.

Abstract Drylands, encompassing over 40% of the conterminous United States (CONUS), are crucial to the global carbon cycle and highly susceptible to climate change. However, Earth system models offer conflicting projections of future drought and vegetation activity in North America, and in-depth analyses of the long-term changes in greenness and its relationship with underlying climate drivers, considering both spatial and temporal variations at the ecosystem scale, are lacking. This study analyzes 20 year (2001–2020) MODIS normalized difference vegetation index (NDVI) observations to assess greenness trends in CONUS drylands and their relationship with climate drivers at 1 km spatial resolution. Results indicate a large scale and systematic greening trend, particularly in the northern Great Plains (NGP) region. Using an empirical linear attribution approach and empirical orthogonal function analysis, we uncover varied relationships between greenness trends and climate drivers, particularly highlighting the dominant role of increased precipitation in driving the observed greening. Trend analysis reveals that while rain use efficiency (RUE) remains stable in most areas, increases in the NGP region suggest potential CO2 fertilization effects, while decreases in southern states correlate with rising temperatures. We also develop an efficiency-based model featuring RUE which successfully reproduces historical NDVI, re-confirming the dominant influence of precipitation in local greenness interannual variability. However, CMIP6 projections for 2021–2040 under the ‘Regional Rivalry’ scenario (SSP370) paint a worrying picture, with projected browning in the NGP region and states near the 42°N latitude, contrasting recent greening trends. This potential reversal underscores the vulnerability of these ecosystems to future climate change, highlighting the need to consider both historical trends and future climate projections when assessing the resilience of drylands ecosystems. Overall, our work re-emphasizes the significance of water availability to drylands vegetation growth and contributes to a more comprehensive understanding of carbon-water cycling in arid and semi-arid regions.

Abstract Understanding the patterns of aerosol-induced perturbation in radiation budget and its drivers is crucial in climate science. Here, we examined spatio-temporal trends in aerosol-induced atmospheric warming and the top-of-the-atmosphere (TOA) and surface cooling over the Indian Subcontinent under clear-sky and all-sky conditions using clouds and the earth’s radiant energy system data for the period 2000–2021. Overall, the regional mean TOA and surface cooling were found to increase by 0.06 W m−2 yr−1 and 0.09 W m−2 yr−1, respectively. Over the last two decades, the aerosol-induced atmospheric warming in all-sky conditions increased over the subcontinent landmass and outflow regions over the ocean while it declined over dust-dominated arid regions. This dipole pattern was driven by a combination of an overall increase in aerosol optical depth, a gradual increase in the fraction of scattering aerosols over the Indian landmass dominated by anthropogenic sources, a decline in dust loading over the arid sources. As a result, atmospheric warming efficiency declined in most parts of the Indian subcontinent. A comparative meta-analysis revealed that aerosol-induced atmospheric warming was over-estimated by the existing studies where aerosol direct radiative forcings were estimated by 1-D radiative transfer model utilizing modeled optical properties based on incomplete information about in-situ physico-chemical properties derived from ground-based measurements. Our analysis showed that TOA and surface cooling by aerosols were higher in clear-sky conditions relative to the actual all-sky condition by up to 11 W m−2 and 16 W m−2, respectively; therefore, atmospheric warming reported for clear-sky conditions would be biased high over the subcontinent. As India embarked on a clean air mission, changes in aerosol loading and its composition are expected to alter the dipole pattern further in the future, impacting the regional climate via dynamic feedback.

Abstract The Antarctic Circumpolar Current is the world’s strongest ocean current and plays a disproportionate role in the climate system due to its role as a conduit for major ocean basins. This current system is linked to the ocean’s vertical overturning circulation, and is thus pivotal to the uptake of heat and CO2 in the ocean. The strength of the Antarctic Circumpolar Current has varied substantially across warm and cold climates in Earth’s past, but the exact dynamical drivers of this change remain elusive. This is in part because ocean models have historically been unable to adequately resolve the small-scale processes that control current strength. Here, we assess a global ocean model simulation which resolves such processes to diagnose the impact of changing thermal, haline and wind conditions on the strength of the Antarctic Circumpolar Current. Our results show that, by 2050, the strength of the Antarctic Circumpolar Current declines by~20% for a high-emissions scenario. This decline is driven by meltwater from ice shelves around Antarctica, which is exported to lower latitudes via the Antarctic Intermediate Water. This process weakens the zonal density stratification historically supported by surface temperature gradients, resulting in a slowdown of sub-surface zonal currents. Such a decline in transport, if realised, would have major implications on the global ocean circulation.

Abstract Faced with increasing tropical cyclone (TC) intensity in the western North Pacific (WNP) in recent decades, the simultaneous decrease in vertical wind shear (VWS) has been considered an important contributor. However, anthropogenic contribution to this decreased VWS remains uncertain. Here, we isolate the individual effects of greenhouse gases (GHS), aerosols, natural forcings, and internal climate variability on the decreased VWS over the WNP using multi-model ensemble simulations. We find that Eurasia’s inhomogeneous aerosol forcing triggers a southeastward-propagating wave train from central Europe and a meridional circulation teleconnection over southeastern Eurasia, inducing anomalous westerlies at 200 hPa in the WNP monsoon trough (MT) region. This dominates the weakening of VWS in the MT region, thereby promoting dynamic conditions favorable for increased TC intensity. Given that aerosol emissions in Europe show limited potential for further reduction, future aerosol emissions mitigation in East Asia is expected to intensify VWS over the WNP, thereby dampening the intensification of TC.

Abstract In July 2023, a series of heat extremes hit the Northern Hemisphere, which posed threats to vulnerable populations and societal infrastructure in Eastern Canada, the Mediterranean, and Central Asia. However, whether these record-shattering extremes were connected to each other remains unknown. Here we identify a dynamical linkage behind the spatiotemporal compounding nature of heatwaves over those three regions. By investigating the 2023 case and conducting historical analysis, we show that the Northern Hemispheric concurrent heatwaves in July 2023 can be attributed to a recurrent wave-6 pattern. In particular, pre-existing warmth and drought over Eastern Canada in early-July intensified the wave-6 teleconnection; which then led to extreme heatwaves over the Mediterranean and Central Asia in mid-July 2023. Furthermore, we reveal that the wave train was generated by early-July convection over the subtropical western Pacific. This, combined with the lowest May snow cover over North America in the past 40 years helped to warm Eastern Canada. Multiple models from the Coupled Model Intercomparison Project 6 are able to simulate those compound extremes connected by the wave-6 pattern with a high inter-model agreement. Our research offers insights into record-breaking compounding heatwaves in disparate parts of world during the mid-summer of 2023, with implications for disaster decision-making and risk management.

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Abstract The Siberian High (SibH), a prominent feature of the Northern Hemisphere atmospheric circulation, exhibited enhanced interdecadal variability since 1970, characterized by a sharp decline from 1970 to 1990 followed by a steep recovery from 1990 to 2010. The factors underpinning these variations are unclear. Using the CanESM5 large ensemble, including the single forcing simulations, we find that anthropogenic aerosols played an important role in influencing the above SibH trends on top of pronounced internally-generated variations. Changes in the SibH during both periods are embedded in aerosol-induced upper-tropospheric mid-latitude wave trains propagating from upstream regions, with subsequent downward propagation of the signal to the surface via three-dimensional dynamical adjustments. Further insights into the physical mechanisms using regional aerosol perturbation experiments with CESM1 reveal a dominant role of decreased North American aerosol emissions in driving the atmospheric wave train through interaction with the North Atlantic jet during the first period. In the second period, European aerosol emissions, characterized by a large and extensive decrease, are crucial to explain the SibH recovery. A better understanding of the factors driving multidecadal variability of the SibH, and in particular of the interplay between internal variability and external forcing, is critical to reducing uncertainties in future projections of regional extremes, such as cold surges, which can cause large social and economic impacts on densely populated East Asia.

Abstract River water temperature (T w) regimes are fundamental to freshwater ecosystem health and socioeconomic activities. Most T w research has focussed on magnitudes and averages, but rates of thermal change have been drastically understudied. Rapid T w increases (‘surges’) or decreases (‘plummets’) have been observed across individual catchments and short-term periods, but remain poorly characterized across broader space-time domains. To address this, we collated high-resolution T w data spanning the conterminous United States (US) between 2008–2023. We demonstrated the national-scale prevalence of surges (n = 6507) and plummets (n = 4787) that were recorded at 88 of the 102 monitoring stations. Both event types spanned freezing (snowmelt-fed systems) to extremely hot (>40 °C—geothermal influences) conditions. Most surges and plummets exhibited constrained durations (<1 h), amplitudes (≈1 °C) and rates of change (≈Δ1 °C/15 min), but some reached 24 h, 18.8 °C, and Δ11.3 °C/15 min, respectively. Successive transitions between rapid T w warming and cooling occurred predominantly in regulated systems, indicating dam-induced T w volatility. Surge and plummet characteristics differed between US climate regions. Such events were less widespread and frequent in the Northwest and West, with surges here most often occurring during regional droughts and heatwaves. Plummets recurred most consistently in the Southwest during summer months, and were also most common during notable hot and dry periods. Surges were most prevalent in space and time across the Southeast, and again were most common in summer. Surge and plummet counts were less variable year-to-year in the Northeast US, but significantly decreased across the study period. This research provides a critical step in characterizing rapid T w changes across broad spatial and temporal scales, thus opening prospects for future research exploring how varying catchment properties and hydroclimatic gradients govern surge and plummet dynamics. Such insights are critical for informing evidence-based management solutions targeting extreme T w variations and volatility.