Erica J. Hendy

X-ray micro-computed tomography (µCT) is widely used in environmental and ecological studies to visualise the complex skeletons of marine calcifying organisms. However, the potential to quantify skeletal density in marine calcifiers is complicated because µCT greyscale intensities are influenced by many factors. Here we constrain sources of error in coral skeletal densitometry and show how errors can be quantified, minimised and reported. We establish the accuracy and precision of density estimates by analysing a population of massive Porites spp. coral that vary in bulk average skeletal density (1.07–1.57 g cm−3), size (4–25 cm in diameter), mass (87.9–2176.5 g) and morphology (41 specimens scanned in 81 individual µCT acquisitions). The population mean offset between the µCT-derived density and actual values was 0.2 ± 4.6% (x- ± 1 SD, n = 41). Following acquisition-specific corrections based on bulk density offsets, equivalent internal regions of low and high density within repeatedly scanned corals under different settings varied by only ±0.8% (1 SD). We present a workflow for µCT laboratories to measure density, and minimise and report errors. Application of these recommendations will ultimately improve data comparison of coral skeletal growth assessments. The workflow recommendations are transferable to the µCT densitometry analysis of other marine calcifying organisms.

A tuned version of HadCM3 (HadCM3t) is used to simulate the climate of the mid‐Pliocene warm period (mPWP) and is compared with the original untuned version of HadCM3 (HadCM3u). After the tuning, HadCM3t performs as well as HadCM3u in simulating the preindustrial climate, but aligns better with the reconstructed mPWP sea surface temperature anomalies, primarily due to a better representation of high latitude warming. Regarding the mPWP climate anomaly relative to the preindustrial, compared to HadCM3u, HadCM3t produces stronger mid‐to‐high latitude warming with polar warming 2.2 times the global mean, which is higher than the 2.0 of HadCM3u. The warming of the mPWP is primarily explained by an increase in emissivity and surface albedo. The warming of the polar regions induced by emissivity and surface albedo from HadCM3t is higher by 0.6C and 0.7C respectively, than that from HadCM3u, leading to warmer mPWP high latitudes. The increase in shortwave radiation over the Polar Regions is driven mainly by changes in surface albedo, which lead to a temperature rise of +0.7C, and by changes in cloud cover, which contribute an additional +0.1C to the temperature increase. Here, the increased cloud‐induced shortwave radiation change is due to decreased cloud fraction and decreased cloud scattering effect; the increased surface albedo‐induced radiative effects result from the increased ice loss due to warm high latitudes. This tuning allows models like HadCM3 to better align with proxy data, offering a more reliable baseline for projecting future scenarios under similar conditions.

X-ray micro–computed tomography (µCT) is increasingly used to record the skeletal growth banding of corals. However, the wealth of data generated is time consuming to analyse for growth rates and colony age. Here we test an artificial intelligence (AI) approach to assist the expert identification of annual density boundaries in small colonies of massive Porites spanning decades. A convolutional neural network (CNN) was trained with µCT images combined with manually labelled ground truths to learn banding-related features. The CNN successfully predicted the position of density boundaries in independent images not used in training. Linear extension rates derived from CNN-based outputs and the traditional method were consistent. In the future, well-resolved 2D density boundaries from AI can be used to reconstruct density surfaces and enable studies focused on variations in rugosity and growth gradients across colony 3D space. We recommend the development of a community platform to share annotated images for AI.

The management of hydrological extremes and impacts on society is inadequately understood because of the combination of short-term hydrological records, an equally short-term assessment of societal responses and the complex multi-directional relationships between the two over longer timescales. Rainfall seasonality and inter-annual variability on the Pacific coast of Central America is high due to the passage of the Inter Tropical Convergence Zone (ITCZ) and the El Niño–Southern Oscillation (ENSO). Here we reconstruct hydrological variability and demonstrate the potential for assessing societal impacts by drawing on documentary sources from the cities of Santiago de Guatemala (now Antigua Guatemala) and Guatemala de la Asunción (now Guatemala City) over the period from 1640 to 1945. City and municipal council meetings provide a rich source of information dating back to the beginning of Spanish colonisation in the 16th century. We use almost continuous sources from 1640 AD onwards, including > 190 volumes of Actas de Cabildo and Actas Municipales (minutes of meetings of the city and municipal councils) held by the Archivo Histórico de la Municipalidad de Antigua Guatemala (AHMAG) and the Archivo General de Centro América (AGCA) in Guatemala City. For this 305-year period (with the exception of a total of 11 years during which the books were either missing or damaged), information relating to Catholic rogation ceremonies and reports of flooding events and crop shortages were used to classify the annual rainy season (May to October) on a five-point scale from very wet to very dry. In total, 12 years of very wet conditions, 25 years of wetter than usual conditions, 34 years of drier conditions and 21 years of very dry conditions were recorded. An extended drier period from the 1640s to the 1740s was identified and two shorter periods (the 1820s and the 1840s) were dominated by dry conditions. Wetter conditions dominated the 1760s–1810s and possibly record more persistent La Niña conditions that are typically associated with higher precipitation over the Pacific coast of Central America. The 1640s–1740s dry period coincides with the Little Ice Age and the associated southward displacement of the ITCZ.

Despite a growing literature on the climate response to solar geoengineering—proposals to cool the planet by increasing the planetary albedo—there has been little published on the impacts of solar geoengineering on natural and human systems such as agriculture, health, water resources, and ecosystems. An understanding of the impacts of different scenarios of solar geoengineering deployment will be crucial for informing decisions on whether and how to deploy it. Here we review the current state of knowledge about impacts of a solar‐geoengineered climate and identify the major research gaps. We suggest that a thorough assessment of the climate impacts of a range of scenarios of solar geoengineering deployment is needed and can be built upon existing frameworks. However, solar geoengineering poses a novel challenge for climate impacts research as the manner of deployment could be tailored to pursue different objectives making possible a wide range of climate outcomes. We present a number of ideas for approaches to extend the survey of climate impacts beyond standard scenarios of solar geoengineering deployment to address this challenge. Reducing the impacts of climate change is the fundamental motivator for emissions reductions and for considering whether and how to deploy solar geoengineering. This means that the active engagement of the climate impacts research community will be important for improving the overall understanding of the opportunities, challenges, and risks presented by solar geoengineering.

More than 5,000 km separates the frequently disturbed coral reefs of the Eastern Tropical Pacific (ETP) from western sources of population replenishment. It has been hypothesized that El Niño events facilitate eastward dispersal across this East Pacific Barrier (EPB). Here we present a biophysical coral larval dispersal model driven by 14.5 years of high-resolution surface ocean current data including the extreme 1997–1998 El Niño. We find no eastward cross-EPB connections over this period, which implies that ETP coral populations decimated by the 1998 bleaching event can only have recovered from eastern Pacific sources, in congruence with genetic data. Instead, rare connections between eastern and central Pacific reefs are simulated in a westward direction. Significant complexity and variability in the surface flows transporting larvae mean that generalized upper-ocean circulation patterns are poor descriptors of inter-regional connectivity, complicating the assessment of how climate change will impact coral gene flow Pacific wide.

Climate change has significant implications for biodiversity and ecosystems. With slow progress towards reducing greenhouse gas emissions, climate engineering (or ‘geoengineering’) is receiving increasing attention for its potential to limit anthropogenic climate change and its damaging effects. Proposed techniques, such as ocean fertilization for carbon dioxide removal or stratospheric sulfate injections to reduce incoming solar radiation, would significantly alter atmospheric, terrestrial and marine environments, yet potential side-effects of their implementation for ecosystems and biodiversity have received little attention. A literature review was carried out to identify details of the potential ecological effects of climate engineering techniques. A group of biodiversity and environmental change researchers then employed a modified Delphi expert consultation technique to evaluate this evidence and prioritize the effects based on the relative importance of, and scientific understanding about, their biodiversity and ecosystem consequences. The key issues and knowledge gaps are used to shape a discussion of the biodiversity and ecosystem implications of climate engineering, including novel climatic conditions, alterations to marine systems and substantial terrestrial habitat change. This review highlights several current research priorities in which the climate engineering context is crucial to consider, as well as identifying some novel topics for ecological investigation.