ALBERT

Description: Proposals to geoengineer Earth's climate by cirrus cloud thinning (CCT) potentially offer advantages over solar radiation management schemes: amplified cooling of the Arctic and smaller perturbations to global mean precipitation in particular. Using an idealized climate model implementation of CCT in which ice particle fall speeds were increased 2×, 4×, and 8× we examine the relationships between effective radiative forcing (ERF) at the top of atmosphere (TOA), near surface temperature and the response of the hydrological cycle. ERF was non-linear with fall speed change and driven by the trade-off between opposing positive shortwave and negative longwave radiative forcings. ERF was –2.0 Wm -2 for both 4× and 8× fall speeds. Global mean temperature decreased linearly with ERF while Arctic temperature reductions were amplified compared with the global mean change. The change in global mean precipitation involved a rapid adjustment, which was linear with the change in the net atmospheric energy balance (~ -1%/Wm -2 ), and a feedback response (~2%/ o C). Global mean precipitation and evaporation increased strongly in the first year of CCT. Intensification of the hydrological cycle was promoted by: intensification of the vertical overturning circulation of the atmosphere, changes in boundary layer climate favorable for evaporation, and increased energy available at the surface for evaporation (from increased net shortwave radiation and reduced sub-surface storage of heat). Such intensification of the hydrological cycle is a significant side effect to the cooling of climate by CCT. Any accompanying negative cirrus cloud feedback response would implicitly increase the costs and complexity of CCT deployment.

Description: In an assessment of how Arctic sea ice cover could be remediated in a warming world, we simulated the injection of SO 2 into the Arctic stratosphere making annual adjustments to injection rates. We treated one climate model realisation as a surrogate ‘real world’ with imperfect ‘observations’ and no re-running or reference to control simulations. SO 2 injection rates were proposed using a novel model predictive control regime which incorporated a second simpler climate model to forecast ‘optimal’ decision pathways. Commencing the simulation in 2018, Arctic sea ice cover was remediated by 2043 and maintained until solar geoengineering was terminated. We found quantifying climate side effects problematic because internal climate variability hampered detection of regional climate changes beyond the Arctic. Nevertheless, through decision maker learning and the accumulation of at least 10 years’ time series data exploited through an annual review cycle, uncertainties in observations and forcings were successfully managed.

Description: Solar radiation management schemes could potentially alleviate the impacts of global warming. One such scheme could be to brighten the surface of the ocean by increasing the albedo and areal extent of bubbles in the wakes of existing shipping. Here we show that ship wake bubble lifetimes would need to be extended from minutes to days, requiring the addition of surfactant, for ship wake area to be increased enough to have a significant forcing. We use a global climate model to simulate brightening the wakes of existing shipping by increasing wake albedo by 0.2 and increasing wake lifetime by ×1440. This yields a global mean radiative forcing of -0.9 ± 0.6 Wm -2 (-1.8 ± 0.9 Wm -2 in the Northern Hemisphere) and a 0.5 °C reduction of global mean surface temperature with greater cooling over land and in the Northern Hemisphere, partially offsetting greenhouse gas warming. Tropical precipitation shifts southwards but remains within current variability. The hemispheric forcing asymmetry of this scheme is due to the asymmetry in the distribution of existing shipping. If wake lifetime could reach ~3 months, the global mean radiative forcing could potentially reach -3 Wm -2 . Increasing wake area through increasing bubble lifetime could result in a greater temperature reduction but regional precipitation would likely deviate further from current climatology as suggested by results from our uniform ocean albedo simulation. Alternatively, additional ships specifically for the purpose of geoengineering could be used to produce a larger and more hemispherically symmetrical forcing.

Description: In this paper, we breakdown the temperature response of coupled ocean-atmosphere climate models into components due to radiative forcing, climate feedback, and heat storage and transport to understand how well climate models reproduce the observed 20th century temperature record. Despite large differences between models' feedback strength, they generally reproduce the temperature response well but for different reasons in each model. We show that the differences in forcing and heat storage and transport give rise to a considerable part of the intermodel variability in global, Arctic, and tropical mean temperature responses over the 20th century. Projected future warming trends are much more dependent on a model's feedback strength, suggesting that constraining future climate change by weighting these models on the basis of their 20th century reproductive skill is not possible. We find that tropical 20th century warming is too large and Arctic amplification is unrealistically low in the Geophysical Fluid Dynamics Laboratory CM2.1, Meteorological Research Institute CGCM232a, and MIROC3.2(hires) models because of unrealistic forcing distributions. The Arctic amplification in both National Center for Atmospheric Research models is unrealistically high because of high feedback contributions in the Arctic compared to the tropics. Few models reproduce the strong observed warming trend from 1918 to 1940. The simulated trend is too low, particularly in the tropics, even allowing for internal variability, suggesting there is too little positive forcing or too much negative forcing in the models at this time. Over the whole of the 20th century, the feedback strength is likely to be underestimated by the multimodel mean.

Description: Iglesias-Prieto et al. (1) present 24 h of continuous temperature, conductivity, and sea-level data recorded at a submarine spring in Mexico and argue that Crook et al. (2) attribute changes in coral calcification only to changes in aragonite saturation (Ωarag) while ignoring these other parameters and their variability. On the...

Description: [1]  Snow and ice albedo feedback plays an important role in the greater warming of the Arctic compared to the tropics. Previous work has estimated the observed Northern Hemisphere cryosphere feedback, but there have been no estimates of surface albedo feedback from observations globally. Here we compare the zonal mean surface albedo feedback from satellite datasets with that from eleven ocean-atmosphere coupled climate models for both climate change and the seasonal cycle. Differences between observed datasets make it difficult to constrain models. Nevertheless, we find that climate change Northern Hemisphere extratropical feedback is considerably higher for observations (potentially 3.1 ± 1.3 W m -2  K -1 ) than models (0.4-1.2 W m -2  K -1 ), whereas the seasonal cycle feedback is similar in observations and models, casting doubt on the ability of the seasonal cycle to accurately predict the climate change feedback. Observed Antarctic sea ice feedback is strongly positive in the seasonal cycle and similar to models.

Description: Historical and documentary records from the Petit Lac d’Annecy, indicate that human activities have been the dominant ‘geomorphic process’ shaping the catchment during the late Holocene, with deforestation, agriculture and artificial drainage profoundly affecting both the pace and spatial distribution of soil erosion. The impact of past climatic change on the evolution of the catchment is less certain because of the lack of long-term climate records for the site. Previous attempts to use the sediment record from the lake to investigate the role past climate change may have played were hampered by the difficulty in isolating and disentangling the climatic signal preserved within the archive, because of overprinting of human activity. This is a common problem in regions with a long history of human activity in the landscape. In this study we use a range of novel statistical techniques (including cross-correlation and cross spectral analysis) to assess the relative importance of climate in driving landscape dynamics. The statistical analysis is carried out on an updated high-resolution palaeo-environmental data set from the Petit Lac d’Annecy. The results of the statistical analysis indicate that regional climate phenomena such as the Atlantic multidecadal oscillation are partly responsible for landscape dynamics at Petit Lac d’Annecy throughout the late Holocene. We find that the Petit Lac d’Annecy catchment typically requires decades, or longer, to respond to changes in precipitation, reflecting the stochastic nature of river sediment storage and transport. The use of a 4 yr integrated lake core record effectively attenuates the ‘signal shredding’ effect of shorter-term internally generated sediment transport processes. Nonetheless, the lake record of climatically induced geormorphic process–responses is weak compared with the pervasive impact of human activities.

Description: How individuals respond to environmental change determines the strength and direction of biological processes like recruitment and growth that underpin population productivity. Ascertaining the relative importance of environmental factors can, however, be difficult given the numerous mechanisms through which they affect individuals. This is especially true in dynamic and complex estuarine environments. Here, we develop long-term otolith-based indices of recruitment and growth for estuary perch Percalates colonorum (Bemm River, Australia), to explore the importance of intrinsic (individual, demographic) and extrinsic (hydrologic, climatic, density-dependent) factors in driving estuarine fish productivity. Analyses involved a novel zero-inflated specification of catch curve regression and mixed effects modelling. The 39 years of recruitment and 46 years of growth data, spanning a period of environmental change including severe drought, displayed considerable inter-annual variation. Recruitment success was strongly related to high freshwater inflows during the spawning season, suggesting that these conditions act as spawning cues for adults and potentially provide favourable conditions for larvae. Individuals displayed age-dependent growth, with highest rates observed at younger ages in years characterised by warm temperatures, and to a lesser degree, greater magnitude base inflow conditions. We detected systematic among-year-class growth differences but these were not attributable to year class strength, suggesting that environmental conditions experienced by individuals as juveniles can have long-lasting effects of greater importance to population productivity than density-dependent growth responses. The primacy of temperature in driving growth variation highlights that under-appreciated climatic variation can affect estuarine fish productivity through direct physiological and indirect food web mechanisms. We predict that climatic warming will promote individual growth in southerly populations of P. colonorum but concurrently limit recruitment due to forecast reductions in spawning season river discharge. Disparate trait responses are likely in other fishes as they respond to multiple and changing environmental drivers, making predictions of future population productivity challenging. This article is protected by copyright. All rights reserved.

Description: Abstract The presence of lipids and urea in elasmobranch tissues can affect carbon (δ13C) and nitrogen (δ15N) stable isotope values, introducing bias in food web interpretations. Information on how lipids and urea affect δ13C/δ15N is only available for 〈 5% of ~ 1150 described elasmobranch species and results are highly variable among existing studies. Here, we investigate the effects of lipid and urea extraction on δ13C, δ15N, and C:N ratios in muscle and blood plasma of two batoids (Pastinachus ater and Himantura australis) and examine the influence of lipid/urea extraction on isotopic niche size and overlap. Lipid extraction (LE) did not affect δ13C, δ15N, or C:N ratios, suggesting low lipid content. Urea extraction (UE), however, increased δ15N and C:N in muscle. The ~ 1‰ δ15N increase represents a shift of ~ 0.5 trophic levels relative to bulk samples, highlighting the importance of UE to accurately assess trophic positions. Although there was no effect of any treatment on niche size, the probability of P. ater occurring within the niche of H. australis increased following UE. Overall, results suggest that urea should be removed from muscle prior to analysis, but LE is not required. Given the interspecific variability in the effects of lipid/urea on elasmobranch δ13C/δ15N, more studies are needed to assess the effects of lipid and urea on a broader range of species to produce a generalized understanding. Where no species‐specific data are available, we recommend pilot samples are analyzed to determine if LE is needed prior to preparation of the overall sample set.