Equilibrium climate sensitivity, the global surface temperature response to CO
2 doubling, has been persistently uncertain. Recent consensus places it likely within 1.5–4.5 K. Global climate models ...(GCMs), which attempt to represent all relevant physical processes, provide the most direct means of estimating climate sensitivity via CO
2 quadrupling experiments. Here we show that the closely related effective climate sensitivity has increased substantially in Coupled Model Intercomparison Project phase 6 (CMIP6), with values spanning 1.8–5.6 K across 27 GCMs and exceeding 4.5 K in 10 of them. This (statistically insignificant) increase is primarily due to stronger positive cloud feedbacks from decreasing extratropical low cloud coverage and albedo. Both of these are tied to the physical representation of clouds which in CMIP6 models lead to weaker responses of extratropical low cloud cover and water content to unforced variations in surface temperature. Establishing the plausibility of these higher sensitivity models is imperative given their implied societal ramifications.
Plain Language Summary
The severity of climate change is closely related to how much the Earth warms in response to greenhouse gas increases. Here we find that the temperature response to an abrupt quadrupling of atmospheric carbon dioxide has increased substantially in the latest generation of global climate models. This is primarily because low cloud water content and coverage decrease more strongly with global warming, causing enhanced planetary absorption of sunlight—an amplifying feedback that ultimately results in more warming. Differences in the physical representation of clouds in models drive this enhanced sensitivity relative to the previous generation of models. It is crucial to establish whether the latest models, which presumably represent the climate system better than their predecessors, are also providing a more realistic picture of future climate warming.
Key Points
Climate sensitivity is larger on average in CMIP6 than in CMIP5 due mostly to a stronger positive low cloud feedback
This is due to greater reductions in low cloud cover and weaker increases in low cloud water content, primarily in the extratropics
These changes are related to model physics differences that are apparent in unforced climate variability
Popular culture is rife with movies, books, and television shows that address our collective curiosity about what the world was like long ago. From historical dramas to science fiction tales of time ...travel, audiences love stories that reimagine the world before our time. But what if there were a field that, through the advancements in technology, could bring us closer to the past than ever before? Written by a preeminent expert in geospatial archaeology, Maps for Time Travelers is a guide to how technology is revolutionizing the way archaeologists study and reconstruct humanity's distant past. From satellite imagery to 3D modeling, today archaeologists are answering questions about human history that could previously only be imagined. As archaeologists create a better and more complete picture of the past, they sometimes find that truth is stranger than fiction.
Increasing optical depth poleward of 45° is a robust response to warming in global climate models. Much of this cloud optical depth increase has been hypothesized to be due to transitions from ...ice‐dominated to liquid‐dominated mixed‐phase cloud. In this study, the importance of liquid‐ice partitioning for the optical depth feedback is quantified for 19 Coupled Model Intercomparison Project Phase 5 models. All models show a monotonic partitioning of ice and liquid as a function of temperature, but the temperature at which ice and liquid are equally mixed (the glaciation temperature) varies by as much as 40 K across models. Models that have a higher glaciation temperature are found to have a smaller climatological liquid water path (LWP) and condensed water path and experience a larger increase in LWP as the climate warms. The ice‐liquid partitioning curve of each model may be used to calculate the response of LWP to warming. It is found that the repartitioning between ice and liquid in a warming climate contributes at least 20% to 80% of the increase in LWP as the climate warms, depending on model. Intermodel differences in the climatological partitioning between ice and liquid are estimated to contribute at least 20% to the intermodel spread in the high‐latitude LWP response in the mixed‐phase region poleward of 45°S. It is hypothesized that a more thorough evaluation and constraint of global climate model mixed‐phase cloud parameterizations and validation of the total condensate and ice‐liquid apportionment against observations will yield a substantial reduction in model uncertainty in the high‐latitude cloud response to warming.
Key Points
GCMs partition condensate phase dependent upon temperature
20–80% of GCM LWP response to warming is due to the repartitioning of condensate
Model spread in LWP response is reduced using a single glaciation temperature
Archaeological evidence of people's choices regarding how they supply themselves with obsidian through direct access and different types of exchanges gives us insight in to mobility, social networks, ...and property rights in the distant past. Here we use collections of obsidian artefacts that date to a period of endemic warfare among Maori during New Zealand's Late Period (1500-1769 A.D.) to determine what strategies people engaged in to obtain obsidian, namely (1) collecting raw material directly from a natural source, (2) informal trade and exchange, and (3) formal trade and exchange. These deposits represent a good cross-section of Late Period archaeology, including primary working of raw material at a natural source (Helena Bay), undefended sites where people discarded rubbish and worked obsidian (Bream Head), and a heavily fortified site (Mt. Wellington). We find that most of the obsidian described here was likely obtained directly from natural sources, especially those located on off-shore islands within about 60-70 km of sites. A smaller amount comes from blocks of material transported from an off-shore island a greater distance away, called Mayor Island, in a formal trade and exchange network. This study demonstrates the value of conducting tandem lithic technology and geochemical sourcing studies to understand how people create and maintain social networks during periods of warfare.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In this study, it is shown that CMIP5 global climate models (GCMs) that convert supercooled water to ice at relatively warm temperatures tend to have a greater mean‐state cloud fraction and more ...negative cloud feedback in the middle and high latitude Southern Hemisphere. We investigate possible reasons for these relationships by analyzing the mixed‐phase parameterizations in 26 GCMs. The atmospheric temperature where ice and liquid are equally prevalent (T5050) is used to characterize the mixed‐phase parameterization in each GCM. Liquid clouds have a higher albedo than ice clouds, so, all else being equal, models with more supercooled liquid water would also have a higher planetary albedo. The lower cloud fraction in these models compensates the higher cloud reflectivity and results in clouds that reflect shortwave radiation (SW) in reasonable agreement with observations, but gives clouds that are too bright and too few. The temperature at which supercooled liquid can remain unfrozen is strongly anti‐correlated with cloud fraction in the climate mean state across the model ensemble, but we know of no robust physical mechanism to explain this behavior, especially because this anti‐correlation extends through the subtropics. A set of perturbed physics simulations with the Community Atmospheric Model Version 4 (CAM4) shows that, if its temperature‐dependent phase partitioning is varied and the critical relative humidity for cloud formation in each model run is also tuned to bring reflected SW into agreement with observations, then cloud fraction increases and liquid water path (LWP) decreases with T5050, as in the CMIP5 ensemble.
Key Points:
Cloud cover and mixed‐phase parameterizations have compensating effects on planetary albedo in GCMs.
Models that maintain liquid to lower temperatures have less cloud cover.
This compensation affects both the climate mean‐state and cloud feedback.
Large celebrations in ancient societies, when viewed through the lens of political economy theory, were opportunities for economic redistribution, elite rivalry and social integration. Metrics to ...evaluate celebratory behaviour - such as festive gatherings, offerings at temples and shrines, games and memorials - remain underdeveloped. Here the author examines the archaeological and historical evidence for the Makahiki festival in the Hawaiian Islands. He takes a direct historical approach combining independent datasets to classify settings of celebrations and evaluate claims that the Makahiki festival originated, and was most elaborate, on Hawai'i Island, as well as that the festival was practised differently across the archipelago. The author finds that the relevant data collected over more than a century of archaeology are not sufficient to support these claims and that the distribution of tracks for the sledding sport (hōlua) might be a fruitful avenue for future research, especially when investigating elite rivalry. More speculatively, the author argues that it is possible to decipher choices in architectural design and location at royal centres that speak to attempts by the elite to artificially increase the density of crowds at low turn-out events while at the same time leaving enough room to accommodate high turn-out events.
Marine environments are rich in natural resources, and therefore, have been targeted for human occupation from at least the Pleistocene. In the modern day, the preservation and documentation of the ...physical archaeological evidence of human occupation and use of coasts, islands, and the ocean must now include mitigating the impacts of global climate change. Here, I review recent efforts to document archaeological sites across the islands of Polynesia using geospatial technology, specifically remote sensing, high-resolution documentation, and the creation of archaeological site geodatabases. I discuss these geospatial technologies in terms of planning for likely future impacts from sea level rise; a problem that will be felt across the region, and based on current evidence, will affect more than 12% of all known sites in New Zealand (Aotearoa).
The extratropical shortwave (SW) cloud feedback is primarily due to increases in extratropical liquid cloud extent and optical depth. Here, we examine the response of extratropical (35°–75°) marine ...cloud liquid water path (LWP) to a uniform 4-K increase in sea surface temperature (SST) in global climate models (GCMs) from phase 5 of the Coupled Model Intercomparison Project (CMIP5) and variants of the HadGEM3-GC3.1 GCM. Compositing is used to partition data into periods inside and out of cyclones. The response of extratropical LWP to a uniform SST increase and associated atmospheric response varies substantially among GCMs, but the sensitivity of LWP to cloud controlling factors (CCFs) is qualitatively similar. When all other predictors are held constant, increasing moisture flux drives an increase in LWP. Increasing SST, holding all other predictors fixed, leads to a decrease in LWP. The combinations of these changes lead to LWP, and by extension reflected SW, increasing with warming in both hemispheres. Observations predict an increase in reflected SW over oceans of 0.8–1.6 W m−2 per kelvin SST increase (35°–75°N) and 1.2–1.9 W m−2 per kelvin SST increase (35°–75°S). This increase in reflected SW is mainly due to increased moisture convergence into cyclones because of increasing available moisture. The efficiency at which converging moisture is converted into precipitation determines the amount of liquid cloud. Thus, cyclone precipitation processes are critical to constraining extratropical cloud feedbacks.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
As spatial technology has evolved and become integrated in to archaeology, we face a new set of challenges posed by the sheer size and complexity of data we use and produce. In this paper I discuss ...the prospects and problems of Geospatial Big Data (GBD) – broadly defined as data sets with locational information that exceed the capacity of widely available hardware, software, and/or human resources. While the datasets we create today remain within available resources, we nonetheless face the same challenges as many other fields that use and create GBD, especially in apprehensions over data quality and privacy. After reviewing the kinds of archaeological geospatial data currently available I discuss the near future of GBD in writing culture histories, making decisions, and visualizing the past. I use a case study from New Zealand to argue for the value of taking a data quantity-in-use approach to GBD and requiring applications of GBD in archaeology be regularly accompanied by a Standalone Quality Report.
•Geospatial Big Data in archaeology today include archival and integrative databases.•Geodata are important to culture history, decision making, and visualization.•Near future impacts of Geospatial Big Data include data access, ethics, and outreach.•Requiring Standalone Quality Reports may help overcome apprehensions regarding the adequacy of GBD and promote improvements.
Irrigated agriculture was central to the economies of many of the world’s best known complex societies. New high-resolution digital elevation models (DEM) derived from remotely sensed lidar data give ...archaeologists the opportunity to study field systems at a scale not previously possible. Here we describe a method called slope contrast mapping that takes advantage of the dissimilarity between artificial and natural slopes to identify and map discrete features. We use this relatively simple method in our own research to identify complexes of agricultural terraces in the North Kohala district, Hawai’i Island. It has also proved useful for mapping the natural landscape, specifically the extent of flat land between valleys suited for irrigated agriculture.
► We present a slope contrast method for interpreting LiDAR in a GIS environment. ► The method is ideal for identifying archaeological features, like earthworks. ► We present revised estimates for agricultural production based on this method.
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