The underestimations include some of the CMIP6 climate models which are used to inform the decisions around limiting global warming to 1.5C in the 2018 Paris Agreement.

A pioneering new study, led by Dr Marc Mallet from MeteoFrance in Toulouse, using satellite and ground-based remote sensing data backed-up by aircraft measurements has identified shortfalls in climate modelling in capturing the real climate effect of biomass-burning aerosols that are transported over the South-East Atlantic.

Professor Jim Haywood from the University of Exeter led the UK’s involvement in the field supporting measurement campaign and was a key partner on the modelling study led by Dr Mallet.

The study is published in the leading journal Science Advances on Friday, October 8th 2021.

Black carbon aerosols are microscopic particulates suspended in the atmosphere. They are generated by human-made and natural fires and absorb a significant amount of sunlight.

Black carbon’s ability to absorb sunlight means it can play a pivotal role in heating the atmosphere, and play a significant role in the effects of climate change at regional and continental scales.

The research team, including scientists from CNRM, the University of Lille and the UK Met Office compared how the CMIP6 models represented several crucial variables — including smoke aerosols, low-level stratocumulus clouds and solar absorption — using innovative and recent space-based remote-sensing observations, backed-up by aircraft observations.

It showed that biomass burning aerosols lead to an increase in absorbed sunlight over the South East Atlantic, something that would likely warm the climate system as a whole, while many models suggested the opposite — an erroneous cooling effect.

The research represents the culmination of several years of international efforts investigating smoke aerosols over the SE Atlantic from seasonal fires over Africa with satellite, surface-based, and in-situ sampling.

These efforts included operations of the UK’s heavily equipped FAAM research aircraft in August and September 2017, when the aircraft was based in Ascension Island in the middle of the Atlantic ocean, and the US-led ORACLES and LASIC programs and the French-led AEROCLO-Sa project.

Professor Jim Haywood, who led the detachment to Ascension Island and is a professor of Atmospheric Science at the University of Exeter and a Research Fellow at the Met Office Hadley Centre said, “The results from the study are quite conclusive. Despite decades of research, the climatic impacts of aerosols are still inadequately modelled by our climate models, which leads to significant uncertainties in future climate projections.”

Dr Ben Johnson, from the Hadley Centre added : “The heating from black carbon aerosol also has unique impacts on clouds and regional rainfall patterns, making it an important process to understand and capture in climate simulations. The Met Office and University of Exeter work closely on these issues together with other academic partners in the UK and wider international community, to better understand the role of aerosols in past and future climate change.”

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One of these structures is the large cylindrical tomb of first-century noblewoman Caecilia Metella. New research shows that the quality of the concrete of her tomb may exceed that of her male contemporaries’ monuments because of the volcanic aggregate the builders chose and the unusual chemical interactions with rain and groundwater with that aggregate over two millennia.

“The construction of this very innovative and robust monument and landmark on the Via Appia Antica indicates that she was held in high respect,” says Marie Jackson, research associate professor of geology and geophysics at the University of Utah, “and the concrete fabric 2,050 years later reflects a strong and resilient presence.”

The research is published in the Journal of the American Ceramic Society and is funded in part by the U.S. Department of Energy ARPA-e “Extreme Durability of Cementitious Materials” program.

Who was Caecilia Metella?

The tomb of Caecilia Metella is a landmark on the Via Appia Antica, an ancient Roman road also known as the Appian Way. It consists of a drum-shaped tower that sits on a square base, in total about 70 feet (21 m) tall and 100 feet (29 m) in diameter. Built about 30 BCE, at the transformation of the Roman Republic to the Roman Empire, led by Emperor Augustus, in 27 BCE, the tomb is considered one of the best-preserved monuments on the Appian Way (a castle attached to the tomb was built in the 14th century).

Caecilia herself was a member of a wealthy family, the daughter of a Roman consul. She married into the family of Marcus Lincius Crassus, a Roman general and statesman who formed a famous triumvirate alliance with Julius Caesar and Pompey.

Not much more is known about Caecilia’s life, but the enduring magnitude of her tomb has caught the attention of visitors for centuries, including Lord Byron who wrote of the tomb in “Childe Harold’s Pilgrimage” in the early 1800s. After describing the fortress-like structure, Byron asks:

“What was this tower of strength? within its cave

What treasure lay so lock’d, so hid? — A woman’s grave.”

Jackson visited the tomb in 2006 with archaeologist Dottoressa Lisa Gianmichele and with a permit from the Soprintendenza Archeologia di Roma to collect small samples of the mortar for analysis.

“It was a very warm day in June,” she says, “yet when we descended the steps to the sepulchral corridor the air became very cool and moist.” She notes the compact, cohesive, nearly perfectly preserved brick masonry walls and the nearly water-saturated volcanic rock outcrop in the sub-structure.

“The atmosphere was very tranquil,” she adds, “except for the fluttering of pigeons in the open center of the circular structure.”

What is Roman concrete?

Before diving into the particulars, let’s get oriented to the terminology of concrete. Walk along most any sidewalk and you’ll see that concrete is made of an aggregate (rock sands and gravels) and a cement binder. The cement in a modern sidewalk is likely Portland cement, produced by heating limestone and clay minerals in a kiln to form clinker, grinding the clinker and adding a small amount of gypsum.

The tomb is an example of the refined technologies of concrete construction in late Republican Rome that contain no cement. The technologies were described by the architect Vitruvius during the period when the tomb of Caecilia Metella was under construction. Building thick walls of coarse brick or volcanic rock aggregate bound with mortar made with hydrated lime and volcanic tephra (porous fragments of glass and crystals from explosive eruptions), would result in structures that “over a long passage of time do not fall into ruins.”

Vitruvius’ words are proven true by the many Roman structures standing today, including Markets of Trajan (built between 100 and 110 CE, more than a century after the tomb) and marine structures like piers and breakwaters, which Jackson and her colleagues have also studied.

What the ancient Romans couldn’t have known, though, is how crystals of the mineral leucite, which is rich in potassium, in the volcanic tephra aggregate would dissolve over time to beneficially remodel and reorganize the cohesion of the concrete.

To understand the mineral structure of the concrete, Jackson teamed up with researchers Linda Seymour and Admir Masic from the Massachusetts Institute of Technology and Nobumichi Tamura at the Lawrence Berkeley National Laboratory. They delved into the microstructure of the concrete with an array of powerful scientific tools.

“Samples such as ancient mortar are highly heterogeneous and complex, made of a mixture of different crystalline phases with grain sizes ranging from a few micrometers down to a few nanometers,” says Tamura, who conducted analyses using the Advanced Light Source beamline 12.3.2. To identify the different minerals in the sample, as well as their orientation, he says, you need an instrument like the microdiffraction beamline at the Advanced Light Source that produces a “micron size, extremely bright and energetic pencil X-ray beam that can penetrate through the entire thickness of the samples, making it a perfect tool for such a study.”

Seymour, who participated in this study as a Ph.D. student at MIT and is now a project consultant with engineering firm Simpson, Gumpertz & Heger, conducted additional analyses on the samples.

“Each of the tools that we used added a clue to the processes in the mortar,” she says. Scanning electron microscopy showed the micro-structures of mortar building blocks at the micron scale. Energy-dispersive X-ray spectrometry showed the elements comprising each of those building blocks. “This information allows us to explore different areas in the mortar quickly, and we could pick out building blocks related to our questions,” she says. The trick, she adds, is to precisely hit the same building block target with each instrument when that target is only about the width of a hair.

Why is the concrete at Caecilia’s tomb so unique?

In the thick concrete walls of Caecilia Metella’s tomb, a mortar that contains volcanic tephra from the nearby Pozzolane Rosse pyroclastic flow (a dense mass of hot tephra and gases ejected explosively from the nearby Alban Hills volcano) binds large chunks of brick and lava aggregate. It is much the same mortar used in the walls of the Markets of Trajan 120 years later.

In previous analysis of the Markets of Trajan mortar, Jackson, Tamura and their colleagues explored the “glue” of the mortar, a building block called the C-A-S-H binding phase (calcium-aluminum-silicate-hydrate), along with a mineral called strätlingite. The strätlingite crystals block the propagation of microcracks in the mortar, preventing them from linking together and fracturing the concrete structure.

But the tephra the Romans used for the Caecilia Metella mortar was more abundant in potassium-rich leucite. Centuries of rainwater and groundwater percolating through the tomb’s walls dissolved the leucite and released the potassium into the mortar. In modern concrete, such a flood of potassium would create expansive gels that would cause microcracking and eventual spalling and deterioration of the structure.

In the tomb, however, the potassium dissolved and reconfigured the C-A-S-H binding phase. Seymour says that X-ray microdiffraction and Raman spectroscopy techniques allowed them to explore how the mortar had changed. “We saw C-A-S-H domains that were intact after 2,050 years and some that were splitting, wispy or otherwise different in morphology,” she says. X-ray microdiffraction, in particular, allowed an analysis of the wispy domains down to their atomic structure. “We see that the wispy domains are taking on a nano-crystalline nature,” she says.

The remodeled domains “evidently create robust components of cohesion in the concrete,” says Jackson. In these structures, unlike in the Markets of Trajan, there’s much less strätlingite formed.

Stefano Roascio, the archaeologist in charge of the tomb, notes that the study has a great deal of relevance to understanding other ancient and historic concrete structures that use Pozzolane Rosse aggregate.

Admir Masic, associate professor of civil and environmental engineering at MIT, says that the interface between the aggregates and the mortar of any concrete is fundamental to the structure’s durability. In modern concrete, he says, the alkali-silica reactions that form expansive gels may compromise the interfaces of even the most hardened concrete.

“It turns out that the interfacial zones in the ancient Roman concrete of the tomb of Caecilia Metella are constantly evolving through long-term remodeling,” he says. “These remodeling processes reinforce interfacial zones and potentially contribute to improved mechanical performance and resistance to failure of the ancient material.”

Can we recreate that effect today?

Jackson and her colleagues are working to replicate some of the Romans’ successes in modern concretes, specifically in a U.S. Department of Energy ARPA-e project to encourage similar beneficially reactive aggregates in concretes that use engineered cellular magmatics in place of the tephra of the ancient Roman structures. The objective, according to ARPA-e, is that a Roman-like concrete could reduce the energy emissions of concrete production and installation by 85% and improve the 50-year lifespan of modern marine concretes four-fold.

“Focusing on designing modern concretes with constantly reinforcing interfacial zones might provide us with yet another strategy to improve the durability of modern construction materials,” Masic says. “Doing this through the integration of time-proven ‘Roman wisdom’ provides a sustainable strategy that could improve the longevity of our modern solutions by orders of magnitude.”

According to Haruna Katayama, a doctoral student in Hiroshima University’s Graduate School of Advanced Science and Engineering, since researchers cannot go to the Hawking radiation, Hawking radiation must be brought to the researchers. She has proposed a quantum circuit that acts as a black hole laser, providing a lab-bench black hole equivalent with advantages over previously proposed versions. The proposal was published on Sept. 27 Scientific Reports.

“In this study, we devised a quantum-circuit laser theory using an analogue black hole and a white hole as a resonator,” Katayama said.

A white hole is a theoretical partner of a black hole that emits light and matter in equal opposition to light and matter a black hole consumes. In the proposed electric circuit, a metamaterial engineered to allow faster-than-light motion spans the space between horizons, near which Hawking radiation is emitted.

“The property of superluminal speed is impossible in a normal medium established in an ordinary circuit,” Katayama said. “The metamaterial element makes it possible for Hawking radiation to travel back and forth between horizons, and the Josephson effect — which describes a continuous flow of current that propagates without voltage — plays an important role in amplifying the Hawking radiation through the mode conversion at the horizons, mimicking the behavior between the white and black holes.”

Katayama’s proposal builds on previously proposed optical black hole lasers by introducing the metamaterial that allows for superluminal speed and exploiting the Josephson effect to amplify the Hawking radiation. The resulting quantum circuit induces a soliton, a localized, self-reinforcing waveform that maintains speed and shape until external factors collapse the system.

“Unlike previously proposed black hole lasers, our version has a black hole/white hole cavity formed within a single soliton, where Hawking radiation is emitted outside of the soliton so we can evaluate it,” Katayama said.

Hawking radiation is produced as entangled particle pairs, with one inside and one outside the horizon. According to Katayama, the observable entangled particle bears the shadow of its partner particle. As such, the quantum correlation between the two particles can be determined mathematically without the simultaneous observation of both particles.

“The detection of this entanglement is indispensable for the confirmation of Hawking radiation,” Katayama said.

However, Katayama cautioned, the lab Hawking radiation differs from true black hole Hawking radiation due to the normal dispersion of light in the proposed system. The components of light split in one direction, like in a rainbow. If the components can be controlled so that some can reverse and bounce back, the resulting lab-made Hawking radiation would mirror the same positive frequency of true black hole Hawking radiation. She is now investigating how to integrate anomalous dispersion to achieve a more comparable result.

“In the future, we would like to develop this system for quantum communication between distinct spacetimes using Hawking radiation,” Katayama said, noting the system’s scalability and controllability as advantages in developing quantum technologies.

The Japan Society for the Promotion of Science supported this research.

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The research is an important step toward forecasting how much carbon will leave the ocean for the atmosphere as greenhouse gas carbon dioxide and how much will end up entombed in marine sediments, said Ryan Mueller, associate professor in OSU’s Department of Microbiology and the leader of the study.

Findings were published today in the Proceedings of the National Academy of Sciences.

“Our research shows that different species of microbes in the ocean are very particular yet predictable in the food sources they prefer to eat,” said first author Brandon Kieft, a recent Oregon State Ph.D. graduate who is now a postdoctoral researcher at the University of British Columbia. “As global climate change continues to alter oceanic environments at a rapid pace, the availability of food sources for microbes will also change, ultimately favoring certain types over others.”

Phytoplankton are microscopic organisms at the base of the ocean’s food chain and a key component of a critical biological carbon pump. Most float in the upper part of the ocean, where sunlight can easily reach them.

The tiny autotrophic plants — they make their own food — have a big effect on the levels of carbon dioxide in the atmosphere by sucking it up during photosynthesis. It’s a natural sink and one of the primary ways that CO₂, the most abundant greenhouse gas, is scrubbed from the atmosphere; atmospheric carbon dioxide has increased 40% since the dawn of the industrial age, contributing heavily to a warming planet.

“We’re studying the consumers — the heterotrophic microbes — of the organic material made by the primary producers, the microbial phytoplankton,” Mueller said. “Both groups are microbes, the former primarily consumes organic carbon as a food source, while the latter ‘fix’ their own organic carbon. Microbes form the basis of the food web and biological carbon pump, and our work is primarily focused on exploring what the consumers are doing in this system.”

The surface ocean stores nearly as much carbon as exists in the atmosphere. As the ocean pulls in atmospheric carbon dioxide, phytoplankton use the CO₂ and sunlight for photosynthesis: They convert them into sugars and other compounds the cells can use for energy, producing oxygen in the process.

This so-called fixed carbon makes up the diet of heterotrophic microbes and higher organisms of the marine food web such as fish and mammals, which ultimately convert the carbon back to atmospheric CO₂ through respiration or contribute to the carbon stock at the bottom of the ocean when they die and sink.

The collective respiratory activity of the heterotrophic microbial consumers is the main way that fixed dissolved organic carbon from phytoplankton is returned to the atmosphere as CO₂.

Mueller, Kieft and collaborators at the Oak Ridge and Lawrence Livermore national laboratories and the universities of Tennessee, Washington and Oklahoma used stable isotope labeling to track carbon as it made its way into the organic matter produced by the phytoplankton and, ultimately, the heterotrophic microbes that consume it.

The scientists used those isotopes to tell which organisms were eating diatoms and which were consuming cyanobacteria, two species of phytoplankton that combine to produce a majority of the ocean’s fixed carbon. The researchers could also tell when the consumption was happening — for example, at times the phytoplankton cells were producing substances known as lysates during their death phase or exudates during their growth phase.

“Our findings have important implications for understanding how marine microbes and photosynthetic algae function together to impact global carbon cycling and how this oceanic food web may respond to continued environmental change,” Kieft said. “This will help us predict how much carbon will go back into the atmosphere and how much will be buried in marine sediments for centuries.”

The research was funded by the Gordon and Betty Moore Foundation Marine Biology Initiative and the U.S. Department of Energy.