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Californian grasslands set to store carbon more reliably than forests

Forests absorb roughly one quarter of the carbon dioxide pollution produced by humans worldwide. Yet in California this century, grasslands and rangelands will be more resilient carbon sinks than forests, a new study has found.

“Looking ahead, our model simulations show that grasslands store more carbon than forests because they are impacted less by droughts and wildfires,” says Pawlok Dass of the University of California Davis, US. “This doesn’t even include the potential benefits of good land management to help boost soil health and increase carbon stocks in rangelands.”

Whilst forests mostly store carbon in woody biomass and leaves, grasslands sequester most of their carbon underground in roots and soil, where it largely remains even after a fire.

Since 2010, about 130 million trees have died in Californian forests due to high tree densities combined with climate change, drought and bark beetle infestation, according to the US Forest Service. Eight of the state’s 20 most destructive fires occurred in the past four years, with the five largest fire seasons all taking place since 2006.

“In a stable climate, trees store more carbon than grasslands,” says Benjamin Houlton, also of the University of California Davis. “But in a vulnerable, warming, drought-likely future, we could lose some of the most productive carbon sinks on the planet. California is on the frontlines of the extreme weather changes that are beginning to occur all over the world. We really need to start thinking about the vulnerability of ecosystem carbon, and use this information to de-risk our carbon investment and conservation strategies in the 21st century.”

California’s cap-and-trade market is designed to reduce the state’s greenhouse gas emissions to 40% below 1990 levels by 2030. The study indicates that grasslands should be given opportunities in the market, according to a UC Davis press release.

The findings could inform similar carbon offset efforts around the globe, particularly those in semi-arid environments, which cover roughly 40% of the planet.

Dass, Houlton and colleagues modelled four scenarios: a substantial decline in carbon emissions, with up to 1.7°C of temperature rise by 2100; business as usual, resulting in up to 4.8°C of warming; periodic drought; and megadrought, lasting for a century or more.

California’s grasslands were more reliable carbon sinks than trees in all but the first scenario. Grasslands continued to store some carbon even during the team’s simulations of extreme drought.

“Trees and forests in California are a national treasure and an ecological necessity,” says Houlton. “But when you put them in assuming they’re carbon sinks and trading them for pollution credits while they’re not behaving as carbon sinks, emissions may not decrease as much as we hope.”

As long as trees are part of the cap-and-trade portfolio, the researchers note, protecting that investment through strategies that would reduce severe wildfire and encourage drought-resistant trees, such as prescribed burns, strategic thinning and replanting, would likely reduce carbon losses.

The team reported the findings in Environmental Research Letters (ERL).

Beam’s eye MRI could guide radiotherapy

Alberta team — B. Gino Fallone, Keith Wachowicz and Brad Murray from the University of Alberta.

Image guided radiotherapy (IGRT) is the state-of-the-art in radiation treatment, and the recent introduction of integrated MRI-linac systems adds potential for real-time tumour tracking during beam delivery. But achieving this requires the ability to quickly and accurately determine the position of the target volume and critical structures from the MR images.

Because radiotherapy uses a divergent beam emanating from a single point, conventional pre-treatment simulation using CT requires the creation of “ray-traced” digital reconstruction radiographs to generate a beam’s-eye-view (BEV) image that represents the path of the treatment beam. Conventional MR image slices, however, have pixels that represent volume elements arranged parallel to each other.

When MRI is used to track structures for real-time radiotherapy guidance, these two coordinate geometries do not match and tracking errors can result, especially for thick image slices. Divergent ray-tracing of MR images is technically possible, but not suitable for real-time guidance due to lengthy 3D acquisition and ray-tracing reconstruction times.

Now, Keith Wachowicz, Brad Murray and B. Gino Fallone from the University of Alberta have developed a theoretical framework that allows – for the first time – direct acquisition of BEV projection images in MRI. They also describe how their concept can be applied to various types of MRI-linac configurations (Phys. Med. Biol. 63 125002).

“The BEV encoding gradients proposed in this work would allow direct acquisition of tracking images in the same geometry as the treatment beam, avoiding any potential for tracking errors due to the geometry mismatch,” explains first author Wachowicz.

Warping fields

To use MRI to track anatomy in real time, the researchers propose the use of non-conventional gradient field patterns, implemented through hardware additions to a standard scanner architecture. They developed nonlinear encoding gradient fields that allow MR images to be generated in a divergent beam geometry. For MRI-linac systems where the radiation source is fixed relative to the magnet, adding two warping coils to the linear X and Y coils can produce these encoding fields.

For MRI-linac architectures in which the beam source is not fixed to the imaging magnet, the identified warping field pattern will only be appropriate for one source position. In such cases, the researchers showed that a basis set of second-order spherical harmonic functions, together with linear gradients, provides a good approximation of the BEV gradient patterns at any angle.

They propose the use of a set of second-order warping coils fixed to the magnet, employed in various combinations to generate the conditions for divergent imaging as the source rotates. This would require four additional warping coils.

Proof of principle

To test their proposed theory, the researchers used a 3T scanner to image a phantom with nonlinear encoding-gradient field patterns. The phantom comprised gel-filled rods oriented to converge at a single point 100 cm away.

As the derived encoding gradients are not readily available, they approximated the ideal warping field to a second-order field gradient and created this using second-order shim coils. Such coils, however, are not currently designed for rapid switching in tandem with the linear encoding gradients.

“To test the feasibility of this approach in an environment without rapid-switching capability, we had to first find a sequence that maintained as much as possible a constant encoding gradient amplitude during image encoding. The closest match we could find was a short-echo radial acquisition,” Wachowicz explains. “Secondly, we had to manually alter the shim coil currents according to our calculations for each of the 102 radial spokes that we acquired.”

To circumvent hardware limitations, the researchers also created a corresponding virtual phantom. They simulated three images, using: conventional linear gradients; switched linear-encoding gradients and unswitched warping fields (to mimic the experiment); and linear-encoding gradients and warping fields switched in tandem (representing an ideal implementation).

Simulated and acquired images — Simulated and physically acquired images with and without BEV companion fields on a phantom with divergent geometry.

Images of the phantom generated with traditional parallel geometry over its full 12 cm thickness exhibited blurring, as expected. When images were acquired with (unswitched) warping field patterns, much of this blurring was absent. However, the tubes still appeared distorted, particularly those farthest from the isocentre.

The authors believed that a switched set of warping fields – as would be present in any physical implementation of this technique – would remove the bulk of this residual distortion. Simulations with companion fields switched in tandem with the read gradients produced images with all of the tubes clearly discernible, successfully validating their technique.

Hybrid linac-MR — The Aurora RT hybrid linac-MR system developed at the Cross Cancer Institute in Edmonton, Alberta.

The team is now planning to move this approach towards clinical application. “We expect to include a set of BEV coils within the Alberta (Edmonton) biplanar linac-MR hybrid design,” says Fallone.

Hydrogen dissociation measurement puts theory at odds with experiment

The most precise experimental value for the dissociation energy of molecular hydrogen has been measured by an international team led by Wim Ubachs at VU Amsterdam and Frédéric Merkt at the Swiss Federal Institute of Technology (ETH Zurich). The measurement delivers an order of magnitude improvement over the previous best and is a significant deviation from the most recent theoretical calculations. Resolving this discrepancy could lead to improvements in molecular quantum theory and could result in a better measured value for the proton radius.

The hydrogen dissociation energy is the amount of energy required to separate the two atoms in a hydrogen molecule. To measure the value, physicists have previously broken down the process into a thermodynamic cycle of intermediate transitions where the molecule is first ionized, and then split into a proton and a hydrogen atom. An electron is then added to the proton, forming two neutral hydrogen atoms. Physicists then calculate the molecular dissociation energy by summing the excitation energies for each of these transitions.

The dissociation energy can also be calculated theoretically; accounting for relativistic and quantum-electrodynamic effects. Comparing the theoretical result with experimental values has previously allowed for stringent tests of quantum theory. Experiment and theory have agreed with each other in previous studies, even as the accuracy of experiments improved.

New transition sequence

To improve accuracy further, Ubachs, Merkt and colleagues obtained a more precise value for the ionization energy – which is the stage of the dissociation process with the largest experimental uncertainty. They achieved this using a new sequence of transitions, which involved measuring a high-energy transition with vacuum-ultraviolet light at VU, then a lower-energy transition with an ultraprecise continuous-wave near-infrared laser spectroscopy at ETH. Combining the results, the researchers calculated a dissociation energy with a relative uncertainty of under 10⁻⁹.

Proton radius mystery deepens as deuterium measurement comes up short

Photograph of the laser system that was used for the laser spectroscopy measurements

The result is in line with previous experimental results, yet it appears to deviate from the most recent theoretical calculations by more than three times the experimental uncertainty. Writing in Physical Review Letters, the physicists note that adjustments may be needed to how relativistic electron motion and quantum vacuum fluctuations are treated in calculations. Alternatively, the mismatch could point a more fundamental problem in molecular quantum theory.

Resolving the discrepancy could offer a new way to determine the radius of a proton and could also lead to better measurements of the proton-to-electron mass ratio. Precise measurements of these quantities have the potential to reveal news physics.

Borrowing Einstein’s body, fluid mechanics of dripping taps, birds and spiders devour insect energy

Are you feeling a bit down on your cognitive abilities on a Friday afternoon? The best way to stay sharp for the rest of the day is to assume the physical identity of Albert Einstein – according to Mel Slater and colleagues at the University of Barcelona. Writing in Frontiers in Psychology, the team describe how they embedded male subjects into “virtual bodies” of either Einstein or an average man. The Einstein-embedded subjects performed better at an IQ test than those who appeared as average blokes. The difference was greatest for people with low self-esteem. So, the next time you have an exam or tough problem to solve, put on a crazy wig and false moustache.

One of the most annoying sounds is surely that produced by a dripping tap. Yet it could be a thing of the past thanks to researchers from the universities of Cambridge and Poitiers. While much work has been done on the fluid mechanics of a falling water droplet into liquid, little research has been carried out on what produces the characteristic “plink, plink” sound as the water droplet hits a liquid surface.

By using an ultra-high-speed camera, a microphone and a hydrophone, the team recorded droplets falling into a tank of water. They found, rather surprisingly, that the sound is not caused by the droplet itself, but by the oscillation of a small air bubble trapped beneath the water’s surface. Thankfully, the team offers a solution to stop the noise: add soap to lower the surface tension of the liquid. “[But] I think the best way to stop the sound being produced is to get whatever is causing the drip fixed,” Sam Phillips from Cambridge told Physics World.

Quiz question: what consumes more energy on a yearly basis, insectivorous birds or New York City? The answer, according to an international team of zoologists, is that they both consume about 2.8 exajoules per year. This, by the way, is the same amount of meat and fish energy consumed annually by all humans on the planet. But that’s nothing on the global spider community, which could eat its way through twice as much insect energy as birds.

Could graphene quantum dots help treat Parkinson’s disease?

Quantum dots made from the carbon material graphene prevent alpha-synuclein from aggregating into strand-like structures known as fibrils. They also help disaggregate fibrils that have already formed. Alpha-synuclein fibrils are thought to be implicated in Parkinson’s disease because they kill dopamine-generating neurons, so the new findings might help in the development of therapies to treat this disease as well as others in which fibrilization occurs.

Synucleins are a family of proteins typically found in neural tissue. Researchers believe that one type of synuclein, alpha-synuclein, twists into fibrils, which then accumulate in the midbrain of patients with Parkinson’s. Treatments with efficient anti-aggregation agents might thus be one way of fighting the disease.

A team led by Byung Hee Hong of Seoul National University and Han Seok Ko of The Johns Hopkins University in Baltimore have now found that graphene quantum dots (GQDs) bind to alpha-synuclein in vitro. Thanks to fluorescence and turbidity assays, as well as transmission electron microscopy measurements, the researchers found that the dots prevent alpha-synuclein from forming into fibrils. The nanostructures also dissociate already-formed fibrils into short fragments, with the average length of the fragments shortening from 1 micron to 235 nm and 70 nm after 6 and 24 hours respectively. The number of fragments starts to decrease after three days too and cannot be detected at all after seven days, which implies that the fibrils completely disintegrate after this time.

Mice show improved symptoms of the disease after six months

In their experiments, Hong and Ko’s team also injected the GQDs into the bloodstream of transgenic mice with Parkinson’s and found that they showed improved symptoms of the disease after six months – as assessed by routine cylinder and pole tests. The mice showed fewer movement problems, were able to use both forepaws to balance themselves on cylinders and ran down poles quicker. The researchers say that these improvements could come from the fact that the quantum dots are small enough to penetrate the blood-brain barrier and protect against dopamine neuron loss induced by alpha-synuclein preformed fibrils.

The GQDs do not show any appreciable in vitro and in vivo toxicity after six months of “prolonged injection” either and can be cleared from the body and excreted into urine, they add. The quantum dots might produce a similar effect in other diseases in which fibrilization occurs. Indeed, previous research by another team has already shown that injecting them into mice with Alzheimer’s inhibits the fibrilization of beta-amyloid peptides.

Full details of the research have been published in Nature Nanotechnology 10.1038/s41565-018-0179-y.

Cosmic neutrino points back to blazar driven by supermassive black hole

A high-energy neutrino detected by IceCube in 2017 was created in a blazar – an intense source of radiation powered by a supermassive black hole. That is the claim of three international teams of astronomers, who have characterized the event using three different instruments in another important breakthrough of multimessenger astronomy. The IceCube team also looked back at previous neutrino detections and say that these particles may have also come from the blazar. Together, the observations make a strong case that blazars are a source of high-energy cosmic rays – a hypothesis that had been discounted by many astronomers.

Located at the South Pole, IceCube comprises more than 5000 photomultiplier tubes buried in the Antarctic ice cap. Very occasionally a neutrino will collide with an atom, creating charged particles that emit light as they travel through the ice. This light is captured by photomultiplier tubes, and in some cases the signal can be used to work-out where in the sky the neutrino came from.

On 22 September 2017, IceCube detected a 290 TeV neutrino that could be traced back to TXS 0506+056, which is a well-known, but poorly studied, blazar that emits copious amounts of gamma rays. A near real-time alerting system meant that astronomers using the Fermi Gamma-ray Space Telescope in space and the MAGIC gamma-ray telescope on the Canary Islands could focus on the blazar less than a minute after the neutrino detection.

Extremely high energy

Fermi immediately spotted a very strong gamma-ray flare from the blazar and follow-up observations by MAGIC detected gamma rays with energies as high as 400 GeV. This emission of extremely high-energy gamma rays, say astronomers associated with the study, is evidence that the blazar could also generate very high energy cosmic rays. These energetic particles could then go on to create the high-energy neutrino detected by IceCube.

The 2017 observation inspired IceCube physicists to look back at previous high-energy neturinos captured by the detector. They found an increase in neutrino detections from the vicinity of the blazar over a five-month period beginning in September 2014. They calculate that the statistical significance of this neutrino “flare” being associated with the blazar to be 3.5σ, which is still well below the value of 5σ for a “discovery” in particle physics. Similarly, the statistical significance of the September observation is also below discovery level at 3σ.

Consensus shattered

Although more observations are need, the research provides strong evidence that blazars are a source of high-energy cosmic rays – a hypothesis that has been contentious. “It is interesting that there was a general consensus in the astrophysics community that blazars were unlikely to be sources of cosmic rays, and here we are,” says Francis Halzen, a of the University of Wisconsin-Madison and IceCube’s lead scientist.

Cosmic rays are charged particles, so they are bent off course by galactic and extragalactic magnetic fields as they travel to Earth – making it impossible for astronomers to trace cosmic rays back to their sources.

The research is reported in two papers in Science.

Irradiation beyond the target may reduce distant metastases

Left: ROI depiction showing the PTV (green) and a 30 mm thick shell (black). Right: 2D example. (Courtesy: A Diamant *et al Radiother. Oncol.* 10.1016/j.radonc.2018.05.012 ©2018, with permission from Elsevier)

Stereotactic body radiation therapy (SBRT) is highly effective in targeting high dose to a tumour while minimizing radiation exposure to surrounding healthy tissue. But if the mean radiation dose reaching potentially cancerous tissues immediately surrounding the tumour is not high enough, a patient may be at risk for developing distant metastases.

A Canadian study of non-small cell lung cancer (NSCLC) patients suggests that irradiation of a secondary margin outside the planning target volume (PTV) of a tumour could dramatically reduce distant metastasis rates, without adverse consequences to patients (Radiother. Oncol. 10.1016/j.radonc.2018.05.012).

If these findings are independently confirmed, radiation dose escalation beyond the PTV may be beneficial. The researchers suggest the use of a secondary margin outside the PTV subject to a dose constraint of at least 20.8 Gy₂ (where Gy₂ is the equivalent dose delivered in 2 Gy fractions) to ensure the eradication of microscopic malignant cells.

In a prior investigation of SBRT outcomes of NSCLC patients, André Diamant from McGill University Health Centre had determined that radiation target volume size was inversely correlated with distant metastasis. Because this finding seemed counter-intuitive, Diamant and colleagues conducted a study to determine whether a correlation exists between the dose immediately outside the PTV and metastatic development in patients with stage 1 NSCLC treated with SBRT.

The researchers analysed the distant metastatic rate in 217 patients with a single primary tumour. The patients had received SBRT either at McGill University Health Centre (96 patients receiving 3D-CRT) or Centre Hospitalier de l’Université de Montréal (121 patients receiving VMAT). Radiotherap was planned using a PTV with a 3-5 mm extension margin to the internal target volume.

Distant metastases developed in 37 patients (17% of the total) at 10 different sites, and loco-regional failure in 26 patients (12%). Eighteen patients (8%) experienced radiation pneumonitis. The researchers determined that two years after treatment completion, 60% of patients who received a mean dose outside the PTV of lower than 20.8 Gy₂ developed distant metastases. This compared with only 5% for patients who received a higher mean dose to the same region.

Distant-metastasis-free survival curve, showing patients who received more (blue) or less (red) than the threshold dose in the region outside the PTV. (Courtesy: A Diamant *et al Radiother. Oncol.* 10.1016/j.radonc.2018.05.012 ©2018, with permission from Elsevier)

The researchers evaluated dose parameters in a region of varying size outside each patient’s PTV. The maximum difference in mean dose fall-off between the two groups (distant metastases versus no distant metastases) was 6.6 Gy₂, at 16 mm away from the PTV. The authors suggest that ROI_cont(30 mm), a shell-shaped region of thickness 30 mm outside the PTV, represents the region most indicative of the risk of distant metastasis. The mean dose received by this region had an area under the curve (AUC) of 0.82.

None of the dose coverage factors (homogeneity index, mean and median PTV) were predictive, nor were differences between planned and delivered dose distributions arising from patient setup error or movement.

The authors note that microscopic disease extensions, which have been reported at least 26 mm beyond gross tumour edges, were killed more efficiently by the higher mean dose. The immunosuppressive nature of radiotherapy may also have influenced the spread of microscopic tumour cells. This might explain the correlation with distant metastasis without seeing any correlation in loco-regional control.

“When it comes to dosimetric outcome analysis, the attention is often solely on the PTV, which is assumed to contain any and all microscopic cancer spread,” Diamant tells Physics World. “Our work indicates that perhaps more attention should be directed towards neglected regions that may contain otherwise unknown cancer cells. If confirmed independently, this calls for more advanced treatment planning strategies which take into account the biological tumour environment,”

“We are very interested in extending the analysis to other treatment modalities and/or cancer types. Additionally, we are actively researching the use of current artificial intelligence technologies to combine both image and dose information to predict oncological outcomes,” Diamant adds.

Finding a niche within scientific computing

Why did you decide to start Tech-X?

John Cary, chief scientist and CEO: When I was a professor of physics at the University of Colorado, and my wife Svetlana (Sveta) was a researcher there, we saw an opportunity for doing tech transfer within the Small Business Innovation Research (SBIR) programme. The US government created this programme to give small businesses a way to get research funding (which would otherwise all go to laboratories, big businesses or universities) and to help them translate that research into commercial products that could grow the economy.

What we did was to develop computer programs that take the fundamental laws of physics and use them to model how systems will behave and evolve. An example would be the klystrons found in particle accelerators. Klystrons are cavities – metal boxes or cylinders – where a beam of electrons enters at one end, and then a small amount of power is injected into the cavity to cause the beam to bunch. By the time the beam reaches a second cavity, it has begun oscillating, and that produces microwaves that can be extracted and used for a variety of purposes. Our software can tell equipment designers how these devices are going to work – how much power is going to come out, how narrow a spectrum, whether the frequency is stable or drifting, how much energy is wasted, and so on. That means they can try many, many configurations on the computer before they make the device, saving money and time.

How has the company changed over the years?

JC: At first, our growth was all based on the SBIR model. The US government would basically pay us to write the software that scientists at the Department of Energy use to build particle accelerators, and then we would turn around and sell that software to laboratories in other countries as well, such as the UK’s ISIS neutron source and facilities in Europe, China and Russia. During that period, the people we hired were mostly scientists and engineers who could write proposals for SBIR funding, and we also contracted with a company to help us understand the paperwork required to work with the federal government.

We developed computer programs that take the fundamental laws of physics and use them to model how systems will behave and evolve

More recently, though, we have started to attract customers from the commercial sector. We’ve worked with a firm called Applied Materials, for example, that builds large plasma devices for manufacturing integrated circuits, and we also work with companies in the aerospace, defence, and oil and gas industries. As we got more into commercial markets, we created a quality-control department, and we also brought in people who can help customers use our software, because it is fairly complex and you need to understand a lot of basic physics principles.

What have been your biggest challenges?

JC: Establishing a sales group has been tough. We have had some success in hiring scientists and engineers and teaching them how to sell, but we have not found the ideal senior person who combines skills in sales and in science or engineering.

Sveta Shasharina, senior scientist and co-founder: I can elaborate on that. Essentially, we tried to hire someone who could help us commercialize our product and find new customers, but we couldn’t find anyone who had a sales-type personality – driven and personable – who could also understand the technical aspects of the software well enough to run it and drive customer-oriented development. For the moment, John has taken on that role in addition to his responsibilities as CEO, but it takes a lot of his time, so we are still looking for that magical person.

What do you know now that you wish you’d known when you started?

SS: I used to think I knew how to communicate with people, but it has taken me several years to become relatively good at it. I’ve learned a lot since becoming a manager. I also wish I hadn’t spread myself so thin early on, because my curiosity led me into lots of projects that didn’t end up contributing to the company’s current direction. My background is in fusion plasma physics, but I was working on distributed computing, and now I’m splitting my time between R&D and the business or commercial side.

JC: When you start a company, you’re trying to find your way in the world. You’re figuring out what you can do. Then, as you grow, you realize where your biggest strengths are, and at that point it’s important to focus. That is hard, especially in a research-driven company where you have a lot of very smart people, and they have lots of ideas about how to go off in their own very smart directions. Running a business is different from managing a research group: it’s important to get people to focus and put their energies into a few areas, rather than doing whatever they want.

Any advice for someone starting a business in scientific computing?

JC: Figure out what your competitive advantage is and then test your theory. If you think your selling point is X, go out and say it a few times: “We are good because of X.” Then, if you don’t get any sales, go and think of an alternative. It is easy to get caught up in how wonderful your software is, but it won’t help unless you can communicate it to someone and they accept it.

Scientists differ on climate’s carbon dioxide sensitivity

Scientists have yet to settle one of the biggest questions of warming: the climate’s carbon dioxide sensitivity. How much more carbon dioxide can the atmosphere absorb – and how will life on Earth respond – before the global temperature ticks past the political milestones of 1.5 °C and 2 °C above the average levels for most of human history?

These were set in 2015 when 195 nations agreed in Paris to contain global warming to “well below” 2 °C by 2100 and spoke openly of holding to no more than a 1.5 °C average rise as the ambition.

But that means doing the sums all over again. In the last century the ratio of the greenhouse gas in the atmosphere has risen from its historic average of around 280 parts per million to more than 400 ppm. And global average temperatures have risen by around 1 °C already: the world has just half a degree of leeway before the Paris target becomes impossible.

But one of the longest-running arguments in climate science is a simple uncertainty known to the professionals as “climate sensitivity”. That is: how much emitted carbon dioxide – emitted from the combustion of fossil fuels – makes a half a degree rise?

And it is a difficult question because forests, grasslands, wetlands, rivers, animals, microbes, rocks and oceans all release and absorb carbon dioxide from the atmosphere, sometimes storing it as hardwood, or peat, or carbonate rocks, sometimes releasing it as organisms decay.

Global temperature and carbon dioxide ratios have varied many times in pre-human history. So the human use of fossil fuels is only one component in a truly global calculation. Another factor is the area of healthy mixed forest and wetland, mangrove and prairie available to absorb that extra carbon, not to mention the algae in the warming oceans.

British scientists report in the journal Nature Climate Change that they asked the big question: how high could carbon levels get while temperatures stayed at no more than 1.5 °C? They calculate that – as long as warming happens slowly – the carbon count could get as high as 765 ppm. Right now, most climate researchers think that this mark will be reached or surpassed at between 425 ppm and 520 ppm.

And what makes the difference is the unresolved question of how the green things respond to all that extra carbon dioxide in the atmosphere. What difference will this make to crop yields (it is, in effect, a fertiliser), to the mix of species in the forests, and to the acidity of the oceans?

Other researchers have already asked the same question: what difference, for instance, will it make just to the tropics? And how will clouds – another factor in temperature control – respond?

“As well as being a major cause of global warming, carbon dioxide also affects life directly,” said Richard Betts, of the UK Met Office, based at the Hadley Centre in Exeter.

“Higher carbon dioxide concentrations cause increased growth in many plant species. This causes a general ‘greening’ of vegetation, but also changes the make-up of ecosystems – some species do better than others. Slower-growing large tree species can lose out to faster-growing competitors,” he said.

“It can also reduce the effects of drought to some extent, because many plants use less water when carbon dioxide is higher. Both of these factors can potentially enhance crop yields, possibly helping to offset some of the negative impacts of climate change – although even if that happens, the nutritional value of the crops can be reducedas a result of the extra carbon dioxide.”

But, Betts warned, the same extra carbon dioxide changed the chemistry of the oceans, making sea water more acidic and potentially more damaging to corals, and to plankton.

The message of such research is that there are a lot more questions to be answered. Nature’s response might buy the world more time to act. But there is no guarantee.

And the Exeter reasoning has its limitations: that is because it considered only the case of carbon dioxide, and although this is the big driver of climate change, it is not the only greenhouse gas. In a warming world, the permafrost is expected to melt to release potentially colossal quantities of buried methane.

The researchers arrived at their estimates by reversing the normal reasoning. They did not try to calculate the probability of so much warming for a stipulated rise in carbon dioxide ratios. Instead, they started with what the carbon dioxide count might look like at a particular temperature.

“This lets us estimate what the range of carbon dioxide concentrations would be when global warming passes those levels, if carbon dioxide were the only thing in the atmosphere that we are changing,” Betts said.

This report was first published at Climate News Network.

A nanotech bonanza in Paris and a journalism boot camp in Sicily

In this episode of Physics World Weekly, Anna Demming is in conversation with Hamish Johnston about her highlights from Nanotech France, which took place in Paris at the end of June. You will hear from Keibock Lee the president at Park Systems, Inc, who speaks about recent developments in atomic force microscopy (AFM) and electrodeposition. You also hear from Keon Jae Lee from Korea Advanced Institute of Science and Technology (KAIST) about the booming industry of microLED lighting technologies.

Later in the podcast, James Dacey is in conversation with the freelance journalist Ben Skuse who has just returned from 2018 International Science Journalism School in Erice, Sicily. Skuse discusses the theme for this year’s event ‘What’s Next: Challenges and Opportunities for Tomorrow’s Fundamental Physics’. He also explains why he felt so inspired by the independent award-winning writer Jacopo Pasotti, then offers some practical advice for anyone considering a career in science journalism.

If you enjoy the podcast then you can subscribe via iTunes or your chosen podcast app.

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Californian grasslands set to store carbon more reliably than forests