Sunday Science is back after a brief holiday hiatus, with a bumper issue, covering a few eye-opening climate change problems and solutions, a new anti-tuberculosis agent from scorpion venom, callused but sensitive feet, and sleeping zebrafish.

First up: cities in the Northern hemisphere will have a climate more like those closer to the equator by 2050. Now, I know some people would quite like London to be like Barcelona (I am not one of them: I hate the heat) but trust me, this isn’t good, and could be accompanied by severe drought. This are eye-popping calculations: nearly 80% of cities will see dramatic change, in some cases with their warmest month being nearly 8C warmer than usual, for which they are ill-equipped to adapt – and 2050 isn’t that far away. It’s also a useful illustration of a fact that people often overlook: when scientists talk about “3C of global warming,” that is an average – some places will have substantially more. There is an interactive map you can explore to see the effect on individual cities. The original study, which examined the potential effects on 520 major cities, may be found here. 

What can we do about it? Well, go to zero carbon emissions as fast as possible. But apart from that, some new research that may help: planting trees could be one of the biggest ways to combat climate change. This got quite a lot of media attention, probably because it’s both a surprisingly low-tech solution, and because it sounds so attractive. Save the planet, just plant trees: lovely, right? It would be rather a lot of trees: the study’s authors calculate that 0.9 billion hectares of land worldwide could be re-forested (over a 25% increase in total forestation), which could potentially capture two thirds of human-made carbon emissions. This is around 500 billion trees. Yes, this is a lot, but bear in mind it’s estimated that humans have cut down more than half the trees on the planet since we started making use of them. Importantly, this reforestation figure only includes land that isn’t being used by humans, immediately making it more feasible. This neat little conceptual figure in a Science magazine Perspective piece on the study sums up the multiple benefits this could provide.

A forest restoration system integrates structures (trunk and roots) that assimilate and distribute resources (soil) to initiate and sustain restoration outcomes (branches). The system ultimately delivers myriad benefits for nature and humanity (fruits). Restoration outcomes and benefits sustain the system, stabilise enabling conditions, and increase capital stocks. 
CREDIT: N. CARY/SCIENCE. DOI: 10.1126/science.aax9539

There are a few issues with this wonderful plan: for one thing, it obviously takes time for the trees to grow: 50-100 years, probably, to have a full effect, and deforestation, which is still proceeding at an alarming rate and is exacerbated by climate change itself, needs to be halted first. Closed-canopy forest should not replace other natural ecosystems (e.g. savannah, marshland), as this will hardly help the extinction crisis. Additionally, whilst it’s great that trees will remove CO2 from the atmosphere, the imperative is to stop putting it in there in the first place, the main culprits being fossil fuel emissions and agriculture. We need to transition to zero carbon emissions within 15 years, really. The original forest study paper may be found here.

So, let’s get on with reducing those emissions (I note in passing the UK government’s dismal record on this front…). Solar power is still striding ahead, becoming cheaper all the time, but there have been a couple of nice recent breakthroughs that could really help.

Firstly, a device that makes both solar power and clean water, solving two critical problems for a large portion of the world’s population (about 780 million people). Most existing methods of purifying water use precious electricity to do it, and many people instead have to walk miles to scarce clean water sources, so this is really exciting. Impressively, the device will purify both seawater and water contaminated with heavy metals. The device makes use of a conventional silicon solar cell, and instead of the 80-90% of energy that is lost as heat just being dumped into the atmosphere, it is used to heat tiers of water and drive a distillation process (see figure below). The original paper  may be found here (open access).

Fig. 1
Schematic illustration of the integrated photovoltaics-membrane distillation (PV-MD) devices. Operate in a dead-end mode (in this mode, the source water is wicked into the evaporation layer in the direction of the red arrow and the condensed water flows out from the condensation layer in the direction of the green arrow) and b cross-flow mode (in this mode, the source water flows to the evaporation layer in the direction of the red arrow and the condensed water flows out from the condensation layer in the direction of the green arrow). From Wang et al, Nature Communications volume 10, Article number: 3012 (2019)

As is probably apparent from that research, one of the main drawbacks of silicon solar cells is that they waste a lot of energy, via high energy photons, as heat. The maximum efficiency of solar conversion is therefore only 30% (this isn’t as bad as it sounds: a typical fossil fuel electricity generating plant, for example, is only going to have a conversion efficiency of around 40-50%). It’s difficult to improve on existing solar cells without significantly increasing their cost or complexity (or both). A new design using a process called singlet fission, could help improve this. This gets quite physics-heavy (by which I mean it’s beyond me!), but essentially what they are doing is using a molecular layer to split a high-energy excitation that is generated by the absorption of a high-energy photon, into two lower-energy excitations. This energy is then transferred across an interface and converted into an electric current. Original paper here.

There’s an increasing interest in isolating potentially useful biological compounds from the toxins produced by various animals and plants. The latest interesting one are two new anti-microbial compounds isolated from scorpion venom.One of the drugs was effective against Staphylococcus aureus, which causes skin and tissue infections (the notorious MRSA being resistant to nearly all antibiotics and a scourge of hospitals). The other was effective against tuberculosis, and even cured a mouse model infected with multidrug resistant tuberculosis without damaging the lungs. Original study here.

When humans started walking upright, they developed highly thickened (callused) skin on their feet. With the invention of footwear, a lot of us don’t have this anymore, with reduced tactile sensitivity, or the ability to preserve the sensation of the ground beneath our feet. But does walking barefoot reduce sensitivity, given that thick layer of dead skin? Apparently not: calluses actually preserve sensitivity because their hardness enables mechanical stimuli from the ground to be transmitted to deeper layers of the skin in where the sensory nerves are located. This has implications for those with disorders affecting their gait or posture, and, of course, for shoe design. Original study here.

Sleep appears to be even more ancient than we thought. It’s known that lizards sleep, and all sorts of animals from worms to insects show something that is like sleep, but it’s been impossible to tell if this is like mammalian sleep. This is characterised by different periods of brain activity, corresponding, for example, to deep sleep or REM sleep (in which dreaming can occur). Now it’s been found that zebrafish demonstrate both slow wave sleep and REM-like sleep too – so it must have evolved over 450 million years ago, in their ancestors. The cute little video below shows a wave of electrical activity sweep across the body of a zebrafish as it sleeps. Original study here.

 

And finally, if you made it to the end, have a reward with six amazing facts about ants.

Featured image

Peruvian Rainforest, via Wikimedia Commons: I, Sémhur [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)%5D

 

Figure sources

Chazdon, R. & Brancalion, P. Restoring forests as a means to many ends: Science  05 Jul 2019: Vol. 365, Issue 6448, pp. 24-25 DOI: 10.1126/science.aax9539

Wang W. et al. Simultaneous production of fresh water and electricity via multistage solar photovoltaic membrane distillation. Nature Communications volume 10, Article number: 3012 (2019)

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