Science – Page 96 – a sibilant intake of breath

A query for any lurking physicists

I was having a conversation this afternoon about the Tunguska event: a huge explosion that occurred in Russia in 1908. I had always heard that it was caused by a meteor impact, though apparently some other explanations have also been considered. One that I just heard about is the possibility that it was caused by a collision between the earth and some antimatter.

Wikipedia suggests that this explanation isn’t credible, but it does leave me wondering: in the event of a collision between a particle of matter and a particle of antimatter, where the two particles are traveling at different velocities in opposite directions, how does the net momentum of the two translate in their annihilation? If antimatter did hit the earth, it would start to strike particles of matter in the upper atmosphere, the particle pairs would annihilate one another, and energy would be released. Would all that happen before the antimatter hit the ground? Presumably, it would strike its mass in antimatter before then. If so, what would the effect on the surface of the planet be?

Conservation of energy dictates that the kinetic energy in the faster particle would need to go somewhere. Presumably, it would manifest in the production of more energy during the annihilation event. As such, I suspect the antimatter clump would get blasted apart in the upper atmosphere and produce some kind of horrible shower of radiation, though nothing in the way of direct physical debris.

HVDC transmission for renewable energy

One limitation of renewable sources of energy is that they are often best captured in places far from where energy is used: remote bays with large tides, desert areas with bright and constant sun, and windswept ridges. In these cases, losses associated with transmitting the power over standard alternating current (AC) power lines can lead to very significant losses.

This is where high voltage direct current (HVDC) transmission lines come in. Originally developed in the 1930s, HVDC technology is only really suited to long-range transmission. This is because of the static inverters that must be used to convert the energy to DC for transmission. These are expensive devices, both in terms of capital cost and energy losses. With contemporary HVDC technology, energy losses can be kept to about 3% per 1000km. This makes the connection of remote generating centres much more feasible.

HVDC has another advantage: it can be used as a link between AC systems that are out of sync with each other. This could be different national grids running on different frequencies; it could be different grids on the same frequency with different timing; finally, it could be the multiple unsynchronized AC currents produced by something like a field of wind turbines.

Building national and international HVDC backbones is probably necessary to achieve the full potential of renewable energy. Because of their ability to stem losses, they can play a vital role in load balancing. With truly comprehensive systems, wind power from the west coast of Vancouver Island could compensate when the sun in Arizona isn’t shining. Likewise, offshore turbines in Scotland could complement solar panels in Italy and hydroelectric dams in Norway. With some storage capacity and a sufficient diversity of sources, renewables could provide all the electricity we use – including quantities sufficient for electric vehicles, which could be charged at times when demand for other things is low.

With further technological improvements, the cost of static inverters can probably be reduced. So too, perhaps, the per-kilometre energy losses. All told, investing in research on such renewable-facilitating technologies seems a lot more sensible than gambling on the eventual existence of ‘clean’ coal.

A grand solar plan for the United States

The latest issue of Scientific American features an article about a ‘grand solar plan.’ The idea is to install massive solar arrays in the American southwest, then use high voltage direct current transmission lines to transfer the energy to populated areas. The intention is to build 3,000 gigawatts of generating capacity by 2050 – a quantity that would require 30,000 square miles of photovoltaic arrays. This would cost about $400 billion and produce 69% of all American electricity and 35% of all energy used in transport (including electric cars and plug-in hybrids). The plan depends upon storing pressurized air in caverns to balance electricity supply and demand. The authors anticipate that full implementation of the plan would cut American greenhouse gas emissions to 62% below 2005 levels by 2050, even assuming a 1% annual increase in total energy usage.

The authors stress that the plan requires only modest and incremental improvements in solar technology. For instance, the efficiency of solar cells must be increased from the present level of about 10% to 14%. The pressurized cavern approach must also be tested and developed, and a very extensive new system of long-distance transmission lines would need to be built. While the infrastructure requirements are daunting, the total cost anticipated by the authors seems manageable. As they stress, it would cost less per year than existing agricultural subsidy programs.

Depending on solar exclusively is probably not socially or economically optimal. The authors implicitly acknowledge this when they advocate combining the solar system with wind, biomass, and geothermal sources in order to generate 100% of American electricity needs and 90% of total energy needs by 2100. Whether this particular grand plan is technically, economically, and politically viable or not, such publications do play a useful role in establishing the parameters of the debate. Given the ongoing American election – and the potential for the next administration to strike out boldly along a new course – such ideas are especially worthy of examination and debate. It is well worth reading the entire article.

Three climatic binaries

One way to think about the issue of mitigating climate change is to consider three binary variables:

Cooperation
Expense
Disaster

By these I mean:

Is there a perception that all major emitters are making a fair contribution to addressing the problem?
Is mitigation to a sustainable level highly expensive?
Are obvious and unambiguous climatic disasters occurring?

These interact in a few different ways.

It is possible to imagine moderate levels of spending (1-5% of GDP) provided the first condition is satisfied. Especially important is the perception within industry that competitors elsewhere aren’t being given an advantage. Reduced opposition from business is probably necessary for a non-ideological all-party consensus to emerge about the need to stabilize greenhouse concentrations through greatly reduced emissions and the enhancement of carbon sinks.

It is likewise possible to imagine medium to high levels of spending in response to obvious climatically induced disasters. For instance, if we were to see 1m or more of sea level rise over the span of decades, causing serious disruption in developed and developing states alike. Such disasters would make the issue of climatic damage much more immediate: not something that may befall our descendants, but something violently inflicted upon the world in the present day.

Of course, if things get too bad, the prospects for cooperation are liable to collapse. Governments facing threats to their immediate security are unlikely to prioritize greenhouse gas emission reductions or cooperation to that end with other states.

We must hope that political leaders and populations will have the foresight to make cooperation work. It may also be hoped that the cost of mitigation will prove to be relatively modest. The issue of disasters is more ambiguous. It is probably better to have a relatively minor disaster obviously attributable to climate change, if it induces serious action, than the alternative of serious consequences being delayed until it is too late to stop abrupt or runaway change.

KombiKraftwerk

Detractors of renewable energy have always stressed the problems brought on by the inconstancy of wind and sun. At the same time, renewable boosters have stressed how storage and amalgamation of energy from different places can overcome that limitation. Now, a project in Germany is aiming to prove that this can be done. KombiKraftwerk will link 36 different power plants: wind, solar, hydro, and biogas. The pilot project aims to provide just 1/10,000th of German power while proving the concept of a purely renewable grid. To begin with, the system should power about 12,000 homes. The intent is to show that Germany could be powered entirely using renewable energy. Another aspect of the plan is to eventually generate enough energy to power carbon sequestration systems for industries where emissions are inevitable.

Particularly when you include hydro in the mix, maintaining a supply of renewable power that matches the minute-by-minute demand becomes feasible. With any luck, this undertaking will successfully highlight the possibility of moving to a climate-neutral and sustainable system of electricity generation at national scales and above.

Be grateful for bees

My favourite reading snack these days is soy-covered almonds. They have lots of delicious umami flavour. Recently, I was surprised to learn that 80% of the world’s almonds are grown in a 600,000-acre section of California’s Central Valley. Since almonds need to be pollinated by honey bees (apini apis) and there is only nectar available in that area when almonds are in bloom, the bees need to be trucked in from elsewhere. Every February, more than a million hives – containing 40,000 bees – get trucked in. By 2005, it proved necessary to import a 747 full of bees from Australia for the ‘pollination event.’

The mutual exposure of those two distantly separated bee populations results in the exchange of microbes and parasites. Therein may lie the cause of the North American Colony Collapse Disorder outbreak that began in 2006. Honey bees are also used to pollinate peaches, soybeans, apples, pears, cherries, raspberries, blackberries, cranberries, watermelons, cantaloupes, cucumbers and strawberries. There are dozens of others, ranging from those that simply benefit from the availability of pollinating bees to those (such as squash and vanilla) where the bees are absolutely indispensable.

Coral reefs and climate change

While the Arctic is the most climatically vulnerable human-inhabited environment, coral reefs will probably see the most comprehensive destruction in coming decades. According to the IPCC, it is highly likely that they will succumb to a combination of heat and oceanic acidification as temperatures rise in response to greenhouse gas emissions. It is estimated that the last 25 years have seen the loss of 30% of warm-water coral cover. The worst summers so far for coral bleaching have been 1998 and 2002: in which 42% and 54% of all reefs worldwide were affected. As much as 80% of Caribbean coral may already have died.

Coral bleaching occurs when the zooxanthella algae that live in coral tissues die. The report of Working Group II of the IPCC highlights high surface temperatures as “almost certain to increase the frequency and intensity of mass coral bleaching events.” Throughout the Third and Fourth Assessment Reports, coral reefs are highlighted as being especially vulnerable to climatic change, with low adaptive capability.

Oceanic acidification reduces the calcifying ability of corals, by making it more difficult for them to extract calcium from seawater. In cases of extreme acidity, existing structures could begin to dissolve. According to the IPCC “the progressive acidification of oceans is expected to have negative impacts on marine shellforming organisms.” Studies have demonstrated that projected future ocean acidity will reduce coral calcification and weaken coral skeletons.

The Fourth Assessment Report projects that most corals will be bleached by a temperature rise of 1 to 3°C, with increasing coral mortality at higher levels of temperature increase. Between 2.5 and 3.5°C above the pre-industrial mean temperature, a summary table in the WGII report predicts simply “Corals extinct, reefs overgrown by algae.” It warns further that: “It is important to note that these impacts do not take account of ancillary stresses on species due to over-harvesting, habitat destruction, landscape fragmentation, alien species invasions… or pollution.” Given the low probability of keeping further temperature increases below 2°C – even with the advent of relatively stringent new international obligations – it is fair to say that most of the world’s coral is doomed to die. That, in turn, will undermine much of the basis of coral reef ecosystems. This is a further burden to some small island states, as coral reefs can be the habitat for important fish stocks. Reefs are also the most diverse marine ecosystems: home to about 25% of all marine species.

One way to interpret the news is this: if you have always dreamed of SCUBA diving in the natural splendour of a coral reef, make sure you do it fairly soon. Your children might not be able to do it at all. To quote the IPCC once more: “Annual or bi-annual exceedance of bleaching thresholds is projected at the majority of reefs worldwide by 2030 to 2050.”

Panda update

An article from the always-interesting Christmas issue of The Economist provides an update on the state of the panda: covering captive and wild populations, as well as new scientific thinking about what caused their endangerment. Pandas are widely cited as a truly hopeless animal. They are inept at and uninterested in reproduction, with females only fertile for 3-4 days a year anyhow. They are also only willing to eat a single food that is thoroughly lacking in calories and dies off en masse at regular intervals.

That said, captive populations seem to be on the rise thanks to better breeding techniques, while policies intended to prevent floods caused by deforestation have served indirectly to protect some wild habitat. It seems that despite their challenges – both natural and man-made – pandas will prove charismatic enough to endure.

Concrete’s climatic consequences

While aviation and ground transport get lots of well-deserved attention, in terms of their climate change impact, the concrete industry seems to get a lot less scrutiny. In a way, this is unsurprising; concrete is hardly glamorous stuff. At the same time, concrete production accounts for about 5% of all greenhouse gas emissions: mostly from the process of manufacturing clinker by heating limestone and clay. This is usually done using coal. The average tonne of concrete produced generates about 800kg of carbon dioxide: both as a result of the coal burning and the product of the chemical reaction involved (CaCO3 -> CaO and CO2, ignoring silicates). This figure does not include emissions relating to quarrying rock or transport.

Cement manufacture can be incrementally improved in three ways: by reducing the ratio of clinker to other additives, by making kilns more efficient, and by using fuels other than coal for the heating. All of these can make contributions, to a certain degree, but only a complete shift to biomass heating could have a terribly significant effect on greenhouse gas emissions (and that effect could be moderated by the emissions from transporting the biomass).

Demand for cement is growing at about 5% a year, and is partially driven by the construction of new hydroelectric dams and nuclear power plants. At present, the rate of demand increase exceeds the rate of efficiency improvements. As such, greenhouse gas emissions associated with concrete are increasing every year. The average North American home uses about 25 tonnes of concrete, mostly in the foundation.

George Monbiot discusses concrete in his book, focusing on geopolymeric cements as a solution. Carbon capture and storage (CCS) is theoretically possible, but with an added problem. Concrete plants must be sited near limestone quarries. These are not necessarily near the salt domes or aquifers where CCS can probably be most effectively deployed. Geopolymeric cements are similar to the pozzolan cement used by the Romans to build the roof of the Pantheon. They are made from clay, certain kinds of sedimentary rock, and industrial wastes. Producing them generates 80-90% less carbon dioxide. This is because they require a lot less heating and the chemical reaction that produces them does not generate CO2 directly.

The modern version of this material was only developed in the 1970s and has yet to be widely adopted. Partly, that is because of the cost of refitting existing cement works or building new ones. Partly, it reflects the hesitation of the construction industry to use new materials. Such objections can probably be most efficiently addressed through carbon pricing. If the concrete and construction industries were paying for those 800kg of CO2, the incentives they face would probably change decisively and fast.

Copper indium gallium selenide solar cells

Nanosolar, a company supported by Larry Page and Sergey Brin (the founders of Google), has announced that it will be selling thin-film solar cells profitably for $1 a watt. Apparently, the cells are printed with copper indium gallium selenide – an alternative to silicon. Cells based on the material can convert solar radiation to electricity with 19.5% efficiency. In theory, this material can applied to foil, plastic, glass or cement – producing electricity generating surfaces. It can also be made into more conventional panels of the sort Nanosolar is starting to sell.

In the 1950s, solar cells cost about $200 per watt. By 2004 they were down to $2.70. Further reductions could make solar power cost competitive with fossil fuels, potentially even in the absence of carbon pricing. Combined with either better storage (to moderate light/dark and sunny/cloudy cycles locally) or better inter-regional transmission (the sun is always shining somewhere), such cells could eventually make a big difference in the overall energy balance. Solar has been discussed here previously.