The 2000-watt challenge sparks a lot of interest (1)
James Dinneen’s article on the challenge of reducing our rate of energy consumption to 2000 watts encouraged me to put some numbers into a calculator(11 February, p 36).
Our car used 748 litres of fuel over a period of 381 days. Taking the energy value and density of diesel as 43.1 megajoules per kilogram and 0.832 kg per litre gives it a score of 816 watts. Our house used 3632 kilowatt-hours of electricity in the 336 days since a heat pump was installed, giving a further 450 watts, while the stovetop’s 2 cubic metres of gas adds a further 3 watts. With flying and public transport both zero, this gives a total of 1269 watts, albeit only for the things directly under our control. This is divided between two of us, so 635 watts each.
However, this doesn’t take into account the, at best, 50 per cent efficiency of gas-fired power stations or the 14 per cent losses in the electricity grid, and thus we have an overly rosy view. It gives a particularly rosy view of the heat pump, since its installation increased electricity consumption, but, in the absence of more wind, solar or nuclear power, it all came from gas-fired power stations.
The 2000-watt challenge sparks a lot of interest (2)
The difference between averaged power usage, as imagined in the 2000-watt challenge, and peak power usage is important. It is the latter value that grids must be designed to supply, with power stations ready to fire up to meet it, especially when renewable inputs are lacking. These stations are usually gas fired, and this makes ending our addiction to fossil fuels hard. New nuclear power plants could help us to meet the demand. Excess produced when consumers don’t need it could be used as off-peak power for industrial tasks, such as the manufacture of some energy intensive products.
The 2000-watt challenge sparks a lot of interest (3)
Dinneen switched from drying his clothes in a powered dryer to hanging them indoors. Does this really use less energy? Surely, the energy to evaporate the water is the same regardless. Of course, the best thing would be to hang clothes outside, but, where this isn’t an option, the evaporation would cool a building and make any heating system work harder.
The 2000-watt challenge sparks a lot of interest (4)
One of the most significant long-term contributions people can make to cutting carbon emissions and energy use is to have fewer children.
Dark matter is just the pull of other universes
There is a relatively simple solution to the question of dark matter 鈥� the unseen mass thought to be exerting an additional gravitational effect on galaxies(11 February, p 46).
In his book The Elegant Universe: Superstrings, hidden dimensions, and the quest for the ultimate theory, Brian Greene explains that string theory postulates that gravity can cross the barrier between universes. Again, according to Greene, our universe may exist immediately next to others, and the gravity from mass in those universes bleeds through into ours. As a result, galaxies in neighbouring universes are drawn into alignment with galaxies in ours, influencing the gravitational attraction we observe.
That idea seems to me to be the best explanation for dark matter.
Eel migration may have got longer very slowly
Reader Chris Hall wonders what Darwinian forces might drive European eels to undertake a 12,000-kilometre journey across the Atlantic and back to breed. This could be an adaptation to the formation of the ocean about 150 million years ago via slow spreading of tectonic plates(Letters, 11 February).
Perhaps eel ancestors had breeding grounds bordering the infant ocean. As the Atlantic got wider, the journey lengthened by a little every year. Selection would favour those that could cope with the increasing distance.
Many cultures don't regard nature this way
You say that “for much of recent human history, nature has been regarded as mere property… to be exploited”. Many cultures don’t see nature that way at all, and I suggest it is the Judaeo-Christian idea that we have “dominion over nature” that is the main problem(11 February, p 26).
Is this how our immune systems keep fighting fit?
Your feature on immunity states that the immune system wastes its resources attacking the cytomegalovirus pathogen, which persists nonetheless. If this virus rings our immune alarm bell so much, you might assume that the immune system would have evolved to kill it off(4 February, p 43).
Could this be like countries holding war games to keep their armies fit for purpose? Rather than being a drag on resources, the immune system may be using the stimulation from this virus to ensure it remains fighting fit.
I fear the spread of bird flu to many more species
You report that mammals such as foxes have been infected by the current bird flu virus. This has been attributed to scavenging of the carcasses of infected birds(11 February, p 8).
It seems to me only a matter of time before other wild mammals 鈥� especially rats, as scavengers, and squirrels, as raiders of bird nests 鈥� become infected. These creatures can be prey for cats, which raises a fear of the virus coming into contact with people that way.
Pondering the limits of mammalian mutualism
You report that mongooses and warthogs display “the only known mammal-mammal mutualism in the world”. That does seem to be true of land-based mammals(4 February, p 44).
I wonder if there are valid examples for marine mammals, such as seals leaving their young pups to be watched over in sea lion nurseries, or seals, dolphins and sea lions playing together. And what about orcas and dolphins cooperating with human fishers?
For the record
Andrew Rogoyski works at the University of Surrey, UK (4 February, p 25)