Avoidance of animal suffering is a given. Lately, it has been acknowledged by the United Nations that a reduced red-meat or meatless diet benefits also the consumer's health.

In the aftermath of COP21, the recent Paris UN climate change conference, it emerges that one of the biggest advantages of limiting meat consumption is reducing significantly one's environmental impact.

Our use of animals raises moral and ethical issues as well as concerns with human health. But remediating the planet's environment, and climate change in particular, must surely rank as one of our highest priorities.

Jorge Gapella, Kaleen

Victor Diskordia (Letters, December 27) argues that existing technologies will be replaced by new ones only if justified by market prices, thus, wind and solar will not replace coal.

Pity economic theory tends to ignore such externalities as the state of the atmosphere. Were there a global carbon price which paid the cost of pollution, however, market prices might give a different picture.

Solar and wind power is already cheaper than new coal-fired stations. Only old coal-fired power, where the costs have been amortised, is cheaper. Add a reasonable carbon price (something wanted by the heads of the World Bank and the International Monetary Fund), and bingo! even old coal is not viable in market terms.

This is not a question of economics, however. It is something far greater. It is about the habitability of the planet.

Jenny Goldie, Michelago NSW

Victor Discordia needs to catch up with developments in renewable energy. In many places wind and solar are the cheapest form of energy available and are being installed for that reason. Inclusion of a carbon price to take care of the externalities of fossil fuel would see installation rates speed up exponentially. As it is, the latest prices for solar energy in India, for example, are already below that of imported coal-fired power generation and falling rapidly.

Doug Hynd, Stirling

Victor Diskordia (Letters, December 27) couples his ill-informed opinion that "Wind power and solar power are, as far as can be seen, utterly impracticable as significant sources of energy" with a potpourri of the myths of capitalism to attack Jenny Goldie's call (Letters, December 20) to phase out fossil fuels and shift to renewables.

If he really has faith in those simplistic myths he should also call for all taxpayer-funded subsidies of the fossil fuel industry to end?

Adrian Gibbs, Yarralumla

Tony Trobe discussed grey water recycling with Andrew Hermann in his last two Sunday columns. Hermann's Canberra company markets grey water systems "exclusively in the US". He would like the ACT to require a grey water collection tank be installed during building of new housing.

Hermann did not mention grey water solutes, particularly detergents.

Some claim "there are no environmentally friendly detergents" (lanfaxlabs.com.au). Choice magazine notes they contain phosphates, that "Australian soils are typically low in phosphorus, and some native species can't tolerate high levels". It also notes they contain various sodium salts "and frequent long-term use would likely harm your garden". Additionally, "Laundry detergents are highly alkaline [and are] likely to harm many plants and soil organisms."

Choice specifically warns not to "water herbs, vegetables, or pot plants" exclusively with grey water.

In the 1960s and '70s the lush Norfolk Island Pines along Manly Beach in Sydney were dying. Just the tiny amount of detergent in the sea foam from sewerage outfall was blamed. It stripped protective resins and exposed the trees to disease.

The problem continues. Last year another 19 of the now bedraggled trees were replaced because they had not grown properly, were damaged or badly misshapen.

Gary J. Wilson, MacGregor

I get at least three letters and often two or three phone calls (usually just at dinner time) a week from charities seeking donations. The letters often contain little "gifts" such as sheets of letter seals printed with my name and address, or greeting cards, all of which get tossed in the bin. Some charities send three of four letters a year.

The phone calls are equally annoying. One charity (which I support through regular donations) started ringing me to give me "updates" on the work they are doing (until I invited the caller not to do it again). Another, for which I do have a great deal of admiration and sympathy, rings every couple of months flogging raffle tickets.

Another recent development is the collection points set up in shopping centres. You approach a table decorated with posters appealing for help for some legitimate and worthy cause, but when you offer money you are told that they cannot accept donations, that you have to buy a scratchie for $10 if you want to help.

It is just such a collection point set up at our local shopping centre yesterday that is the cause of this rant. It was for a well-known and worthy cause and I reached for my purse. But no, they couldn't accept money, they had forms for me to fill in. I was in a tearing hurry and the chap said well, perhaps I could see them on my way back.

Thinking that they were only set up for credit card donations, I duly stopped on my way back and started filling out the form.

The collector started dropping my name into his spiel just about every second sentence and asked me how my day was going (I swear that I will bite the next twit who asks me that idiotic question).

The patter kept up until it became obvious that they weren't collecting one-off donations but signing people up for regular direct debit contributions.

I said I did not want to do this for any more charities and was told "Oh, but look at it this way – instead of one large donation you just split it into monthly contributions", which he said would then be "barely noticeable".

Like most people, I have some charities that I support regularly, and I'm always willing to make one-off donations to genuine causes. It is the professional, manipulative aspect of these campaigns that annoys me: the "gifts" in the begging letters are little more than moral blackmail; the constant use of my name and inquiries after my health and well-being in the phone calls are designed to make the caller sound "caring"; and the well-rehearsed spiel of the collector which was designed to sucker me into feeling that I could not back out of pledging a regular donation (it did not work).

The charities are obviously employing professional fund-raisers who plan their campaigns, and the result is downright insulting to one's intelligence.

Barbara Fisher, Cook