Will Prince Charles finish what he has started?

Thus he will visit Todmorden, in West Yorkshire, to praise "guerrilla gardeners" growing free vegetables on any spare land (from car parks to a cemetery), sit through a "sustainable fashion show" in Manchester, and drop in on a pensioner in Nottingham who has installed solar panels on her roof.

Back in London, meanwhile, he is throwing open the gardens of Clarence House – and next-door Lancaster House and Marlborough House – to the public for a 12-day "garden party to make a difference".

Described as a combination of the "Hay-on-Wye festival, the Ideal Home Show and Grand Designs with a sprinkling of a summer festival", it will eclectically include environmentally friendly products and buildings, feet-painting, a workshop making tote bags out of the Prince's old curtains, demonstrations by celebrity chefs, earnest debates among the great and the green, and a whole ecosystem of (predominantly, at least middle-aged) celebrities ranging from Ben Elton to Pen Hadow, Rory Bremner to the inevitable David Attenborough.

And, if all that were not enough, there is to be a nine-day summit of "business and industry thought leaders" to discuss "the next steps that should be taken to enable economic, environmental and societal sustainability".

The whole shebang is in aid of the Prince's latest project, Start, which aims to "help people across Britain lead more sustainable lives and to show what a more energy-efficient, cleaner and healthier future could look like".

It dispenses a bewildering amount of practical advice: if you want to know how best to pick your own fruit or insulate your loft, how to choose a (relatively) green car, or what to take on a "wild swimming" trip, you need look no further.

The Prince himself has urged people to "snub the tub" by taking short showers, to recycle water and to avoid eating "unsustainably harvested" fish. He has even advised Vogue readers to wear old clothes.

Inevitably, this has led to charges of hypocrisy from commentators who suggest that the Prince's baths are drawn by flunkeys and insist on recycling old (and hotly denied) chestnuts – such as the one where he chooses his breakfast from seven boiled eggs solemnly lined up before him.

But leaving aside the predictable jibes from people whose own lifestyles are far from parsimonious, there is a real problem in an extremely wealthy man with three huge homes, four cars and a record of travelling by private jet, urging people to live modestly. Even one supporter and former collaborator calls it "pretty preachy" and admits that it "invites ridicule".

Aides say he "understands the criticism" and insist he "does as much as he can within the confines of his role as heir to the throne". Certainly, he is no Airmiles Andy and – unlike his father – has not combined an evangelical belief in population control with siring four children. He does practise much of what he preaches, from turning Highgrove organic to wearing a pair of shoes made from leather salvaged from an 18th-century shipwreck.

His new initiative, moreover, latches on to two essential points. The first is that there is now a huge range of products and practices ready to start the transition to low-carbon prosperity: the Prince sees his campaign as the equivalent of his great-great-great-grandfather Prince Albert's Great Exhibition: designed as "a new starting point from which all nations would be able to direct their further exertions".

Secondly, he is right to reject doomsaying in favour of the positive, stressing that a more sustainable future would be better and more prosperous than continuing on the present course. That is why he has called the campaign "Start" – to contrast with the traditional environmentalist call to "stop" bad practices.

All the same, if he could provide an example of where it has really cost him to change his ways – or undertake one if none such already exists – it would do wonders for the credibility of his campaign.

Heat-resistant – or are we shrinking?

Shrinking from the slanging match that passes for the climate-change debate is a natural enough response. The sheer nastiness of extremists on both sides ensures that. But how about this? New research suggests that mammals (presumably, ourselves included) might actually get smaller as the world heats up.

A University of Florida study into a natural period of global warming 55 million years ago, has discovered that a hyena-type animal seems to have evolved in such a fashion that it shrank to half the size of its ancestors – scaling down from the stature of a bear to that of a coyote – during a 200,000-year period when temperatures rose some 15F. When things cooled down, it grew back up again.

Such downsizing has already been seen in fossils of plant-eating mammals during this period, but the study – to be published in the December issue of the Journal of Mammalian Evolution – is the first to identify it in a carnivore. Scientists don't know why it happened. One theory is that higher carbon dioxide reduced plant nutrients, but since the animal – named Palaeonictis wingi – mainly ate meat, another factor must have been involved.

But there may be something in it. Mammals in warmer climates tend to be smaller than their colder cousins: brown bears are generally bigger in Alaska than in Montana. So if humanity is too small-minded to recognise the dangers of climate change, it might find its bodies shrinking to fit.

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