Imagine this: There is a forceful-sounding knock at your door. Who should it be but the unsmiling, bristling Greta Thunberg!

She is doorknocking, personally confronting people of your generation, demanding to know of you (in the spirit of her impassioned and guilt-pinning "How dare you!" speech at the UN Climate Summit) why you did nothing to help stop our planet become the poor ravaged thing it is now.

What will you say to her? How will you justify having spent decades blissfully caught up in capitalism's whirligig, just ravenously, recklessly consuming, consuming, consuming, estranged from nature, from our planet's fragility? Will Ms Thunberg's withering gaze wither you?

Not to excuse himself, but only to try to explain to himself his "neanderthal" failure to be fully planet-sensitive until now (he is 84), the great left-liberal writer and thinker Lewis H. Lapham has just been writing on related subjects. In his online piece Paying the Piper: Acquiring an acquaintance with nature when capitalism has put nature's future at risk, he gives a Thunbergesque diagnosis of the planet's present dire plight.

Then he continues "eighty-five per cent of the carbon now present in the atmosphere is the value added during the course of my lifetime, 2.5 trillion tons ... I was 50 years old before I knew it was there, much less understood it to be a problem.

"I grew up in the city of San Francisco in the 1940s, so far apart from nature I assumed most of it located in Africa, picturesque specimens to be seen in the San Francisco Zoo. The streets in my neighbourhood bore the names of trees - walnut and cherry, laurel, chestnut, and spruce. I didn't wonder what the trees themselves might look like."

In the piece he gives a short history of environmental awareness and says that in his long lifetime it wasn't really until the Club of Rome's 1972 report The Limits to Growth that anyone in his capitalistically gung-ho USA (and methinks in the materialistic West generally) ever heard a contrary voice arguing that breakneck greedy growth was threatening the planet.

It is true, isn't it, mature-age readers (your columnist is 73) that the wealth of climate warnings now, in this Anthropocene epoch into which anxious dynamos like Ms Thunberg has been born, is quite new. How were we, today's oldies, to know how dire things were?

Lapham notes what a planet-ravaging species we are.

"Wherever man plants his foot on the earth, he destroys the harmonies of nature. He had been doing so since he first began planting crops and husbanding animals, building cities and staking out empires. Yuval Noah Harari author of the 2014 history of mankind, Sapiens, rates Homo sapiens as 'the deadliest species in the annals of planet Earth,' the historical record making him 'look like an ecological serial killer'. Harari offers as case in point the settlement in Australia of the first hunter-gatherers crossing from Asia and climbing on arrival to the top of the food chain. Within the relatively brief span of a few thousand years, they permanently transformed the ecosystem. Of 24 animal species weighing a hundred pounds or more, 23 disappear, among them a marsupial lion ... and a two-and-a-half-ton wombat."

Impressed by Ms Thunberg, in recent days I have been everywhere online following what is being written and said about her. Everyone, everywhere, feels the need to have a gale-force opinion of her. The hostility of so much of that opinion seems shocking to me. I have had to invent a new word, pedomisogyny, to label a phenomenal dislike of her that seems part pedophobia (fear and loathing of the young) and part misogyny (dislike of women and dismissal of their worth).

My temporary diagnosis is that what we are seeing in Greta Thunberg is a girl of high intelligence (but of only average wisdom) who is suffering her first shocking realisation of just how planet-plunderingly awful her own species is. This realisation must have a special piquancy for thinking members of her generation born into the consciousness-raising Anthropocene epoch, the epoch in which (the inventors of the name say) human-kind's behaviour is making lasting, polluting, planet-altering impacts.

That she is showing her shock, her fears, her disappointments in us so publicly, on such huge world stages, is unnerving for us.

I am still making up my mind about her and her crusade but notice in myself that before I can get to a rational, intellectual assessment of her and her beliefs I have to overcome strong parentalish, even grandparentalish reactions to her distress. The hostility some are showing to her seems so cruel. Her distress is so transparently genuine and her beliefs so heartfelt. Those accusing her of being an artful demagogue need their heads read.

Anyone who has a heart and who has ever instinctively leapt to try to comfort a terrified child, perhaps one waking from a nightmare, surely should have some compassionate feelings for this well-intentioned Swedish child suffering from her waking nightmares (not dream-delusions at all, but horrible possibilities forecast by dispassionate climate science) about what it to become of us.