PORTLAND (NYTIMES) - It would hit Ms Alina Black in the snack aisle at Trader Joe's, a wave of guilt and shame that made her skin crawl.

Something as simple as nuts. They came wrapped in plastic, often in layers of it, that she imagined leaving her house and travelling to a landfill, where it would remain through her lifetime and the lifetime of her children.

She longed, really longed, to make less of a mark on the Earth.

But she had also had a baby in diapers, and a full-time job, and a five-year-old who wanted snacks. At the age of 37, these conflicting forces were slowly closing on her, like a set of jaws.

In the early morning hours, after nursing the baby, she would slip down a rabbit hole, scrolling through news reports of droughts, fires, mass extinction. Then she would stare into the dark.

It was for this reason that, around six months ago, she searched "climate anxiety" and pulled up the name of Dr Thomas J. Doherty, a Portland psychologist who specialises in climate.

A decade ago, Dr Doherty and a colleague, Dr Susan Clayton, a professor of psychology at the College of Wooster in Ohio, published a paper proposing a new idea.

They argued that climate change would have a powerful psychological effect - not just on the people bearing the brunt of it, but on people following it through news and research. At the time, the notion was seen as speculative.

That scepticism is fading. Eco-anxiety, a concept introduced by young activists, has entered mainstream vocabulary. And professional organisations are hurrying to catch up, exploring approaches to treating anxiety that is both existential and, many would argue, rational.

Though there is little empirical data on effective treatments, the field is expanding swiftly.

The Climate Psychology Alliance provides an online directory of climate-aware therapists; the Good Grief Network, a peer support network modelled on 12-step addiction programmes, has spawned more than 50 groups; professional certification programmes in climate psychology have begun to appear.

As for Dr Doherty, so many people now come to him for this problem that he has built an entire practice around them: An 18-year-old student who sometimes experiences panic attacks so severe that she cannot get out of bed; a 69-year-old glacial geologist who is sometimes overwhelmed with sadness when he looks at his grandchildren; a man in his 50s who erupts in frustration over his friends' consumption choices, unable to tolerate their chatter about vacations in Tuscany, Italy.

The field's emergence has met resistance, for various reasons.

Therapists have long been trained to keep their own views out of their practices. And many leaders in mental health maintain that anxiety over climate change is no different, clinically, from anxiety caused by other societal threats, such as terrorism or school shootings.

Some climate activists, meanwhile, are leery of viewing anxiety over climate as dysfunctional thinking - to be soothed or, worse, cured.

But Ms Black was not interested in theoretical arguments; she needed help right away.

She was no Greta Thunberg type, but a busy, sleep-deprived working mum. Two years of wildfires and heatwaves in Portland had stirred up something sleeping inside her, a compulsion to prepare for disaster.

She found herself up at night, pricing out water purification systems. For her birthday, she asked for a generator.

She understands how privileged she is; she describes her anxiety as a "luxury problem".

But still: The plastic toys in the bathtub made her anxious. The disposable diapers made her anxious. She began to ask herself, what is the relationship between the diapers and the wildfires?

"I feel like I have developed a phobia to my way of life," she said.

Last fall, Ms Black logged on for her first meeting with Dr Doherty, who sat, on video, in front of a large, glossy photograph of evergreens.

At 56, he is one of the most visible authorities on climate in psychotherapy, and he hosts a podcast, Climate Change And Happiness.

In his clinical practice, he reaches beyond standard treatments for anxiety, like cognitive behavioural therapy, to more obscure ones, like existential therapy, conceived to help people fight off despair, and ecotherapy, which explores the client's relationship with the natural world.

He did not take the usual route to psychology; after graduating from New York's Columbia University, he hitchhiked across the country to work on fishing boats in Alaska, then as a whitewater rafting guide - "the whole Jack London thing" - and as a Greenpeace fundraiser.

Entering graduate school in his 30s, he fell in naturally with the discipline of "ecopsychology".

At the time, ecopsychology was, as he put it, a "woo-woo area", with colleagues delving into shamanic rituals and Jungian deep ecology.

Dr Doherty had a more conventional focus, on the physiological effects of anxiety. But he had picked up on an idea that was, at that time, novel: That people could be affected by environmental decay even if they were not physically caught in a disaster.

Recent research has left little doubt that this is happening.

A 10-country survey of 10,000 people aged 16 to 25 published last month in The Lancet found startling rates of pessimism. Forty-five per cent of respondents said worry about climate negatively affected their daily life.

Three-quarters said they believed "the future is frightening", and 56 per cent said "humanity is doomed".

The blow to young people's confidence appears to be more profound than with previous threats, such as nuclear war, Dr Clayton said.

"We've definitely faced big problems before, but climate change is described as an existential threat," she said. "It undermines people's sense of security in a basic way."

Many of Dr Doherty's clients sought him out after finding it difficult to discuss climate with a previous therapist.

Ms Caroline Wiese, 18, described her previous therapist as "a typical New Yorker who likes to follow politics and would read The New York Times, but also really didn't know what a Keeling Curve was", referring to the daily record of carbon dioxide concentration.

Ms Wiese had little interest in "Freudian BS".

She sought out Dr Doherty for help with a concrete problem: The data she was reading was sending her into "multi-day panic episodes" that interfered with her schoolwork.

In their sessions, she has worked to carefully manage what she reads, something she says she needs to sustain herself for a lifetime of work on climate.

"Obviously, it would be nice to be happy," she said, "but my goal is to more to just be able to function."

As for Ms Black, she had never quite accepted her previous therapist's vague reassurances. Once she made an appointment with Dr Doherty, she counted the days. She had a wild hope that he would say something that would simply cause the weight to lift.

That didn't happen. Much of their first session was devoted to her doomscrolling, especially during the night-time hours. It felt like a baby step.

"Do I need to read this 10th article about the climate summit?" she practised asking herself. "Probably not."

Several sessions came and went before something really happened.

Ms Black remembers going into an appointment feeling distraught. She had been listening to radio coverage of the Intergovernmental Panel on Climate Change meeting in Glasgow, Scotland, and heard a scientist interviewed. What she perceived in his voice was flat resignation.

That summer, Portland had been trapped under a high-pressure system known as a "heat dome", sending temperatures to 46 deg C.

Looking at her own children, terrible images flashed through her head, like a field of fire. She wondered aloud: Were they doomed?

Dr Doherty listened quietly. Then he told her, choosing his words carefully, that the rate of climate change suggested by the data was not as swift as what she was envisioning.

"In the future, even with worst-case scenarios, there will be good days," he told her, according to his notes.

"Disasters will happen in certain places. But, around the world, there will be good days. Your children will also have good days." At this, Ms Black began to cry.

She is a contained person - she tends to deflect frightening thoughts with dark humour - so this was unusual. She recalled the exchange later as a threshold moment, the point when the knot in her chest began to loosen.

"I really trust that when I hear information from him; it's coming from a deep well of knowledge," she said. "And that gives me a lot of peace."

Her goal is not to be released from her fears about the warming planet, or paralysed by them, but something in between: She compares it with someone with a fear of flying, who learns to manage his fear well enough to fly.

"On a very personal level," she said, "the small victory is not thinking about this all the time."