Boris Johnson's partner Carrie Symonds has said he and other politicians have a "gigantic responsibility to make the right decisions" over the environmental crisis, in her first public speech since moving into 10 Downing Street.
Ms Symonds, 31, also condemned "cruel" trophy hunters, but expressed optimism that the number of people who care about the environment "far outnumber the people who don't".
She was speaking at Birdfair, an event described as "birdwatching's Glastonbury", at the Rutland Water Nature Reserve in Leicestershire.
"There are no simple answers to the environmental crisis this planet faces," she said.
"It is immensely complicated. There is no escaping the fact that politicians, business leaders and journalists have a gigantic responsibility to make the right decisions, to change the way they do business and report the truth about what is happening in the world.
"But so too do scientists, naturalists, campaigners, birdwatchers and all of us individuals.
"We all share this crowded little planet. We all have a duty to take care of it and we all have a massive role to play in doing so.
"And that means we all need to make the little changes that will help make a big difference."
She went on: "I'm far from perfect, but I try to remember to take a canvas bag to the supermarket, take my reusable bottle rather than buy plastic, and tonight I'm wearing a sustainable dress.
"I can't always do that, and I'm learning and I'm trying.
"Yes, it's only a start, only the beginning of what we can do, but we shouldn't let the perfect be the enemy of the good.
"And we should applaud everyone who makes any effort to reduce the impact they have on the world.
"We have no excuse not to make that effort. We are more informed than ever before.
"We know the impact we have, we know the changes we need to make."
However, offering a glimmer of hope she said she felt "profoundly optimistic that the people who care far outnumber the people who don't, especially among young people."
Turning to the "sick" practice of trophy hunting, the 31-year-old described her delight at seeing a puffin at Bempton Cliffs in the East Riding of Yorkshire, then her horror at seeing photographs in a newspaper of puffins "slaughtered by so-called trophy hunters" on trips to Iceland.
My video of the little puffin I spotted 🤩 pic.twitter.com/BkvIV0PpNZ— Carrie Symonds (@carriesymonds)July 28, 2019
"A trophy is meant to be a prize," she said. "Something you're awarded if you've achieved something of merit that requires great skill and talent.
"Trophy hunting is the opposite of that.
"It is cruel, it is sick, it is cowardly and I will never, ever understand the motivation behind it.
"And when we look at trophy hunting, when we look at habitat loss, when we look at climate change and the catastrophic levels of plastic pollution in our oceans - a million sea birds die every year as a result of ingesting plastic - when we look at all that we see why events like Birdfair are so important.
"Because, quite simply, there is still so much that needs to be done."
She held an umbrella and wore a floral-patterned dress, wellies and a red handbag as she arrived on the muddy site on a drizzly Friday afternoon ahead of her evening speech.
After her speech she took a seat in the front row for a question and answer session, which featured guests including BBC Springwatch presenter Chris Packham and entrepreneur Deborah Meaden, of Dragons' Den.
Tim Appleton, founder of the birdwatching conference, said ahead of the event: "We're absolutely over the moon that Carrie is supporting us and we hope she will continue supporting us and conservation for many years to come."
Public relations expert Ms Symonds resigned as director of communications for the Conservatives last year.
Today she is a senior adviser at US-based environmental campaign group Oceana, working with its marketing operation in London.
A profile on the charity's site describes her as being "passionate about protecting the oceans and marine life".