Boris Johnson’s partner Carrie Symonds said politicians had a “gigantic responsibility to make the right decisions” over the climate crisis, in her first solo public appearance since moving into Downing Street.

Symonds also condemned “cruel” trophy hunters, but expressed optimism that the number of people who cared about the environment “far outnumber the people who don’t”.

She addressed an audience in a marquee at Birdfair, which is described as “birdwatching’s Glastonbury”, at Rutland Water nature reserve.

“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.”

She said everyone had a role to play. “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,” she said. “I can’t always do that, and I’m learning and I’m trying.”

She 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”.

She said: “A trophy is meant to be a prize. 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.”

After her speech, she took a seat in the front row for a question and answer session, which featured guests including BBC presenter Chris Packham and the entrepreneur Deborah Meaden, of BBC Two’s Dragons’ Den.

Tim Appleton, the founder of the birdwatching conference, said before 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.”

Symonds, 31, who resigned as director of communications for the Conservatives last year, is now a senior adviser at Oceana, a US-based environmental campaign group, 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”.