Johnson was taking questions ahead of COP26, the UN’s climate summit which will be hosted by the UK in Glasgow between October 31 and November 12.
Apprehension is growing as critics question just how effective the climate conference will be after both Russian president Vladimir Putin and China’s President Xi Jinping – two of the world’s largest CO2 contributors – dropped out.
Others have questioned the UK’s self-assigned title as a leading green nation – and pondered whether questionable environment policies here could undermine Britain’s authority at COP26.
Here are all of the prime minister’s most unusual responses during the press conference – and people’s reactions to them.
1. ‘Recycling isn’t the answer’
The prime minister said recycling “doesn’t work” and said the priority should be reducing how much we use instead.
He continued: “It doesn’t begin to address the problem. You can only recycle plastic a couple of times really. What you’ve got to do is stop the production of plastic.”
WWF’s chief executive Tanya Steele then seemed to counter Johnson’s response as she said: “We have to reduce, we have to reuse – I do think we need to do a little bit of recycling, PM, and have some system to do so.”
The prime minister replied: “It doesn’t work. I don’t want to be doctrinaire about this, but if people think we can just recycling our way out of the problem, we’ll be making a huge mistake.”
Simon Ellin, chief executive of Recycling Association, told BBC Radio 4 in response: “It’s very disappointing. I think he has completely lost the plastic plot here, if I’m honest.”
He added that a recent Downing Street strategy about taking on waste seemed to prioritise recycling so the prime minister “seems to be completely contradicting his own government’s policy”.
2. Cop26 agreements are going to be ‘touch and go’
The prime minister told the schoolchildren: “It is going to be very, very tough this summit.
“I am very worried because it might go wrong and we might not get the agreements that we need and it is touch and go, it is very, very difficult, but I think it can be done. It’s very far from clear that we’ll get the progress that we need.”
Johnson was referring to the binding commitments all countries need to enter into to make a real difference towards climate change.
The government spokesperson later claimed that the prime minister was only being “realistic about what a challenge this represents”.
However, this is a real change in tone compared to what Johnson said about the summit earlier this year.
Speaking at the United Nations General Assembly in September, Johnson said it is “easy, lucrative and right” to be green.
Several people spotted this on Twitter and noted how the prime minister was now trying to U-turn on his previous promises about the summit.
3. ‘We could feed some of the human beings to the animals’
When WWF UK chief executive Tanya Steele started discussing “rewilding our oceans”, the prime minister said: “We could feed some of the human beings to the animals, that would, that would be...”
Steele quickly joked: “We could have a vote later and ask if there’s any candidates. But certainly we need to take our responsibilities seriously and help bring nature back because when you give nature the chance it will recover, it regenerates very quickly.”
Johnson also said “we have to encourage cows to stop burping” to stop them from producing so much methane.
The prime minister’s spokesman later said: “I think most people took that in the nature in which it was intended – not to be taken seriously”.
Some critics online said the prime minister’s light-hearted approach was not appropriate about such a serious conversation days before the summit begins.