Four climate change activists were arrested in London on Saturday after they scaled the gates of Queen Elizabeth II's Buckingham Palace residence and chained themselves to the railings.
The campaigners from the Climate Siren group wore t-shirts bearing the words "climate emergency. 10% annual emission cuts," and shouted slogans through megaphones.
The group said they wanted the queen to follow the lead of her son Prince Charles in speaking out about climate change.
Protesters unfurled a banner citing a 2008 speech given by the Prince of Wales to the European Parliament. It read: "The doomsday clock of climate change is ticking ever faster towards midnight. We are simply not reacting quickly enough."
In an open letter to the queen posted on their website, Climate Siren called for urgent action on greenhouse gas emissions.
"It is time that you and all public figures with influence followed the example of your son by speaking up... about the escalating threat of catastrophic climate change," the letter said.
London's Metropolitan Police said they arrested three men and a woman on suspicion of breaching Royal Parks regulations, as they broke up the protest after more than four hours.
Around 100 bystanders had stood watching the demonstration.
The queen was not in the palace at the time as she was attending a horse racing event in Ascot, southern England.
On its website Climate Siren calls for "a great effort of civil disobedience" in Britain to tackle "catastrophic destabilisation of global climate".
The group says its protest was timed to follow the Rio+20 global conference on sustainable development in Rio de Janeiro, Brazil, which drew to a close Friday. They criticised "the failure of the conference to achieve any meaningful results".