Protestors greeted newly-elected councillors when they turned up for their first meeting.
More than 50 gathered outside West Norfolk council's AGM to call for the authority to declare a climate emergency.
Pressure group Extinction Rebellion wants the authority to commit to reducing carbon emissions to zero by 2030 and set up a citizen's assembly to draw up a plan of action.
So far around 100 councils around the country, including North Norfolk, have signed up to the pledge.
There was a police presence around the town hall, as protestors gathered.
Campaigner Dr Charlie Gardner said: "After all the demonstrations in London, they're prepared for anything. This is the first time we're speaking to the councillors, so we want to speak to them politely and ask them to act for us as citizens of West Norfolk." Fellow activist and Lynn GP Pallavi Devulapalli said: "I'm here because I'm very concerned about climate change and the loss of biodiversity.
"We want an ambitious council. We want to see a beautiful, flourishing West Norfolk."
Protestors staged a die-in opposite the council chamber, as members and guests arrived. But there was no attempt to disrupt the meeting, where Geoff Hipperson was elected mayor and Margaret Wilkinson deputy.
Mr Hipperson said he intended to reach out to all corners of the borough during his mayoral year. His charities for the year will be West Norfolk Riding for the Disabled and King's Lynn Mind.
Earlier, buildings in the centre of Lynn were symbolically decorated with blue tape to show the height of the flood waters campaigners fear will immerse the town by the end of the century if carbon emissions are not cut.
West Norfolk's carbon emissions are the highest in Norfolk for industry and land use and the third highest in the county for transport.
Extinction Rebellion says West Norfolk is one of the most vulnerable areas of the country to rising sea levels, with much of the Fens to the south of the town below sea level.
Thousands of homes and tens of thousands of acres of farmland are at risk, along with Lynn's historic quarter.
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