The cost of policing the UN climate change conference in Glasgow later this year has now been estimated at £250m.
The "indicative" figure is detailed in a paper which will go before the Scottish Police Authority on Wednesday.
About 30,000 people, including 200 world leaders, are expected to attend COP26 from 9 to 20 November.
Police Scotland, the second largest force in the UK after the Met, will draft in officers from across the country for the summit under mutual aid arrangements.
The COP26 paper states: "The UK government have been advised of the indicative policing costs which are estimated to be £250m.
"The UK government have been provided with a high-level breakdown of these costs which are presented on the basis that there will be no financial detriment to the Scottish policing budget.
"In the absence of assured planning assumptions, these figures are based on reasonable worst-case scenario assumptions and will remain indicative and will be subject to internal validation and independent security and financial assurance work between now and March 2020."
The report, which will be presented by event gold commander Assistant Chief Constable Bernard Higgins, also included a reference to the political tensions between Holyrood and Westminster.
Last week, First Minister Nicola Sturgeon insisted the summit would not cause "squabbles" between the Scottish and UK governments.
Her comments came after Claire O'Neill, who had been co-ordinating plans for the summit, was sacked by Downing Street.
Assistant Chief Constable Higgins said: "Police Scotland remains concerned about the current lack of governance coordination between governments, and the lack of clarity on agreed outcomes for this event."
As well as the security of delegates, planning for the global summit must also consider the potential impact of protests.
Last month, Chief Constable Livingstone said major events such as the European football championships and continuing uncertainty about the Brexit settlement were adding to pressure on the force, even before policing of COP26 was taken into account.
Scottish ministers previously said they expected the UK government to cover the "core costs", including emergency services funding.
The UK government has said discussions with the Scottish government on the conference costs are "currently ongoing".
An SPA report last month said the summit will see the largest mobilisation of police officers in the UK.
On Sunday, a potential security breach was highlighted after detailed diagrams of the Scottish Events Campus site, which will host the summit, were accidentally put online.