Community advocate David Johnston submitted a request to the environment directorate on December 15, but it was only answered on Monday, well outside the 30 days prescribed in legislation.

The Commonwealth Ombudsman's office has confirmed it's investigating the delay.

The documents provided to Mr Johnston show the November trip to the United Nations climate change conference in Marrakesh cost ACT taxpayers $16,159 including the expense for senior public servant Stephen Bygrave.

The minister signed a memorandum of understanding with other sub-national governments to reduce greenhouse gas emissions.

He told The Canberra Times he was proud to represent the ACT at the international event, which followed the Paris Agreement.

"The conference was a great opportunity to drive investment in Canberra by building our profile as a renewable energy economy," he said.

"My attendance at COP22 offered invaluable insights and international contacts that will continue to benefit the ACT.

"I travelled economy class on all flights during the trip, and the entire cost of my trip totalled less than $8000.

"At COP22, the ACT was acknowledged by delegates, jurisdictions and country representatives for its leadership on climate action and was congratulated on its target of 100 per cent renewable electricity by 2020. As a small jurisdiction we are punching far above our weight.

"However, it is important that the ACT ensures that other countries are also addressing climate change with the urgency required, so we must work with other world leaders and have representation on the international stage."

Mr Johnston said the minister should direct his efforts closer to home.

"The ACT government needs to focus on the delivery of services for all including the disabled rather than expensive travel and big noting itself on the world stage," he said.

"Mr Rattenbuy needs to explain what value ACT ratepayers received from the trip."

Mr Johnston said the minister's directorate resisted his FOI request and failed to acknowledge it in the 14-day required timeframe.

"The ACT government needs to lift its game in processing FOI requests," he said.

"There is a need for Mr Rattenbury as the responsible minister to ensure good administration and that his agency takes its FOI responsibilities seriously, with all requests being processed in a timely, efficient and effective manner in accordance with the legislation."

Shadow environment minister Elizabeth Lee took up the issue with Mr Rattenbury.

"The right of a citizen to make an FOI request is a fundamental aspect of open government," she said.

"If we have directorates and ministers being lax in their duty to respond to FOI requests, it puts at risk our right to a transparent and accountable government.

"I'm pleased to see that my representations to Minister Rattenbury have resulted in not only having this FOI request eventually answered, but also an undertaking that his directorate will review current processes to improve the way in which FOI requests are dealt with."

Mr Rattenbury said the directorate had indicated "an administration error" in processing the request and had apologised to Mr Johnston.

"I have asked the directorate to review its FOI procedures and have been advised that they have put in place additional assurance mechanisms to ensure future requests are not overlooked," he said.