He said if institutions moved out of fossil fuels,other investors would simply step in to fill the void.
"Divestment from coal shares does not exclude coal companies from impacting climate change... someone will still own the coal shares,"he said.
Mr Sicilia was responding to criticism from Market Forces,an affiliate of Friends of the Earth that targets miners to reduce greenhouse gas emissions,as well as financial institutions to demand they quit fossil fuel company investments.
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The activist made headlines with an unsuccessful shareholder resolution atRio Tinto's annual meeting in May,urging the miner to align its business with the goals of 2015 Paris climate agreement,and to set targets for emissions reduction.
In a series of emotive exchanges with Market Forces on Twitter,Mr Sicilia said it was critically important that companies and super funds have appropriate disclosure of climate risks and how these are prudently managed.
"But they are not answerable to Market Forces’ views as to whether these are adequate. They are guided by the law and relevant regulators,"he said.