The use of fossil fuels to power the centre prompted criticism from environmental campaign group Friends of the Earth Cymru.
Its interim director Jenny Lloyd said: ”After a summer of heat waves and drought and worries about flooding over the autumn and winter, it’s completely irresponsible to give the green light to this climate-wrecking piece of infrastructure.”
Plaid Cymru MS Nick Carter, who represents Cardiff’s Caerdydd Fynnon Taf constituency, said: “There is no reason why a data centre needs to be sited in an urban area close to schools and care homes, when in fact underneath the headlines is a small gas-fired power station.”
Senior Labour councillor Lee Bridgeman added his voice to those objecting this week.
The member of the Cardiff Council cabinet and Llanrumney ward councillor said in a letter it was “hard to reconcile” the centre’s emissions “with Cardiff’s climate emergency declaration and Planning Policy Wales”.
As well as the data centre, the plans included a new bridge and link road for pedestrians and cyclists.
Curtis Hall previously had planning permission for a logistics centre. According to Cardiff Council the company had switched to a data centre because of “changing market demand”.
The company said the gas generation was “not the data centre’s permanent power supply, and once the grid connection is live it would no longer be needed”.
“If the connection arrives in time, the energy centre will not be needed at all,” it said.
“Gas turbines appear in the planning documents because they represent the worst case for emissions and noise, so assessing them tests the upper limit of any impact.”
The company said the technology was “not confirmed” for the energy centre – suggesting fuel cells that convert gas or hydrogen to electricity could be used.
It said the air quality effects of gas and diesel generators were also “not significant”.
In response to climate change concerns, Curtis Hall said south Wales’ electricity grid was “decarbonising fast” with plans for floating offshore wind.
A spokesperson for the company said the development would bring “significant benefits”, such as “the delivery of the new road bridge” and by helping “attract much-needed investment, create well-paid jobs and provide new training opportunities”.