Coun Glen Sanderson insisted that green energy was "the future" and said carbon emissions had to be reduced for the sake of the county's children.
His comments came after Reform leader Mark Peart questioned the amount of cash the council had put into green initiatives. Coun Peart, who represents Blyth's Croft ward, branded the council's target of becoming carbon neutral by 2030 as "unrealistic".
The county council declared a climate emergency in 2019, setting the carbon neutral goal at the same time. Nationally, Reform has said it will scrap net zero plans and cut all renewable energy subsidies.
Speaking at a meeting of the county council, Coun Peart said: "How much has been spent to date on the net zero, climate change agenda including staffing, communications, external contractors and consultancy fees?
"A figure of £1.6billion has previously been mentioned for Northumberland to become carbon neutral by 2030. What is the estimated figure now to include the new datacentre, which will be a large carbon dioxide producer?
"Can the council do the right thing and modify its unachievable and costly target?"
The council's cabinet approved the 2024-2026 action plan last year. It recommitted the council to achieving the net zero targets for carbon dioxide, with a longer-term target of net zero for all greenhouse gas emissions by 2040.
The plan acknowledged that this would require a "concerted national shift in behaviours" alongside "significant technological advancements". Initiatives have ranged from the development of a clean energy hub at the Port of Blyth to giving out free trees to households.
Responding to Coun Peart, Coun Sanderson said: "I am surprised it has taken until now for Reform to ask that question. I welcome it because it allows me to explain how important the issue of caring for our environment and climate change is for this council.
"It is important that we do this and remain steady for the sake of our young people. I'm absolutely certain that if you went to every high school in Northumberland and asked each child how important climate change is, they would say it's hugely important to them and their generation.
"I was pleased to be joined last week by some Reform councillors at the opening of a new, fantastic project at Catapult in Blyth. That set the whole scene for what we're doing in Northumberland.
"The future is around renewable energy. We have £0.9million a year in revenue costs put towards net zero. Almost half is paid for by external funding.
"We have allocated £14.5million to capital projects, including the energy saving measures in homes. Around 860 homes have benefited, saving each of those households £1,000 a year.
"We also have the excellent environment and climate fund, which sits at £50,000. All of these together are key to underlining our commitment to doing what we can in our way to meet the climate change issue.
"To say there isn't one - it's made quite clear by the visit to Catapult. The whole future is around green, renewable energy.
"We will always make sure there's a balance in our funding and that we take people with us. We're doing what we can, but we're keeping everything in perspective."
US firm QTS has plans to build a vast datacentre at Cambois to provide the computing power needed to drive new technology such as AI. The plans will require a significant amount of energy.
On this, Coun Sanderson added: "The brilliant new datacentre, from which the whole county will benefit - in the details of the planning application they have done carbon offsetting with specific bits of land."