''It's certain the sea level will rise,'' University of Otago emeritus Prof Blair Fitzharris said.
''What's uncertain is by how much.''
The former Intergovernmental Panel on Climate Change (IPCC) scientist was responding to Finance Minister Bill English saying he would not be heeding the report's recommendation to set aside funds for sea-level-rise adaptation.
Mr English was quoted calling the report's findings ''speculative'' in yesterday's New Zealand Herald.
Prof Fitzharris said the ''excellent'' Parliamentary Environment Commissioner's report was far from speculative.
''It's not speculative; it's based on scientific study,'' he said.
''It'd be unwise to say that because of the range ... that we don't have to worry about it.''
The report's predictions were based on a 2013 IPCC analysis that foresaw sea-level rise at anywhere from 26cm to 82cm.
And those predictions might have to be revised upwards based on more recent research, putting the upper limit of sea-level rise by the end of the century at 1.6m, Prof Fitzharris said.
Scientific predictions were almost always referred to in a range, he said.
''Some people think that science is certain about everything, but it's not. And sometimes the layperson finds that hard.''
Prof Fitzharris said he agreed with Mr English that climate change and sea-level rise were not the only risks to be addressed.
''He pointed out there's lots of risks and matters we have to attend to ... like the risk for terrorism ... or the tax base. All that sort of thing.''
Still, sea-level rise was coming, and something needed to be done about it.
''Governments aren't very good at looking at long-term things. If they can put it off, they will,'' he said.
''Some of the stuff's not going to happen tomorrow, but it will happen in the next three or four decades. And by the end of the century, it's going to be quite serious.''
