There are gaps and weaknesses in the province's climate change strategy that is supposed to limit the damage from fiercer and more frequent ice storms, heavy rains and heat waves, said Miller.
"We have an infrastructure built for a climate we no longer have," Miller told reporters.
"So how much of that infrastructure has to be rebuilt and replaced is really the question."
Echoing a report issued Sunday warning that climate change is a real threat to outdoor hockey rinks, Miller noted non-refrigerated outdoor rinks are becoming less and less common in Ontario.
"We define ourselves on the hockey rink, on the back of our five-dollar bill is kids playing shinny on an outdoor rink," he said.
"I’m not sure you can do that even up in North Bay where I live any more."
Environment Minister Jim Bradley agreed with Miller's findings, and said Ontario is preparing its infrastructure for a very different future.
"When you’re building new bridges and other structures you take into account the fact that we could see significant climate change," he said.
"What engineers call the 100-year storm now will show up every 20 years, so in our planning processes we have to ensure that we take this into account."
The Ministry of Energy isn't mentioned in the province's climate change plan, said Miller, even though scientists predict an increase in devastating ice storms and other extreme weather events.
However, Energy Minister Chris Bentley said one of the reasons electricity prices are rising is Hydro One is building a more robust system of towers and transmission lines that will be better able to withstand stronger storms.
"There are opportunities that new technologies present us," said Bentley.
"Through the smart grid for example, we can identify outages and reroute the power long before you even send people out to repair it."
The environmental watchdog also warned that climate change will mean more warm-climate diseases such as Lyme disease and West Nile virus and an influx of new warm-weather pests in Ontario.
"I took my advisory committee to southwestern Ontario, looking at some things in the Pelee Island area a couple of years ago, and one of them came down with Lyme disease," said Miller.
"It is a real impact on people’s lives and one we never had to face just a few years ago in Ontario."
There are of course costs associated with preparing for and adapting to climate change, said Miller, but it's hard to say just how much.
"What we don't spend on adaptation now will cost us much more in the future," he said.
"The government itself has indicated that the cost of extreme weather events could rise to $5.66 billion per year by mid-century."
Some changes can be made without spending a lot of money, said Bradley.
"(Miller) made a good point when he said in some cases if you make these investments, the consequences down the line will not be as great," he said.
"But a lot of times it’s simply shifting priorities within government to address these matters."
The Opposition said Miller's report on climate change shows the Liberals are falling down on the job, and still haven't closed all of Ontario's coal-fired electrical generating stations.
"The commissioner highlighted the fact this government has no plan," said Progressive Conservative critic Michael Harris.
"They sat on their hands with the coal-fired plants, keep moving their targets and timelines back."
The New Democrats were also critical of the Liberals' climate change strategy.
"It’s a plan that doesn’t have timelines, it doesn’t have targets, doesn’t have very many specifics at all," said NDP critic Jonah Schein.
"We need to hear some of those specifics if we are to feel confident about dealing with climate change in Ontario."