“Imagine a 43- or 44-degree day, which we have repeatedly had this summer with the humidex, and then with a severe thunderstorm,” muses Franz Hartmann, executive director of the Toronto Environmental Alliance.

“Imagine the electricity system goes down and we get severe flooding,” he continues.

Imagine collapsed culverts, backed up basement drains, sewage bubbling up in toilets, high winds, hail, highway sinkholes, toppled trees, maybe a twister.

Imagine people are trapped in their sweltering highrises, with no access to drinking water because most pumps don’t have pressure above the sixth floor. Imagine cars floating along the Bayview extension. Imagine downed century-old maples blocking fire trucks and ambulances.

Imagine.

It isn’t that hard to do.

In 2003, the entire northeast electrical grid was knocked out, and during last month’s heat wave, downtown Toronto went black for hours. In August 2005, a torrential downpour destroyed part of Finch Ave., resulting in what experts say was the costliest environmental event ever to hit the city.

In June, part of Highway 401 at Avenue Rd. buckled under the heat. Last month, Scarborough homes were flooded during a sudden rainstorm. Last week, the same thing happened to basements in the Beach.

All of this could happen at once. One downpour could paralyze Toronto for days, or weeks. People would die. Billions would be lost.

It could take months, even years, to recover.

Which is why climate change experts at all levels of government, universities, insurance companies, emergency services and environmental non-governmental organizations are imagining the worst that more frequent unpredictable weather could bring.

“We are very concerned about the increase in the intensity of storms,” says Lawson Oates, director of the Toronto Environment Office at city hall. “It’s not just the mean increases, but the spikes that we’re seeing in the temperatures and rainfall. That’s where we get the major impact on our infrastructure and the stress on our social system.”

In this weekend’s Insight sections, the Star is looks at those possible impacts, and what we are doing and could do to prepare our water systems, electrical grid, transit and vegetation for climate change. In coming decades, those measures may well have to be ramped up as greenhouse gases continue to accumulate in the atmosphere.

Even most scientists who once denied climate change now concede that those who sounded the alarm years ago — scientists such as NASA’s James E. Hansen, who brought climate change to the world’s attention in 1988, and Pennsylvania State University’s Michael E. Mann, whose “hockey stick” graph of soaring global temperatures was popularized in Al Gore’s An Inconvenient Truth — were correct.

Late last month, when renowned climate change skeptic Richard Muller, a physicist at University of California at Berkeley, announced his “total turnaround,” it made international news. All of a sudden, the merchants of denial, led by Fox News, the Wall Street Journal and scientists in the pay of energy companies, had no credible expert witnesses for their side.

Climate change is here. We’re not about to stop it. So we had better get used to it, say the experts.

“Unless there is a huge political commitment and fundamental paradigm shift in our dependency upon our carbon-based system, there is going to be some degree of climate change that is inevitable,” says Toronto-based Quentin Chiotti, an environmental science and policy consultant. “Many of the Intergovernmental Panel on Climate Change (IPCC) experts have known this for some time.”

Adapt or die. If you can slow down climate change at the same time, it’s a bonus. But the realistic thing to do at this point is to batten down the hatches, literally and metaphorically.

“It’s not a question of whether climate will change, but by how much and how fast,” maintains Chiotti, a pioneer in the field of adaptation, having served on dozens of government and industry task forces and committees.

Since record-keeping began in 1948, the average annual temperature in Ontario has risen 1.4 C, with variations depending on where you live (the increase has been much greater in the north). In Toronto, partially due to the “heat island effect” caused by the paving and building over of vegetation, annual temperature is up by 2.7 C over the past century.

It doesn’t sound like much, but it’s enough to reshape the city and our lives.

Some say the city has done a great job of adapting.

“Toronto has earned international recognition for work that it has done in assessing climate-related risks,” says Al Douglas, director of the Ontario Centre for Climate Impacts and Adaptation Resources. “I would give Toronto a good grade for sure.”

Others are less complimentary.

“We’re just trying to build everything to the bare minimum and we’ll worry about what problems happen in the future in the future,” says Gabriella Kalapos, acting executive director of the Clean Air Partnership, who hastens to add, “Toronto is doing a lot more than other cities in North America.”

But not as much as Vancouver, the commonly accepted Canadian “gold standard” in climate change adaptation strategies. Last month its council voted on a comprehensive plan that will research and revamp everything from building bylaws to urban forest management.

Still, Toronto is getting ready, despite efforts by the Ford regime to cut back on the Toronto Environment Office. That after cancelling Transit City, his first act after getting into office in 2010.

The transit plan would have relieved traffic congestion, encouraged people to leave their cars at home and drastically reduced the carbon emissions in our air. (Currently, traffic contributes about 36 per cent of our greenhouse gases.) Transit City was the perfect combination of climate change mitigation and adaptation.

“I don’t think it’s any secret that for Mayor David Miller, climate change and getting the city ready for climate change and dealing with climate change was a key priority for him,” observes Hartmann. “Mayor Ford has not made that a priority at all.”

But he could find himself in the hot seat on this issue if disaster hits.

According to a recently published report prepared for the city by SENES Consultants, by the 2040s Toronto’s average winter and summer temperatures are projected to increase by 5.7 C and 3.8 C respectively.

The good news? Less shovelling in the winter.

The bad? Summers will be blistering, with extreme maximums up by 7.6 C. Projected scenarios include a jump from a maximum “extreme humidex” at Pearson airport in July of 45.7 C in the years 2000-2009 to a gasping-scary 56.5 C in 2040-2049.

And, even though we’re nowhere near that yet, the heat is already affecting train and subway tracks, causing them to expand and slowing down traffic. Roadways are being rutted because softening asphalt is being gouged out by car and bus tires. Traffic control systems now need to be cooled with fans because their computer equipment is failing as the temperature rises.

Pretty soon, the heat might even affect the construction industry.

“I was watching a report from the United States where some concrete failed which made a bridge unusable,” says Oates. “When they tried to repair it, they had to pour the concrete at night because the temperatures were so high. You need a certain amount of time for concrete to cure, and if they did it midday it would cure too fast and then crumble. These are the types of adaptation taking place in the face of these weather extremes.”

As for “extreme daily precipitation” — i.e., a really bad storm — we’re facing a 165.6-millimetre downpour in the 2040s compared to today’s average of 66 millimetres.

To put that in perspective, the torrent that collapsed the Finch Ave culvert in 2005, costing taxpayers, homeowners and the insurance industry some $640 million, delivered a mere 103 millimetres in one hour.

And, to put that into perspective, devastating Hurricane Hazel of 1954 dropped 183 millimetres over 24 hours.

All that has shifted things for insurance executives in the past 15 years, says University of Waterloo sustainable development expert Blair Feltmate, who chairs both the Climate Change Adaptation Project (Canada) and Pollution Probe.

“It’s no longer fire that they’re worried about,” he says. “It’s flooded basements that keep them up at night.”

Feltmate is currently studying whether the increase in insurance claims for flooding is caused by extreme rainfall events, or more and more houses with finished basements, or more residences being built on low-lying ground as higher ground gets used up.

Even long-established houses are getting hit. And so the city, which has identified four major flooding regions, including upscale Hogg’s Hollow at Yonge St. and York Mills Rd., is offering incentives to homeowners to retrofit their drainage systems with backflow water valves.

Feltmate fears that the city will resort to “management by disaster,” forcing through building code changes only after the damage has been done.

Consider roofing, which is very vulnerable in high winds.

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“We can show very clearly that, if you go from putting eight nails per shingle to 10 nails per shingle, with extreme weather events the shingle with the 10 nails will stay on the roof much more than that with only eight nails,” he says. “It’s not much more cost to add another two nails per shingle when you’re building a roof. The question is, can we get the builders and the roofers to embrace this?”

Can we get taxpayers to embrace any of this?

They’re starting to, but only indirectly.

Kalapos points to new rules making “green roofs” compulsory for new buildings of a certain size as just one example of what Toronto is doing right. The implementation of our Heat Alert system and cool centres help to safeguard health. Increased tree planting to deepen our shade and filter the air. The downspout disconnection program to prevent rainwater from overloading the sewers.

But is it enough?

“There are two things,” Kalapos says. “One is that it’s hard for municipalities to factor in what climate change adaptation means in day-to-day decision-making. But it’s important to do it because they’re making decisions that will be with us for the next 10, 15, 50, 75 years. It’s due diligence to factor in what the future conditions are going to look like. You can’t make decisions on what things looked like 50 years ago.”

So what’s the problem?

“Even though it will cost us more in the future, right now we’re not willing to take that additional risk or cost,” she points out.

No wonder. One study, which examined what is needed to upgrade our waste and storm water infrastructure, parts of which date back to the late 1800s, found it would take anywhere from $633 million to $9.4 billion — and those were the estimates in 2001.

But water is not our biggest worry. Power is.

“Electricity is central, and there’s a cascading effect if we don’t have electricity,” says Oates.

“Most of our electricity is generated by a small number of big plants,” Hartmann points out. “Right now it’s mostly a combination of coal, natural gas and nuclear, very specific places. If any one of those transmission lines breaks down or stops working because of an ice storm or extreme overheating, then all of a sudden we’re screwed.”

What’s needed is a more resilient electricity system, especially since traditional sources are being affected by climate change in other ways.

For example, nuclear plants are running into trouble because the sea and lake waters they rely on for cooling are getting warmer. Just last week, one plant in Connecticut had to partially shut down for that reason. Ontario’s nuclear generation could well be affected by a warming of Lake Ontario.

That’s why Hartmann says that Toronto Hydro should be diversifying. That means backing up the current systems with many smaller renewable energy generators — wind, solar, geothermal .

“So this way you don’t have all your eggs in one basket,” he says. “If one of the lines goes down, it doesn’t matter because of these other generators. And the beauty of this is, by moving to renewable energy, you’re reducing greenhouse gases.”

But, say all the experts, we’re beyond the point of no return.

“We’re heating up faster than the models predicted, severe weather events are happening more frequently than people have predicted, and I really think that the really nasty severe weather events could be happening much sooner than we expected and probably be much more severe,” says Hartmann.

Whether that weather will come in torrents of water or ice storms that stop the city dead, we should brace ourselves for the worst.

“You can put Teflon coatings on (electrical) transmission towers and so forth, but really what you need is your emergency departments need to be ready,” offers Laurentian University’s David Pearson, a professor in the department of Earth sciences.