Bill’s costly rehab job

Invoking rising seas and a President so in climate denial that he stormed off from the Paris accord, Mayor de Blasio says he’ll force bigbuilding owners to sharply cut their buildings’ planet-warming emissions for the good of the city and globe. You could say New York’s mayor is taking a game-changing stand, as the first in the nation and likely the world to set such a sweeping mandate on private property holders — if only there existed yet a feasible or fair program to discuss.

He hauls out a sledgehammer to deliver on his important goal of reducing New York City’s greenhouse gas emissions 80% by 2050 — targeting buildings as the source of most of the city’s output — with a great many details yet to be decided.

To the City Council members who will have to sign off and are already complaining de Blasio isn’t mandating enough: be very, very careful what you wish for.

Was only yesterday that de Blasio reckoned voluntary actions would get the job done — like replacing dirty old boilers with high-tech new ones when their time came due, saving enough on energy bills to pay for the upgrades.

Why the change? “Time was up,” proclaimed de Blasio in announcing the measures Thursday. Strong words, and strange ones, from a mayor who had never set a deadline sooner than 35 years hence.

Now, he intends to sic his sustainability shop on all buildings larger than 25,000 square feet, requiring the half of them that spew the most greenhouse gases to reduce emissions until they’re as clean as the typical building in the greener half. If they fail, they’ll be on the hook for hefty fines.

That’s 14,500 buildings in all, from hospitals to high-rise towers, on the whole less well maintained and more financially rickety than buildings with the wherewithal to have already invested in state-of-the-art systems.

That includes oodles of affordable housing and low-margin co-ops that can scarcely withstand higher costs — burdened suddenly with a new obligation that just slightly greener buildings need not shoulder. Neither will homeowners — including the mayor himself — who hardly live lightly on this Earth.

Lo! De Blasio intends to roll out long-term, lowinterest loans to help strapped property owners pay for the improvements — new windows, new insulation, new heaters — to be paid back on property tax bills, while they make back the money invested in upgrades as they spend less money on fuel.

He could have and should have rolled out the financing first, to iron out complications. With savings in store, many owners will seize them voluntarily.

Under a mandate, what’s more, nothing stops landlords from passing costs on to tenants in the form of rent increases — something de Blasio says he’ll ask Albany to block for regulated units after the next legislative election, so confident is he that Democrats will seize control.

An edifice built of hopes upon wishes upon the very best of intentions.

The science of climate change and urgency to act are undeniable. The case de Blasio has made so far for his response, boding high cost to others, is still far from proven.