City Comptroller Brad Lander is using the city’s $240 billion in pension-fund assets to push “decarbonization” — with taxpayers on the line to cover the inevitable downside of this madness.

Sadly, he’s gotten other trustees of the funds to go along with his “Net Zero Implementation Plan,” which aims to muscle the private sector into taking more aggressive steps to reach net-zero carbon emissions.

Lander’s goal is to make the city retirement funds’ investment portfolio entirely anti-climate-change — that is, anti-fossil fuels — by 2040.

He calls it a “roadmap toward decarbonization across our investment portfolio and the global economy.”

In fact, it’s either an empty con or a betrayal of the trustees’ legal fiduciary duties.

That is: If it’s a real policy change, he’s gambling with house money.

Pension payouts are guaranteed.

So if the green investments don’t have returns as good as the rest of the stock market, city taxpayers have to make up the difference.

Eight of the 10 biggest ESG funds underperformed the S&P average last year; the other two basically matched it.

So Lander’s move at a minimum will slow city pension-fund performance in the near future, adding to Gotham’s coming budget woes.

Longer term, though, pension promises might still take a haircut: In a serious crisis, “guarantees” sometimes give way.

And a crisis is all too likely.

This move is only legal because the Biden Labor Department has issued a rule allowing fund managers to use ESG (environmental, social, governance) metrics when investing retirement funds.

Ever-ambitious Lander’s likely just the first of a wave of lefty fund trustees who’ll jump on this bandwagon now.

Which translates to a wave of money chasing the same goal.

The conceit is that this will lead to innovations that produce the future the greens imagine.

But it’s more likely to create yet another bubble that collapses when no one actually finds practical solutions — and all those “investments” melt to pennies on the dollar.

And the city government will have a huge pension shortfall to make up.

But that’s a longer-term worry, and Lander plainly doesn’t care about it: By then, he plans to have won higher office on the basis of all his progressive achievements as comptroller.