for heating, cooling, lighting, and other services.

The Empire State Building in Manhattan

is one of the world's most famous landmarks.

It was built in 1931.

Then, nine years ago, it was given a $550 million refit,

including an attempt to give it some of the world's most demanding energy efficiency standards.

We've cut our energy consumption by $4.4 million annually,

reduced energy consumption by 38 percent,

achieve a 3.1 year payback, and create better tenant spaces that are healthier for tenants and more productive.

The chiller plant here in the basement,

which provides the air conditioning for the building,

was kept in the same space in the refit

but completely rebuilt internally.

Conditions around the building are recorded in real time.

And an automated system called Cortex

advises on how to run the air conditioning most efficiently while keeping temperatures comfortable.

The efficiency project was backed by businesses,

including Johnson Controls and environmental groups,

including Rocky Mountain Institute,

as a flagship to demonstrate to other buildings what's possible.

Eighty percent of the energy use in New York

is used by the 20 percent largest buildings.

And if those 20 percent largest buildings replicated the Empire State Building's deep energy retrofit model -

here we've reduced our energy use by over 40 percent with a 3-year payback.

If they all followed suit, the energy use of New York City would be reduced by 25 percent. .

One of the big problems with improving efficiency in buildings

can be that both property owners and tenants need to be convinced that the effort is worthwhile.

Hotels present similar challenges.

We are approaching the global water challenges by tracking, monitoring, and evaluating our water consumption.

Hilton has, for a decade, operated a programme called LightStay to monitor and control its energy and water use.

It recently set a target of cutting energy use per occupied room by 40 per cent by 2030.

That'll mean encouraging customers to help.

I mean, it was their business, right?

It was really looking at this from a very smart business perspective, like sustainability was a priority.

But also, what gets measured gets managed.

So you have to measure it.

You have to track it to get your baseline,

to understand where you are,

and then to be able to set long-term targets.

Some of the biggest opportunities for saving energy are in emerging economies.

The rationale for this is that these are countries that are building their energy systems up for the first time.

So what they want to do is escape

the pathway of development the developed world has followed.

And this is a multi-multi-multitrillion dollar business opportunity.

And we're starting to see real innovation around that now.

Amory Lovins, of Rocky Mountain Institute, argued in a paper earlier this year for what's called integrative design.

That means developing entire systems for a building or an industrial process

could release much greater energy savings than is generally understood.

The Empire State Building is a remarkable example of how energy consumption can be reduced,

even in quite old buildings.

But to make a significant difference to global greenhouse gas emissions, these kind of changes will have to be replicated around the world.

Ed Crooks for the Financial Times in New York.