How can advertisers reduce the carbon cost of their digital advertising? With scary headlines around the increasing threat posed by climate change dominating the news agenda and Adland seemingly taking more responsibility for the negative impact it has on the environment, it's a question that is going to be asked a lot more in the coming months.

Of course, there's no doubt there are industries with far more hefty carbon footprints than Adland. But that's not to say the ad industry is blameless and should spend the next 25 years with its arms folded, nodding its head accusingly in the direction of the transport, food, fuel and airline industries. Far from it.

From ad production to the vast amount of energy required to power huge global ad agencies, Adland contributes heavily to carbon emissions around the world. However, digital advertising is an area that's largely overlooked when evaluating advertising's impact on the environment.

Did you know the internet is responsible for 4% of global CO2 emissions? That's the same as the airline industry -- a sizable chunk of which is taken up by digital advertising, particularly data-rich formats such as video. In fact, a typical online ad campaign emits 5.4 tonnes of carbon dioxide -- a third of what an average US consumer produces in a year.

And that's just the ads we actually see. Because of the rise of programmatic advertising, we not only need to factor in the carbon dioxide used to transfer the ad onto the page and display the ad to the user, but also the trillions of auctions that take place every day without any ads being served at all.

So what can advertisers do to reduce the carbon footprint of their digital campaigns?

Here are 4 tips, originally published in The Drum :

1. Scrub the supply path

Over the last few years, supply path optimization (SPO) has been high on the priority list for programmatic advertisers - consolidating relationships and improving performance along the way.

It's time to look at a new phase of this around green energy - only utilizing publishers, tech vendors and suppliers that can evidence utilising renewable energy. It's vital advertisers use their budgets to incentivise the supply chain to change.

2. Bigger ≠ better

Having ensured the path is as clean as it can be, we must then focus on the ad itself. Every kb that a reader's device has to load on a page uses power.

As such, creative teams must compress file sizes as much as possible. For example, at Good-Loop we've been able to compress files as much as 85% without losing meaningful quality. Remember your asset will be shown in a relatively small digital box, not a giant billboard - you don't need that ultra HD file.

We then need to consider the formats and devices where the ads will run - this is especially true for emerging popular formats such as connected TV (CTV).

It's highly unlikely the energy efficiency of a viewer's TV was top of the list when they bought it - and in sheer pixel size, it's the biggest digital ad you'll likely ever run that isn't a digital billboard.

As such, that makes it the most carbon-intensive. As the growth of this channel continues, broadcasters and advertisers must apply pressure on manufacturers to improve product efficiency.

3. Mandate to curate

As fears over inventory quality and the much-publicised decline of the cookie grow, advertisers have moved closer to publishers again in a bid to improve ad quality and optimise supply paths. In turn, the quality of inventory that remains on the open web can be expected to decline.

Surfacing large quantities of inventory through open auctions increases the computing requirements to process. Advertisers should seize this opportunity to migrate from the open exchange and focus on curated private marketplace lists and programmatic guarantee deals.

There are savings, both for the budget and planet, that can be made here - it enables better conversations with publishers regarding rates, and requires significantly less energy to deliver a high-quality campaign while also ensuring the supply chain stays clean.

4. Accept the problem

Changes in our approach to internet carbon have the potential to make a demonstrable difference in our fight against climate change - both in removing our own footprints and influencing others to do the same.

Adland must accept that it has played a part in creating the climate crisis - we run and operate the attention economy, focused on driving consumer behavior and creating wants and desires.

That's not in itself a bad thing. But if we want to get serious about cleaning up our society, advertising is the pointy end of the spear - it's how our biggest businesses in the world engage with the world at large.

It's time to plant seeds, not pull up trees.