A growing number of industries are trying to reduce or at least curtail carbon footprints and energy use. Emissions standards have been set for the automotive, construction, and even telecommunications industries. Yet the internet’s carbon footprint is growing out of control: a whopping 830 million tons of CO 2 annually, which is bigger than that of the entire aviation industry. That amount is set to double by 2020.

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It is time for web designers to join the cause.

Right now, at least 332 million tons of CO 2 —40 percent of the internet’s total footprint—falls at least partially under the responsibility of people who make the web. It needn’t be that large, but with our rotating carousels, high-res images, and more, we have been designing increasingly energy-demanding websites for years, creating monstrous HUMVEE sites where we could be just as well served by slender hybrids or, better yet, bicycles.

The good news is that we have several methods for fixing obese websites and simultaneously attacking our industry’s carbon footprint—methods that conveniently dovetail with good business practice: mobile-ready design demands a thoughtful and efficient approach to page design, and increasingly sophisticated web ROI metrics are already driving businesses to pursue faster and lighter sites.

Before getting into the nitty-gritty, let’s first look at how to estimate a website’s footprint.

What is the web’s carbon footprint?#section2

Just as we refer to a car’s energy usage in terms of miles per gallon, we can think about website energy usage in terms of the amount of data downloaded. This, in turn, gives us a framework for guessing the relationship between page size and carbon footprint. Unfortunately, working out a website’s carbon footprint is, on the best of days, tricky and imprecise. Here’s my shot at it:

A 2008 paper from the Lawrence Berkeley National Laboratory suggests it takes 13kWh to transmit 1GB.

According to EPA figures, the average U.S. power plant emits 1.2 pounds of carbon dioxide equivalent (called CO 2 e) per kWh produced (other countries have higher or lower averages depending on their energy policy).

e) per kWh produced (other countries have higher or lower averages depending on their energy policy). If we multiply 13kWh by 1.2 pounds, we get 15.6 pounds of CO 2 e—and that’s just to transfer 1GB of data.

e—and that’s just to transfer 1GB of data. If one million users each download a typical page, which now averages 1.4MB, that’s a total of 1,367GB of data.

At 15.6 pounds per gigabyte, that’s more than 10 tons of CO 2 e.

e. Mobile data, with its reliance on 3G/4G, is up to five times more polluting—77 pounds CO 2 per gigabyte.

per gigabyte. If a million mobile users on 3G download a 1.4MB page, that’s 1,367GB times 77 pounds, which totals 52 tons of CO 2 .

Based on these figures, we can estimate that a site the size of Tumblr, with 183 million pageviews per day and approximately 10 percent of those from mobile, has the potential to be responsible for a staggering 2,600 tons of CO 2 daily.

That doesn’t take into account important factors like how much of the data center’s electricity comes from renewable or fossil fuels or end-user electricity usage, both of which could significantly influence the total. But these numbers do give us a framework for seeing the relationship between page size and carbon footprint—and make it clear that cutting gigabytes saves CO 2 .

The first place to start trimming? In our designs.

Reducing CO 2 by tackling page bloat#section3

At 1.4MB, today’s average page is 15 times larger than it was 10 years ago, primarily due to images (881kB) and script (224kB). Plain old HTML totals just 54kB—but when’s the last time you saw an HTML-only site? This average page also makes more than 100 HTTP requests. Whether they fetch a big object or a small one, these add up to more delay and more power wastage. The average site is also slow: Alexa’s top 2,000 retailer sites now take an average of more than seven seconds to load—much longer than users consider acceptable.

Budgeting for a lean, mean, and green website#section4

No one intentionally sets out to build a 1.4MB page, but clients often demand eye-catching images, advanced social features, and plenty of design bells and whistles, and that’s pretty much all it takes to get to that size. The best way to prevent this kind of obesity is to set a page size budget: start with a target page size, and stick to it.

At MadPow, we’ve adopted the page size budget approach to help us chase better page-load performance, with the holy grail being a page that loads in two seconds or less. Of course, the more page weight we shave off, the smaller the site’s carbon footprint. To keep track of this, I multiply the page size by analytics on user visits to arrive at a rough total for site traffic, not forgetting to separate out the more-polluting mobile traffic and account for caching.

Sticking to the page budget means considering data-weight at each stage of design:

Content strategy: If you are retrofitting a site to reduce page weight, a quick fix might be to trade higher-weight content for lighter alternatives, like still pictures instead of video, or text instead of images—so long as the same user and business goals are served. Better yet, if you use a “content first” approach, you can bake the size considerations into your content planning, so as to make content choices that are appropriate for the audience and the data budget.

Interaction design: The experience definition phase of design is the perfect time to intercept the more data-hungry site features that threaten a page budget. The ubiquitous carousel is a prime offender—a typical one has three to six big images, plus the JavaScript needed to make it move, typically adding up to hundreds of kilobytes. The value of carousels is debatable anyway; if you need to make a metrics-driven case for reduction or replacement, take the Brad Frost Carousel Challenge. Other candidates for reappraisal include sharing buttons, embedded maps, auto-play video, Flash, ads, and syndicated third-party content services—all of which come with a hefty data overhead.

Visual design: Images are the largest part of the footprint for most sites (60 percent on average), and are ripe for data reduction. To start, can you get by with fewer images? Many images on the web are also saved in the incorrect format, are improperly sized, or are badly optimized. Free services like smush.it can optimize your images better than your regular editing tool, and they’ll do batch processing, too.

Consolidating all the small images on your site by using CSS sprites or web icon fonts will save data and HTTP requests; pure CSS icons will be the lightest-weight option, when browser support catches up. And since mobile data is so much more polluting than wired data, make sure responsive sites use a working responsive images solution. Good optimization could shave 72 percent off mobile image weight.

Code design: Front-end optimization is burgeoning with low-hanging fruit: shrinking scripts, compressing downloads, setting appropriate caching times, and combining files can all help reduce data overhead and HTTP requests. For a quick taste, point Google Page Speed at your site, and it will identify which techniques could be applied to help speed it up. For a deeper dive, I recommend reading “Web Performance 101,” or Lara Swanson’s recent ALA article.

Green hosting: Even before you start minimizing your site’s carbon footprint through design and optimization, you could consider moving to a green host. Many of these are powered by renewable energy—particularly in Iceland, where data centers have opened to take advantage of cheap geothermal power. Green hosting might not be for everyone yet (it can be more expensive, and Iceland might be far from your customers), but more local green hosts are starting to appear. Some cloud-based services are getting greener, too: Google, Apple, and Rackspace get some of their power from renewables, though according to Greenpeace, Amazon Web Services does not.

Offsetting the rest: Even after applying a lean design, optimizing, and moving to a green web host, your site will still have a carbon footprint. To account for that, you can buy an offset, which typically costs $19 per ton, depending on the project. Offsetting doesn’t actually take the CO 2 out of the atmosphere, and it is a poor substitute for reducing emissions. However, many programs have additional benefits, such as funding education in the developing world or protecting fragile habitats.

Persuading people to optimize#section5

Optimizing for lower emissions is tantamount to optimizing for general performance, so even non-green businesses have several compelling reasons to put their site on a diet: faster pages make for happier users, especially on mobile; they convert better and have better SEO, too.

Adding climate benefit to that list makes an overwhelming case for cutting page size and data, especially for companies that are already sympathetic to a climate case (such as those that have signed the Climate Declaration).

The internet as climate hero#section6

Despite its huge carbon footprint, the internet could also be a climate savior. The transition of old industries and services to the internet has the potential to save eight billion tons of CO 2 by 2020, more than counterbalancing the projected 1.4 billion ton 2020 internet footprint.

For instance:

As we continue these shifts toward an increasingly online economy, though, we’ll also soon be welcoming five billion new users to the internet. As the internet’s overall share of world climate pollution continues to grow, so does the climate responsibility of those who architect it. But by building lean and clean, we can reduce the damage—and make happier customers and profitable businesses to boot.

Perhaps we’re conditioned to frame environmentally-friendly choices as sacrifices, but it isn’t so with the web. We can have cleaner, greener websites while also making users happier and improving the bottom line. And while the problem may be large, as any dietician can tell you, small changes add up. Why wouldn’t we get started?