ShareThe conversation around sustainability has expanded beyond physical waste and energy consumption to include the carbon footprint of our online activities. Every action we take on the internet—whether it’s sending an email, streaming a video, or loading a webpage—requires energy.
This energy, often derived from fossil fuels, contributes to global carbon dioxide (CO2) emissions. A critical yet often overlooked aspect of this digital energy consumption is the size of the data we transfer across the web, particularly images.
The hidden cost of image sizes
Images are integral to the modern web, enhancing the visual appeal and user experience of websites. However, they are also one of the most significant contributors to the size of a webpage. Large image files require more data to be transferred from servers to users’ devices, consuming more energy in the process.
To understand the impact, consider this: the average size of a webpage in 2024 is around 2.4 MB, and images account for approximately 50-60% of that size. Every time a webpage is loaded, data is transferred through a network of servers, which requires energy to power data centres and keep the network infrastructure running. The more data (or the larger the file), the more energy is required, leading to higher CO2 emissions.
For example, a typical image file size might range from 100 KB to 2 MB or more, depending on the resolution and format. Multiply this by the number of images on a page and you can quickly see how the size adds up. Larger images mean more data, leading to increased energy consumption. When you consider the billions of web pages loaded every day, the cumulative impact on our environment is substantial.
The carbon footprint of page loads
The energy used to transfer data over the internet has a direct correlation with CO2 emissions. According to a study by the International Energy Agency (IEA), the internet accounts for about 1% of global electricity use, and this percentage is growing. While this might seem small, it translates to about 300 million tons of CO2 annually—which is equivalent to the carbon footprint of the aviation industry.
For every megabyte of data transferred, a certain amount of CO2 is produced. Estimates suggest that transferring 1 GB of data results in the emission of approximately 3 kg of CO2. Therefore, reducing the size of the data transferred, particularly the size of images, can lead to a significant reduction in CO2 emissions.
Strategies for minimising image sizes
Reducing image sizes without compromising quality is key to enhancing digital sustainability, but it can be tricky to pull off the balancing act between quality and file size. There are lots of factors to take into account:
Use the right format:
- JPEG is excellent for photographs due to its compression capabilities, balancing quality and file size.
- PNG is ideal for images requiring transparency or sharp details, but use it sparingly as it tends to result in larger file sizes.
- WebP is a newer format that provides superior compression, reducing file sizes by up to 30% compared to JPEG and PNG without noticeable quality loss.
Optimise image dimensions:
Scale images to the exact dimensions required for display on your website. Avoid uploading images that are larger than necessary, as this adds unnecessary weight to the page.
Compress images:
Use compression tools (such as TinyPNG, ImageOptim, or online compressors) to reduce the file size of images without significantly affecting their quality. This process removes unnecessary data from the image file, making it smaller and faster to load.
Implement responsive images:
Use responsive image techniques, such as the ‘srcset’ attribute in HTML, to serve different image sizes based on the user’s device. This ensures that mobile users, for instance, do not download a large desktop-sized image, thereby saving data and energy.
Leverage lazy loading:
Implement lazy loading, a technique that loads images only when they come into the user’s view. This reduces the initial page load time and the amount of data transferred, especially for long pages with many images.
Consider vector graphics:
Where appropriate, use vector graphics (SVG) for icons and simple illustrations. SVG files are typically smaller than raster images and scale perfectly on any screen size without losing quality.
Cache images efficiently:
Use caching techniques to store images locally on users’ devices after their first visit. This reduces the need to download the same images repeatedly, conserving bandwidth and reducing energy consumption.
The impact of small changes
While it might seem that reducing image sizes is a small step, the collective impact can be substantial. For a website that receives thousands of visitors daily, optimising images can save gigabytes of data transfer every month, which in turn reduces the associated CO2 emissions.
For example, if a website reduces its average image file size by just 50 KB and receives 10,000 visits a day, this equates to a daily saving of 500 MB of data. Over a year, this could prevent the emission of approximately 180 kg of CO2—the equivalent of planting several trees.
A greener web is within reach
Digital sustainability isn’t just about reducing our screen time; it’s about making conscious decisions in the design and development of digital content.
By optimising image sizes and reducing unnecessary data transfer, we can significantly lower the carbon footprint of our online activities. As we move towards a more sustainable future, every kilobyte saved counts, making the internet a greener place for everyone.
Need some help calculating the carbon footprint of your website and finding out how you can improve it? Get in touch with our experts, who will be able to help point you in the right direction – one image at a time.