Google will update its search algorithms this week in a move that could dramatically lower the page rankings of thousands of sites that are not 'mobile-friendly'.
The intention is to measure sites against mobile optimisation criteria and penalise those that do not meet certain standards, according to a post on Google's Webmaster Central blog from February.
Google said that it has given plenty of warning of the changes, but many are unprepared for what one company has dubbed a potential 'Mobilegeddon'.
The changes have been flagged up by Google since February, and the company said in 2013 that it was promoting changes that would provide mobile internet users with the best, most accurate and most search-friendly service.
"Starting April 21, we will be expanding our use of mobile-friendliness as a ranking signal. This change will affect mobile searches in all languages worldwide and will have a significant impact in our search results," said Google at the time.
"Consequently, users will find it easier to get relevant, high-quality search results that are optimised for their devices."
Google used the opportunity to point webmasters in the direction of the firm's testing and compatibility tools.
"If you want to test a few pages, you can use the Mobile-Friendly Test. If you have a site, you can use your Webmaster Tools account to get a full list of mobile usability issues across your site using the Mobile Usability Report," Google said.
Much of this has fallen on deaf ears, according to research. Web optimisation firm Somo Global reported that a number of high-profile brands and businesses are likely to suffer under the new system.
"When developing your site's mobile experience, the first step is typically to consider the customer journey and how they interact with your brand at each touch-point," the firm said.
"However, while some brands think apps alone are enough to tick the ‘mobile' box in terms of best mobile user experience, Google doesn't. As a result, these companies are about to see their mobile traffic declining."
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