Starting April 21, 2015, Google Search will be expanding its 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 Google Search results. Users will find it easier to get relevant, high quality search results optimized for their devices. To help you make sure your website is ready for this search change, we've put together the following frequently asked questions:
https://support.google.com/adsense/answer/6196932?hl=en
That means websites not currently optimized for variously sized mobile devices will be buried under an avalanche of results, while mobile-friendly sites rocket to the top.