A recent update to the Google Algorithm is penalising websites that feature too much ad space above the fold of the website. The fold is the point at which the page cuts off at the bottom of a particular screen. The fold can be at different points for different people depending on their screen size or resolution. If the user sees mostly ads when the page loads and not much content, they are forced to scroll down and this is inconvenient and Google is addressing this issue.
Google isn’t penalising sites for having too many ads on the page in particular, but is just penalising the placement. No one would recommend clogging up your page with advertising, but if you want ads on your site, just make sure it doesn’t fill up the top of the page.
The top and left side of the page will often have navigation tools on it; these are not ads but if they are too bulky they could push your site content too low below the fold. Try to keep as much actual content above the fold as possible.
There is a free Google tool called the Browser Size Tool. This shows how much of your page the user is going to see when they first see the page. URL:
Source: Google Webmaster Central Blog
Anyone who gets caught up in this change and notices their ranking dropping will have to wait until the spider crawls their page again, you might be waiting a few weeks before any noticeable changes take place.
Google claims that only about 1% of websites will be affected and that most typical users will not even notice a change in rankings.