Thanks for contacting AdSense support.

Earnings can fluctuate from time to time as our network is a dynamic marketplace that is still growing and evolving. Geography, user base, site type and general market conditions can all impact the type of ads available to you and subsequently impact earnings.

CPCs are determined by advertiser bids and are not directly under publisher control. To optimize their ad campaigns, advertisers often experiment with different keywords and ads, and also change the sites they choose to target based on past performance. Advertisers can choose to target specific sites by time of day, and may shift budgets based on their specific advertising goals. We also know from previous experience that advertising is seasonal and because of this CPCs may be weaker in the early part of the year. Advertising spend is seasonally weak due to the subtraction of holiday spend and the exhaustion of end of year budgets.

If you have noticed a significant change in your earnings, we would recommend reviewing any changes in your site's implementation that might have impacted ad serving.

Rest assured, we're working hard to maintain a mutually beneficial ecosystem for both advertisers and publishers. Please let me know if there is anything else I can help you with.

Have a nice day,

Ricky
The Google AdSense Team