Are there summer opportunities to teach English abroad? 

YES, however options will be more limited than if you were looking to teach English abroad for a year or even for six months.  Except for some short-term contract work, most language schools look to hire full-time teachers for 10-12 month contracts.  This means that most short-term opportunities for English teachers will be either in summer camps or in a volunteer capacity.  

Teaching English abroad in the summer as a volunteer or at a summer camp may not pay much (if anything at all), but you can find great opportunities to spend a couple of months abroad and any experience you gain will be a great addition to your resume, especially if you decide to teach English abroad again at a later date.