The phrase "decade of effort" means that for a period of ten years, someone has put in a significant amount of work and dedication towards achieving a certain goal or completing a specific task. Full definition
Despite decades of effort, scientists do not know precisely what temperatures or greenhouse gas concentrations in the atmosphere constitute a danger. (scientificamerican.com)
After decades of effort, a great deal has been learned and accomplished, but a practical fusion power concept has not been forthcoming. (dotearth.blogs.nytimes.com)
And despite decades of effort, none has made it to market. (sciencemag.org)