The authors of this study - two academics from Oxford - aren't saying that we will definitely lose 47% of current jobs to automation. They are saying its possible as artificial intelligence - AI - becomes reality.
In "The Future of Employment: How Susceptible Are Jobs to Computerisation?," Frey and Osborne estimate that 47 percent of U.S. jobs are "at risk" of being automated in the next 20 years. This does not mean that they necessarily will be automated (despite the way the study has been portrayed in some media outlets)--rather, the authors argue, it is plausible over the next two decades that existing and foreseeable AI technologies could be used to cost-effectively automate those jobs out of existence. Machines may not (and probably won't) do the jobs the same way as people, however--just remember the last time you used an automated check-out system at a grocery store. There's a difference between machines doing something cheaply and doing it well. Frey and Osborne took into account the possibility of such "task simplification" in their analysis.
Which jobs are most at risk? According to The Jetsons, we should expect robots to clean our houses and do other working-class occupations that educated elites have historically looked down upon as "unskilled." But anyone who has done such a job, or has watched an episode of Undercover Boss and seen highly-paid CEOs fumble while trying to carry out the demanding minimum wage jobs usually performed by their underlings, knows that there is no such thing as unskilled labor anymore (if there ever was), especially if you are comparing humans and machines in the same breath. The gap between humans and current AI is vastly greater than the differences between humans.
Frey and Osborne focus on "engineering bottlenecks" in AI and robotics, and compare these stumbling points with the requirements of jobs in order to determine which are most and least likely to be vulnerable to automation. The biggest bottlenecks are perception and manipulation, creative intelligence, and social intelligence, all of which computers struggle mightily at (but Rosie the Robot excelled at, by the way). While the trend in recent decades has been towards a hollowing out of "middle-skill" jobs and an increase in low-paying service sector jobs and high-paying, highly educated jobs, Frey and Osborne expect that automation in the future will mainly substitute for "low-skill and low-wage" jobs.
You can imagine entire industries like fast food being revolutionized by automation. Some other service industries will also become more efficient with robots doing the work previously done by humans.
But it doesn't appear to me that the authors of this study took into account the creative destruction of capitalism. Surely many jobs will be lost to automation, but someone still has to build the machines, maintain them, and invent new ones. It's a good question as to whether or not the new jobs will pay any better than the old ones, but even if automation is widespread, I would be surprised if there was a net job loss as a result.