Nobody should take this study seriously. This study should be taken as seriously as when IBM releases a study saying that IBM has a positive economic impact on society, or when the organic food industry releases a report non-organic foods will kill you. Nobody believes those organizations because they have a financial (and/or non-financial) incentive to make these claims.
Likewise, the incentives for objective climate change research are not there. Look at who's writing this report - academics and government officials. Their research funding (which you could instead call their livelihood, their income, their vacations, or their kids' college tuition fund) will only continue if there continues to be a "problem" with climate change.
A quick glance through tells us the study - and when I say study, I mean the website that's set up like a campaign website, I couldn't find a report - is flawed. Where is the detailed discussion of the positive economic benefits from climate change? Surely some regions are better off from climate change, right? Is every single area really worse off?
Unfortunately, reports like this are what we came to expect of former communist countries, where researchers/people were simply paid to promote the party line.