Han, welcome back! Missed your side of the discussion the past few days (I mean that genuinely).
"First you must convince me that warming of this magnitude is likely."
My philosophy regarding biodiversity protection is pretty simple. Plan for the worst, hope for the best.
Whether you like it or not, most biodiversity impact assessments use current climate predictions as they're regarded as the most likely scenario. As that situation changes, the information used by ecologists will change. There is no bias, we are simply using the tools and data provided by other scientific sectors. Where else should we get climatic data from with which to carry out ecological modeling?
This paper is not alarmist, it is simply a look at how this particular organism might react to a change in temperature/salinity and pH. It is in exactly the same vein as the paper linked a few days earlier about larval fish otoliths in differing CO2 regimes.
