The mitigation here should be pretty obvious, though perhaps easier said than done: Work to stay ahead of the curve in terms of product development. Fortunately, we're seeing plenty of innovation from hardware makers in their server and chip designs.
Alternatively, a company could also find itself being sued for bringing harm to individual or a class, or to a city through pollution, due to its general GHG emissions. This, too, would be difficult to prove in court, but there would be pesky legal fees, increased insurance rates, bad PR, and the like.
One of the mitigations is repeated time and again in the report to address just about every potential legal threat: reduce greenhouse-gas emissions and participate in emissions-offset activities.
Hardly anyone (exceptions might include certain types of lawyers and litigants) wants to see any of the litigation scenarios enumerated in the study (of which I've just scratched the surface). They're all-around bad: bad for business, bad for our health, bad for the environment.
The good news is, there are plenty of ways for companies to reduce the threats and the associated costs. At the same time, cutting your carbon emissions means you're cutting your power consumption, which translates into not just reduced risks but reduced bills.
"Limiting Liability in the Greenhouse" is available here [PDF]. Again, I highly recommend you read it if you're all at concerned about the legal implications of global warming, the impact it might have on your insurance, the future of your business, or global warming.