Yes, plugin hybrids are a good one.  

But geo heat exchange heating/cooling would save more GHG.  And a renewable energy distributed generation and storage smart grid is another that would save even more GHG.  

In fact, if those who tout "clean" coal as the only practical alternative (like you Jeremy), or fuel farming lobbyists, or the marvelous hydrogen energy economy fans, or those who tout nuclear power, lose the energy policy battle, then the time, capital, and political will wasted on clean coal (and these other awful corporate boondoggle diversions), could be devoted to plugin hybrids, geo heat exchange, and a renewable smart grid.

The dity coal (and oil)would only be needed for a decade or so, eventually totally replaced by renewable and conservation.  While this is ongoing, coal to natural gas underground conversion could take the grid from coal as the steady backup source to natural gas.  

Furthermore going to geo heat exchange could eliminate a huge amount of natural gas heating.  Freeing up existing natural gas supplies for grid power backup.  then a transition to solid oxide fuel cell/turbine distributed backup generation could save natural gas with double the efficiency of standard natural gas power generation.  This also allows the waste heat from natural gas generation to be used via this distributed cogeneration.

You ought to do a better job on these issues Jeremy, you are in a catbird seat as far as energy issues.  You owe it to yourself and all of US who support Stanford through our tax dollars.

Your POV tends to play into the hand of  the coal industry.  allowing them to use clean coal research as an excuse to delay real solutions to coal GHG.

Thanks for taking the time to visit, sorry if my critique was too harsh on a personal level.  But a serious wake up call is needed for the status quo academic establishment, along with  government and industry.

One other thing:

How difficult is it to replace coal fired boilers (many aging and in need of replacement anyway) with natural gas boilers to feed the same turbine generator systems now powering the grid?

Conversion to natural gas is a viable interim alternative to clean coal.  If natural gas use in heating is replaced by geo heat exchange, gas can replace coal.  Start adding in biogas from the waste stream too. And lowering electric power demand by cooling buildings with geo heat exchange.

These are solutions that fit together in an organic design.  It is a lot different than the mechanistic so-called "free" market approach.  

Peak moments of delusion set the scene for a change, a revolution.  Duuhbya, an agent of change.

Think about it.  He has brought US to the very brink, the herd needs to turn or go over the cliff to extinction.  

Maybe dolphins will be the next species to try for global domination.

The nature of reality, the relationship between the microcosim, the single particle.  And the macrocosm, the infinity of space/time.  The quality of existence, not the quantity.  

Consciousness, Idle consciousness.  Forever speculating on a street corner named desire.