This is a comment from Anthony Watt’s blog.
Arthur Glass (03:11:29) :
Not immediately germane, but if hydrogen powered engines emit H2O, aren’t they worse polluters than the internal combustion engine, since water vapor is a much more powerful ‘greenhouse’ gas than CO2?
For some background into atmospheric absorption efficiency of common gases compared to the electromagnetic spectrum, this graph is valuable:
Note the CO2 peak at 15 microns is the only significant one, as the 2.7 and 4.3 micron CO2 peaks have little energy to absorb in that portion of the spectrum. But the H2O (water vapor) has many peaks from .8 to 8 microns, two that are fairly broad, and H2O begins absorbing almost continuously from 10 microns on up, making it overwhelmingly the major “greenhouse gas”.