We don’t have records for water vapor that match the length or resolution of records for temperature and CO2. The physical principles involved in the water vapor feedback haven’t changed, though, so water vapor would have increased in response to warming in the past very much as it does today.

However, ice core records can provide some insight over longer time periods. That’s because ice layers contain dust, which scientists use as an indirect proxy for dry conditions. In general, cold glacial periods have been dustier than warm interglacial periods, but there’s no globally coherent trend in the timing between temperature and dustiness – certainly nothing as clear as the lag between temperature and CO2 during past glacial-interglacial cycles.

One final thought – remember that the lag between temperature and CO2 in the past does not mean that CO2 has nothing to do with global warming today. As Bill described in his post about past climate change, it’s vitally important to recognize the difference between the initial trigger of the warming and the phenomena that can enhance warming. The trigger for today’s rapid global warming is clear – greenhouse gases emitted by human activities.

http://blogs.edf.org/climate411/2007/02/28/water_vapor_fallacy/

And CO2 has little effect on global warming anyway.

As for the timeline on NOx fixes for diesels (of any flavor), as we said in our post: not fast enough. We can't put a timeline on automakers' efforts, but do believe that it would speed up if a carbon cap is put in place.