Well, in retrospect, the diesel engine manufacturers over promised and under delivered, while the regulation agencies looked the other way. In fact, most of the governmental responses to the problems of human induced climate change - which as signatories to the Paris accord they have acknowledged is a real threat - have been ineffectual, as evidenced by the
ever increasing percentage of CO2 in the atmosphere. The average is approaching 410 ppm, compared with about 310 ppm when measurements were started at the Mauna Loa Observatory in Hawaii in 1950. This is higher than at any time in the past 400,000 years, so it's unsurprising that we've just had the two
warmest years on record, globally, and
record low sea ice extent at both poles.
In aviation terms, higher temperatures are manifested as more water vapour and energy in the atmosphere, which
rarely improves flying conditions.