The changes have been seen across all seasons, and all of Europe
Quite what Keats would have made of it is anyone's guess, but "mist and mellow fruitfulness" appears to be on the decline in Europe.
The number of foggy, misty and hazy days is diminishing across the continent, say scientists who have analysed the meteorological data.
The researchers found this clearing of the air in the past 30 years may have amplified the warming of Europe.
They report their findings in the journal Nature Geoscience.
The research was led by Robert Vautard at the Atomic Energy Commission, Gif sur Yvette, France.
Since the 1970s, European temperatures have risen by about half-a-degree Celsius per decade.
This warming rate is faster than the global mean change (roughly equal to 0.18C per decade) and the trend averaged over all the Earth's land (roughly equal to 0.27C per decade) during the same period.
The regional climate models used by scientists have failed to simulate the European experience, say Vautard and colleagues; and they point to legislation that has cleaned up Europe's air as the probable cause.
This has limited the presence of the tiny particles, or aerosols, in the atmosphere which help trigger the low-visibility phenomena.
With fewer fogs, mists and haze, more of the Sun's energy has been reaching the surface, leading to a rise in temperatures, they tell Nature Geoscience.
The team's analysis suggests the clearer air's contribution to the background warming trend may have been about 10-20% across Europe as a whole; and in Eastern Europe specifically, it may have been as much as 50%.
The team looked at horizontal visibility data from 342 meteorological stations across Europe. The changes recorded affect all seasons and all distances from zero to eight km.
However, the team says the data also indicates that the decline in the low-visibility phenomena has slowed since 2000.
"We conclude that the large improvements in air quality and visibility achieved in Europe over the past decades may mean that future reductions in visibility will be limited, possibly leading to less rapid regional warming," the team write.
The group says its findings emphasise the importance of ground-level atmospheric processes in understanding the differences in regional climates.