With all the talk of global warming, this seems counter-intuitive. But according to a recent Guardian piece, some researchers claim the earth has received a declining amount of sunlight the past few decades:
Records show that over the past 50 years the average amount of sunlight reaching the ground has gone down by almost 3% a decade. It’s too small an effect to see with the naked eye, but it has implications for everything from climate change to solar power and even the future sustainability of plant photosynthesis.
. . .
[T]he scientific record now shows several other research papers published during the 1990s on the subject, all finding that light levels were falling significantly. Among them they reported that sunshine in Ireland was on the wane, that both the Arctic and the Antarctic were getting darker and that light in Japan, the supposed land of the rising sun, was actually falling. Most startling of all was the discovery that levels of solar radiation reaching parts of the former Soviet Union had gone down almost 20% between 1960 and 1987.
What might explain this? The amount of solar radiation hitting the earth is the same; but some of the light may be bounced away by the atmosphere. The theory, as I understand it, is that small particles of pollution promote cloud formation and make clouds darker by reflecting sunlight.
To “cloud” the picture even further (so to speak), one study suggests the global dimming trend may have reversed–or at least leveled off–during the 1990s.
I’m not sure how much to make of this theory, but it’s an interesting claim.