Scientists have discovered the awful truth; we are all dimmed.
New research shows that much less sunlight is reaching the earth than 50 years ago. "Global dimming", as it has inevitably become called, has been suspected for nearly 20 years, since a Swiss geography researcher, routinely checking sunshine levels across Europe in 1985, found that they had dropped, even on the brightest days. Studies all around the world found similar results, showing drops in sunlight ranging from 2 to 37 per cent since the 1950s.
The research, published in Science, is the first to prove that the dimming is a global phenomenon. Scientists at the New Jersey and California Institutes of Technology remembered how Leonardo da Vinci had worked out that the dark side of the moon was illuminated by sunlight reflected from the Earth. By measuring this "Earthshine" they worked out that the world is about 10 per cent darker than half a century ago, reports independent.co.uk
According to BBC researchers think this may be because of the natural variability in cloud cover, which can act to push back the Sun's heat and light away from Earth.
The effect must be taken into account in estimates of future global warming, they report in the journal Science.
But from 2001 to 2003 things changed. The Earth brightened to pre-1995 values. The researchers attributed the brightening to global changes in cloud properties.
"At the moment, the cause of these variations is not known, but they imply large shifts in Earth's radiative budget," says Steven Koonin of Caltech.
"Continued observations and modelling efforts will be necessary to learn their implications for climate."
Enric Palle, of NJIT, added: "Our most likely contribution to the global warming debate is to emphasise the role of clouds in climate change must be accounted for, illustrating that we still lack the detailed understanding of our present and past climate system to confidently model future changes.