Over our history eclipses have been the portent of the gods wrath, new things to come, or simply a pretty light show. But would you have expected our last lunar eclipse to have been of any help to researchers looking at climate change?
Researchers at the University of Colorado in Boulder, US, found that Earth’s atmosphere contained very little light-blocking volcanic dust. During the eclipse, Earth blocks sunlight from reaching the moon – hence why the moon is obscured in darkness for a time. Naturally, some light will make it through, refracted through the Earth’s atmosphere.
However the amount that refracts through is normally tempered by how much volcanic dust is in the atmosphere to block it. “All the big dimmings of the Moon during eclipses can be attributed to specific volcanoes,” says Richard Keen of UC Boulder.
Keen and his fellow researchers at UC Boulder have been charting the brightness of lunar eclipses back to 1960, as well as adding a few years either side of the 1883 eruption of Indonesia’s Krakatoa volcano to the mix. From this data, they have been tracking the changes in opacity of Earth’s atmosphere.
This obviously has implications for our climate in that, the less dust there is reflecting light away from the planet’s surface the more there is reaching it.
Keen and his colleagues calculate that, because more sunlight is reaching the surface, Earth should be 0.1 to 0.2° Celsius warmer in recent years than it was back in the late 60s.
This increase in temperature is a hitherto unforeseen addition to the .06° Celsius rise that our planet has encountered of late. The IPCC has pinned the majority of that warming on greenhouse gas. They add that other factors including fluctuating patterns in ocean circulation and slight changes in the Sun’s brightness could also have influenced the climate.
“All of these have been contributing to a warming, adding on top of each other,” Keen told New Scientist. “The difficulty is, of course, what are the relative magnitudes [of these effects],” he says.
Susan Solomon of the US National Oceanic and Atmospheric Administration in Boulder, Colorado, a member of the Nobel-prize-winning team that put together the 2007 IPCC report said however that volcanic haze fluctuations were introduced in to the models used for their report. She disputes Keen’s concerns; “There’s no evidence for a significant warming trend over the last several decades [due to a decline in volcanic haze],” she told New Scientist. “In fact, it’s exactly the opposite.”
Solomon notes that over the past 40 years – compared to the 20 years prior – the amount of haze in the stratosphere has been higher. Thus, over the past 60 years, there would have – if anything – been a slight cooling trend if volcanic haze were the only influence on the climate.
And while Keen acknowledges this, he argues that the relatively long period since 1995 with a relatively haze-free atmosphere could be having a considerably larger than anticipated impact on our climate. He points also to theories of long term effects through the current-day heating of our oceans, as an impact the added sunshine could be having.
Keen is now compiling more precise estimates of the brightness of our most recent lunar eclipse, occurring on the 20-21 of last February, so that the amount of haze in the atmosphere can be calculated more efficiently.
New Scientist – Lunar eclipse may shed light on climate change
Image Courtesy of NASA