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Iridium Flare May 18th  – Sky News magazine Photo of the Week – click here

The Iridium communication satellites have a peculiar shape with three polished door-sized antennas, 120 degrees apart and at 40 degree angles with the main bus. The forward mirror faces the direction in which the satellite is travelling. Occasionally an antenna will directly reflect sunlight down to the Earth, creating a predictable and quickly moving illuminated spot of about 10 km diameter. To an observer this looks like an extremely bright flare in the sky with a duration of a couple of seconds.

Dramatic action is needed to save the Arctic and Antarctic ice shelves from global warming, a NASA researcher says.

“We probably need a full court press on both CO2 emission rates and non-CO2 forcings to avoid tipping points and save Arctic sea ice and the West Antarctic ice sheet,” James Hansen, from the NASA Goddard Institute for Space Studies, said in a release.

Another decade of “business-as-usual” will make it difficult to avoid the change, he added.

His comments were made just a day after NASA administrator Michael Griffin told U.S. National Public Radio that “I have no doubt that global – that a trend of global warming exists. I am not sure that it is fair to say that it is a problem we must wrestle with.”

Hansen and co-researcher Makiko Sato from the Columbia University Earth Institute concluded that global warming has driven the Earth’s climate near to “critical tipping points,” which occur when a small temperature increase triggers an effect that gets worse as it feeds on itself.

An increase of one degree above the global temperature in 2000 “is likely to be dangerous,” because it will push the climate to a tipping point.

Hansen and Sato identified the Arctic and Antarctic ice as two vulnerable areas in a study based on simulations published Thursday in Atmospheric Chemistry and Physics. They acknowledged that identifying “dangerous” effects is partly subjective.

The study found global warming of 0.6 degrees in the past 30 years was mainly caused by greenhouse gases made by humans, and a “moderate” additional rise “is likely to set in motion disintegration of the West Antarctic ice sheet and Arctic sea ice.”

Higher temperatures melt ice, exposing darker surfaces that absorb more heat and speed the ice sheet breakup. As oceans warm, the ice shelves that otherwise slow ice flows melt more quickly, so the whole process speeds up.

Freshwater sources and species habitat are also threatened, the authors said.

Atmospheric carbon dioxide has increased from the pre-industrial level of 280 parts per million (ppm) to 383 ppm today, and is rising by about two ppm per year. Sato said “CO2 exceeding 450 ppm is almost surely dangerous, and the ceiling may be even lower.”