Global warming is fueled by human activities, it's escalating quickly and some of its worst effects are probably irreversible. Those are the grim conclusions in a leaked draft of a major new United Nations report on climate change, scheduled to be formally released in early November.
"Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reduction in snow and ice, and in global mean-sea-level rise; and it is extremely likely to have been the dominant cause of the observed warming since the mid-20th century," the unfinished 127-page draft states, as reported by the New York Times. "The risk of abrupt and irreversible change increases as the magnitude of the warming increases."
Today Mars is an arid, frigid desert, suggesting that the mother of all climate changes happened there, about four billion years ago or so. The question that haunts planetary scientists is why? And could it happen here?
"I think the short story is the atmosphere went away and the oceans froze but are still there, locked up in subsurface ice," said Chris McKay, an astrobiologist and Mars expert at NASA's Ames Research Center.
In September a new spacecraft known as Maven, the Mars Atmosphere and Volatile Evolution mission, swung into orbit around the planet. Its job is to get a longer answer to one part of the mysterious Martian climate change, namely where the planet's atmosphere went.
"This new work shows that the climate signals of late 20th- and early 21st-century volcanic activity can be detected in a variety of different observational data sets," said Benjamin Santer, a Lawrence Livermore National Laboratory scientist and lead author of the study.
The warmest year on record is 1998. After that, the steep climb in global surface temperatures observed over the 20th century appeared to level off. This "hiatus" received considerable attention, despite the fact that the full observational surface temperature record shows many instances of slowing and acceleration in warming rates. Scientists had previously suggested that factors such as weak solar activity and increased heat uptake by the oceans could be responsible for the recent lull in temperature increases. After publication of a 2011 paper in the journal Science by Susan Solomon of the Massachusetts Institute of Technology, it was recognized that an uptick in volcanic activity might also be implicated in the warming hiatus.