Climate change: Scientists now 95 percent certain we are mostly to blame
A draft summary prepared for the Intergovernmental Panel on Climate Change says that more than half of global warming is caused by human emissions of greenhouse gases.
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For instance, when the first working group's volume was released in 2007, researchers criticized it for failing to include in its sea-level projections the contributions from melting ice sheets in West Antarctica and Greenland. The working group didn't include those because they weren't well understood. Yet research published after the deadline for that report indicated that the melting appeared to be increasing.Skip to next paragraph
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This time around, Greenland and Antarctica have reappeared in the mix. The draft's authors suggest that under the worst-case emissions scenario the modelers considered, global sea levels could rise by up to 1 meter by the end of the century, about two centimeters higher than the top of the range offered in 2007.
The IPCC authors also have modified their entries on tropical cyclones between this final draft, and an earlier draft leaked in December. The earlier draft indicated that the number of tropical storms, hurricanes, and typhoons globally are likely to hold steady or decrease, while the frequency of the most-intense storms are more likely than not expected to increase. The final draft reduced that to a chart entry indicating that increases in intense tropical-cyclone activity are more likely than not by century's end.
But that perspective may be changing.
A study published by the Proceedings of the National Academy of Sciences in early July found that the number of tropical cyclones is likely to increase globally by the end of the century, in addition to intensifying.
The study, which used the output from upgraded models used for this new round of IPCC reports, was conducted by Kerry Emanuel, a tropical climate specialist at the Massachusetts Institute of Technology in Cambridge, Mass.
In addition, the IPCC draft acknowledges that its projections could get thrown off by events that are difficult, if not impossible, to predict so far in advance. Volcanic eruptions represent one kind of natural event whose lofting of sulfur dioxide high into the stratosphere can create tiny particles that can have a temporary cooling effect. Solar activity is another wild card.
This has prompted some researchers to explore the potential impact of these "forcings," especially solar variability, on global warming's future.
Solar physicists have been looking at trends in sun-spot behavior and characteristics over the past decade and have raised the possibility that when the current sun-spot cycle peaks in the next few months, the sun could enter an unusually long period where it generates few, if any sunspots.
Some climate scientists have looked at the potential impact of such an event and concluded that it likely would delay additional global warming – but only until the sun returned to more-normal swings in sun-spot activity.