From the largest scales (global climate) to the smallest (cell research), this was a year punctuated by significant developments in science. USA TODAY highlights the findings.
It led the pack as the main science story of 2007. This was a year in which the topic moved from being theory to fact in the scientific world and, perhaps more important, in the minds of many Americans.
It also was the year in which the gold-standard scientific body on the topic, the United Nations' Intergovernmental Panel on Climate Change, won the Nobel Peace Prize. It shared the award with former vice president Al Gore.
In its long-awaited report in February, the U.N. panel said that global warming was unequivocal and that humankind's reliance on fossil fuels — coal, fuel oil and natural gas — was to blame. Discussion has shifted in scientific and political circles to "What effects will it have?" and "What can we do about it?"
The year ended with this month's international climate talks in Bali. The sometimes-fractious discussions resulted in a plan-to-make-a-plan to fight global warming by 2009. That plan will replace the Kyoto Protocol, the 1997 agreement to reduce the emission of heat-absorbing "greenhouse" gases. Much of the protocol expires in 2012.
Stem cell breakthrough
In November, two teams of scientists reported success in reprogramming human skin cells to behave as embryonic stem cells, which can become any cell in the body.
Their papers appeared in two prestigious journals, Cell and Science. The Cell report was from a group led by Shinya Yamanaka of Kyoto University in Japan. The Science study was from Junying Yu and James Thomson at the University of Wisconsin-Madison.
The new technique uses a chemical cocktail that contains gene-controlling proteins to turn the skin cells back to their pluripotent, or unlimited, state. The hope is that the promise of stem cells — to provide cures for diseases such as diabetes and Parkinson's and repairs for those with spinal cord damage — might be accomplished without the moral issues that have dogged the research. Until now, creating human embryonic stem cells required destroying a human embryo.
The brightest supernova
Astronomers began seeing the brightest supernova of a star ever observed in May. That's when light from the death of SN 2006gy finally reached Earth. The star was 240 million light-years away. (One light-year is about 5.9 trillion miles.) It was about 150 times heavier than our sun when it exploded. It still burned brightly in the sky more than 250 days after its initial explosion.
A planet like our own?
In April, astronomers announced they had discovered the first potentially habitable planet outside our solar system that might contain oceans, and thus life.
The small planet circles the red dwarf Gliese 581. It's just far enough away from its sun that liquid water is possible. The mantra among NASA exobiologists is "follow the water," for where liquid water exists, life is possible.
The planet is one of three that circle its star and was prosaically named Gliese 581 c. It's about 20.5 light-years away in the constellation Libra.
New species, looming extinctions
Scientists all over the world discovered thousands of new species, including:
• A medium-size, tree-dwelling primate called a highland mangabey in the mountains of East Africa.
• A new variety of clouded leopard on Borneo and Sumatra.
• A black toad with purple rings in Suriname.