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Blood Red Ocean: Not Exactly The End of Days
A massive algae bloom along Australia’s beaches turn the ocean the color of blood.
It looks like something straight out of Dr. Seuss's world, but this is no imaginary scene. A form of algae has been spreading across Australia's eastern coast since Tuesday, turning the water an alarming shade of red and forcing at least ten beaches, including Sydney'spopular Bondi Beach, to close.
Known as an algae bloom or "red tide," the event occurs when unicellular organisms—in this case dinoflagellates from the genus Noctiluca—find optimal conditions (including sunlight and nutrients) and reproduce quickly. "It's sort of like the rapid growth of bacteria," said Stanford University marine biologist William F. Gilly.  (See related photos: "Algae BlanketsChina Beaches; Dead Zone Brewing?")
Large red tides can be harmful to fish, said Lauren Freeman, a Ph.D. candidate at Scripps Institution of Oceanography in San Diego, California. "As the algae die and sink in the shallow coastal water, they decompose and oxygen is taken from the water column. This can lead to temporary low oxygen zones," she added. These zones can kill marine animals if theoxygen depletion is severe enough.
So can red tides hurt humans? It depends on the species that's blooming, said Gilly. Blooms of certain dinoflagellates are associated with saxitoxin, a shellfish toxin that can cause paralytic shellfish poisoning in people. "If it's in a harbor or contained bay, it's probably a serious matter," he said.
But as for the notion that this is some kind of harbinger ofdoom, don't worry. Said Gilly: "I've seen patches like this in the Gulf of California and Monterey Bay, so such events are not rare. They certainly don't merit 'end of days' status or the Mayan prophecy of Dec. 21, 2012, being fulfilled."

A man swims in a pool at Clovelly beach in Australia as algae blooms in the seawater alongside him.

What Is Global Warming?
The Planet Is Heating Up—andFast
Glaciers are melting, sea levels are rising, cloud forests are drying, and wildlife is scrambling to keep pace. It's becoming clear that humans have caused most of the past century's warming by releasing heat-trapping gases as we power our modern lives. Called greenhouse gases, their levels are higher now than in the last 650,000 years.
We call the result global warming, but it is causing aset of changes to the Earth's climate, or long-term weather patterns, that varies from place to place. As the Earth spins each day, the new heat swirls with it, picking up moisture over the oceans, rising here, settling there. It's changing the rhythms of climate that all living things have come to rely upon.
What will we do to slow this warming? How will we cope with the changes we've already setinto motion? While we struggle to figure it all out, the face of the Earth as we know it—coasts, forests, farms and snow-capped mountains—hangs in the balance.
Greenhouse effect
The "greenhouse effect" is the warming that happens when certain gases in Earth's atmosphere trap heat. These gases let in light but keep heat from escaping, like the glass walls of a greenhouse.
First, sunlight shinesonto the Earth's surface, where it is absorbed and then radiates back into the atmosphere as heat. In the atmosphere, “greenhouse” gases trap some of this heat, and the rest escapes into space. The more greenhouse gases are in the atmosphere, the more heat gets trapped.
Scientists have known about the greenhouse effect since 1824, when Joseph Fourier calculated that the Earth would be muchcolder if it had no atmosphere. This greenhouse effect is what keeps the Earth's climate livable. Without it, the Earth's surface would be an average of about 60 degrees Fahrenheit cooler. In 1895, the Swedish chemist Svante Arrhenius discovered that humans could enhance the greenhouse effect by making carbon dioxide, a greenhouse gas. He kicked off 100 years of climate research that has given us a...