The smokestacks of Kremikovtzi steel mill on Sofia's outskirts may have shut down years ago, but ancient cars ensure that Bulgaria's capital is still the most polluted in Europe.

When the steel plant went bankrupt in 2008, it did little to improve the thick smog that still hangs over Sofia.

Nigeria's biggest city Lagos is home to some 20 million people and produces a staggering 10,000 tonnes of waste every day, a lot of which piles up on the busy streets or floats in open sewers.

Currently, an estimated 40 percent of the megacity's waste is collected and taken to massive rubbish dumps, where scavengers pick through it for scrap and salvage to sell.

A training exercise designed to showcase the government's ability to recover a space capsule at sea was scrubbed after NASA ran into trouble off the Southern California coast, the space agency said Friday.

Crews had difficulty tying down a mock-up of the Orion capsule aboard an amphibious warship off the shores of San Diego.

Google, environmentalists and governments on Thursday unveiled a state-of-the-art database to track deforestation, hoping to ramp up enforcement of a major culprit behind climate change.

The website, www.globalforestwatch.org, will show tree loss around the world in high resolution and with frequent updates. The data -- aimed both at policymakers and companies buying from forest areas -- will be available for free and not require much technical skill to use.

Indonesia is now the world's largest sanctuary for manta rays, after officials were persuaded by evidence that the gentle giants known for delighting tourists are worth more alive than dead.

The government on Friday announced that manta rays within the archipelago's 5.8 million square kilometers (2.2 million square miles) of ocean will be protected from fishing and export. It will take time and cooperation at multiple levels to enforce the ban on poaching in the biggest global shark and ray fishery.

The melting of ice in the Antarctic is considered a top threat to global sea level rise, and scientists said Thursday the trend could continue for decades or even centuries to come.

Researchers focused on the Pine Island Glacier in Antarctica, which has been thinning at an increasingly rapid pace for about the past 20 years, as the waters beneath get warmer along with the rest of the ocean.

When the air gets really bad, Beijing says it has an emergency plan to yank half the city's cars off the road. The only problem is: It may be difficult to ever set that plan in motion.

A rare alert issued Friday was an "orange" one, the second-highest in the four levels of urgency. It prompted health advisories, bans on barbeques, fireworks and demolition work, but no order to pull cars from the streets.

The world's only captive leopard seal, which washed up in Sydney with a shark bite to his abdomen seven years ago, has been put down at an Australian zoo, officials said Thursday.

Casey stopped eating at the start of the year and his health and condition deteriorated to such an extent that he had to be euthanised.

A dam which Laos plans to build across the Mekong River could wipe out critically endangered dolphins in downstream Cambodia, the World Wildlife Fund (WWF) warned on Thursday.

If built, the controversial Don Sahong dam in southern Laos would be just a kilometer upstream of the main stretch of water favored by the rare freshwater Irrawaddy dolphin, WWF said in a statement.

When stars explode, it's a messy business. But the massive blasts are also useful, seeding the universe with such key elements as calcium, iron and titanium.

And with the help of a new high-energy X-ray telescope, NASA said Wednesday astronomers are closer than ever to seeing just what's going on.