Like sparring siblings, China and the United States -- the world’s two biggest carbon dioxide emitters -- keep passing the climate-action buck back and forth: “Why should I cut emissions if they don’t have to?” Well, China is either the more mature of the pair, or just majorly sucking up to Mama Earth. The country is reportedly gearing up to set firm limits on greenhouse-gas emissions, seriously weakening one of the U.S.’s go-to excuses for climate inaction.

China's powerful National Development and Reform Commission has proposed an absolute cap on emissions starting in 2016. The proposal still needs to be accepted by the Chinese cabinet, but experts say the commission’s influence makes it likely to pass. China today also announced the details of trial carbon-trading programs that will roll out in seven regions by 2014. In February, the country had said it would implement a carbon tax, but backed off a few weeks later, saying it will wait until early next year to get started on that.

The commission’s carbon-cap proposal calls for Chinese emissions to peak in 2025, five years earlier than previously planned. RenewEconomy explains:

China has already pledged to cut its emissions intensity – the amount of Co2 it emits per economic unit – by up to 45 per cent by 2020. The significance of an absolute cap is that it promises to rein in emissions even if the economy grows faster than expected.

"Oops."

Gulf Coast oil refiners and chemical processors say that a lot, but regulators are doing precious little to rein in what the industry euphemistically calls "upset" emissions.

Upset emissions are inadvertent releases of chemicals by industrial operations when something goes awry. And things seem to go awry awfully frequently. An ExxonMobil refinery in Baton Rouge, La., was averaging two accidental releases every week during one grim stretch.

That's according to an analysis by The Center for Public Integrity, which found that upset emissions are more prevalent than industry admits or government knows. Some highlights from the center's investigative report:

It often seems like teenagers are powered mainly by social media, so it only makes sense that a group of high school students would build a car that really was. This 1967 Volkswagen Karmann Ghia, converted to an electric car by at-risk students from five Kansas City high schools, will turn Twitter mentions and Facebook likes into wattage to complete a 1,000-mile trip to Washington, D.C.

As if it's not enough that bees provide honey, wax, ecosystem balance, and tragic endings to Macaulay Culkin movies, researchers in Croatia are using the insects to locate the unexploded landmines that litter the Balkan landscape. They don't call it a "hive mind" for nothing.

May hasn't gone so hot for some of the sharing economy's most promising entrepreneurs. 2012 might have hinted of challenges to come, but so far 2013 has overdelivered. In the last two weeks, New York regulators and courts have essentially shut three of these companies down, at least temporarily.

SideCar Technologies, a donation-based rideshare start-up, ceased its New York business after a judge said even free rides from the company would violate the city's laws governing cars-for-hire, according to the Wall Street Journal.

Then last week, RelayRides, which allows car owners to rent out their vehicles, came under fire from the state Financial Services Department for what officials called "repeated false advertising and violations of insurance law, which are putting the public at risk." Basically: RelayRides told car owners that the company's insurance policy covered them 100 percent in the case of a car renter, say, mowing down a pedestrian, but the car owners could actually be found liable.

But the issue really came to a head this week, when a New York judge deemed vacation rental middle-people Airbnb illegal in New York City and New York state. Airbnb's services violate laws against underground and underregulated hotels, as well as a state-wide ban on short-term rentals enacted in 2011. Airbnb is now lobbying in Albany to change the law, but the East Village host who rented out his apartment for a few days and was made an example of got slapped with a $2,400 fine.

Last year, California cracked down on ridesharing and car-hire start-ups. The state hasn't shut them down -- it's looking for a way to regulate them within the current system -- but it's asking a lot of the same questions about insurance and liability that are vexing New York.

Whatever oil and gas true believers want to think, the world is doing this solar power thing. It's getting cheaper and cheaper to make solar panels, and the panels are getting more and more effective. For example: A team in Australia just built a gigantic printer that spits out solar cells at rate, Gizmodo reports, of about 33 feet every minute.

It's not even particularly complicated technology, according to the researchers. Gizmodo writes:

[The printer system] utilizes only existing printer technology to embed polymer solar cells (also known as organic or plastic solar cells) in thin sheets of plastic or steel at a rate of ten meters per minute. "We're using the same techniques that you would use if you were screen printing an image on to a T-Shirt," project coordinator and University of Melbourne researcher Dr David Jones said in a press release.

Bad news, Fage fans and Chobani lovers (we're gonna call you "Chobuccaneers"). All that Greek yogurt you're eating is creating a toxic byproduct: gallons upon gallons upon gallons of acid whey.

This is the same whey that Miss Muffett so enjoyed. Apparently she was a fish-hating sociopath in addition to being an arachnophobe. Modern Farmer reports:

It’s a thin, runny waste product that can’t simply be dumped. Not only would that be illegal, but whey decomposition is toxic to the natural environment, robbing oxygen from streams and rivers. That could turn a waterway into what one expert calls a "dead sea," destroying aquatic life over potentially large areas. Spills of cheese whey, a cousin of Greek yogurt whey, have killed tens of thousands of fish around the country in recent years.

Solar Impulse, the world's most advanced solar aircraft, is trekking across the United States. It's already made it from the Bay Area to Phoenix, Ariz. Check out photos from its U.S. flights, and read more about the all-solar plane's journey.

Standing beside Solar Impulse -- the world’s most advanced solar aircraft -- in a hangar at the Phoenix Sky Harbor International Airport on a recent afternoon, Bertrand Piccard attempted to diagnose humankind’s biggest problem.

We are being bored to death, he opined.

“People talk about protecting the environment and it’s boring,” the 53-year-old Swiss aviator/psychiatrist said. Discussions about climate change are even worse. "Those," he added, "are boring and depressing."

Piccard’s prescription: Make environmentalism inspiring, exciting, and sexy. Not coincidentally, those adjectives are frequently used to describe Solar Impulse itself, the aircraft Piccard piloted 650 miles, from Mountain View, Calif., to Phoenix, Ariz., on May 3, the first of five legs in a coast-to-coast voyage.

“We want to motivate people to be pioneers,” said Piccard, stressing the syllable with the intensity of a hypnotist (which he is). “We want to show solutions. To show hopes. We want to show what is possible.”

Farragut Square is a classic, austere Washington, D.C., park with much landscaping and statuary but few amenities for actual people. It does at least have a lot of benches, which come in handy during the typical weekday. Come noontime, hundreds of local office workers swarm, blinking, into the sunlight, desperate for sustenance, and run headlong into bounteous providence: a veritable armada of food trucks.

It varies by the day, but Farragut typically has among the densest truck congregations in the city. When I visited last, in the space of 50 feet I could choose between a half-dozen curries, steak sandwiches, tacos, Korean barbecue -- and kebabs, lots of kebabs.

But these trucks may not be here for long. The D.C. City Council is currently considering new regulations that would curtail, potentially drastically, the number of trucks allowed in much of the district.

It’s a familiar story. Similar fights have unfolded in several other cities. But this time some Big Name Conservatives have spied an opportunity to get young, urban voters onto the anti-government bandwagon. (Mitt Romney losing 18- to 29-year-old voters by 24 points would tend to focus the mind.) As they see it, these humble taco-delivery systems are just the thing to demonstrate the tyrannical, hungering grasp of Big Government.

“What they need is for people to see this and say, 'I’m on the side of the people that the government is messing with,'" none other than Grover Drown-The-Government-In-The-Bathtub Norquist told National Journal.