Well that's a fine kettle of fish!

The lungs of the planet are belching methane:

IT'S not just farting cows and belching sheep that spew out methane. Living plants have been disgorging millions of tonnes of the potent greenhouse gas into the atmosphere every year - without anybody noticing.
...
When the group repeated the tests with living plants they were stunned by the amount of methane created. They estimate that, globally, living plants produce between 63 and 236 million tonnes of methane per year, with plant debris adding another 1 to 7 million tonnes. This would make plants responsible for roughly 10 to 30 per cent of global methane production.

It's darn ecologically irresponsible of those pesky weeds if you ask me!.