[cbennett]

>> This person is literally saying we need to be alarmed.

And why shouldn't we (he) be doing that? Actually the author's goal is transparent, to shake up perception, to provide fodder in the imagination of folks to ultimately change how urgently we treat this in public forums. I thought this was a quite trenchant point (from the article):

>>Over the past decades, our culture has gone apocalyptic with zombie movies and Mad Max dystopias, perhaps the collective result of displaced climate anxiety, and yet when it comes to contemplating real-world warming dangers, we suffer from an incredible failure of imagination. The reasons for that are many: the timid language of scientific probabilities, which the climatologist James Hansen once called “scientific reticence” in a paper chastising scientists for editing their own observations so conscientiously that they failed to communicate how dire the threat really was; the fact that the country is dominated by a group of technocrats who believe any problem can be solved and an opposing culture that doesn’t even see warming as a problem worth addressing;

Back to you: >>I really didn't understand the part where they said methane has 34 times the greenhouse effect as carbon over a period of time and then changes the timeframe to bring the multiplier put to 84 times.

I also thought this statement was scientifically unclear, but I think the author was trying to say that the rate of methane release increases, thus, the impact on climate systems multiplies relative to an equivalent release of CO2 in that period (100 yrs v 24 yrs). If someone else can mention exactly how he got from 34x to 84x though, id love to hear it; i didn't get it.. I do want to mention, however the 30x GHG effect number is not set in stone. In fact, depending on the rate of release, there may be 'force multipliers' depending on how (quickly) ecosystems can absorb and use these gases. Ominously, this multiplier seems to go up anyways as temps rise. [1]

[1] http://www.nature.com/nature/journal/v507/n7493/full/nature1...

[epall]

Methane deteriorates in the upper atmosphere fairly quickly, whereas CO2 sticks around. Methane is a dramatically better insulator than CO2, so in the short run its impact is higher, but when you stretch out the timescale, your methane is deteriorating while the CO2 sticks around, so the relative impact tilts slowly toward CO2.

[cbennett]

While you are right that methane wont naturally stick around for ever, and that it breaks down sooner than CO2. After googling around a little, I finally managed to find the source of the author's two numbers, and in the end I am more troubled than ever :/

>>At issue is the global warming potential (GWP), a number that allows experts to compare methane with its better-known cousin, carbon dioxide. While CO2 persists in the atmosphere for centuries, or even millennia, methane warms the planet on steroids for a decade or two before decaying to CO2. In those short decades, methane warms the planet by 86 times as much as CO2, according to the Intergovernmental Panel on Climate Change. But policymakers typically ignore methane's warming potential over 20 years (GWP20) when assembling a nation's emissions inventory. Instead, they stretch out methane's warming impacts over a century, which makes the gas appear more benign than it is, experts said. The 100-year warming potential (GWP100) of methane is 34, according to the IPCC.[1]

Doesn't 'reducing' (really, normalizing) the GWP for the ~80 yrs of the 100yr period (when it is not existing) seem sort of like an accounting trick? In other words, if 20GT of CH4 were released next year from the Bering Sea into the atmosphere (this would be spectacularly bad), the overall shock to the climate/atmosphere systems is precisely the same.

[1]https://www.scientificamerican.com/article/how-bad-of-a-gree...