It's incredibly potent stuff, so much that despite the relatively quick breakdown, an initial mass of methane will have a warming effect that is 20-35x that of an equivalent mass of carbon dioxide over a century. GWP numbers take the brief half-life of methane into account when calculated. You're making the mistake of looking at the absolute quantity of methane and short half-life, and thinking that it couldn't possibly have much of an effect. Well, people have already run the numbers, and it can have a huge effect.
The risk is from 100s's of Gigatons which is a extremely massive quantity. How much of that is going to be liberated and how soon has a massive impact on estimates.
Anyway, your first link says " In the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, methane has a lifetime of 12.4 years" (If that's X ln(2) for half life it's 8.6 years)
"This means that a methane emission will have 28 times the impact on temperature of a carbon dioxide emission of the same mass over the following 100 years." https://en.wikipedia.org/wiki/Atmospheric_methane
PS: As to small quantities, we are talking about billions of tons of a gas.
The point of everything I have said is that it would take only a small quantity of methane, relatively speaking, to make a significant contribution to global warming. You don't need to emit as much methane as would match all the warming caused by current levels of CO2. Even an extra tenth of a degree is bad news. Every tenth of a degree shaves off a decade from the time we have to fix our planet. Any significant source of greenhouse gases.
The 34x potential I gave is for methane over a hundred years. https://en.wikipedia.org/wiki/Global_warming_potential
It's incredibly potent stuff, so much that despite the relatively quick breakdown, an initial mass of methane will have a warming effect that is 20-35x that of an equivalent mass of carbon dioxide over a century. GWP numbers take the brief half-life of methane into account when calculated. You're making the mistake of looking at the absolute quantity of methane and short half-life, and thinking that it couldn't possibly have much of an effect. Well, people have already run the numbers, and it can have a huge effect.
Current rates of methane leaks from mining natural gas could very well offset the benefits of moving away from coal: http://blog.nature.org/science/2016/06/24/natural-gas-coal-l...
Methane's very bad news, even in small quantities.