I was a bit confused by this sentence (which is a direct excerpt from the piece). Reading the whole article, the `this` refers to the methane lifetime. Oddly (to me), the lifetime methane in the atmosphere increases with the amount of methane in the atmosphere. That's what the author has been working to understand. Very interesting!
The opposite is true, that the higher the methane concentration, the lower the rate of effect would be to degrade all atmospheric methane. The rates of methane accumulation and its degradation are inversely proportional beyond the limit of the atmosphere to degrade it.
The reality is more complicated because the cut off is very blurry - absorbsion does still increase as methane increases, just not fast enough to keep up, and it falls further behind the more methane we put out.
And it seems like there are methods for capturing methane: https://news.mit.edu/2022/dirt-cheap-solution-common-clay-ma...