The letter describes the current status oil in the world as finite. This means that the process of extraction will at first grow, and then quickly fall. As a result, these experts believe that the world will be at a lack of oil in the very near future. They ask that their government look further into the issue because they claim that the lack of oil will bring tremendous negative changes to all aspects of life as we know it. These people are describing the effect that the lack of oil will have plainly and directly in a constructive manner. If you are unfamiliar with the peak oil phenomenon, or you simply want to read a well written letter depicting the issue, I would recommend reading it.
The article can be found here