There is a class of scientific problems, of central importance to humanity's understanding and control of the environmental crises with which it is faced, which is insoluble, either in the present or in the foreseeable future.
There are classic mathematical problems and conjectures that have defied solution for decades and even centuries. There are however also scientific problems relating to the environment which cannot be solved. Examples of such questions include: the extent and timing of global warming given increasing levels of "greenhouse gases"; long-term effects of exposure to low-level concentrations of certain compounds or to low-level radioactivity; or the degree of dependence of the ecosystems on particular levels of biodiversity.
Unanswered questions inspire and motivate scientific research. An enthusiasm for investigating mysteries leads to new discoveries. It is therefore essential to scientific investigation that there always be questions for which we have no answer.