The value of any action taken today will depend on what happens in the future. This is of course true in a trivial sense. For instance, if we were to discover that there was a meteor hurtling for Earth, and that humanity had only a few years of life left, then this would decrease the expected value of work on climate change.
However, future events can also determine the value of present actions in more subtle ways. First, some actions taken to address present-day problems may turn out to have long-term indirect effects that dwarf their short-term impact. For example, work that lessens the burden of disease in the developing world could have an economic impact that compounds across generations.
Second, the value of progress on many present-day problems will depend on how the severity of the problems and the attention they receive evolve over time. If synthetic meat will make factory farming disappear, for instance, then this could lessen the value of present efforts to end factory farming.
Third, it is possible that some of the most high-value actions available today, such as actions to combat climate change, are ones that will not have any payoff until significantly in future.