We'll need decades to install a system that could solve this problem when given weeks of notice. Perhaps those decades of effort will start soon? Alternatively

We'll need decades to install a system that could solve this problem when given weeks of notice. Perhaps those decades of effort will start soon? Alternatively, if we knew a particular asteroid would threaten us in one decade, that one decade might be enough to do something about it. Many asteroids won't give us that sort of notice, since orbits can have century-long periods.