You use 'could' because you cannot say with 100% certainty that there will be problems. There probably will be, but nobody knows yet for certain. So we use 'could' to indicate that evidence points to this possibility, but it remains unknown what exactly will happen.

Yes, 'could' is correct here. Using 'could' adds a degree of uncertainty to the statement, it is not definite that the big problems will come if we do nothing, but certainly definitely possible, possibly very likely, but something less than 100 percent certainty.