The ratio is likely to fall to less than 1 for Italy and Japan - that's right, in a few decades these two countries will be looking at a population situation in which they will have fewer workers than retirees. Demographic movements of this magnitude will require significant policy changes.
The public costs of retirement systems will rise markedly unless countries raise their age of eligibility for retirement program benefits or cut these benefits. Moreover, small tax increases or benefit cuts will not do the job - the implicit actuarial deficits of these programs are so large that halfway measures will not be adequate.