While I couldn't find the exact divorce rates from the seventies, there is something very important to be taken into account: In 1973 (the year Scenes from a Marriage was launched) a new law was issued in Sweden which made divorce much easier than it used to be:

In 1973, new legislation of a purely autonomous character was enacted. In this legislation the institutions of judicial separation and marriage annulment were abandoned, as were special divorce grounds. ‘Fault’ in the breakdown of marriage lost all relevance, also in respect of the ancillary claims to divorce. A spouse’s wish to dissolve the marriage alone became sufficient to obtain a divorce and no reasons have to be given in support of the application. Divorce can be granted immediately upon application, but must in certain cases be preceded by a reconsideration period of six months. [Source]

One would assume that every notable change in divorce rates would rather depend on this legal change than on the TV series. Nevertheless I think it's interesting to see that the series and the law come from the same year, as they both bear witness to a critical public dialogue on the institution of marriage at that time.