Last autumn countless Europeans said they wished they could vote in the American election. The Nobel committee acted on that wish yesterday, albeit eleven months later.

The prize reflects just how strongly many Europeans felt that a conflictive rift opened up between the United States and the rest of the world during the Bush years. In their view, Mr. Obama’s election and his determination to reengage globally already have done much to heal this rift and thus merit reward.

In several past cases the Nobel boost was short-lived.

This isn’t the first peace prize to look forward as much as backward. The prize to South Korean President Kim Dae Jung in 2000 came just after his historic summit with North Korea. It sought to bolster the chances that a promising but as yet only preliminary diplomatic step might pay off in terms of peace down the road.

Kofi Annan’s prize in 2001 came in the first half of his tenure as secretary general of the United Nations, possibly aiming to fortify him for what the Nobel committee expected would be hard times ahead for international peace in the aftermath of September 11.

The award to Iranian human rights lawyer Shirin Ebadi in 2003 was not simply a recognition of her past accomplishments defending human rights in Iran. It aimed to boost her future efforts at a time when Iran’s reform movement was losing steam and troubling political waters clearly lay ahead.

Iran may also been on the Nobel committee’s mind this time as well. Europeans are extremely anxious for Mr. Obama’s diplomatic overture to Iran to succeed. The committee may have calculated that it will be harder domestically and internationally for Iran’s Supreme Leader and president to bite an outstretched hand if it that hand comes not just from an American president but the holder of a Nobel Peace Prize.

Yet optimism must be qualified by the record. In those past cases the Nobel boost was short-lived. Peace with North Korea remained elusive. Kofi Annan locked horns unsuccessfully with the Bush administration over the invasion of Iraq. And despite Shirin Ebadi’s continued valiant work, human rights in Iran deteriorated steadily after 2003.