In all the conversation around Barack Obama’s announcement that he now supports same-sex marriage, one thing is often forgotten: just how quickly public opinion is shifting on this issue.

It’s often been reported, for instance, that black Americans oppose same-sex marriage by a 49-39 margin. What’s less often mentioned is that that figure, from April of this year, represents a 27-point tightening from 2008, when 63% of blacks opposed same-sex marriage, and only 26% supported it. At that rate of change, same-sex marriage will reach plurality support late next year and majority support sometime in 2015. To put it another way, black views on same-sex marriage today are exactly where whites’ positions stood just four years ago.

And if you look at charts of public opinion on the issue, it’s clear that views aren’t just changing quickly, the rate of change is accelerating. We’ve reached a tipping point on the question, and we may reach something approaching consensus far sooner than we think.

Don’t believe me? Check this out:

More Americans support same-sex marriage today than supported marriage between blacks and whites in 1994.

That’s right. Same-sex marriage is more popular in the United States in 2012 than interracial marriage was just eighteen years ago. And as with same-sex marriage, polling results on interracial marriage show a long period of slow change followed by a dramatic, rapid shift.

In 1968, only 20% of Americans approved of interracial marriage. Support grew at a rate of about one point a year over the next quarter century, and actually slowed in the eighties and early nineties. But then the dam broke, and support shot up 38 points in the next 18 years. Today, support for interracial marriage stands well above 90% for all but the oldest Americans.