A couple of weeks ago, I wrote about the dramatic decline in family caregivers who will be available to assist Baby Boomers in their old age. Today, according to estimates by AARP, there are about 7 people aged 45-64 to care for each person who is 80 or older. By 2030 there will be only 4 and by 2050 there will be fewer than 3.

This sharp decline in the ratio of caregivers to care recipients is critically important, especially as the U.S. further shifts its focus to delivering more long-term supports and services at home. We all want care at home. But who will provide it?

Already more than eight in ten people who need assistance get help at home, rather than in nursing homes or assisted living facilities. But thanks to changes in government policy and growing consumer demands, the percentage of people staying home is likely to increase.

We are already facing a massive shortage of paid aides. Not only are these difficult jobs that come with low pay and poor benefits, but the same demographic trends that will reduce the availability of potential family caregivers will also cut into the ranks of paid aides.

But the vast bulk of care is provided by friends and family. This week, AARP released a more detailed report that described in more detail what is going to happen to those caregivers. It is a story about powerful changes in the nature of American families. And it raises a loud alarm. As a society and as individuals we need to prepare for a time when more of us will need help, yet fewer family members will be there to deliver it.

The AARP study–by Don Redfoot, Lynn Feinberg, and Ari Hauser–shows that 2010 was a demographic turning point. That was when the ratio of caregivers to recipients peaked. The huge cohort of Boomers who have been caring for their own parents began their inexorable slide from middle-age to old-age. By 2025 the first of the Boomers will reach 80, an age at which they are likely to need some level of assistance.

The math is brutal: The population in the prime caregiving ages of 45-64 will grow by only 1 percent from 2010 to 2030 but the numbers of those 80 and over (who are most likely to need care) will grow by nearly 80 percent.

Why so few potential caregivers? Women who were aged 80-84 in 2010 had an average of 3.1 children. Women who reach that age in 2030 average only two children.

More striking, however, are the number of boomers who have no kids. In 2010, one in nine women aged 80-84 were childless. By 2030, it will be one of every six. And by 2050, almost one in five women aged 80-84 will have no children.

One bit of good news is that rates of widowhood have been falling as men live longer. In 1990, for instance, 81 percent of women 85 and older were widows but by 2010 the share had fallen to 73 percent.

However, that may be offset by another trend—more divorce. Men may live longer but not necessarily with their long-time spouses. For women, higher divorce rates and lower rates of widowhood will roughly balance out. But not so for men. In 2010, about 29 percent of older men could expect to be unmarried for 10 years or more. By 2030, 36 percent will be alone for a decade or longer.

It is impossible to predict divorce rates 20 years or more from now, of course, but this phenomenon (including the recent increase in divorces among those 60 and older) could well increase the shortage of family caregivers.

Finally, the AARP study looked the pool of caregivers by states. In 2030, when the national average will be about 4 caregivers for each adult over 80, the ratio in retirement meccas such as Arizona and Florida will be much lower, 2.6 percent and 2.9 percent respectively. On the other hand, elders in Georgia and Illinois may have more potential caregivers than average, nearly five for every older person.

These demographic changes are largely the result of irreversible trends that began long ago. They are unlikely to be revised very much. The AARP study helps provide some important context to our current debate over the future of long-term care. We want to stay home in frail old age. But we need to think a lot more about who will be there to care for us. If not, many of us will be on our own at a very vulnerable time.