How Human Warming Paused the Next Ice Age

A cap of ice on Baffin Island in Canada has been shrinking since about 1960. It is called the Barnes Ice Cap. Scientists say human-caused warming stopped a new ice age from beginning. That may sound odd, but the proof is in ancient plants and rocks.

Long ago, a massive ice sheet covered large parts of North America. The Barnes Ice Cap is the last piece left from that old sheet. For thousands of years, the ice cap grew and shrank. Between 3,600 and 2,000 years ago, it was smaller than it is now. Then, around 2,000 years ago, it started growing again. Researchers believe this growth marked the beginning of a new ice age.

The growth happened because summer sunlight in the north was slowly going down. Less sun lets snow stick around longer. Slow shifts in Earth's orbit caused this natural cooling. Scientists call these orbital changes Milankovitch cycles. It is a process that takes a very long time.

By 1960, the ice cap was bigger than it had been in two thousand years. After that, it began to retreat. Recent warming has been stronger than the natural drop in summer sunlight. Now, the ice sheds more in summer than it rebuilds in winter. One researcher said this shows how strongly people have changed the climate. He said the natural cooling would not have been obvious for thousands of years without human-caused warming. Growing the old ice sheet back to its full size would have taken about thirty thousand years.

In the past, this ice cap helped the larger ice sheet spread. Where ice exists, more ice can form. Today, models suggest the Barnes Ice Cap could vanish completely in a few hundred years. If this final piece melts away, the next ice age could play out differently than past ones. Experts have not yet figured out when the next ice age will begin.