These orbital changes led to a cold period known as the little ice age during the 17th, 18th and 19th centuries.

They could see that the cold period was not ended.

However, the commercial industry was wiped out during a very cold period in the late 1930s.

A nearly identical increase was observed in the coldest period of the next years, she said.

On the other hand, the dry season includes a cold period and a period of heat.

But they all agree that the cold period is necessary.

More serious is that the oceans could perhaps freeze over during cold periods.

Then a cold period must follow, to break down inhibitors, before baby plants can emerge.

Most cold periods begin very slowly because glaciers take a long time to develop.

However there were several less cold periods after this.