What does the writer mainly talk about in the passage?

In recent years, the daily weather reports have sounded like real news— surprising and sometimes even frightening. For example, in the United States, there was June snowfall in Colorado and floods in the Southern California desert. The worst drought in fifty years broke out in a large part of the African continent. So, what is up with the weather? Are we seeing a worldwide change in climate, or are snowy summer days not really that unusual at all? In fact, they say we should always expect extreme hot and cold or wet and dry periods. Scientists also point out that natural disasters can cause extreme weather that lasts for months or even years. Volcanic eruptions for example, can change temperatures around the world. Other experts, however, point out that these explanations do not explain some major changes in the earth’s climate—such as the rapid growth of the Sahara Desert during the last ten years.