Smoke & Rain

Podcast

Smoke & Rain

Transcript

How smoke keeps the home fires burning. I’m Bob Hirshon and this is Science Update.

A raging forest fire is one of nature's most uncontrollable forces. And it's not just because it spreads so easily. According to new research, the smoke from a fire actually keeps rain from falling and putting it out.

The evidence comes from a high-tech NASA satellite. According to cloud physicist Daniel Rosenfeld of Hebrew University in Jerusalem, it's shown that smoky clouds produce far less rain than their smoke-free counterparts nearby.

Rosenfeld:
"It has been suspected for many years, but this is the first time that we have the means with the new tropical rainfall formation satellite to actually measure and prove it."

He says rain normally happens when the water droplets in a cloud clump together and fall to the ground. But when smoke particles get into a cloud, they attract water too. As a result, the water gets spread too thinly, and the drops never get heavy enough to fall.

Now the researchers are wondering if particles of pollution have the same effect.

Rosenfeld:
"And we have some evidence towards that, over Manila, for example. Which is a huge city which is notorious for being very polluted."

Since rain is so critical to human life, he says it's important to know if our own activities are keeping it away.

For the American Association for the Advancement of Science, I’m Bob Hirshon.

Making Sense of the Research

One of the important lessons of the twentieth century is how humans have become a dominant force on the planet, sometimes inadvertently causing global changes to the earth. In the story you just heard, researchers discovered that smoke from forest fires enters clouds and stops them from producing rain. The researchers are wondering if the same effect may result from air pollution. If so, the emissions we discharge into the atmosphere could be altering earth's rain patterns.

Now try to answer the following questions:

1. How are forest fires affecting the earth's rain patterns?
2. Researchers have long suspected that smoke alters rain patterns. How have they finally been able to prove it?
3. Describe what happens when smoke particles enter a cloud. How might this compare to the effects of particles of pollution entering a cloud?
4. Are there any beneficial aspects of forest fires? Do you think that these benefits outweigh the drawbacks described in the transcript? Why or why not?
5. How else have humans caused global changes to the earth? Do you think that these changes were caused deliberately or inadvertently? Can these changes be reversed? If so, how?

Going Further

For a comprehensive look at climatic change, go to the National Oceanic & Atmospheric Administration (NOAA) website. Relevant resources can be found in the following sections of the website:

• Global Warming
• National Climatic Data Center
• NOAA Education Resources