Quick Answers to Tough Questions About Climate Change.

• Author: Smith, Patricia
• Position: ENVIRONMENT

The planet is warming, but understanding why isn't easy. These 10 questions will help you grasp the basics.

Two degrees Fahrenheit. That's roughly how much Earth's average temperature has risen since the 1880s. It may not sound like much, but the change is having effects all over the globe: Ice is melting at the North and South poles. Ocean levels are rising. In some places, rainfall is getting heavier; in others, droughts are becoming more severe.

This increase in Earth's average temperature over a long period of time is called global warming. The increase along with all its side effects are known as climate change. Scientists have linked climate change to human activities.

Some people remain unconvinced that humans are causing the warming or that it's even happening. In a 2016 Pew Research Center survey, 20 percent of Americans said there's no solid proof of global warming. But the vast majority of climate scientists--97 percent, according to studies by the Center for Climate Change Communication at George Mason University in Virginia--agree that the problem is real and urgent. If dramatic steps aren't taken, they say, life on Earth could become very challenging.

"It's difficult to make people understand how urgent this is when you look outside and the weather seems pretty normal," says James Hansen, a climate scientist at Columbia University in New York City.

Here's what you need to know about the causes and effects of climate change and what can be done about it.

1 What are greenhouse gases, and how do they cause climate change?

Greenhouse gases are invisible gases in the air that act like the glass panes of a greenhouse, trapping some of the sun's heat close to Earth. Some of them, such as carbon dioxide, occur naturally in our atmosphere. But when we bum fossil fuels (such as coal and oil) to power homes, cars, and factories, we release even more greenhouse gases.

The so-called greenhouse effect is a good thing--to some extent. Without it, our planet would be a frozen wasteland. The problem, climate scientists say, is that we're producing too much of these greenhouse gases. Since the Industrial Revolution, the amount of carbon dioxide in the atmosphere has increased by more than 40 percent. That means more heat is being trapped and, as a result, Earth's average temperature has been rising.

2 Do we know that human activity is responsible?

Experts have examined the natural factors known to affect Earth's temperature and concluded that these factors are not changing nearly enough to cause the current warming. Carbon dioxide levels did rise and fall naturally long ago, but those changes occurred gradually over thousands of years. Now, through the burning of fossil fuels, humans are releasing carbon dioxide into the air much faster than nature has ever done, scientists say. That explains the rapid warming better than anything else, most climate scientists have concluded.

3 If Earth is getting warmer, why is it stilt so cold in some places?

To understand how cold weather occurs in a warming world, it helps to know the difference between climate and weather. Weather is what's going on outside in a certain place on any given day. It can change quickly and be hard to predict. Climate describes what weather conditions are usually like in a place over a prolonged period of time-- and it changes slowly. Scientists say that Earth's climate has been getting hotter for decades (see "Tracking the Warming Trend," left).

"Two weeks of really cold temperatures don't negate decades of warming," says Jake Crouch of the National Oceanic and Atmospheric Administration (NOAA).

In Canada, for example, winters are still bitterly cold--but not as consistently cold as they used to be. The warming trend means that the ice in the country's outdoor skating rinks is melting earlier in the season. Researchers estimate that the number of outdoor ice-skating days will drop by 34 percent in Toronto and 19 percent in Calgary by 2090.

4 Is global warming to blame for all the recent wild weather?

Scientists have published strong evidence that the wanning trend is making heat waves more frequent and intense. Coastal flooding is also increasing as the oceans rise. As for hurricanes and other storms, while global warming doesn't necessarily cause them, it likely makes them worse. For example, during Hurricane Harvey last August, up to 40 percent more rain poured down than would have if the exact same hurricane had happened decades earlier, experts say.

Climate change, says Kathleen Hayhoe, a climate scientist at Texas Tech University, "takes the natural risks that we've always faced and exacerbates them."

5 Why are the seas rising--and how fast?

Sea water levels are rising for two main reasons...