ENVIRONMENT Geography • Science · Chennai, one of India’s biggest cities, last May. Earth’s average temperature, which has been linked to human activities.) Some people don’t

Geography • ScienceENVIRONMENT

The planet is warming, but understanding why isn’t easy. These 12 questions and answers will help you grasp the basics.BY LAURA ANASTASIA

Two degrees Fahrenheit.That’s roughly how much Earth’s average temperature

has risen since the 1880s. While it may not sound like much, 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 shift in Earth’s average temperature and precipitation over a long period of time is called climate change. (You’ve probably also heard the term global warming. That refers to one specific part of climate change: the increase in

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Earth’s average temperature, which has been linked to human activities.)

Some people don’t believe humans are causing the warming or that it’s 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 say

the problem is urgent. If dramatic steps aren’t taken, they say, life on Earth could become very difficult.

“We built our cities, our water systems, our food systems, our energy systems... on the assumption that you can have heat waves and cold waves, but over time, it all averages out,” says

climate scientist Katharine Hayhoe. “That assumption was accurate for the last few thousand years, but it doesn’t work anymore.”

The good news is that people are working to keep the worst effects of climate change from happening— and you can help. But first, here’s what you need to know. —►

JUNIOR.SCHOLASTIC.COM 13

ENVIRONMENT

W h a t a re g re e n h o u s e

gases, a n d h o w d o th e y

cause g lo b a l w a rm in g ?

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 (see graphic, right). Some of them occur naturally in our atmosphere. But when we burn fossil fuels (such as coal and oil) to power homes, cars, and factories, we release even more greenhouse gases, such as carbon dioxide.

The so-called greenhouse effect is a good thing—to a certain extent. Without it, our planet would be a frozen wasteland. The problem is that we are producing too much of these greenhouse gases. Since the Industrial R evolution, 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 H o w d o w e k n o w th a t

h u m an a c t iv ity is

re s p o n s ib le fo r th e in c re a s e

in g re e n h o u s e gases?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, many scientists have concluded. Experts have also looked at the natural factors known to affect Earth’s temperature and believe that these factors are not changing nearly enough to cause the current warming.

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b y E a r th ’s s u rfa c e .

How the Greenhouse Effect Works

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g a s e s in th e a ir re s u lts In g lo b a l

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3 If Earth is gettingwarmer, why is it still 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 chart, below).

“Two weeks of really cold temperatures don’t negate decades of warming,” says Jake Crouch of the National Oceanic and Atmospheric Administration.

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.

“The fact that this could be taken away and is tied to climate has been

Som aliaD R O U G H T K ids w a it fo r a id in a re fu g e e ca m p . M illio n s o f S om alis a re s tru g g lin g to fin d fo o d a fte r d ro u g h t k ille d o ff th e ir c ro p s and liv e s to c k .

a real eye-opener,’’says Colin Robertson, a Canadian geography professor who tracks ice-skating conditions in North America.

4 1s clim ate change to blame for all the recent

wild weather?Scientists have published strong evidence that the warming 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 climate change 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 Hayhoe, “takes the natural risks that we’ve always faced and exacerbates them.”

Tracking the W arm ing TrendScientists began recording

Earth’s average global tem peratu re in the 1880s.Nine o f the 10 hottest years

on record took place in the

21st century. How m any have

occurred since 2010?Note: Average global temperature includes land and ocean surface areas.

2016201520172014201020132005200919982012

SOURCE: National Oceanic and Atmospheric Administration

5 W hy are the seas rising— and how fast?

Sea water levels are rising for two main reasons. The oceans are getting warmer—and water expands as it heats up, causing sea levels to rise. Plus, melting glaciers and ice sheets are adding more water to the oceans (see map, p. 16).

The seas are now rising at an average rate of about 1 foot per century. If that were to continue, the increase would probably be manageable, some experts —►

JUNIOR.SCHOLASTIC.COM IS

ENVIRONMENT

say. The risk is that the rate will increase even more. Because of the changes that have already happened, some experts fear an eventual sea level rise of more than 20 feet. That’s enough to flood many coastal cities, but just how long it will take to happen is unclear. Our best bet, experts say, is to try to slow the process of sea level rise by cutting emissions.

6 W h ic h p la c e s w ill be

th e f irs t to fe e l th e

e ffe c ts o f c lim a te ch an g e?People around the world are already feeling the effects. In Cape Town, South Africa, for example, years of warmer weather—coupled with less rainfall—have led to three straight years of drought. The city of 4 million people now faces a water shortage so extreme that its water supply may run out in 2019.

In other places, too much water is the problem. Because of sea level rise, the Marshall Islands in the Pacific Ocean flood frequently and

Shrinking Arctic IceThe A rctic is warm ing

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next generation.

could be unfit for human habitation within decades, scientists say.

7 So w h a t ’s th e w o rs t-c a s e

scen ario ?Over the next 25 or 30 years, the climate is likely to continue to warm, causing more extreme weather, scientists say.

In the long term, if greenhouse gas emissions rise unchecked, climate effects could become so

severe that they lead to unrest in some countries and produce waves of refugees—as well as eventually cause a mass extinction of both plants and animals.

8 C an th e w a rm in g

b e s to p p e d ?Scientists say the warming can be slowed to a potentially manageable pace—z/humans stop producing greenhouse gas emissions. Some countries, such as Sweden, have already seen their emissions fall after investing in renewable energy. Other countries have set emissions limits for power plants. But experts say we need to do much more to avoid the worst effects of climate change.

9 W h a t e lse a re c o u n trie s

d o in g to h e lp p re v e n t

c lim a te chan g e?Nearly all 196 countries have signed a pact known as the Paris Agreement, which took effect in 2016. The agreement is a vow to voluntarily limit future greenhouse gas emissions.

The goal is to keep Earth's temperature from rising more than 3.6 degrees Fahrenheit this century.

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That would “hold warming to something we actually can largely adapt to without fundamental changes and impacts on our civilization,” says Hayhoe.

Is the U.S. dropping out of the agreement?

That’s the plan, but formally exiting the deal will take a while. Last year, President Donald Trump said that the U.S.—the second-largest emitter of carbon dioxide after China—would withdraw from the Paris Agreement. He says the pact imposes unfair environmental standards on American businesses and could hurt the economy.

However, under the rules of the deal, the soonest any country can drop out is November 4, 2020. (That’s coincidentally the day after the next U.S. presidential election.)

In the meantime, a growing number of U.S. cities, businesses, universities, and individuals have pledged to reduce greenhouse gas

emissions on their own in order to help meet the original Paris goals.

Can we get energy without producing so

many greenhouse gases?Yes, and those alternative energy sources may end up being cheaper than burning fossil fuels, some scientists say. Wind turbines, solar panels, hydroelectric dams, and nuclear power plants produce among the fewest emissions. Converting to such power sources would be more expensive now, but ultimately they could pay for themselves by reducing climate damage and health problems associated with air pollution.

This is all pretty overwhelming. What

can I personally do about it?A lot, actually. You can start by cutting greenhouse gas emissions in easy ways, like making sure the lamps in your house use energy-

efficient bulbs and turning off the lights when you leave a room. Also, wasting less food helps because uneaten or spoiled food ends up in landfills and releases methane, a greenhouse gas. Walk, bike, or opt for public transportation when possible to help curb emissions and air pollution.

You can also try to shop at businesses that are working to reduce their carbon dioxide emissions—and use social media to encourage other companies to reduce their emissions as well.

Finally, share what you have learned about climate change with your friends and family. After all, Hayhoe says, “talking about it is one of the most important things we can do.” ♦

Additional reporting by TheNewYork

Times and Tricia Culligan

CORE QUESTION What are the main ways climate change is affecting people?

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