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1.The world is getting warmer.

Global temperature, difference from 20th century average, in degrees Fahrenheit

-0.9° F

1.7° F

Earth’s temperature goes up and down from year to year—but over the past half century it has gone up a lot.

The heat in 2016 broke the historic record set in 2015, which broke the one from 2014. Last year’s average global surface temperature, compiled from measurements made by thousands of weather stations, buoys, and ships, was 1.69 degrees Fahrenheit warmer than the 20th-century average. Satellites probing the atmosphere also have documented a clear warming trend.

Global average surface temperature, difference from 20th century average (in degrees Fahrenheit)

SOURCE: NOAA

2.It’s because of us.

1870

1960

2016

Atmospheric carbon dioxide departures from the 19th century average, parts per million

Carbon dioxide warms the planet, and we’ve increased the amount in the air by nearly half, mostly since the 1960s.

El Niño added to last year’s temperature record by temporarily releasing heat from the Pacific. But no natural cause explains the half-century warming trend. The sun’s output cycles up and down every 11 years; volcanic eruptions sporadically cool the planet. Only CO2 and other human-emitted greenhouse gases have gone steadily up, forming a thickening blanket that traps heat at the Earth’s surface.

Atmospheric carbon dioxide, 1800-2016, in parts per million

SOURCES: NOAA, Carbon Dioxide Information Analysis Center

3.We’re sure.

These scientists have concluded humans are causing global warming

These scientists haven’t

More than nine out of 10 climate scientists agree: Our carbon emissions are the main cause of global warming.

We’ve known about the greenhouse effect since the 1800s. Swedish physicist Svante Arrhenius even predicted in 1896 that carbon dioxide from coal burning would warm the planet. He saw it as a good thing—and just how bad it will turn out to be is still a matter for debate. But it’s real, and it’s dangerous.

A 2013 review of 4,014 research papers found that 97 percent (and 98 percent of the authors) said humans cause global warming.

Papers

Authors

1.9% Reject

1 Uncertain

97.1 Agree

1.2 Reject

0.4 Uncertain

98.4 Agree

4.Ice is melting fast.

Extent of Arctic sea ice at its annual minimum in September, 1979-2016

Arctic sea ice is shrinking, and glaciers are retreating worldwide. Seas could rise three feet by 2100—or maybe more.

The Arctic has warmed more than the rest of the planet, and its ice cover has thinned and shrunk. Last September, at the end of the summer melt season, the ice extent was about 825,000 square miles smaller than the long-term average—a loss equal to the size of Alaska and California combined. That loss speeds the warming, as sunlight is absorbed by dark ocean instead of reflected into space by ice.

Extent of Arctic ice, September average, millions of square miles

Melting sea ice doesn’t raise sea level—it’s already in the water—but melting land ice does. Mountain glaciers are in global retreat. The total sea level rise of eight or nine inches since 1900 has contributed to a sharp increase in flooding along coasts. During Superstorm Sandy, for example, floods and winds caused $68 billion in damage on the U.S. East Coast.

The big threat is the ice sheets covering Greenland and Antarctica. They hold enough ice to raise seas more than 200 feet—and they’re losing it. When Earth was just a bit warmer, 125,000 years ago, they seem to have lost a lot: Sea levels were 20 to 30 feet higher. Such a rise today would swamp coastal cities.

SOURCE: National Snow and Ice Data Center

5.Weather is wreaking havoc.

Global natural disasters, 1980 compared to 2016

Storms

Floods and landslides

Droughts, heat waves, and forest fires

Worldwide, the number of climate-related disasters has more than tripled since 1980.

In the crapshoot that is our weather, climate change loads the dice. It doesn’t cause a particular drought or storm, but it can make such events more likely or intense—a lot more, in the case of heat waves. The extraordinary heat wave that killed some 70,000 people in Europe in 2003 should have been a once-in-500-years event; at the current level of global warming, it has become a once-in-40-years event, according to a study published last year. In Paris alone, that analysis found, climate change caused 506 excess deaths in 2003. If it continues unchecked, another recent study said, by late this century people living along the Persian Gulf may face many days so hot that it will be unsafe to go outside.

It’s not just the heat: Global warming adds moisture to the air, removing it from land and ocean. Where rain is lacking, it makes the drought worse. When rain or snow falls, it’s more likely to be extreme; think of the 2016 floods in Paris or Houston. How climate change affects hurricanes and other tropical cyclones is less certain. But by heating the ocean—the storms’ energy source—it’s likely to make them more intense, if less frequent.

Global natural disasters, 1980-2016

Earthquakes, tsunamis, volcanic activity

Storms

Floods and landslides

Droughts, heat waves, and forest fires

SOURCE: Munich RE Natcatservice

6.Species are being disrupted.

Animals and plants are already vanishing from parts of their range that are now too hot. Extinctions come next.

In 2016 scientists announced that the last Bramble Cay melomys, a ratlike rodent found on one low-lying island in Australia’s Torres Strait, had vanished, the victim of forces including rising seas. It’s being called the first documented case of a mammal being driven to extinction by climate change. More will surely follow.

Of 976 species surveyed in a 2016 study, 47 percent had vanished from areas they had previously occupied on the warm edge of their range.

47% species vanished

Rising temperatures are depressing some plant and animal populations, driving species toward the poles, shifting migrations and behavior. Populations of Adélie penguins on the Antarctic Peninsula have plummeted. An Arctic shorebird called the red knot is getting smaller. Ice loss is forcing walruses by the thousands onto land in Alaska. Entire regions are being transformed: Alpine ecosystems from the Rockies to the Swiss Alps are being squeezed off mountaintops. The exceptional ocean warmth of the past few years has triggered coral bleaching and die-offs at reefs around the world.

There will be winners. For now, humpback whales are thriving in newly ice-free waters off Antarctica. Sea urchins too are proving to be resilient. But climate change isn’t the only threat that spreading human populations impose on other species; we’re also fragmenting and destroying natural habitats. Some species will adapt to the jarring changes in their world—but how many, and for how long?

SOURCES: John J. Wiens, University of Arizona; Mark C. Urban, University of Connecticut

7.We can do something about it.

Projected growth of energy sources as a percentage of their 1990 totals

Renewables

Liquid fuels

Natural gas

Coal

Nuclear

Renewables, the fastest-growing energy source, are projected to triple by 2040.

Free markets are often lauded for their efficient results. In this connected age, there’s something like a free market of ideas. So ask yourself: If climate change weren’t a serious danger, would 195 countries have signed the Paris Agreement, pledging to try to keep the warming below 2°C (3.6°F)?

Though shadowed by the new U.S. administration’s threat to withdraw from it, the agreement stands as one hopeful sign. The graph below, right, shows another: The cost of solar energy is plummeting. Even without a carbon tax—the most efficient way to wean an economy off fossil fuels—renewables soon may be cheaper sources of electricity. Worldwide, they accounted for more than half the new generating capacity in 2015. In the U.S., solar now employs more people than coal, oil, and gas combined.

World energy consumption, 1990-2040, quadrillion Btus

Cost by energy type, dollars per megawatt hour

The switch from fossil fuels is still just beginning. Every little bit matters: Every ton of CO² we emit melts 32 square feet of Arctic ice, according to a 2016 study, which means the average American melts 525 square feet a year. Every energy-saving building, retired gas-guzzler, and acre of preserved forest helps. But none of it will help much if the world doesn’t switch to a carbon-free energy supply soon.

SOURCES: EIA, Bloomberg New Energy Finance

Design and development: Kennedy Elliott and Jason Treat, text: Rob Kunzig, research: Ryan Williams, NGM staff

Seven things to know about climate change

It’s not a myth, hoax or a conspiracy among scientists. As we argue about the path we take, let’s recall the facts that compel the journey.

Read more on our Climate Hub.



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