Seven Things To Know About Climate Change

National Geographic - Kennedy Elliott | Jason Treat | Rob Kunzig | Ryan Williams

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.

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

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

SOURCE: NOAA

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.

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

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

SOURCES: NOAA, Carbon Dioxide Information Analysis Center

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.

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

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

SOURCE: Cook et al. Quantifying the consensus on anthropogenic global warming in the scientific literature. 2013.

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.

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

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

SOURCE: National Snow and Ice Data Center

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.

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.

5.Weather is wreaking havoc.
Worldwide, the number of climate-related disasters has more than tripled since 1980.

SOURCE: Munich RE Natcatservice

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.

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

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.

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

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?

7. We can do something about it.
Renewables, the fastest-growing energy source, are projected to triple by 2040.

SOURCES: EIA, Bloomberg New Energy Finance

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.

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.

Links

• ‘A Tsunami In The Sky’: Climate Change Is Melting Bhutan’s Glaciers And The Danger Is Real
• How Much Will The Planet Warm If Carbon Dioxide Levels Double?
• Sensitive Planet: Scientists Narrow The Expected Heating From CO2 Rise
• Major New Climate Study Rules Out Less Severe Global Warming Scenarios
• Pandemic Shows Climate Has Never Been Treated As Crisis, Say Scientists
• Climate Change: Siberian Heatwave 'Clear Evidence' Of Warming
• Larger Waves In Store As The Planet Warms
• Experts Issue Dire Warning That Rising Temperatures May Exceed Crucial Threshold Within 5 Years