CAUSES AND EFFECTS OF CLIMATE CHANGE
Glaciers are melting, sea levels are rising, cloud forests are dying, and wildlife is scrambling to keep pace. It has become clear that humans have caused most of the past century's warming by releasing heat-trapping gases as we power our modern lives. Called greenhouse gases, their levels are higher now than at any time in the last 800,000 years.
We often call the result global warming, but it is causing a set of changes to the Earth's climate, or long-term weather patterns, that varies from place to place. While many people think of global warming and climate change as synonyms, scientists use “climate change” when describing the complex shifts now affecting our planet’s weather and climate systems—in part because some areas actually get cooler in the short term.
Climate change encompasses not only rising average temperatures but also extreme weather events, shifting wildlife populations and habitats, rising seas, and a range of other impacts. All of those changes are emerging as humans continue to add heat-trapping greenhouse gases to the atmosphere, changing the rhythms of climate that all living things have come to rely on.
What will we do—what can we do—to slow this human-caused warming? How will we cope with the changes we've already set into motion? While we struggle to figure it all out, the fate of the Earth as we know it—coasts, forests, farms, and snow-capped mountains—hangs in the balance.
An iceberg melts in the waters off Antarctica. Climate change has accelerated the rate of ice loss across the continent.
PHOTOGRAPH BY PAUL NICKLEN, NAT GEO IMAGE COLLECTION
As sea levels rise, salty ocean waters encroach into Florida’s Everglades. Native plants and animals struggle to adapt to the changing conditions.
PHOTOGRAPH BY KEITH LADZINSKI, NAT GEO IMAGE COLLECTION
The western U.S. has been locked in a drought for years. The dry, hot weather has increased the intensity and destructiveness of forest fires.
PHOTOGRAPH BY PAUL NICKLEN, NAT GEO IMAGE COLLECTION
Bunches of oil palm fruit are harvested by hand and then trucked to a mill in mainland Malaysia, where they are processed. Ancient forests around the tropics are being cut down to
… PHOTOGRAPH BY PASCAL MAITRE, NAT GEO IMAGE COLLECTION
In the high plains of Bolivia, a man surveys the baked remains of what was the country’s second largest lake, Lake Poopó. Drought and management issues have caused the lake to dry up.
PHOTOGRAPH BY MAURICIO LIMA, NAT GEO IMAGE COLLECTION
Climate change is impacting flora and fauna across the Arctic. Although scientists don't know specifically what killed this individual polar bear, experts warn that many of the bears are having trouble finding food as the sea ice they historically relied on thins and melts earlier.
PHOTOGRAPH BY CRISTINA MITTERMEIER, NAT GEO IMAGE COLLECTION
Lake Urmia, in Iran, is a critical bird habitat and used to be a popular tourist destination. It is drying up because of climate change and management issues.
PHOTOGRAPH BY NEWSHA TAVAKOLIAN, NAT GEO IMAGE COLLECTION
The Scherer power plant in Juliet, Georgia, is the largest coal-fired power plant in the U.S. It burns 34,000 tons of coal daily, pumping over 25 million tons of carbon dioxide into the atmosphere each year.
PHOTOGRAPH BY ROBB KENDRICK, NAT GEO IMAGE COLLECTION
Ice melts on a mountain lake. Lakes around the world are freezing less and less over time, and in a few decades, thousands of lakes around the world may lose their winter ice cover entirely.
PHOTOGRAPH BY ORSOLYA HAARBERG, NAT GEO IMAGE COLLECTION
The Amazon is losing the equivalent of nearly one million soccer fields of forest cover each year, much of which is cut down to make way for agriculture. When forest is lost, the carbon it sequestered ends up in the atmosphere, accelerating climate change.
PHOTOGRAPH BY FRANS LANTING, NAT GEO IMAGE COLLECTION
In Glacier National Park, forests are feeling the effects of early snowmelt and long, dry summers. The stresses on the park's flora are exacterbated by climate change.
PHOTOGRAPH BY KEITH LADZINSKI, NAT GEO IMAGE COLLECTIONUnderstanding the greenhouse effect
The "greenhouse effect" is the warming that happens when certain gases in Earth's atmosphere trap heat. These gases let in light but keep heat from escaping, like the glass walls of a greenhouse, hence the name.
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Sunlight shines onto the Earth's surface, where the energy is absorbed and then radiate back into the atmosphere as heat. In the atmosphere, greenhouse gas molecules trap some of the heat, and the rest escapes into space. The more greenhouse gases concentrate in the atmosphere, the more heat gets locked up in the molecules.
Scientists have known about the greenhouse effect since 1824, when Joseph Fourier calculated that the Earth would be much colder if it had no atmosphere. This natural greenhouse effect is what keeps the Earth's climate livable. Without it, the Earth's surface would be an average of about 60 degrees Fahrenheit (33 degrees Celsius) cooler.
A polar bear stands sentinel on Rudolf Island in Russia’s Franz Josef Land archipelago, where the perennial ice is melting.
PHOTOGRAPH BY CORY RICHARDS
In 1895, the Swedish chemist Svante Arrhenius discovered that humans could enhance the greenhouse effect by making carbon dioxide, a greenhouse gas. He kicked off 100 years of climate research that has given us a sophisticated understanding of global warming.
Levels of greenhouse gases have gone up and down over the Earth's history, but they had been fairly constant for the past few thousand years. Global average temperatures had also stayed fairly constant over that time—until the past 150 years. Through the burning of fossil fuels and other activities that have emitted large amounts of greenhouse gases, particularly over the past few decades, humans are now enhancing the greenhouse effect and warming Earth significantly, and in ways that promise many effects, scientists warn.
Aren't temperature changes natural?
Human activity isn't the only factor that affects Earth's climate. Volcanic eruptions and variations in solar radiation from sunspots, solar wind, and the Earth's position relative to the sun also play a role. So do large-scale weather patterns such as El Niño.
But climate models that scientists use to monitor Earth’s temperatures take those factors into account. Changes in solar radiation levels as well as minute particles suspended in the atmosphere from volcanic eruptions, for example, have contributed only about two percent to the recent warming effect. The balance comes from greenhouse gases and other human-caused factors, such as land use change.
The short timescale of this recent warming is singular as well. Volcanic eruptions, for example, emit particles that temporarily cool the Earth's surface. But their effect lasts just a few years. Events like El Niño also work on fairly short and predictable cycles. On the other hand, the types of global temperature fluctuations that have contributed to ice ages occur on a cycle of hundreds of thousands of years.
For thousands of years now, emissions of greenhouse gases to the atmosphere have been balanced out by greenhouse gases that are naturally absorbed. As a result, greenhouse gas concentrations and temperatures have been fairly stable, which has allowed human civilization to flourish within a consistent climate.
Greenland is covered with a vast amount of ice—but the ice is melting four times faster than thought, suggesting that Greenland may be approaching a dangerous tipping point, with implications for global sea-level rise.
PHOTOGRAPH BY MICHAEL MELFORD, NAT GEO IMAGE COLLECTION
Now, humans have increased the amount of carbon dioxide in the atmosphere by more than a third since the Industrial Revolution. Changes that have historically taken thousands of years are now happening over the course of decades.
Why does this matter?
The rapid rise in greenhouse gases is a problem because it’s changing the climate faster than some living things can adapt to. Also, a new and more unpredictable climate poses unique challenges to all life.
Historically, Earth's climate has regularly shifted between temperatures like those we see today and temperatures cold enough to cover much of North America and Europe with ice. The difference between average global temperatures today and during those ice ages is only about 9 degrees Fahrenheit (5 degrees Celsius), and the swings have tended to happen slowly, over hundreds of thousands of years.
But with concentrations of greenhouse gases rising, Earth's remaining ice sheets such as Greenland and Antarctica are starting to melt too. That extra water could raise sea levels significantly, and quickly. By 2050, sea levels are predicted to rise between one and 2.3 feet as glaciers melt.
As the mercury rises, the climate can change in unexpected ways. In addition to sea levels rising, weather can become more extreme. This means more intense major storms, more rain followed by longer and drier droughts—a challenge for growing crops—changes in the ranges in which plants and animals can live, and loss of water supplies that have historically come from glaciers.
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