Global Climate Change: What You Need to Know

The lowdown on the earth’s central environmental threat.
AIRS instrument on NASA’s Aqua spacecraft shows high carbon dioxide concentrations in the Northern Hemisphere.

NASA/Goddard Space Flight Center Scientific Visualization Studio/NASA/JPL AIRS Project

Record floods. Raging storms. Deadly heat. Climate change manifests itself in myriad ways, and it’s the ultimate equalizer: a challenge faced by every living being. Here are the basics on what causes climate change, how it’s affecting the planet, and what we can do about it.

What is climate change?

The term climate refers to the general weather conditions of a place over many years. In the United States, for example, Maine’s climate is cold and snowy in winter while South Florida’s is tropical year-round. Climate change is a significant variation of average weather conditions—say, conditions becoming warmer, wetter, or drier—over several decades or more. It’s that longer-term trend that differentiates climate change from natural weather variability. And while “climate change” and “global warming” are often used interchangeably, global warming—the recent rise in the global average temperature near the earth’s surface—is just one aspect of climate change.

How is climate change measured over time?

Earth-orbiting satellites, remote meteorological stations, and ocean buoys are used to monitor present-day weather and climate, but it’s paleoclimatology data from natural sources like ice cores, tree rings, corals, and ocean and lake sediments that have enabled scientists to extend the earth’s climatic records back millions of years. These records provide a comprehensive look at the long-term changes in the earth’s atmosphere, oceans, land surface, and cryosphere (frozen water systems). Scientists then feed this data into sophisticated climate models that predict future climate trends—with impressive accuracy.

What causes climate change?

The mechanics of the earth’s climate system are simple. When energy from the sun is reflected off the earth and back into space (mostly by clouds and ice), or when the earth’s atmosphere releases energy, the planet cools. When the earth absorbs the sun’s energy, or when atmospheric gases prevent heat released by the earth from radiating into space (the greenhouse effect), the planet warms. A variety of factors, both natural and human, can influence the earth’s climate system.

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Natural causes of climate change

As we all know, the earth has gone through warm and cool phases in the past, and long before humans were around. Forces that contribute to climate change include the sun’s intensity, volcanic eruptions, and changes in naturally occurring greenhouse gas concentrations. But records indicate that today’s climatic warming—particularly the warming since the mid-20th century—is occurring much faster than ever before and can’t be explained by natural causes alone. According to NASA, “These natural causes are still in play today, but their influence is too small or they occur too slowly to explain the rapid warming seen in recent decades.”

Anthropogenic causes of climate change

Humans—more specifically, the greenhouse gas (GHG) emissions we generate—are the leading cause of the earth’s rapidly changing climate. Greenhouse gases play an important role in keeping the planet warm enough to inhabit. But the amount of these gases in our atmosphere has skyrocketed in recent decades. According to the Intergovernmental Panel on Climate Change (IPCC), concentrations of carbon dioxide, methane, and nitrous oxides “have increased to levels unprecedented in at least the last 800,000 years.” Indeed, the atmosphere’s share of carbon dioxide—the planet’s chief climate change contributor—has risen by 40 percent since preindustrial times.

A waterfront factory pumping out clouds of smoke

The burning of fossil fuels like coal, oil, and gas for electricity, heat, and transportation is the primary source of human-generated emissions. A second major source is deforestation, which releases sequestered carbon into the air. It’s estimated that logging, clear-cutting, fires, and other forms of forest degradation contribute up to 20 percent of global carbon emissions. Other human activities that generate air pollution include fertilizer use (a primary source of nitrous oxide emissions), livestock production (cattle, buffalo, sheep, and goats are major methane emitters), and certain industrial processes that release fluorinated gases. Activities like agriculture and road construction can change the reflectivity of the earth’s surface, leading to local warming or cooling, too. 

Though our planet’s forests and oceans absorb greenhouse gases from the atmosphere through photosynthesis and other processes, these natural carbon sinks can’t keep up with our rising emissions. The resulting buildup of greenhouse gases is causing alarmingly fast warming worldwide. It’s estimated that the earth’s average temperature rose by about 1 degree Fahrenheit during the 20th century. If that doesn’t sound like much, consider this: When the last ice age ended and the northeastern United States was covered by more than 3,000 feet of ice, average temperatures were just 5 to 9 degrees cooler than they are now.

The effects of global climate change

According to the World Economic Forum’s 2016 Global Risks Report, the failure to mitigate and adapt to climate change will be “the most impactful risk” facing communities worldwide in the coming decade—ahead even of weapons of mass destruction and water crises. Blame its cascading effects: As climate change transforms global ecosystems, it affects everything from the places we live to the water we drink to the air we breathe.

Extreme weather

A view of the Seine river flood in Paris near Bir-Hakeim bridge, which reached a 30-year high in June 2016


As the earth’s atmosphere heats up, it collects, retains, and drops more water, changing weather patterns and making wet areas wetter and dry areas drier. Higher temperatures worsen and increase the frequency of many types of disasters, including storms, floods, heat waves, and droughts. These events can have devastating and costly consequences, jeopardizing access to clean drinking water, fueling out-of-control wildfires, damaging property, creating hazardous-material spills, polluting the air, and leading to loss of life.

Dirty air

Smog in Turin, Italy

Mike Dotta/Shutterstock

Air pollution and climate change are inextricably linked, with one exacerbating the other. When the earth’s temperatures rise, not only does our air gets dirtier—with smog and soot levels going up—but there are also more allergenic air pollutants such as circulating mold (thanks to damp conditions from extreme weather and more floods) and pollen (due to longer, stronger pollen seasons).

Health risks

The Aedes mosquito can spread serious diseases such as dengue fever, yellow fever, and the Zika virus.

U.S. Air Force/Master Sgt. Brian Ferguson

According to the World Health Organization, “climate change is expected to cause approximately 250,000 additional deaths per year” between 2030 and 2050. As global temperatures rise, so do the number of fatalities and illnesses from heat stress, heatstroke, and cardiovascular and kidney disease. As air pollution worsens, so does respiratory health—particularly for the 300 million people living with asthma worldwide; there’s more airborne pollen and mold to torment hay fever and allergy sufferers, too. Extreme weather events, such as severe storms and flooding, can lead to injury, drinking water contamination, and storm damage that may compromise basic infrastructure or lead to community displacement. Indeed, historical models suggest the likelihood of being displaced by a disaster is now 60 percent higher than it was four decades ago—and the largest increases in displacement are driven by weather- and climate-related events. (It’s worth noting that displacement comes with its own health threats, such as increases in urban crowding, trauma, social unrest, lack of clean water, and transmission of infectious diseases.) A warmer, wetter world is also a boon for insect-borne diseases such as dengue fever, West Nile virus, and Lyme disease.

Rising seas

Aerial of the Marshall Islands landscape, which are feeling the effects of rising sea levels

Erin Magee, DFAT

The Arctic is heating twice as fast as any other place on the planet. As its ice sheets melt into the seas, our oceans are on track to rise one to four feet higher by 2100, threatening coastal ecosystems and low-lying areas. Island nations face particular risk, as do some of the world’s largest cities, including New York, Miami, Mumbai, and Sydney.

Warmer, more acidic oceans

Fish and corals near Limestone Island, Indonesia


The earth’s oceans absorb between one-quarter and one-third of our fossil fuel emissions and are now 30 percent more acidic than they were in preindustrial times. This acidification poses a serious threat to underwater life, particularly creatures with calcified shells or skeletons like oysters, clams, and coral. It can have a devastating impact on shellfisheries, as well as the fish, birds, and mammals that depend on shellfish for sustenance. Rising ocean temperatures are also altering the range and population of underwater species and contributing to coral bleaching events capable of killing entire reefs—ecosystems that support more than 25 percent of all marine life.

Imperiled ecosystems

Two polar bears on a small ice floe


Climate change is increasing pressure on wildlife to adapt to changing habitats—and fast. Many species are seeking out cooler climates and higher altitudes, altering seasonal behaviors, and adjusting traditional migration patterns. These shifts can fundamentally transform entire ecosystems and the intricate webs of life that depend on them. As a result, according to a 2014 IPCC climate change report, many species now face “increased extinction risk due to climate change.” And one 2015 study showed that mammals, fish, birds, reptiles, and other vertebrate species are disappearing 114 times faster than they should be, a phenomenon that has been linked to climate change, pollution, and deforestation—all interconnected threats. On the flip side, milder winters and longer summers have enabled some species to thrive, including tree-killing insects that are endangering entire forests.

Climate change facts

Despite what climate deniers and fossil fuel lackeys claim—for instance, that the science on global warming is “far from settled”—there’s nothing to debate; climate change is a reality. In its most recent report, the IPCC—the foremost international scientific body for the assessment of climate change—states, “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen.” Our last decade—2000 to 2009—was hotter than any other decade in at least the past 1,300 years. Analyses indicate that 2016 was the hottest year on record. The previous record year was 2015. Before that, 2014.

The responsibility to reverse this worrying trend lies with us. At least 97 percent of actively publishing climate scientists endorse the consensus position that humans are the lead drivers of climate change. As the IPCC states with its highest degree of confidence, “It is extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in GHG concentrations and other anthropogenic forcings together.”

Climate change solutions

We can mitigate global climate change and help stem its detrimental impacts, but doing so will require tackling its root cause: pollution from burning fossil fuels.

Paris climate agreement

At the 2015 Paris Climate Change Conference, nearly every nation on earth committed to actions aimed at shifting away from dirty fossil fuels and toward cleaner, smarter energy options in order to limit global temperature rise this century to 2 degrees Celsius—or 1.5 degrees Celsius, if possible.

For its part, the United States—the second-largest contributor to global emissions, after China—pledged to cut its output by 26 percent to 28 percent (relative to 2005 levels) by 2025. Making good on that pledge, however, will require the country to fully implement the Clean Power Plan, which establishes the first national limits on carbon pollution from power plants. We must also move forward with the Obama administration’s Climate Action Plan, which includes steps to promote renewable energy sources, increase fuel economy standards, prioritize energy efficiency, and reduce emissions of greenhouse gases beyond carbon, such as methane.

Fast-forward to today, and President Trump has threatened to abandon the Paris climate agreement and to eliminate “harmful and unnecessary policies such as the Climate Action Plan.” Indeed, his America First Energy Plan not only promises to shackle the United States to climate-polluting fossil fuels but also ignores the ongoing clean energy revolution, which is creating millions of jobs and saving billions of dollars through investments in solar, wind, and other renewable energy resources.

Pulling out of the Paris climate agreement and reneging on our climate commitments will scuttle the United States’ global lead on climate change and put our environment, prosperity, and national security at risk. It will also fly in the face of the 71 percent of Americans, including 57 percent of Republicans, who support U.S. participation in the accord. “Americans know that if we retreat from the Paris agreement, we’re retreating from our fundamental obligation to leave our children a livable planet,” says NRDC President Rhea Suh. We must fight to keep a seat at the table, and to ensure the Trump administration doesn’t water down the climate commitments to which we agreed.

Climate action at home

Tackling global climate change is a Herculean task, one that depends on international consensus and the efforts of communities, companies, and individuals alike. To that end, California, Illinois, Iowa, and other states are championing clean energy industries, such as solar and wind; cities like Philadelphia and New York are taking action to mitigate climate change and bolster climate resilience; and in November 2016, hundreds of American companies voiced their support for low-emissions policies and the Paris climate agreement. There are myriad ways that you can help, too. Picking up the phone to call Congress about environmental policies that matter, supporting renewable energy projects, and prioritizing fuel and energy efficiency will not only curb individual carbon emissions but bolster clean alternatives to dirty fossil fuels. We must all step up—and now.

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