Record floods. Raging storms. Deadly heat. 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.

What causes climate change?

A variety of factors, both natural and human, can influence the earth’s climate system. 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.  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.

How will climate change affect humans? 

As climate change transforms global ecosystems, it affects everything from the places we live to the water we drink to the air we breathe.

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.

Climate change will also increase the intensity of air pollution. 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).

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.

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.

Climate change also places increasing pressure on wildlife to adapt to changing habitats—and fast. 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.

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.

Tackling global climate change is a Herculean task, one that depends on international consensus and the efforts of communities, companies, and individuals alike. 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.

Read the full article about climate change by Melissa Denchak at Natural Resources Defense Council.