Long-term warming trends and increases in extreme weather events have the potential to impact all life on Earth. Even though at least 97 percent of climate scientists agree that human activities have contributed to rising global temperatures, the predominance and causes of these phenomena continue to be debated and many Americans deny global warming.Read the overms global warming and climate change are often used interchangeably, they have different meanings. Climate change describes long-term shifts in Earth's weather patterns that affect temperature, humidity, wind, cloud cover, and precipitation. Global warming refers explicitly to an increase in Earth's average surface temperatures caused by human activities, primarily the burning of fossil fuels. Anthropogenic climate change refers to changes in the climate caused by human activity, particularly industrialization and agricultural practices that release pollutants into the atmosphere.

Overwhelming scientific evidence supports the existence of both global warming and climate change. Through the United Nations' (UN) Intergovernmental Panel on Climate Change (IPCC), thousands of scientists work together to collect and analyze the latest available research related to climate change, its effects, and potential responses. In an interim update to its Sixth Assessment Report (AR6) in 2023, the IPCC estimated that global surface temperatures increased by 1.1°C (1.98°F) between the latter half of the nineteenth century and the first two decades of the twenty-first century. The IPCC has linked climate change and global warming to the increased occurrence and severity of storms, floods, droughts, and wildfires, warning that such disasters will increase further if temperatures continue to rise. The scientists' group also identifies water availability and food production as well as health and wealth being as experiencing observable, widespread, and substantial changes related to climate change. These threats have led scientists to identify global warming and climate change as a climate crisis. The IPCC recognizes human activity, particularly industrialization and certain agricultural practices that release carbon dioxide (CO2), as the primary driver of global warming and climate change.

Despite substantial evidence and a consensus among the scientific community, a vocal minority continues to challenge the science behind climate change. These critics characterize climate change as a natural phenomenon and dispute assertions that human activity has contributed to rising global temperatures. This position may be referred to as climate denial, and those who reject the scientific consensus are considered climate deniers. Fossil fuel companies often provide financial support to politicians, media campaigns, and organizations that promote climate denial.

MAIN IDEAS

Climate change refers to long-term shifts in weather patterns. Global warming is the increase in the planet's average surface temperatures caused by human activities such as the burning of fossil fuels.

Causes of climate change related to human activity are referred to as anthropogenic. Natural causes of climate change are called naturogenic.

Earth's atmosphere contains several gases that trap heat from the sun and prevent it from escaping into space. These gases are called greenhouse gases (GHGs).

July 2023 was the hottest month ever recorded on Earth.

Global warming has the potential to cause disruptions in the food supply, harm ecosystems and wildlife habitats, and threaten the planet's biodiversity.

Countries that experience the harshest effects of climate change are often low- and middle-income countries who contribute fewer greenhouse gas emissions than wealthier countries that do not experience the effects so intensely.

The United States has joined other countries in making commitments to fight climate change, but that commitment has largely depended on the country's leadership.

Though the administration of President Joe Biden has taken more aggressive steps to combat the climate crisis, critics question whether these steps will meet the administration's ambitious goals and whether those goals are sufficient.

CAUSES OF CLIMATE CHANGE

Earth's atmosphere contains several gases that trap heat from the sun and prevent it from escaping into space. This phenomenon is known as the greenhouse effect, and the gases are called greenhouse gases (GHGs). The main GHGs in nature are carbon dioxide, methane, and nitrous oxide. Without the greenhouse effect, Earth would be too cold to support life. Over time, the amount of GHGs trapped in Earth's atmosphere has increased significantly, causing worldwide temperatures to rise.

Natural processes on Earth constantly create and destroy GHGs. For example, plant and animal matter decay produce carbon dioxide, which plants then absorb during photosynthesis. This natural cycle stabilizes atmospheric levels of carbon dioxide. Climate change scientists at the National Aeronautics and Space Administration (NASA) and other federal and international agencies recognize that natural factors, including volcanic activity and shifts in the planet's crust, continue to play a role in climate change. However, they generally agree that these factors alone do not explain the substantial rise in Earth's temperature. Natural causes of climate change are referred to as naturogenic, while causes of climate change related to human activity are called anthropogenic.

Earth's vegetation releases and absorbs over two hundred billion metric tons of carbon dioxide annually. Human activities, such as the burning of fossil fuels, add approximately seven billion metric tons per year. Climate scientists believe the cumulative effect of this additional carbon dioxide has had a dramatic impact on the atmosphere. Deforestation has also contributed to this increase by releasing carbon dioxide stored in trees and eliminating forests that would continue to absorb many tons of carbon dioxide. According to the National Oceanic and Atmospheric Administration (NOAA), as of 2023 the amount of carbon dioxide in the atmosphere had increased by 50 percent since the beginning of the Industrial Revolution in Great Britain in the eighteenth century.

Increased levels of other GHGs, such as nitrous oxide and methane, have also resulted from human activity. Several agricultural and industrial processes, such as the use of certain fertilizers in farming, produce extensive amounts nitrous oxide. Methane emissions come from fossil fuel production, landfills, and livestock. Though much smaller quantities of these gases exist in Earth's atmosphere, some scientists believe they cause more harm than carbon dioxide. Methane, for example, is about twenty-one times as potent as carbon dioxide at trapping heat. Humans have also created and released GHGs that do not occur in nature. These include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). These gases, released during industrial processes such as aluminum production and electrical transmission, trap thousands of times more heat in the atmosphere than carbon dioxide.

CLIMATE CHANGE PREDICTIONS

A broad consensus exists in the scientific community that the consequences of climate change may be devastating, though the exact nature of the changes is difficult to predict. No model to chart climate patterns has had complete accuracy. For instance, most climate models failed to predict a slowdown in rising temperatures starting in 1998 and ending in 2012. The slowdown was attributed to volcanic eruptions that blocked out the sun and cooled temperatures, low levels of solar activity, and naturally occurring variability. Similarly, some predictions have underestimated threats.

In its initial assessment of rising sea levels in 1990, the IPCC initially anticipated a sea level rise of 1.9 millimeters per year from that year onward. However, as of 2023, the IPCC reports that sea levels rose at a rate of 3.7 millimeters per year between 2006 and 2018. Sea level rise contributes to increased flooding and the damage caused by extreme storms such as hurricanes in coastal cities. The IPCC predicts that sea level rise could threaten as many as one billion people living in low-lying cities and communities by 2041, noting the threats to livelihoods, cultural heritage, and the existence of many island nations.

US PUBLIC OPINION ON CLIMATE CHANGE

The effects of human activities on global warming and climate change are acknowledged and accepted by most people in the United States. According to annual polls conducted by Gallup since 2001, the public's beliefs in anthropogenic climate change has increased. In 2023, 62 percent of Americans accepted that human activities cause climate change (up from 61 percent in 2001), 60 percent believed that the effects have begun (up from 54 percent), and 46 percent stated that global warming will soon pose a serious threat (up from 31 percent).

Researchers have observed a strong correlation between Americans' political affiliations and their acceptance of climate science and levels of concern about global warming. In 2023, about 85 percent of Democrats believed the effects of global warming were already apparent, and 88 percent believed humans caused them. In comparison, only 33 percent of Republicans agreed with the first statement and 29 percent agreed with the second. Most independents believed both statements (61 and 66 percent, respectively). However, further analysis by Gallup in 2022 revealed that Republicans under age fifty-five expressed greater concern about global warming than those age fifty-five and older but still significantly fewer than Democrats or Independents of any age group.

EFFECTS OF GLOBAL WARMING

The potential consequences of global warming remain an issue of great debate and uncertainty. However, most experts predict dramatic and severe problems for future generations. Warmer oceans could result in stronger and more frequent hurricanes. As temperatures climb, some regions could experience frequent heat waves that bring devastating droughts and wildfires. In the United States, the 2023 summer season experienced a series of heat waves that broke temperature records in different parts of the country, particularly in Washington and Oregon. In July 2023, heat waves also affected many countries in the Northern Hemisphere, including Canada, China, and some European countries. NASA has confirmed that July 2023 was the hottest month ever recorded on Earth by a significant margin, identifying global warming as the principal causal factor.

Climate change has been linked to severe, exceptional droughts across several western states, including Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, and Washington. Climate scientists refer to this phenomenon a "megadrought," and it has contributed to massive wildfires in the first decades of the twenty-first century.

From 2018 to 2021, California and Oregon endured massive wildfires that burned millions of acres and led to the displacement of thousands of residents, widespread destruction of property, and the deaths of dozens of people. California had a record-breaking wildfire season in 2020, including the state's first gigafire—a blaze that burned over one million acres of land. By the end of the year, wildfires burned more than four million acres throughout the state. Though wildfires were less frequent throughout the United States from 2022 to 2023 than in the preceding several years, the effects of global warming and the federal and state governments' lack of emergency preparedness led to one of the deadliest wildfires in recorded history. In August 2023 a small brush fire that a broken powerline may have caused started burning just outside the town of Lahaina on the island of Maui in Hawaii. In just a few minutes, winds blew the fire toward town, devouring wooden buildings, telephone and electric power lines, and water pipes. Without enough water pressure, Lahaina's fire department failed to contain the wildfire, and with the town's communication and power systems down, residents were not immediately alerted. As of September 2023, authorities had confirmed that ninety-seven people had been killed in the wildfire and thirty-one individuals were still missing in what had become the eleventh deadliest wildfire in world history.

A megadrought could also lead to water shortages. For example, the US government issued its first Tier 1 federal water shortage declaration in August 2021 for the Colorado River. The river provides water for several US states and parts of Mexico. The first cuts to state water supplies took effect in October in Arizona and Nevada. Upon revisiting the issue in August 2022, the government intensified its alarm, raising the classification to a Tier 2 federal water shortage and issuing drastic cuts to state water allowances. In August 2023, the government announced that the Colorado River water shortage would return to Tier 1 in 2024 and that water restrictions would be eased. The government's decision came after an unusually high amount of snowpack formed on the mountains near the Colorado River during the 2022–2023 winter season.

Many coastal areas worldwide could also face severe flooding due to rising sea levels. Low-lying islands in the Pacific Ocean would eventually become uninhabitable. From 1880 to 2022, sea levels rose about eight to nine inches worldwide. The hurricane season of 2017 proved to be the costliest hurricane season since 1900, causing over $265 billion of property damage in the United States and more than three thousand deaths in Florida, Texas, and Puerto Rico. The year 2020 experienced thirty named storms, the most to ever occur in a single hurricane season. The first hurricane to make landfall in 2022 was Hurricane Fiona, which struck Puerto Rico and other Caribbean Islands in September. All of Puerto Rico, which was still recovering from devastating hurricanes in 2017, lost power, and several areas suffered flooding and landslides. Though twenty tropical storms affected the United States during the 2023 hurricane season, only three made landfall. One of them, Hurricane Idalia, was the strongest hurricane to hit Florida's Big Bend region since 1950, leaving over $1 billion worth of damages.

Global warming also threatens vulnerable ecosystems and wildlife habitats. Extended periods of drought can turn fertile lands into deserts with little vegetation. Plants and animals may not survive the rapid changes caused by global warming and could become extinct. Over the long term, such changes would negatively affect Earth's biodiversity. Environmental scientists warn that some ecosystems, such as coral reefs and coastal mangrove swamps, will likely disappear entirely.

The climate crisis also threatens to disrupt the global food supply, worsen economic inequality, and create security issues. Some areas might become too dry or too wet to support agriculture. As global warming causes more places to become uninhabitable, such displacement can drive mass migration. Communities struggle to recover from climate disasters, often exacerbating existing problems in those areas. Disputes over access to water have arisen in several states, including those with areas that rely on Colorado River water. Around the world, some water disputes have developed into armed conflicts.

CRITICAL THINKING QUESTIONS

For what reasons do you think perceptions of anthropogenic climate change vary among Democrats and Republicans in the United States?

What potential long-term consequences of climate change do you think will be the most difficult to manage? Explain your reasoning.

In what ways, if at all, do you think the federal government could change its approach to address climate change more effectively? Explain your answer.

INTERNATIONAL RESPONSE AND US POLICY

The scope and global nature of the climate crisis necessitate that countries work together. Because an effective response requires countries to make sacrifices, negotiations to develop a coordinated international response have encountered repeated obstacles. Further, industrialized countries have contributed a disproportionate amount to the crisis. In contrast, less industrialized, lower-income countries have disproportionately felt the effects of the crisis and often lack the resources and infrastructure for climate change mitigation and adaptation.

Since 1995, the UN has hosted annual conferences to discuss climate change as part of its Framework Convention on Climate Change (UNFCCC). In 1997, delegates gathered in Kyoto, Japan, to negotiate an international treaty known as the Kyoto Protocol. This treaty required industrialized countries to reduce their GHG emissions by a certain percentage over five years. As of November 2023, 191 countries and the European Union had ratified the Kyoto Protocol. The United States has not ratified the agreement, citing concerns that it does not impose restrictions on China and India. Canada withdrew in 2011.

In 2015, world leaders set new climate goals at the UNFCCC conference (COP21) in Paris, France. The resultant Paris Agreement aimed to limit the rise in global temperatures to less than 2°C (3.6°F) above preindustrial levels and provide countries with the tools needed to counteract climate change. President Barack Obama played a leading role in brokering the Paris Agreement and pushed for greater environmental restrictions during his presidency. The Paris Agreement went into effect with the commitment of the United States and seventy-three other parties in November 2016. Obama's successor, Donald Trump, announced in 2017 that the United States would withdraw its support. After a required period, the United States officially withdrew from the agreement in November 2020.

Upon taking office in January 2021, President Joe Biden reentered the country in the Paris Agreement. Biden vowed that his administration would prioritize climate policy and issued several executive orders that made sustainability and addressing climate change important considerations across all federal government agencies. In April 2021, the president hosted a virtual climate summit attended by forty world leaders and pledged that the United States would reduce its carbon emissions to half of 2005 levels by 2030. In June 2022, the Biden administration experienced a setback when the Supreme Court ruled in West Virginia v. Environmental Protection Agency (EPA) that the Clean Air Act did not grant the EPA authority to regulate GHG emissions without Congress passing additional legislation.

In August 2022, Biden signed the Inflation Reduction Act, a law promoting a sustainable green economy by incentivizing emissions reductions, supporting clean energy projects, and requiring the wealthiest individuals and corporations to pay more taxes. Though many advocates celebrated the law as the federal government's most aggressive step to combat the climate crisis, the law has also attracted criticism. Some detractors contend that the law remains insufficient to have a meaningful impact on the climate crisis or its other targets, which include health care costs, worker protections