Climate Change


Climate is the general, cumulative form of regional or global weather patterns. The most apparent aspects of climate are trends in air temperature and humidity, wind, and precipitation. Climate change is any significant change in measures of climate over time. The changes might be in temperature, precipitation, wind patterns, or other measurements that occur over many decades.


Impact of climate change on human health

Impact of climate change on human health
Source: Centers for Disease Control (CDC). “Climate Effects on Health.”
Risk factors

Climate change is a publicly debated topic, and its concepts difficult for some to grasp. Still, measurements of climate indicators, particularly of temperature, tell the story of a planet that is warming more rapidly than it has ever warmed before. Various factors can be attributed to climate change, and scientists have uncovered fossil evidence that could explain when human behavior began affecting the planet's climate. The report said that crop domestication in Mexico is linked to a shift in the local and regional environment. This would have occurred in the postglacial period. The effect people have had on climate change worsened in the twentieth century with the release of greenhouse gases into the atmosphere mostly as a result of energy production, industrial practices, and deforestation.


National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA) data in 2018 showed that the average Earth temperature has risen by an average of 1.8 degrees Fahrenheit since 1880. The factors affecting climate change may also alter weather patterns, inducing droughts and floods, and contribute to sea level changes. Seventeen of the 18 warmest years on record have occurred since 2001, indicating a more rapid warming than in previous centuries. Climate models based on accumulating amounts of greenhouse gases predict that temperatures at the end of the twenty-first century could be 3.2 to 7.2 degrees Fahrenheit above 1990 temperatures. In 2018, the United Nations stated climate change now affected every country in the world.

Cost to society

Though climate change might affect some groups more than others, it can have an impact on nearly every aspect of people's lives. Global warming could affect social, cultural, and natural resources by impacting people's health, communities' or countries' infrastructures, transportation systems, and supplies of food, water, and energy. People who live in areas more vulnerable to drought or rising seas are more likely to see their day-to-day lives affected, but even people from inland cities might experience extreme heat or rising food or energy costs. As climate change increases the chance of extreme weather events, it can have devastating effects, leading to potentially more damage and deaths from natural disasters.

Causes and symptoms

Solar energy is the driving force in Earth's climate. Incoming radiation from the sun warms the atmosphere and raises air temperature, warms Earth's surface, and evaporates water, which then becomes humidity, rain, and snow. Earth's surface reflects or re-emits energy into the atmosphere, further warming the air. Warming air expands and rises, creating air movement patterns in the atmosphere that reach over several degrees of latitude. Differences in atmospheric pressure force air masses to move. Movement of air masses creates wind on Earth's surface. When these air masses carry evaporated water, they can create precipitation as they move to cooler regions.

The sun's energy comes to Earth as a collection of long and short radiation wavelengths. The shortest wavelengths are microwaves and infrared waves. Infrared radiation is felt as heat. Long and short wavelengths react differently when they encounter Earth and its atmosphere. Solar energy approaching Earth encounters filters, reflectors, and absorbers in the form of atmospheric gases, clouds, and Earth's surface. Atmospheric gases filter incoming energy, selectively blocking some wavelengths and allowing other wavelengths to pass through. Blocked wavelengths are either absorbed and heat the air or are scattered and reflected back into space. Clouds also reflect or absorb energy but allow some wavelengths to pass through.

Some energy reaching Earth's surface is reflected; a great deal is absorbed in heating the ground, evaporating water, and promoting photosynthesis. Most energy that Earth absorbs is re-emitted in the form of short, infrared wavelengths, which are sensed as heat. Some of this heat energy circulates in the atmosphere for a time, but eventually it all escapes. If this heat did not escape, Earth would overheat and become uninhabitable.

The term greenhouse gases comes from this heating effect. Global warming is caused by increased levels of carbon dioxide (CO2), methane, and other gases in the upper atmosphere. Most solar energy enters the atmospheric system as short wavelengths and is reflected back into space in the form of long wavelength (heat) energy. Carbon dioxide blocks these long, warm wavelengths as they leave Earth's surface. Unable to escape, this heat energy remains in the atmosphere and keeps Earth warm enough for life to continue.

The burning of fossil fuels and biomass (e.g., slash-and-burn agriculture) has raised atmospheric carbon dioxide levels. Rising CO2 levels could raise global air temperatures by amounts that would be dangerous. Extreme temperature changes have the potential to disturb precipitation patterns and overheat ecosystems, killing plant and animal species. Polar ice caps could melt, raising global ocean levels and threatening certain human settlements. In 2012, Arctic ice levels were the lowest ever recorded. The warming is likely to lead to increased droughts in some regions and change ocean and climate patterns all over the world.

Effects on public health
A complex biological community of living organisms and the environment that supports them.
Fossil fuels—
Natural but limited fuels, formed in the geological past from living things (fossils) such as coal or gas.
Greenhouse gases—
Gases from earth that trap heat in the atmosphere.

When droughts or floods affect water supplies, communities might have to treat water to make it safe for drinking or experience diseases from unsafe water. Consistently high or unseasonable temperatures add to heat stress problems, particularly for people who are ill or elderly, and if combined with poor air quality it can cause breathing difficulties for people at risk. Climate change also can spread disease if it affects availability of water for proper sanitation and hygiene or contributes to higher mosquito populations.

Public health role and response

The United States has a well-developed public health system, and many communities are prepared for the types of disasters that could occur in their areas, such as droughts, hurricanes, or floods. Still, climate change can affect public health, and the changing climate patterns can bring unexpected problems to areas. For example, a 2012 drought occurred in areas of the country normally not vulnerable to drought, and hurricanes have increased in frequency and intensity. Hurricane Harvey, which struck Texas in 2017, produced unprecedented levels of rain, flooding Houston and other communities.

Pubic health professionals monitor and respond to health concerns following natural disasters. The best public health response for climate change in general is prevention. Because climate change is a global issue, the United Nations (UN) and other international organizations are working with local governments to try to address the problem.

Efforts and solutions

Researchers are investigating how human activity is affecting the climate. Earth's climate is so complex that human alterations to the atmosphere (such as those caused by carbon dioxide emission) amount to an experiment having an unknown—and possibly lifethreatening—outcome. The United Nations Sustainable Development Goals (SDGs) are part of the 2030 Agenda for Sustainable Development, a plan adopted by world leaders. Although several of the 17 SDGs interact with climate change effects and improvement, SDG 13 directly addresses goals to combat climate change. The SDGs are not laws but serve as a framework for governments to use in setting their own goals and plans. The purpose of the goals is to ensure a sustainable future. In addition, the Paris Agreement to address climate change was passed in 2015 and entered force in November 2016. As of March 2018, nearly 200 countries had agreed to and signed the agreement. President Barack Obama signed the accord in 2016, but President Donald Trump signaled that he would withdraw unless the United States could alter the terms of the agreement. He could not withdraw until 2020, however.

See also Environmental Protection Agency (EPA) ; Global Public Health ; Hurricanes .



Aguado, Edward, and James E. Burt. Understanding Weather and Climate, 7th ed. Upper Saddle River, NJ: Pearson/Prentice Hall, 2014.

McCaffrey, Paul. Climate Smart and Energy Wise: Advancing Science Literacy, Knowledge, and Know-How. Thousand Oaks, CA: Corwin, 2015.


Anderson, G. B., et al. “Classifying Heatwaves: Developing Health-based Models to Predict High-mortality Versus Moderate United States Heatwaves.” Climate Change 146, no. 3 (2018): 439–53.


Centers for Disease Control and Prevention. “When Every Drop Counts. Protecting Public Health During Drought Conditions.” (accessed April 10, 2018).

NASA. “Global Climate Change.” (accessed April 10, 2018).

National Oceanic and Atmospheric Administration National Climatic Data Center. “State of the Climate.” (accessed April 10, 2018).

United Nations. “Sustainable Development Goals.” (accessed April 9, 2018).

United Nations Environment Programme. “Climate Change.” (accessed April 10, 2018).


Environmental Protection Agency, 1200 Pennsylvania Ave. NW, Washington, DC, 20460, (202) 272-0167, .

United Nations, 7 bis, Avenue de la Paix, 1202, Geneva, Switzerland, 41 (22) 730-8636, .

Mary Ann Cunningham, PhD
Revised by Teresa G. Odle

  This information is not a tool for self-diagnosis or a substitute for professional care.