Climate Change

• Global Climate Change
• Greenhouse Gases and Climate Change
• Climate Trends in Florida
• Climate Change Impacts in Florida and the Southeast U.S.

Global Climate Change

Climate change refers to the variation in the Earth's global or regional climates over time. Warming of the climate system is evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level. The increasing levels of greenhouse gases in the atmosphere, including carbon dioxide (CO₂), methane (CH₄), and nitrous oxides (NOx), contribute to a general warming of our planet (Figure 1). Continued greenhouse gas emissions, as well as past emissions already added to the atmosphere, will continue to warm the land, ocean, and atmosphere and influence climate.

Climate Change versus Global Warming

Climate change refers to the variation in the Earth's global or regional climates over time scales ranging from weeks to decades to millions of years. These changes can be caused by natural processes internal to the Earth, such as continental drift which affects ocean currents, external forces, such as variations in sunlight intensity, or human activities, such as greenhouse gas emissions and land use change. Natural, long-term changes occur in response to fluctuations in the amount of solar energy reaching the Earth, changing ocean currents, formation or loss of ice sheets, and many other causes. Global climates also vary naturally in response to shorter-term events, such as volcanoes, which send sun-blocking particles into the stratosphere to cool the Earth, or the Pacific Ocean event known as the El Niño Southern Oscillation (ENSO), which affects global wind patterns, rainfall, temperatures, and other climate features thousands of miles away.

“Global warming” has come to refer to an increase in average global temperatures as influenced by increased greenhouse gas concentrations without regard to other factors that may cause climate to change. Human activities can influence climate in many other ways. Land use changes, such as irrigation of historically semi-arid areas for farmland, paving and development of sprawling urban areas, draining of wetlands, and emissions of greenhouse gases or aerosols into the atmosphere are all human activities that affect the Earth’s climate and hydrological systems.

Greenhouse Gases and Climate Change

Much of the CO₂ that we release to the atmosphere is a by-product of energy use, whether through burning fossil fuels for transportation, generation of electricity, or other purposes. Burning fossil fuels releases carbon dioxide into the atmosphere, increasing atmospheric carbon and altering the pre-existing balance of greenhouse gases.

Greenhouse gases, including CO₂ and CH₄, have the property of allowing the atmosphere to retain more heat energy as their concentration in the atmosphere increases. Water vapor is the Earth’s most important greenhouse gas. Water vapor and clouds cause most of the Earth’s greenhouse effect, accounting for about 90% of the total heat-retaining capacity of the atmosphere. Two bases for the conclusion that human activity has contributed to recent trends in climate change are: 1) observations that atmospheric CO₂ concentrations have increased from about 280 parts per million (ppm) to approximately 420 ppm over the past 172 years while global average temperatures have warmed about 1.40° C (or 2.5°F) above the 1850-1900 average, though the temperature vs. CO₂ correlation is not perfect, and 2) scientific theories of atmospheric physics and heat transfer. This rise in global average temperature has tracked increases in CO₂ emissions from burning fossil fuels, deforestation, and other sources, which supports the hypothesis formulated by physical scientist Guy Stewart Callendar in 1930 that CO₂ emissions could enhance the greenhouse effect, as well as the work of other scientists dating back to the mid-1800s on the warming effect of greenhouse gases. Atmospheric greenhouse gases are at record high levels and are the highest they have been in at least 800,000 years (Figure 2).

Figure 2. Global atmospheric carbon dioxide concentrations (in parts per million) over the past 800k years, from the Scripps Institution of Oceanography at UC San Diego. Data since 1958 are from the Mauna Loa record from the Scripps CO2 program; data prior to 1958 are from ice core records.2

Climate Trends in Florida

Temperature Trends:

• The long-term trend since 1895 in Florida’s average annual temperature is an increase of approximately 0.2°F per decade, or 2.6°F, which is roughly equal to the average long-term global trend since 1895. The trend in the statewide annual average temperature has accelerated in more recent decades. Since 1970, Florida's average annual temperature trend has been 0.5°F per decade.
• There is considerable year-to-year and decade-to-decade variability in the instrumental record. However, long-term warming in average temperatures has been observed in every season in Florida.
• Daytime and nighttime temperatures have been rising in Florida in recent decades. Nighttime temperatures have been rising faster than daytime temperatures, though daytime temperatures are catching up.
• Extreme heat days, defined as days that reach at least 95°F, are projected to increase. Under a 2°C (3.6°F) level of global warming, eastern coastal Florida is expected to see up to 30 more extreme heat days per year, on average, while other locations right along the coast could see 10-20 more extreme heat days per year compared to normal (1991-2020). The Panhandle is expected to experience roughly 30-40 more extreme heat days per year. The areas of Florida expected to see the greatest increase in extreme heat are inland portions of the Peninsula, with 40 or more extreme heat days per year by 2050.

Precipitation Trends:

• Florida’s precipitation varies considerably from year to year and on a decadal basis, as well as in the timing of rainfall within each year. There is also a great deal of variation over relatively small distances and statewide and regional averages can mask a great deal of variability between and even within counties.
• Rainfall is among the most important climate variables for agriculture and water resource management. Since 1895, annual total rainfall in the three Southeast states of Florida, Georgia and Alabama shows great year-to-year variability, with rainfall increasing about 10% for all three states during the past century.
• Compared to the first half of the last century, there have been small changes in seasonal precipitation in Florida. Winter precipitation has increased in the Panhandle, North Florida, and South Florida. Summer precipitation has increased across the Peninsula but it has decreased in the central Panhandle.
• Extreme precipitation events are expected to become more frequent and intense as average temperatures rise. Recent heavy rainfall events, such as the extreme rainfall event in Fort Lauderdale on April 12, 2023 and recent hurricanes (Idalia, Ian, Nicole), are consistent with expected increases in precipitation, tropical cyclone intensity, and coastal storm surge flooding with higher evaporation rates and atmospheric moisture.
• Future changes in average annual and seasonal precipitation remains uncertain. Average annual precipitation is projected to increase in North Florida and decrease in South Florida, with higher confidence in changes for North Florida.

Climate Change and Hurricanes

Of particular importance to Florida and the Southeast is how changes in climate will influence tropical cyclone activity and associated hazards. Southeast rainfall totals are strongly influenced by tropical cyclones. One notable change over the past century is an increased frequency of rainfall events of two inches or more. While tropical cyclones increase the total annual rainfall, they are less useful to agriculture than smaller rainfall events distributed evenly during the growing season. With continued warming of the land and ocean, changes in hurricane frequency remain uncertain; however, more hurricanes are expected to reach major category strength (Category 3 or higher) when they do occur. There has been an increase in the number of storms undergoing rapid intensification in recent decades, defined as an increase in wind speed of at least 35 mph within 24 hours, but whether that trend will continue is an active area of research. Many hazards associated with tropical cyclones, including coastal storm surge inundation, rainfall flooding, and high winds, are likely to worsen due to physical processes and more people in harm's way.

Changes in tropical storm/hurricane frequency over the historical record is at least partially explained by better detection of storms in the post-satellite era. Figure 6 shows the annual numbers of Atlantic basin tropical storms and hurricanes since 1855. Several periods of increased activity can be seen in the late 1800’s, the 1930’s, the 1950’s, and since about 1995. Relatively inactive periods occurred around 1920, 1970, and 1985. There is a general trend of increasing activity over the whole period, but whether or how much of that is real or just an artifact of poor detection of storms before aircraft reconnaissance or satellites is a subject of intense research as scientists actively work to improve the historical record during the pre-satellite era. Read our Hurricanes page for more information about tropical storms and hurricanes.

Climate Change Impacts in Florida and the Southeast U.S.

As the average temperature rises, the likelihood of experiencing more frequent and intense extreme heat will also increase. Florida has seen a remarkable warming trend over the past decade, particularly in nighttime or minimum temperatures. Part of this can be explained by a corresponding increase in humidity. Warming ocean temperatures contribute to higher humidity on land and when marine heatwaves occur near Florida, this can further contribute to heatwaves felt on land.

Another impact of increasing global temperatures is rising sea levels. Relative sea levels rose by about 6 inches during the 1970-2020 period, and the rate of sea level rise has increased in recent decades. Sea level rise and rates have varied across the Southeast U.S. and over time. See our Sea Level Rise page for more information.

The impacts of a changing climate will also be driven by demographic and land use changes happening in the state and elsewhere. Florida has one of the fastest growing populations in the country and its population is expected to continue to rise. Population growth, along with development, can expose more people, communities, and assets to extreme weather and climate, which can increase the state’s overall risk to climate variability and weather events without hazard mitigation strategies.

More Resources

• Climate Change Basics for the Southeast USA (from AgroClimate)

References

1. Park, T., Hashimoto, H., Wang, W., Thrasher, B., Michaelis, A. R., Lee, T., et al. (2023). What does global land climate look like at 2°C warming? Earth's Future, 11, e2022EF003330. https://doi.org/10.1029/2022EF003330.

2. Lüthi, D., M. Le Floch, B. Bereiter, T. Blunier, J.-M. Barnola, U. Siegenthaler, D. Raynaud, J. Jouzel, H. Fischer, K. Kawamura, and T.F. Stocker. (2008.) High-resolution carbon dioxide concentration record 650,000-800,000 years before present. Nature, Vol. 453, pp. 379-382, 15 May 2008.

3. Hoffman, J.S., S.G. McNulty, C. Brown, K.D. Dello, P.N. Knox, A. Lascurain, C. Mickalonis, G.T. Mitchum, L. Rivers III, M. Schaefer, G.P. Smith, J.S. Camp, and K.M. Wood. (2023.) Ch. 22. Southeast. In: Fifth National Climate Assessment. Crimmins, A.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, B.C. Stewart, and T.K. Maycock, Eds. U.S. Global Change Research Program, Washington, DC, USA. https://doi.org/10.7930/NCA5.2023.CH22.

4. Marvel, K., W. Su, R. Delgado, S. Aarons, A. Chatterjee, M.E. Garcia, Z. Hausfather, K. Hayhoe, D.A. Hence, E.B. Jewett, A. Robel, D. Singh, A. Tripati, and R.S. Vose, 2023: Ch. 2. Climate trends. In: Fifth National Climate Assessment. Crimmins, A.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, B.C. Stewart, and T.K. Maycock, Eds. U.S. Global Change Research Program, Washington, DC, USA. https://doi.org/10.7930/NCA5.2023.CH2.