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Climate Change Indicators

Climate Change Indicators: Coastal Flooding

This indicator shows how the frequency of coastal flooding has changed over time.Â

Figure 1. Frequency of Flooding Along U.S. Coasts, 2010â€“2015 Versus 1950â€“1959

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This map shows the average number of days per year in which coastal waters rose above the local threshold for minor flooding at 27 sites along U.S. coasts. Each small bar graph compares the first decade of widespread measurements (the 1950s in orange) with the most recent decade (the 2010s in purple).

Data source: NOAA, 20163
Web update: AugustÂ 2016

Figure 2. Average Number of Coastal Flood Events per Year, 1950â€“2015

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This graph shows the average number of days per year in which coastal waters rose above the local threshold for minor flooding at 27 sites along U.S. coasts. The data have been averaged over multi-year periods for comparison.

Data source: NOAA, 20164
Web update: AugustÂ 2016

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Figure 1. Frequency of Flooding Along U.S. Coasts, 2010â€“2015 Versus 1950â€“1959

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Figure 2. Average Number of Coastal Flood Events per Year, 1950â€“2015

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			Key Points

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			Background

About the

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			Indicator Notes

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Technical

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Key Points

Flooding is becoming more frequent along the U.S. coastline. Nearly every site measured has experienced an increase in coastal flooding since the 1950s (see Figure 1). The rate is accelerating in many locations along the East and Gulf Coasts (see Figure 2).

The Mid-Atlantic region suffers the highest number of coastal flood days and has also experienced the largest increases in flooding. Since 2010, Wilmington, North Carolina, has flooded most oftenâ€”49 days per yearâ€”followed by Annapolis, Maryland, at 46 days per year. Annapolis, Wilmington, and two locations in New Jersey (Sandy Hook and Atlantic City) have also seen some of the most dramatic overall increases in frequency: floods are now at least 10 times more common there than they were in the 1950s. The Mid-Atlanticâ€™s subsiding land and higher-than-average relative sea level rise both contribute to this increase in flooding (see the Sea Level indicator).

Flooding has increased less dramatically in places where the local flood threshold is higher (for example, the Northeast and locations on the Gulf of Mexico) or where relative sea level has not risen as quickly as it has elsewhere in the United States (for example, Hawaii and the West Coast, as shown by the Sea Level indicator).

Background

Changing sea levels are affecting human activities in coastal areas. Rising sea level inundates low-lying wetlands and dry land, erodes shorelines, contributes to coastal flooding, and increases the flow of salt water into estuaries and nearby groundwater aquifers. Higher sea level also makes coastal infrastructure more vulnerable to damage from storms.

â€œRelative sea level changeâ€? refers to the height of the ocean relative to the land at a particular location. As relative sea level rises due to climate change (see the Sea Level indicator), one of the most noticeable consequences is an increase in coastal flooding. Flooding typically occurs during seasonal high tides (â€œking tidesâ€?) and storms that push water toward the shore. In recent years, however, coastal cities are increasingly flooding on days with less extreme tides or little wind, even on sunny days. Floods are happening more often as rising sea level reduces the gap between average sea level and the height of the land.

Many coastal cities have defined minor or â€œnuisanceâ€? flooding thresholds. When water rises above this level, minor flooding typically occurs in some streets, many storm drains become ineffective, and a coastal flood advisory may be issued. Recurrent coastal flooding can cause impacts such as frequent road closures, reduced stormwater drainage capacity, and deterioration of infrastructure not designed to withstand frequent inundation or exposure to salt water. These impacts are of particular concern because more than 8.6 million Americans live in areas susceptible to coastal flooding, and more than $1 trillion of property and structures is within a few feet of current sea level.1 Coastal flooding can also affect human healthâ€”for example, by increasing the risk that drinking water and wastewater infrastructure will fail, putting people at risk of being exposed to pathogens and harmful chemicals.2

About the Indicator

This indicator tracks coastal flooding based on measurements from tide gauges at locations along U.S. coasts. These devices measure water levels continuously, which makes them ideal for measuring the height of the tides, tracking long-term local relative sea level rise, and detecting coastal floods. This indicator focuses on 27 tide gauges where local weather forecasting offices have defined thresholds for minor, moderate, and major flooding and where complete data are available from 1950 to present. The indicator tracks the number of days per year when each tide gauge measured water that was higher than the minor flooding level. Figure 1 shows the 27 stations on a map and compares the first and last decades of data, while Figure 2 provides a more detailed comparison using all the available years of data.

Indicator Notes

Flood thresholds are defined locally based on observed impacts. They vary from one city to another, depending on land cover, topography, and the presence of flood defenses such as seawalls. For example, the minor flood level is set at approximately 10 inches above an average high-water mark in Wilmington, North Carolina, compared with 31 inches in Galveston, Texas. A city with flat land and infrastructure close to sea level will likely have a lower flooding threshold than a more elevated city, and it will naturally experience more days of coastal flooding. For this reason, it is more useful to compare change over time at a single location than it is to compare patterns across different locations.

This indicator is limited to tide gauges with defined flood levels and several decades of data. These tide gauges tend to be clustered along the East Coast, particularly in the Mid-Atlantic region. Other parts of the U.S. coast have fewer tide gauges with defined flood levels and long-term data.

Data Sources

This indicator is based on hourly water level data that are publicly available from the National Oceanic and Atmospheric Administration at: https://tidesandcurrents.noaa.gov. Flood thresholds are defined by the National Weather Service at: http://water.weather.gov/ahps/forecasts.php.

Technical Documentation

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References

1. Melillo, J.M., T.C. Richmond, and G.W. Yohe (eds.). 2014. Climate change impacts in the United States: The third National Climate Assessment. U.S. Global Change Research Program. http://nca2014.globalchange.gov.

2. Trtanj, J., L. Jantarasami, J. Brunkard, T. Collier, J. Jacobs, E. Lipp, S. McLellan, S. Moore, H. Paerl, J. Ravenscroft, M. Sengco, and J. Thurston. 2016. Chapter 6: Climate impacts on water-related illness. The impacts of climate change on human health in the United States: A scientific assessment. U.S. Global Change Research Program. https://health2016.globalchange.gov.

3. NOAA (National Oceanic and Atmospheric Administration). 2016 update to data originally published in: NOAA. 2014. Sea level rise and nuisance flood frequency changes around the United States. NOAA Technical Report NOS CO-OPS 073. https://tidesandcurrents.noaa.gov/publications/NOAA_Technical_Report_NOS_COOPS_073.pdf.

4. NOAA (National Oceanic and Atmospheric Administration). 2016 update to data originally published in: NOAA. 2014. Sea level rise and nuisance flood frequency changes around the United States. NOAA Technical Report NOS CO-OPS 073. https://tidesandcurrents.noaa.gov/publications/NOAA_Technical_Report_NOS_COOPS_073.pdf.

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Climate Change Indicators

Greenhouse Gases

Weather and Climate

Oceans

Ocean Heat

Sea Surface Temperature

Sea Level

A Closer Look: Land Loss Along the Atlantic Coast

Coastal Flooding

Ocean Acidity

Snow and Ice

Health and Society

Ecosystems

Frequent Questions


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Climate Change Indicators

Climate Change Indicators: Climate Forcing

This indicator measures the â€œradiative forcingâ€? or heating effect caused by greenhouse gases in the atmosphere.

Figure 1. Radiative Forcing Caused by Major Long-Lived Greenhouse Gases, 1979-2015

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This figure shows the amount of radiative forcing caused by various greenhouse gases, based on the change in concentration of these gases in the Earthâ€™s atmosphere since 1750. Radiative forcing is calculated in watts per square meter, which represents the size of the energy imbalance in the atmosphere. On the right side of the graph, radiative forcing has been converted to the Annual Greenhouse Gas Index, which is set to a value of 1.0 for 1990.

Data source: NOAA, 20161
Web update: AugustÂ 2016

Figure 2. Radiative Forcing Caused by Human Activities Since 1750

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This figure shows the total amount of radiative forcing caused by human activitiesâ€”including indirect effectsâ€”between 1750 and 2011. Radiative forcing is calculated in watts per square meter, which represents the size of the energy imbalance in the atmosphere. Each colored bar represents scientistsâ€™ best estimate, while the thin black bars indicate the likely range of possibilities. The natural change in the energy received from the sun over this time period is provided for reference.

Data source: IPCC, 20132
Web update: May 2014

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Figure 1. Radiative Forcing Caused by Major Long-Lived Greenhouse Gases, 1979â€“2015

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Figure 2. Radiative Forcing Caused by Human Activities Since 1750

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			Key Points

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			Background

About the

			Indicator

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			Indicator Notes

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			Data Sources

Technical

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Key Points

In 2015, the Annual Greenhouse Gas Index was 1.37, which represents a 37 percent increase in radiative forcing (a net warming influence) since 1990 (see Figure 1).

Of the greenhouse gases shown in Figure 1, carbon dioxide accounts for by far the largest share of radiative forcing since 1990, and its contribution continues to grow at a steady rate. Carbon dioxide alone would account for a 30 percent increase in radiative forcing since 1990.

Although the overall Annual Greenhouse Gas Index continues to rise, the rate of increase has slowed somewhat since the baseline year 1990. This change has occurred in large part because methane concentrations have increased at a slower rate in recent years and because chlorofluorocarbon (CFC) concentrations have been declining, as production of CFCs has been phased out globally due to the harm they cause to the ozone layer (see Figure 1).

Greenhouse gases produced by human activities have caused an overall warming influence on the Earthâ€™s climate since 1750. The largest contributor to warming has been carbon dioxide, followed by methane and black carbon. Although aerosol pollution and certain other activities have caused cooling, the net result is that human activities on the whole have warmed the Earth (see Figure 2).

Background

When energy from the sun reaches the Earth, the planet absorbs some of this energy and radiates the rest back to space as heat. The Earthâ€™s surface temperature depends on this balance between incoming and outgoing energy. Average conditions tend to remain stable unless the Earth experiences a force that shifts the energy balance. A shift in the energy balance causes the Earthâ€™s average temperature to become warmer or cooler, leading to a variety of other changes in the lower atmosphere, on land, and in the oceans.

A variety of physical and chemical changes can affect the global energy balance and force changes in the Earthâ€™s climate. Some of these changes are natural, while others are influenced by humans. These changes are measured by the amount of warming or cooling they can produce, which is called â€œradiative forcing.â€? Changes that have a warming effect are called â€œpositiveâ€? forcing, while changes that have a cooling effect are called â€œnegativeâ€? forcing. When positive and negative forces are out of balance, the result is a change in the Earthâ€™s average surface temperature.

Changes in greenhouse gas concentrations in the atmosphere affect radiative forcing (see the Atmospheric Concentrations of Greenhouse Gases indicator). Greenhouse gases absorb energy that radiates upward from the Earthâ€™s surface, re-emitting heat to the lower atmosphere and warming the Earthâ€™s surface. Human activities have led to increased concentrations of greenhouse gases that can remain in the atmosphere for decades, centuries, or longer, so the corresponding warming effects will last for a long time.Â

About the Indicator

Figure 1 of this indicator measures the average total radiative forcing of 20 long-lived greenhouse gases, including carbon dioxide, methane, and nitrous oxide. The results were calculated by the National Oceanic and Atmospheric Administration based on measured concentrations of the gases in the atmosphere, compared with the concentrations that were present around 1750, before the Industrial Revolution began. Because each gas has a different ability to absorb and emit energy, this indicator converts the changes in greenhouse gas concentrations into a measure of the total radiative forcing (warming effect) caused by each gas. Radiative forcing is calculated in watts per square meter, which represents the size of the energy imbalance in the atmosphere.

The National Oceanic and Atmospheric Administration also translates the total radiative forcing of these measured gases into an index value called the Annual Greenhouse Gas Index (right side of Figure 1). This number compares the radiative forcing for a particular year with the radiative forcing in 1990, which is a common baseline year for global agreements to track and reduce greenhouse gas emissions.

For reference, this indicator also presents an estimate of the total radiative forcing associated with a variety of human activities from 1750 to the present. Figure 2 shows the influence of:

Tropospheric ozone, a short-lived greenhouse gas.

Emissions that indirectly lead to greenhouse gases through chemical reactions in the atmosphere. For example, methane emissions also lead to an increase in tropospheric ozone.

Aerosol pollution, which consists of solid and liquid particles suspended in the air that can reflect incoming sunlight.

Black carbon (soot), which can make the Earthâ€™s surface darker and less reflective when it is deposited on snow and ice.

Several other factors, like land use change, that affect radiative forcing.

Indicator Notes

The index in Figure 1 does not include short-lived greenhouse gases like tropospheric ozone, reflective aerosol particles, black carbon (soot), or the indirect influence of methane through its effects on water vapor and ozone formation. Figure 2 includes these and other indirect influences.

Data Sources

Data for Figure 1 were provided by the National Oceanic and Atmospheric Administration. This figure and other information are available at: www.esrl.noaa.gov/gmd/aggi. Data for Figure 2 came from the Intergovernmental Panel on Climate Change (www.ipcc.ch), which publishes assessment reports based on the best available climate science data.Â

Technical Documentation

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References

1. NOAA (National Oceanic and Atmospheric Administration). 2016. The NOAA Annual Greenhouse Gas Index. Accessed June 2016. www.esrl.noaa.gov/gmd/aggi.

2. IPCC (Intergovernmental Panel on Climate Change). 2013. Climate change 2013: The physical science basis. Working Group I contribution to the IPCC Fifth Assessment Report. Cambridge, United Kingdom: Cambridge University Press. www.ipcc.ch/report/ar5/wg1.

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Climate Change Indicators

Climate Change Indicators: Snowfall

This indicator uses two different measures to show how snowfall has changed in the contiguous 48 states.

Figure 1. Change in Total Snowfall in the Contiguous 48 States, 1930â€“2007

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This figure shows the average rate of change in total snowfall from 1930 to 2007 at 419 weather stations in the contiguous 48 states. Blue circles represent increased snowfall; red circles represent a decrease.

Data source: Kunkel et al., 20092
Web update: May 2014

Figure 2. Change in Snow-to-Precipitation Ratio in the Contiguous 48 States, 1949â€“2016

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This figure shows the percentage change in winter snow-to-precipitation ratio from 1949 to 2016 at 246 weather stations in the contiguous 48 states. This ratio measures what percentage of total winter precipitation falls in the form of snow. A decrease (red circle) indicates that more precipitation is falling in the form of rain instead of snow. Solid-color circles represent stations where the trend was statistically significant.

Data source: NOAA, 20163
Web update: AugustÂ 2016

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Figure 1. Change in Total Snowfall in the Contiguous 48 States, 1930â€“2007

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Figure 2. Change in Snow-to-Precipitation Ratio in the Contiguous 48 States, 1949â€“2016

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			Key Points

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			Background

About the

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			Data Sources

Technical

			Documentation

Key Points

Total snowfall has decreased in many parts of the country since widespread observations became available in 1930, with 57 percent of stations showing a decline (see Figure 1). Among all of the stations shown, the average change is a decrease of 0.19 percent per year.

In addition to changing the overall rate of precipitation, climate change can lead to changes in the type of precipitation. One reason for the decline in total snowfall is because more winter precipitation is falling in the form of rain instead of snow. Nearly 80 percent of the stations across the contiguous 48 states have experienced a decrease in the proportion of precipitation falling as snow (see Figure 2).

Snowfall trends vary by region. The Pacific Northwest has seen a decline in both total snowfall and the proportion of precipitation falling as snow. Parts of the Midwest have also experienced a decrease, particularly in terms of the snow-to-precipitation ratio. A few regions have seen modest increases, including some areas near the Great Lakes that now receive more snow than in the past (see Figures 1 and 2).

Background

Snowfall is an important aspect of winter in much of the United States. Many people depend on snow to provide water when it melts in the springâ€”including 60 million people in the western United States1â€”and many communities rely on snow for winter recreation. Some plants and animals also depend on snow and snowmelt for survival. The amount of snow that falls in a particular area directly influences both snow cover and snowpack, which refer to snow that accumulates on the ground (see the Snow Cover indicator and the Snowpack indicator).

Warmer temperatures cause more water to evaporate from the land and oceans, which leads to more precipitation, larger storms, and more variation in precipitation in some areas. In general, a warmer climate causes more of this precipitation to fall in the form of rain instead of snow. Some places, however, could see more snowfall if temperatures rise but still remain below the freezing point, or if storm tracks change. Areas near large lakes might also experience more snowfall as lakes remain unfrozen for longer periods, allowing more water to evaporate. In contrast, other areas might experience less snowfall as a result of wintertime droughts.

Changes in the amount and timing of snowfall could affect the spawning of fish in the spring and the amount of water available for people to use in the spring and summer. Changes in snowfall could also affect winter recreation activities, like skiing, and the communities that rely on these activities.

About the Indicator

This indicator tracks total snowfall as well as the percentage of precipitation that falls in the form of snow versus rain. These data were collected from hundreds of weather stations across the contiguous 48 states.

Total snowfall is determined by the height of snow that accumulates each day. These measured values commonly appear in weather reports (for example, a storm that deposits 10 inches of snow). Figure 1 shows how snowfall accumulation totals changed between 1930 and 2007 at more than 400 weather stations. These stations were selected because they had high-quality data for this entire time period.

Figure 2 shows trends in the proportion of total precipitation that falls in the form of snow during each winter season. This is called the â€œsnow-to-precipitationâ€? ratio, and it is based on comparing the amount of snowfall with the total amount of precipitation (snow plus rain) in each year. For this comparison, snow has been converted to the equivalent amount of liquid water. These data are available from 1949 to 2016.

Indicator Notes

Several factors make it difficult to measure snowfall precisely. The snow accumulations shown in Figure 1 are based on the use of measuring rods. This measurement method is subject to human error, as well as the effects of wind (drifting snow) and the surrounding environment (such as tall trees). Similarly, snow gauges for Figure 2 may catch less snow than rain because of the effects of wind. Steps have been taken, however, to limit this indicator to weather stations with the most consistent methods and the highest-quality data.4 As a result, some parts of the country have a higher station density than others.

Both figures are limited to the winter season. Figure 1 comes from an analysis of October-to-May snowfall, while Figure 2 covers November through March. Although these months account for the vast majority of snowfall in most locations, this indicator might not represent the entire snow season in some areas. Most of the data shown for mountainous regions come from lower elevations (towns in valleys) because that is where weather stations tend to be located.

Data Sources

This indicator shows trends based on two sets of weather records collected and maintained by the National Oceanic and Atmospheric Administration. Figure 1 was adapted from an analysis by Kunkel et al. (2009)5Â based on records from Cooperative Observer Program weather stations. Figure 2 is an updated version of an analysis by Feng and Hu (2007)6 using data from the Global Historical Climatology Network. Additional information about the Cooperative Observer Program is available online at: www.nws.noaa.gov/om/coop. Information about the Global Historical Climatology Network can be found at: www.ncdc.noaa.gov/oa/climate/ghcn-daily.

Technical Documentation

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References

1. Barnett, T.P., J.C. Adam, and D.P. Lettenmaier. 2005. Potential impacts of a warming climate on water availability in snow-dominated regions. Nature 438:303â€“309.

2. Kunkel, K.E., M. Palecki, L. Ensor, K.G. Hubbard, D. Robinson, K. Redmond, and D. Easterling. 2009. Trends in twentieth-century U.S. snowfall using a quality-controlled dataset. J. Atmos. Ocean. Tech. 26:33â€“44.

3. NOAA (National Oceanic and Atmospheric Administration). 2016. National Centers for Environmental Information. Accessed June 2016. www.ncdc.noaa.gov.

4. Kunkel, K.E., M. Palecki, L. Ensor, K.G. Hubbard, D. Robinson, K. Redmond, and D. Easterling. 2009. Trends in twentieth-century U.S. snowfall using a quality-controlled dataset. J. Atmos. Ocean. Tech. 26:33â€“44.

5. Kunkel, K.E., M. Palecki, L. Ensor, K.G. Hubbard, D. Robinson, K. Redmond, and D. Easterling. 2009. Trends in twentieth-century U.S. snowfall using a quality-controlled dataset. J. Atmos. Ocean. Tech. 26:33â€“44.

6. Feng, S., and Q. Hu. 2007. Changes in winter snowfall/precipitation ratio in the contiguous United States. J. Geophys. Res. 112:D15109.

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Weather and Climate

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Arctic Sea Ice

Antarctic Sea Ice

Glaciers

Lake Ice

Community Connection: Ice Breakup in Two Alaskan Rivers

Snowfall

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Snowpack

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Climate Change Indicators

Climate Change Indicators: Global Greenhouse Gas Emissions

This indicator describes emissions of greenhouse gases worldwide.

Figure 1. Global Greenhouse Gas Emissions by Gas, 1990–2010

This figure shows worldwide emissions of carbon dioxide, methane, nitrous oxide, and several fluorinated gases from 1990 to 2010. For consistency, emissions are expressed in million metric tons of carbon dioxide equivalents. These totals include emissions and sinks due to land-use change and forestry.

* HFCs are hydrofluorocarbons, PFCs are perfluorocarbons, and SF6 is sulfur hexafluoride.

Data sources: WRI, 2014;2 FAO, 20143
Web update: May 2014

Figure 2. Global Greenhouse Gas Emissions by Sector, 1990–2010

This figure shows worldwide greenhouse gas emissions by sector from 1990 to 2010. For consistency, emissions are expressed in million metric tons of carbon dioxide equivalents. These totals include emissions and sinks due to land-use change and forestry.

Note that the sectors shown here are different from the economic sectors used in U.S. emissions accounting (see the U.S. Greenhouse Gas Emissions indicator). Emissions from international transport (aviation and marine) are separate from the energy sector because they are not part of individual countries’ emissions inventories. The energy sector includes all other transportation activities.

Data sources: WRI, 2014;4 FAO, 20145
Web update: May 2014

Figure 3. Global Carbon Dioxide Emissions by Region, 1990–2012

This figure shows carbon dioxide emissions from 1990 to 2012 for different regions of the world. These totals do not include emissions or sinks related to land-use change or forestry. Inclusion of land-use change and forestry would increase the apparent emissions from some regions while decreasing the emissions from others.

Data source: WRI, 20156
Web update: August 2016

Figure 1. Global Greenhouse Gas Emissions by Gas, 1990–2010

Figure 2. Global Greenhouse Gas Emissions by Sector, 1990–2010

Figure 3. Global Carbon Dioxide Emissions by Region, 1990–2012

Key Points

Background

About the
Indicator

Indicator Notes

Data Sources

Technical
Documentation

Key Points

In 2010, estimated worldwide emissions from human activities totaled nearly 46 billion metric tons of greenhouse gases, expressed as carbon dioxide equivalents. This represents a 35 percent increase from 1990 (see Figures 1 and 2). These numbers represent net emissions, which include the effects of land use and forestry.

Between 1990 and 2010, global emissions of all major greenhouse gases increased (see Figure 1). Net emissions of carbon dioxide increased by 42 percent, which is particularly important because carbon dioxide accounts for about three-fourths of total global emissions. Nitrous oxide emissions increased the least—9 percent—while emissions of methane increased by 15 percent. Emissions of fluorinated gases more than doubled.

Energy production and use (including fuels used by vehicles) represent the largest source of greenhouse gas emissions worldwide (about 71 percent of the total in 2010), followed by agriculture (13 percent in 2010) (see Figure 2). While land-use change and forestry represent a net sink for emissions in the United States, absorbing carbon dioxide and offsetting emissions from other sources (see the U.S. Greenhouse Gas Emissions indicator), these activities are a net source of emissions on a global scale, largely because of deforestation.1

Carbon dioxide emissions are increasing faster in some parts of the world (for example, Asia) than in others (see Figure 3). The majority of emissions come from three regions: Asia, Europe, and the United States, which together accounted for 88 percent of total global emissions in 2012.

Background

Increasing emissions of greenhouse gases due to human activities worldwide have led to a substantial increase in atmospheric concentrations of long-lived and other greenhouse gases (see the Atmospheric Concentrations of Greenhouse Gases indicator). Every country around the world emits greenhouse gases into the atmosphere, meaning the root cause of climate change is truly global in scope. Some countries produce far more greenhouse gases than others, and several factors—such as economic activity (including the composition and efficiency of the economy), population, income level, land use, and climatic conditions—can influence a country’s emissions levels. Tracking greenhouse gas emissions worldwide provides a global context for understanding the United States’ and other nations’ roles in climate change.

About the Indicator

Like the U.S. Greenhouse Gas Emissions indicator, this indicator focuses on emissions of gases covered under the United Nations Framework Convention on Climate Change: carbon dioxide, methane, nitrous oxide, and several fluorinated gases. These are all important greenhouse gases that are influenced by human activities, and the Convention requires participating countries to develop and periodically submit an inventory of these emissions.

Data and analysis for this indicator come from the World Resources Institute’s Climate Analysis Indicators Tool (CAIT), which compiles data from peer-reviewed and internationally recognized greenhouse gas inventories developed by EPA and other government agencies worldwide. Global estimates for carbon dioxide are published annually, but estimates for other gases, such as methane and nitrous oxide, are available only every fifth year. CAIT includes estimates of emissions and sinks associated with land use and forestry activities, which come from global estimates compiled by the Food and Agriculture Organization of the United Nations.

Each greenhouse gas has a different lifetime (how long it stays in the atmosphere) and a different ability to trap heat in our atmosphere. To allow different gases to be compared and added together, emissions are converted into carbon dioxide equivalents. This step uses each gas’s 100-year global warming potential, which measures how much a given amount of the gas is estimated to contribute to global warming over a period of 100 years after being emitted. Carbon dioxide is assigned a global warming potential equal to 1. This analysis uses global warming potentials from the Intergovernmental Panel on Climate Change’s (IPCC’s) Second Assessment Report. In that report, methane has a global warming potential of 21, which means a ton of methane emissions contributes 21 times as much warming as a ton of carbon dioxide emissions over 100 years, and that ton of methane emissions is therefore equal to 21 tons of carbon dioxide equivalents. See the table for comparison with global warming potentials from IPCC’s Fifth Assessment Report.

Indicator Notes

Like the U.S. Greenhouse Gas Emissions indicator, this indicator does not include emissions of gases that affect climate but are not covered under the United Nations Framework Convention on Climate Change. For example, this indicator excludes ozone-depleting substances such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which have high global warming potentials, because these gases have been or are currently being phased out under an international agreement called the Montreal Protocol. This indicator also excludes black carbon and aerosols, which most emissions inventories do not cover. There are also various emissions of greenhouse gases of natural origin, which this indicator does not cover.

Global emissions inventories for gases other than carbon dioxide are limited to five-year intervals. The United Nations Framework Convention on Climate Change database has more comprehensive data; however, these data are available mainly for a group of mostly developed countries that account for only about half of global greenhouse gas emissions. Thus, to provide a more representative measure of global greenhouse gas emissions, this indicator uses the broader CAIT database.

Data Sources

Data for this indicator came from the World Resources Institute’s CAIT database, which is accessible online at: http://cait.wri.org. CAIT compiles data that were originally collected by organizations including the International Energy Agency, EPA, the U.S. Carbon Dioxide Information Analysis Center, and the Food and Agriculture Organization of the United Nations. Other global emissions estimates—such as the estimates published by the Intergovernmental Panel on Climate Change7—are based on many of the same sources.

Technical Documentation

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References

1. IPCC (Intergovernmental Panel on Climate Change). 2014. Climate change 2014: Mitigation of climate change. Working Group III contribution to the IPCC Fifth Assessment Report. Cambridge, United Kingdom: Cambridge University Press. www.ipcc.ch/report/ar5/wg3.

2. WRI (World Resources Institute). 2014. Climate Analysis Indicators Tool (CAIT) 2.0: WRI’s climate data explorer. Accessed May 2014. http://cait.wri.org.

3. FAO (Food and Agriculture Organization). 2014. FAOSTAT: Emissions—land use. Accessed May 2014. http://faostat3.fao.org/faostat-gateway/go/to/download/G2/*/E.

4. WRI (World Resources Institute). 2014. Climate Analysis Indicators Tool (CAIT) 2.0: WRI’s climate data explorer. Accessed May 2014. http://cait.wri.org.

5. FAO (Food and Agriculture Organization). 2014. FAOSTAT: Emissions—land use. Accessed May 2014. http://faostat3.fao.org/faostat-gateway/go/to/download/G2/*/E.

6. WRI (World Resources Institute). 2015. Climate Analysis Indicators Tool (CAIT) 2.0: WRI’s climate data explorer. Accessed December 2015. http://cait.wri.org.

7. IPCC (Intergovernmental Panel on Climate Change). 2014. Climate change 2014: Mitigation of climate change. Working Group III contribution to the IPCC Fifth Assessment Report. Cambridge, United Kingdom: Cambridge University Press. www.ipcc.ch/report/ar5/wg3.

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Greenhouse Gases

U.S. Greenhouse Gas Emissions

Global Greenhouse Gas Emissions

Atmospheric Concentrations of Greenhouse Gases

Climate Forcing

Weather and Climate

Oceans

Snow and Ice

Health and Society

Ecosystems

Frequent Questions


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Climate Change Indicators: River Flooding

This indicator examines changes in the size and frequency of inland river flood events in the United States.

Figure 1. Change in the Magnitude of River Flooding in the United States, 1965–2015

This figure shows changes in the size of flooding events in rivers and streams in the United States between 1965 and 2015. Blue upward-pointing symbols show locations where floods have become larger; brown downward-pointing symbols show locations where floods have become smaller. The larger, solid-color symbols represent stations where the change was statistically significant.

Data source: Slater and Villarini, 20164
Web update: August 2016

Figure 2. Change in the Frequency of River Flooding in the United States, 1965–2015

This figure shows changes in the frequency of flooding events in rivers and streams in the United States between 1965 and 2015. Blue upward-pointing symbols show locations where floods have become more frequent; brown downward-pointing symbols show locations where floods have become less frequent. The larger, solid-color symbols represent stations where the change was statistically significant.

Data source: Slater and Villarini, 20165
Web update: August 2016

Figure 1. Change in the Magnitude of River Flooding in the United States, 1965–2015

Figure 2. Change in the Frequency of River Flooding in the United States, 1965–2015

Key Points

Background

About the
Indicator

Indicator Notes

Data Sources

Technical
Documentation

Key Points

Floods have generally become larger in rivers and streams across large parts of the Northeast and Midwest. Flood magnitude has generally decreased in the West, southern Appalachia, and northern Michigan (see Figure 1).

Large floods have become more frequent across the Northeast, Pacific Northwest, and northern Great Plains. Flood frequency has decreased in some other parts of the country, especially the Southwest and the Rockies (see Figure 2).

Increases and decreases in frequency and magnitude of river flood events generally coincide with increases and decreases in the frequency of heavy rainfall events.2,3

Background

Rivers and streams experience flooding as a natural result of large rain storms or spring snowmelt that quickly drains into streams and rivers. Although the risk for flooding varies across the United States, most areas are susceptible to floods, even in dry and mountainous regions. The size, or magnitude, of flood events is influenced by how much water enters the waterway upstream—and how quickly. Flood frequency largely depends on the frequency of weather events.

Large flood events can damage homes, roads, bridges, and other infrastructure; wipe out farmers’ crops; and harm or displace people. Although regular flooding helps to maintain the nutrient balance of soils in the flood plain, larger or more frequent floods could disrupt ecosystems by displacing aquatic life, impairing water quality, and increasing soil erosion. By inundating water treatment systems with sediment and contaminants, and promoting the growth of harmful microbes, floods can directly affect the water supplies that communities depend on.

Climate change may cause river floods to become larger or more frequent than they used to be in some places, yet become smaller and less frequent in other places. As warmer temperatures cause more water to evaporate from the land and oceans, changes in the size and frequency of heavy precipitation events may in turn affect the size and frequency of river flooding (see the Heavy Precipitation indicator).1 Changes in streamflow, the timing of snowmelt (see the Streamflow indicator), and the amount of snowpack that accumulates in the winter (see the Snowpack indicator) can also affect flood patterns.

About the Indicator

The U.S. Geological Survey maintains thousands of stream gauges across the United States. Each gauge measures water level and discharge—the amount of water flowing past the gauge. This indicator uses total daily discharge data from about 500 long-term stream gauge stations where trends are not substantially influenced by dams, reservoir management, wastewater treatment facilities, or land-use change.

One way to determine whether the magnitude of flooding has changed is by studying the largest flood event from each year. This indicator examines the maximum discharge from every year at every station to identify whether peak flows have generally increased or decreased. This indicator also analyzes whether large flood events have become more or less frequent over time, based on daily discharge records.

This indicator starts in 1965 because flood data have been available for a large number of sites to support a national-level analysis since then.

Indicator Notes

This indicator is based on U.S. stream gauges that have recorded data consistently since 1965. Besides climate change, many other types of human influences could affect the frequency and magnitude of floods—for example, dams, floodwater management activities, agricultural practices, and changes in land use. To remove these influences, this indicator focuses on a set of sites that are not heavily influenced by human activities, in watersheds that do not have a large proportion of impervious surfaces such as concrete and asphalt. Increased flooding does not necessarily result in an increased risk to people or property if an area has protective infrastructure, such as levees or floodwalls.

Data Sources

Daily stream gauge data were collected by the U.S. Geological Survey. These data came from a set of gauges in watersheds with minimal human impacts, which have been classified as reference gauges.6 Daily discharge data are stored in the National Water Information System and are publicly available at: http://waterdata.usgs.gov/nwis.

Technical Documentation

Download related technical information PDF

References

1 Mallakpour, I., G. Villarini. 2015. The changing nature of flooding across the central United States. Nature Climate Change 5:250–254.

2 Mallakpour, I., G. Villarini. 2015. The changing nature of flooding across the central United States. Nature Climate Change 5:250–254.

3 Melillo, J.M., T.C. Richmond, and G.W. Yohe (eds.). 2014. Climate change impacts in the United States: The third National Climate Assessment. U.S. Global Change Research Program. http://nca2014.globalchange.gov.

4 Slater, L., and G. Villarini. 2016 update and expansion to data originally published in: Mallakpour, I., G. Villarini. 2015. The changing nature of flooding across the central United States. Nature Climate Change 5:250–254.

5 Slater, L., and G. Villarini. 2016 update and expansion to data originally published in: Mallakpour, I., G. Villarini. 2015. The changing nature of flooding across the central United States. Nature Climate Change 5:250–254.

6 Lins, H.F. 2012. USGS Hydro-Climatic Data Network 2009 (HCDN-2009). U.S. Geological Survey Fact Sheet 2012-3047.

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Greenhouse Gases

Weather and Climate

U.S. and Global Temperature

High and Low Temperatures

U.S. and Global Precipitation

Heavy Precipitation

Tropical Cyclone Activity

River Flooding

Drought

A Closer Look: Temperature and Drought in the Southwest

Oceans

Snow and Ice

Health and Society

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Climate Change Indicators: U.S. and Global Temperature

This indicator describes trends in average surface temperature for the United States and the world.

Figure 1. Temperatures in the Contiguous 48 States, 1901â€“2015

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This figure shows how annual average temperatures in the contiguous 48 states have changed since 1901. Surface data come from land-based weather stations. Satellite measurements cover the lower troposphere, which is the lowest level of the Earthâ€™s atmosphere. â€œUAHâ€? and â€œRSSâ€? represent two different methods of analyzing the original satellite measurements. This graph uses the 1901â€“2000 average as a baseline for depicting change. Choosing a different baseline period would not change the shape of the data over time.

Data source: NOAA, 20161
Web update: AugustÂ 2016

Figure 2. Temperatures Worldwide, 1901â€“2015

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This figure shows how annual average temperatures worldwide have changed since 1901. Surface data come from a combined set of land-based weather stations and sea surface temperature measurements. Satellite measurements cover the lower troposphere, which is the lowest level of the Earthâ€™s atmosphere. â€œUAHâ€? and â€œRSSâ€? represent two different methods of analyzing the original satellite measurements. This graph uses the 1901â€“2000 average as a baseline for depicting change. Choosing a different baseline period would not change the shape of the data over time.

Data source: NOAA, 20162
Web update: AugustÂ 2016

Figure 3. Rate of Temperature Change in the United States, 1901â€“2015

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This figure shows how annual average air temperatures have changed in different parts of the United States since the early 20th century (since 1901 for the contiguous 48 states and 1925 for Alaska). The data are shown for climate divisions, as defined by the National Oceanic and Atmospheric Administration.

Data source: NOAA, 20163
Web update: AugustÂ 2016

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Figure 1. Temperatures in the Contiguous 48 States, 1901â€“2015

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Figure 2. Temperatures Worldwide, 1901â€“2015

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Figure 3. Rate of Temperature Change in the United States, 1901â€“2015

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Key Points

Â
Background

About the
Indicator

Â
Indicator Notes

Â
Data Sources

Technical
Documentation

Key Points

Since 1901, the average surface temperature across the contiguous 48 states has risen at an average rate of 0.14Â°F per decade (see Figure 1). Average temperatures have risen more quickly since the late 1970s (0.29 to 0.46Â°F per decade since 1979). Eight of the top 10 warmest years on record for the contiguous 48 states have occurred since 1998, and 2012 and 2015 were the two warmest years on record.

Worldwide, 2015 was the warmest year on record and 2006â€“2015 was the warmest decade on record since thermometer-based observations began. Global average surface temperature has risen at an average rate of 0.15Â°F per decade since 1901 (see Figure 2), similar to the rate of warming within the contiguous 48 states. Since the late 1970s, however, the United States has warmed faster than the global rate.

Some parts of the United States have experienced more warming than others (see Figure 3). The North, the West, and Alaska have seen temperatures increase the most, while some parts of the Southeast have experienced little change. Not all of these regional trends are statistically significant, however.

Background

Temperature is a fundamental measurement for describing the climate, and the temperature in particular places can have wide-ranging effects on human life and ecosystems. For example, increases in air temperature can lead to more intense heat waves, which can cause illness and death, especially in vulnerable populations. Annual and seasonal temperature patterns also determine the types of animals and plants that can survive in particular locations. Changes in temperature can disrupt a wide range of natural processes, particularly if these changes occur more quickly than plant and animal species can adapt.

Concentrations of heat-trapping greenhouse gases are increasing in the Earthâ€™s atmosphere (see the Atmospheric Concentrations of Greenhouse Gases indicator). In response, average temperatures at the Earthâ€™s surface are increasing and are expected to continue rising. Because climate change can shift the wind patterns and ocean currents that drive the worldâ€™s climate system, some areas are warming more than others, and some have experienced cooling.

About the Indicator

This indicator examines U.S. and global surface temperature patterns over time. U.S. surface measurements come from weather stations on land, while global surface measurements also incorporate observations from buoys and ships on the ocean, thereby providing data from sites spanning much of the surface of the Earth. This indicator starts at 1901 except for the detailed map of Alaska, where reliable statewide records are available back to 1925. For comparison, this indicator also displays satellite measurements that can be used to estimate the temperature of the Earthâ€™s lower atmosphere since 1979.

This indicator shows annual anomalies, or differences, compared with the average temperature from 1901 to 2000. For example, an anomaly of +2.0 degrees means the average temperature was 2 degrees higher than the long-term average. Anomalies have been calculated for each weather station. Daily temperature measurements at each site were used to calculate monthly anomalies, which were then averaged to find an annual temperature anomaly for each year. Anomalies for the contiguous 48 states and Alaska have been determined by calculating average anomalies for areas within each state based on station density, interpolation, and topography. These regional anomalies are then averaged together in proportion to their area to develop national results. Similarly, global anomalies have been determined by dividing the world into a grid, averaging the data for each cell of the grid, and then averaging the grid cells together.

Indicator Notes

Data from the early 20th century are somewhat less precise than more recent data because there were fewer stations collecting measurements at the time, especially in the Southern Hemisphere. The overall trends are still reliable, however. Where possible, the data have been adjusted to account for any biases that might be introduced by factors such as station moves, urbanization near the station, changes in measuring instruments, and changes in the exact times at which measurements are taken.

Hawaii and U.S. territories are not included, due to limitations in available data.

Data Sources

The data for this indicator were provided by the National Oceanic and Atmospheric Administrationâ€™s National Centers for Environmental Information, which maintains a large collection of climate data online at: www.ncei.noaa.gov. The surface temperature anomalies shown here were calculated based on monthly values from a network of long-term monitoring stations. Satellite data were analyzed by two independent groupsâ€”the Global Hydrology and Climate Center at the University of Alabama in Huntsville (UAH) and Remote Sensing Systems (RSS)â€”resulting in slightly different trend lines.

Technical Documentation

Download related technical information PDF

References

1 NOAA (National Oceanic and Atmospheric Administration). 2016. National Centers for Environmental Information. Accessed February 2016. www.ncei.noaa.gov.

2 NOAA (National Oceanic and Atmospheric Administration). 2016. National Centers for Environmental Information. Accessed February 2016. www.ncei.noaa.gov.

3 NOAA (National Oceanic and Atmospheric Administration). 2016. National Centers for Environmental Information. Accessed February 2016. www.ncei.noaa.gov.Â

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Learn about other indicators in this section

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Climate Indicators

Climate Change Indicators

Greenhouse Gases

Weather and Climate

U.S. and Global Temperature

High and Low Temperatures

U.S. and Global Precipitation

Heavy Precipitation

Tropical Cyclone Activity

River Flooding

Drought

A Closer Look: Temperature and Drought in the Southwest

Oceans

Snow and Ice

Health and Society

Ecosystems

Frequent Questions


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Climate Change Indicators

Climate Change Indicators: Lake Ice

This indicator measures the amount of time that ice is present on lakes in the United States.

Figure 1. Date of First Freeze for Selected U.S. Lakes, 1850â€“2015

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This figure shows the â€œice-onâ€? date, or date of first freeze, for nine U.S. lakes. The data are available from as early as 1850 to 2015, depending on the lake, and have been smoothed using a nine-year moving average.

Data source: Various organizations2
Web update: AugustÂ 2016

Figure 2. Date of Ice Thaw for Selected U.S. Lakes, 1840â€“2015

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This figure shows the â€œice-offâ€? date, or date of ice thawing and breakup, for 14 U.S. lakes. The data are available from as early as 1850 to 2015, depending on the lake, and have been smoothed using a nine-year moving average.

Data source: Various organizations3
Web update: AugustÂ 2016

Figure 3. Change in Ice Thaw Dates for Selected U.S. Lakes, 1905â€“2015

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This figure shows the change in the â€œice-offâ€? date, or date of ice thawing and breakup, for 14 U.S. lakes during the period from 1905 to 2015. All of the lakes have red circles with negative numbers, which represent earlier thaw dates. Larger circles indicate larger changes.

Data source: Various organizations4
Web update: AugustÂ 2016

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Figure 1. Date of First Freeze for Selected U.S. Lakes, 1850â€“2015

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Figure 2. Date of Ice Thaw for Selected U.S. Lakes, 1840â€“2015

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Figure 3. Change in Ice Thaw Dates for Selected U.S. Lakes, 1905â€“2015

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Key Points

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Background

About the
Indicator

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Indicator Notes

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Data Sources

Technical
Documentation

Key Points

The lakes covered by this indicator are generally freezing later than they did in the past. Freeze dates have shifted later at a rate of roughly half a day to one-and-a-half days per decade (see Figure 1).

Thaw dates for most of these lakes show a trend toward earlier ice breakup in the spring (see Figure 2). Spring thaw dates have grown earlier by up to 24 days in the past 110 years (see Figure 3). All of these lakes were found to be thawing earlier in the year.

The changes in lake freeze and thaw dates shown here are consistent with other studies. For example, a broad study of lakes and rivers throughout the Northern Hemisphere found that since the mid-1800s, freeze dates have occurred later and thaw dates have occurred earlier, both shifting at an average rate of 0.8 days to one day per decade.1

Background

The formation of ice cover on lakes in the winter and its disappearance the following spring depends on climate factors such as air temperature, cloud cover, and wind. Conditions such as heavy rains or snowmelt in locations upstream or elsewhere in the watershed also affect the length of time a lake is frozen. Thus, ice formation and breakup dates are key indicators of climate change. If lakes remain frozen for longer periods, it can signify that the climate is cooling. Conversely, shorter periods of ice cover suggest a warming climate.

Changes in ice cover can affect the physical, chemical, and biological characteristics of a body of water. For example, ice influences heat and moisture transfers between a lake and the atmosphere. Reduced ice cover leads to increased evaporation and lower water levels, as well as an increase in water temperature and sunlight penetration. These changes, in turn, can affect plant and animal life cycles and the availability of suitable habitat. Additionally, ice cover affects the amount of heat that is reflected from the Earthâ€™s surface. Exposed water will absorb and retain heat, making the Earthâ€™s surface warmer, whereas an ice- and snow-covered lake will reflect more of the sunâ€™s energy and absorb less. (For more information on ice and snow reflecting sunlight, see the Snow Cover indicator.)

The timing and duration of ice cover on lakes and other bodies of water can also affect societyâ€”particularly in relation to shipping and transportation, hydroelectric power generation, and fishing. The impacts can be positive or negative. For example, reduced ice cover on a large lake could extend the open-water shipping season but require vessels to reduce their cargo capacity, as increased evaporation leads to lower water levels.

About the Indicator

This indicator analyzes the dates at which lakes freeze and thaw. Freeze dates occur when a continuous and immobile ice cover forms over a body of water. Thaw dates occur when the ice cover breaks up and open water becomes extensive.

Freeze and thaw dates have been recorded through human visual observations for more than 150 years. The National Snow and Ice Data Center maintains a database with freeze and thaw observations from more than 700 lakes and rivers throughout the Northern Hemisphere. This indicator focuses on 14 lakes within the United States that have the longest and most complete historical records. The lakes of interest are located in Minnesota, Wisconsin, New York, and Maine.

Indicator Notes

Although there is a lengthy historical record of freeze and thaw dates for a much larger set of lakes and rivers, some records are incomplete, with breaks ranging from brief lapses to large gaps in data. This indicator is limited to 14 lakes with sufficiently complete historical records. The four Maine lakes and Lake Osakis only have data for ice thaw, so they do not appear in Figure 1 (first freeze date).

Data used in this indicator are all based on visual observations. While the procedures for making observations of lake ice are consistent over time, visual observations by individuals are open to some interpretation and can differ from one individual to the next. In addition, historical observations for lakes have typically been made from a particular spot on the shore, which might not be representative of lakes as a whole or comparable to satellite-based observations. Considerations for defining the thaw date are specific to each lake.

Data Sources

Data through 2004 for most lakes were obtained from the Global Lake and River Ice Phenology Database, which is maintained by the National Snow and Ice Data Center. These data are available at: http://nsidc.org/data/lake_river_ice. More recent data were obtained from state, local, and other organizations that collected or compiled the observations.

Technical Documentation

Download related technical information PDF

References

1. Benson, B.J., J.J. Magnuson, O.P. Jensen, V.M. Card, G. Hodgkins, J. Korhonen, D.M. Livingstone, K.M. Stewart, G.A. Weyhenmeyer, and N.G. Granin. 2012. Extreme events, trends, and variability in Northern Hemisphere lake-ice phenology (1855â€“2005). Climatic Change 112(2):299â€“323.

2. [see full list provided below]

3.Â [see full list providedÂ below]

4.Â [see full list providedÂ below]

Lake Ice: Citations for Figures 1, 2, and 3

Figure 1

Detroit Lake, Minnesota, 2006â€“2015

	Minnesota Department of Natural Resources. Accessed June 2016.Â www.dnr.state.mn.us/ice_in.

Geneva Lake, Wisconsin, 2005â€“2015

	Geneva Lake Environmental Agency Newsletters. Accessed June 2016.Â www.genevaonline.com/~glea/newsletters.php.

Lake George, New York, 2005â€“2014

	Lake George Association. Accessed June 2016.Â www.lakegeorgeassociation.org/who-we-are/documents/Ice-In-Ice-Out2015.pdf.

Lake Mendota and Lake Monona, Wisconsin, 2011â€“2015

	North Temperate Lakes Long Term Ecological Research site. Accessed June 2016.Â https://lter.limnology.wisc.edu/lakeinfo/ice-data?lakeid=MEÂ andÂ https://lter.limnology.wisc.edu/lakeinfo/ice-data?lakeid=MO.

Otsego Lake, New York, 2005â€“2014

	State University of New York (SUNY) Oneonta Biological Field Station. Annual Reports. Accessed May 2015.Â www.oneonta.edu/academics/biofld/PUBS/ANNUAL/2013/29-Otsego-Ice-History-2014.pdf.

Shell Lake, Wisconsin, 2005â€“2015

	Washburn County Clerk. 2016. Personal communication.

Mirror Lake, New York, 2016

	Lake Placid News. Accessed June 2016.Â www.lakeplacidnews.com.

All other data

	NSIDC (National Snow and Ice Data Center). 2014. Global lake and river ice phenology. Last updated January 2014.Â http://nsidc.org/data/lake_river_ice.

Figure 2

Cobbosseecontee Lake, Damariscotta Lake, Moosehead Lake, and Sebago Lake, Maine, 1800sâ€“2008
Hodgkins, G.A. 2010. Historical ice-out dates for 29 lakes in New England, 1807â€“2008. U.S. Geological Survey Open-File Report 2010-1214.

Cobbosseecontee Lake, Damariscotta Lake, Moosehead Lake, and Sebago Lake, Maine, 2009â€“2015

	U.S. Geological Survey. 2016. Personal communication.

Detroit Lake, Minnesota, 2006â€“2015

	Lake Osakis, Minnesota, 1867â€“2015

	Minnesota Department of Natural Resources. Accessed June 2016.Â www.dnr.state.mn.us/ice_out/index.html.

Geneva Lake, Wisconsin, 2005â€“2015

	Geneva Lake Environmental Agency Newsletters. Accessed June 2016.Â www.genevaonline.com/~glea/newsletters.php.

Lake George, New York, 2005â€“2014

	Lake George Association. Accessed June 2016.Â www.lakegeorgeassociation.org/who-we-are/documents/Ice-In-Ice-Out2015.pdf.

Lake Mendota and Lake Monona, Wisconsin, 2011â€“2015

	North Temperate Lakes Long Term Ecological Research site. Accessed June 2016.Â https://lter.limnology.wisc.edu/lakeinfo/ice-data?lakeid=MEÂ andÂ https://lter.limnology.wisc.edu/lakeinfo/ice-data?lakeid=MO.

Mirror Lake, New York, 2007â€“2012

	Adirondack Daily Enterprise. Accessed December 2013.Â www.adirondackdailyenterprise.com.

Mirror Lake, New York, 2013â€“2015

	Lake Placid News. Accessed June 2016.Â www.lakeplacidnews.com.

Otsego Lake, New York, 2005â€“2014

	State University of New York (SUNY) Oneonta Biological Field Station. Annual Reports. Accessed May 2015.Â www.oneonta.edu/academics/biofld/PUBS/ANNUAL/2013/29-Otsego-Ice-History-2014.pdf.

Shell Lake, Wisconsin, 2005â€“2015

	Washburn County Clerk. 2016. Personal communication.

All other data

	NSIDC (National Snow and Ice Data Center). 2014. Global lake and river ice phenology. Last updated January 2014.Â http://nsidc.org/data/lake_river_ice.

Figure 3

Cobbosseecontee Lake, Damariscotta Lake, Moosehead Lake, and Sebago Lake, Maine, 1905â€“2008

	Hodgkins, G.A. 2010. Historical ice-out dates for 29 lakes in New England, 1807â€“2008. U.S. Geological Survey Open-File Report 2010-1214.

Cobbosseecontee Lake, Damariscotta Lake, Moosehead Lake, and Sebago Lake, Maine, 2009â€“2015

	U.S. Geological Survey. 2016. Personal communication.

Detroit Lake, Minnesota, 2006â€“2015

	Lake Osakis, Minnesota, 1905â€“2015

	Minnesota Department of Natural Resources. Accessed June 2016.Â www.dnr.state.mn.us/ice_out/index.html.

Geneva Lake, Wisconsin, 2005â€“2015

	Geneva Lake Environmental Agency Newsletters. Accessed June 2016.Â www.genevaonline.com/~glea/newsletters.php.

Lake George, New York, 2004â€“2015

	Lake George Association. Accessed June 2016.Â www.lakegeorgeassociation.org/who-we-are/documents/Ice-In-Ice-Out2015.pdf.

Lake Mendota and Lake Monona, Wisconsin, 2011â€“2015

	North Temperate Lakes Long Term Ecological Research site. Accessed June 2016.Â https://lter.limnology.wisc.edu/lakeinfo/ice-data?lakeid=MEÂ andÂ https://lter.limnology.wisc.edu/lakeinfo/ice-data?lakeid=MO.

Mirror Lake, New York, 2007â€“2012

	Adirondack Daily Enterprise. Accessed December 2013.Â www.adirondackdailyenterprise.com.

Mirror Lake, New York, 2013â€“2015

	Lake Placid News. Accessed June 2016.Â www.lakeplacidnews.com.

Otsego Lake, New York, 2005â€“2014

	State University of New York (SUNY) Oneonta Biological Field Station. Annual Reports. Accessed May 2015.Â www.oneonta.edu/academics/biofld/PUBS/ANNUAL/2013/29-Otsego-Ice-History-2014.pdf.

Shell Lake, Wisconsin, 2005â€“2015

	Washburn County Clerk. 2016. Personal communication.

All other data

	NSIDC (National Snow and Ice Data Center). 2014. Global lake and river ice phenology. Last updated January 2014.Â http://nsidc.org/data/lake_river_ice.

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Learn about other indicators in this section

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Climate Indicators

Climate Change Indicators

Greenhouse Gases

Weather and Climate

Oceans

Snow and Ice

Arctic Sea Ice

Antarctic Sea Ice

Glaciers

Lake Ice

Community Connection: Ice Breakup in Two Alaskan Rivers

Snowfall

Snow Cover

Snowpack

Health and Society

Ecosystems

Frequent Questions