---
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-annual-greenhouse-gas-index-2021.yaml
  identifier: indicator-annual-greenhouse-gas-index-2021
  in_library: ~
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points:\r\n\r\nThe warming influence of greenhouse gases in the atmosphere continues to increase substantially as it has over the last several decades. In 2020, the AGGI was 1.47, representing an increase of 47% since 1990, the base year for the Kyoto Protocol (an international agreement in which countries pledged to reduce greenhouse gas emissions to below 1990 levels). Carbon dioxide (CO2) is the largest contributor to radiative forcing. Year-to-year variations in how much the AGGI value increases generally correspond to how much CO2 increases each year, because CO2 is responsible for about two-thirds of the radiative forcing among all greenhouse gases.\r\n\r\nAbout the Indicator:\r\n\r\nThis indicator demonstrates the change in radiative forcing resulting from changing concentrations of multiple greenhouse gases stored in Earth’s atmosphere:\r\n- carbon dioxide (CO2)\r\n- methane (CH4)\r\n- nitrous oxide (N2O)\r\n- chlorofluorocarbons (CFCs*)\r\n- hydrochlorofluorocarbons (HCFCs*)\r\n- hydrofluorocarbons (HFCs*)\r\n\r\n* The “CFC” grouping includes some other long-lived gases that are not CFCs, but the CFCs account for the majority of the radiative forcing in this category. The “HCFC” grouping includes the three most abundant HCFCs. The “HFC” grouping includes the most abundant HFCs and SF6 for completeness. See The NOAA Annual Greenhouse Gas Index page for full details.\r\n\r\nThis indicator measures the average total radiative forcing of multiple long-lived, well mixed greenhouse gases, including the three most abundant: carbon dioxide, methane, and nitrous oxide. Due to their long lifetimes and because of transport by winds, these gases become well mixed throughout the global atmosphere. The results were calculated by the National Oceanic and Atmospheric Administration (NOAA) based on measured concentrations of the gases in the atmosphere, compared with the concentrations that were present around 1750 (a baseline concentration of 0 watts per square meter), 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. Learn more about radiative forcing.\r\n\r\nNOAA's Global Monitoring Laboratory provides high-precision measurements of the abundance and distribution of long-lived greenhouse gases that are used to calculate global average concentrations. Radiative forcing for each gas is computed from these concentrations, and total radiative forcing for all gases is used to calculate the AGGI.\r\n\r\nThe atmospheric abundance and radiative forcing of the three main long-lived greenhouse gases (CO2, CH4, and N2O) continue to increase. While the combined radiative forcing of these and all other greenhouse gases included in the AGGI rose 47% from 1990 to 2020 (by ~1.02 watts per square meter), carbon dioxide has accounted for about 80% of this increase (~0.82 watts per square meter), which makes it by far the biggest contributor to increases in climate forcing since 1990. Radiative forcing from methane has steadily increased since 2007, after having been nearly constant from 1999 to 2006. Owing to the Montreal Protocol, an international agreement signed in 1987, CFCs have been decreasing since the mid- to late 1990s after a long period of increase; however, the current warming influence from CFCs and related gases is still larger than that from HCFCs and HFCs. CFC replacements (HCFCs and HFCs) have been increasing since the phase-out of CFCs.\r\n\r\nWhy it's Important:\r\n\r\n- The warming influence of greenhouse gases in the atmosphere—the cause of global warming today—has increased substantially over the last several decades.\r\n- AGGI is a measure of what human activity has already done to affect the climate system through greenhouse gas emissions.\r\n- Decision makers can use this indicator to inform mitigation strategies."
  title: 'Indicator: Annual Greenhouse Gas Index'
  topic: ~
  uri: /report/indicator-annual-greenhouse-gas-index-2021
  url: http://www.globalchange.gov/browse/indicators/annual-greenhouse-gas-index
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-arctic-glacier-mass-balance-2021.yaml
  identifier: indicator-arctic-glacier-mass-balance-2021
  in_library: ~
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points:\r\nThe loss of land-based ice in the Arctic has accelerated in recent decades, contributing to global sea level rise.\r\n\r\nAbout the Indicator:\r\nThis indicator provides information on the cumulative change in mass balance of glaciers over time. Glacier mass balance data are calculated based on a variety of measurements at the surface of a glacier, including measurements of snow depths and snow density. The net balance is the average mass balance of the glacier from data collected over a glaciological year, the time between the end of the summer ablation season from one year to the next. \r\n\r\nThe overall Arctic average change in mass balance declined, consistent with the retreat of glaciers observed in other parts of the world. The Engabreen glacier, situated near the coast of Norway, gained mass over the period of record and is more strongly influenced by precipitation than glaciers elsewhere in the Arctic.  \r\n\r\nRapid changes are occurring across the Arctic where air temperatures are warming twice as fast as the global average temperature. The loss of land-based ice in the Arctic has accelerated in recent decades and since at least 1972, the Arctic has been the dominant source of global sea-level rise. After Greenland, the largest contributor to global sea-level rise from Arctic land ice, are the Arctic’s glaciers.\r\n\r\nWhy It Is Important:\r\nGlaciers provide visible evidence of changes in temperature and precipitation.\r\nIf increases in greenhouse gas concentrations continue at current rates, it is expected that many of the smallest glaciers across the Arctic would disappear entirely by mid-century."
  title: 'Indicator: Arctic Glacier Mass Balance'
  topic: ~
  uri: /report/indicator-arctic-glacier-mass-balance-2021
  url: https://www.globalchange.gov/browse/indicators/arctic-glacier-mass-balance
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-arctic-sea-ice-extent-2021.yaml
  identifier: indicator-arctic-sea-ice-extent-2021
  in_library: ~
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points:  \r\n\r\nThe September minimum sea ice extent in the Arctic has continued to decrease over the past four decades. Some projections suggest that the Arctic will be virtually ice-free during summers by the middle of this century.\r\n\r\n\r\nAbout the Indicator:  \r\n\r\nSea ice extent is estimated using daily satellite images to calculate the total ocean area that has an ice concentration of 15% or more. Trends in sea ice extent are calculated from average values measured during the month of September, which is typically when sea ice extent reaches its annual minimum. Minimum sea ice extent in the Arctic has decreased by about 44% since 1979 (the first full year of satellite data). At this rate, some projections suggest that the Arctic will be virtually ice-free during summers by the middle of this century. \r\n\r\nThe melting of sea ice reduces the area of white surface that reflects the sun’s radiation, simultaneously increasing the area of dark ocean surface that absorbs it. This albedo affect results in a cycle of further sea ice melt and more warming of the ocean. Before melting begins, snow-covered sea ice absorbs only about 20% of the solar radiation that reaches it, whereas the ice-free ocean surface absorbs over 90%. A warmer ocean may melt ice from below, or may release heat back into the atmosphere before the ocean refreezes in the winter—leading over time to less sea ice and a warmer climate.\r\n\r\n\r\nWhy It's Important:\r\n\r\n- As sea ice cover declines and the Arctic atmosphere warms, wind patterns in the northern hemisphere may shift.\r\n- The loss of ice increases the risk of erosion along coastlines and changes the presence of marine species in certain areas, affecting commercial fish stocks and the economies of some coastal towns.\r\n- Decision-makers can use this indicator to understand the magnitude and rate of sea ice loss and prepare for the associated impacts on coastlines and commercial industries."
  title: 'Indicator: Arctic Sea Ice Extent'
  topic: ~
  uri: /report/indicator-arctic-sea-ice-extent-2021
  url: http://www.globalchange.gov/browse/indicators/arctic-sea-ice-extent
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-atmospheric-carbon-dioxide-2021.yaml
  identifier: indicator-atmospheric-carbon-dioxide-2021
  in_library: 1
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points:\r\n\r\nThe amount of CO2 in the atmosphere has increased more than 20% in 40 years, owing largely to human activities, and representing well over 50% of the total increase in atmospheric carbon dioxide since the onset of the industrial revolution (1750).\r\n\r\nAbout the Indicator:\r\n\r\nGreenhouse gases such as carbon dioxide trap heat in the atmosphere. Increasing concentrations of these gases have driven an increase in global temperatures. The Annual Greenhouse Gas Index (AGGI) shows that over the past decade, increases in carbon dioxide are responsible for about 82% of the increase in the heat-trapping capacity of the atmosphere. Although the atmospheric concentration of carbon dioxide fluctuates over seasonal cycles, as illustrated by the saw-tooth pattern in the graph, the overall trend has been a steady increase since data collection began. Global monthly average concentrations of carbon dioxide have risen from around 339 parts per million in 1980 (averaged over the year) to 412 parts per million in 2020, an increase of more than 20%. \r\n\r\nThe NOAA Global Monitoring Laboratory has measured carbon dioxide and other greenhouse gases for several decades through a globally distributed network of about 70 air sampling sites, including the Mauna Loa Observatory in Hawai’i. The data for this indicator come from a subset of about 40 of these sites located in isolated regions of the ocean.\r\n\r\nWhy it's Important:\r\n\r\nCarbon dioxide concentration is an important measure of how human activity has increased the heat-trapping capacity of the atmosphere.\r\n\r\nThis indicator can inform carbon emissions policies at national and international levels."
  title: 'Indicator: Atmospheric Carbon Dioxide'
  topic: ~
  uri: /report/indicator-atmospheric-carbon-dioxide-2021
  url: http://www.globalchange.gov/browse/indicators/atmospheric-carbon-dioxide
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-billion-dollar-disasters-2021.yaml
  identifier: indicator-billion-dollar-disasters-2021
  in_library: ~
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points:  \r\n\r\n1. The number of weather and climate-related disasters exceeding 1 billion dollars has increased in the United States since 1980. \r\n2. The increase in Billion Dollar Disasters over time represents a combination of factors, including an increase in the magnitude and frequency of some kinds of hazards (flooding, extreme heat, a driving component of drought and wildfire hazards) and changes in the value and placement of assets and property.\r\n3. From January 1980 through December 2020, the U.S. experienced 290 weather and climate disasters with overall damage costs reaching or exceeding $1 billion, including Consumer Price Index (CPI) adjustments, for each individual event. The cumulative costs for these 290 events exceed $1.900 trillion.\r\n\r\n\r\nAbout the Indicator: \r\n\r\nThe Billion Dollar Disaster indicator provides insight into the frequency and the total estimated costs of major weather and climate events that occur in the United States. This indicator compiles the annual number of weather and climate-related disasters across seven event types. Events are included if they are estimated to cause more than one billion U.S. dollars in direct losses. The cost estimates of these events are adjusted for inflation using the Consumer Price Index (CPI) and are based on costs documented in several Federal and private-sector databases.\r\n\r\nIn recent decades, the U.S. has experienced a rising number of weather and climate disasters that cause significant economic damages and societal losses. From 1980 to 2020, the annual average number of billion-dollar events was 7.1, including CPI adjustments. For the most recent 5 years (2016–2020), the annual average was 16.2 events.\r\n\r\n2020 set a new annual record of 22 events - shattering the previous annual record of 16 events that occurred in 2011 and 2017. 2020 is the sixth consecutive year (2015-2020) in which 10 or more billion-dollar weather and climate disaster events have impacted the United States. Over the last 41 years (1980-2020), the years with 10 or more separate billion-dollar disaster events include 1998, 2008, 2011-2012, and 2015-2020 (Smith 2021).\r\n\r\nThe distribution of damage from U.S. Billion-dollar disaster events from 1980 to 2020 is dominated by tropical cyclone losses. Tropical cyclones have caused the most damage ($1,010.4 billion) and also have the highest average event cost ($19.4 billion per event). Hurricanes are responsible for slightly more than half (53.0%) of the total losses for all the U.S. billion-dollar disasters but represent approximately one-fifth (17.9%) of all the billion-dollar events we have assessed since 1980.\r\n\r\nThe increase in population and material wealth over the last several decades are important factors for the increased damage potential. Climate change is also playing an increasing role in the increasing frequency of some types of extreme weather that lead to billion-dollar disasters. Most notably, the rise in vulnerability to drought, lengthening wildfire seasons and the potential for extremely heavy rainfall and inland flooding events are most acutely related to the influence of climate change (USGCRP 2018).\r\n\r\nWhy It’s Important:  - \r\n\r\n- In addition to direct threats to life and safety, major weather and climate disasters claim property, disrupt business, and affect daily life.\r\n- All U.S. states, Puerto Rico, and the U.S. Virgin Islands have been impacted by at least one billion-dollar disaster since 1980.\r\n- Climate change is playing a role in the increasing frequency of some types of extreme weather that lead to billion-dollar disasters."
  title: 'Indicator: Billion Dollar Disasters'
  topic: ~
  uri: /report/indicator-billion-dollar-disasters-2021
  url: https://www.globalchange.gov/browse/indicators/billion-dollar-disasters
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-global-surface-temperature-2021.yaml
  identifier: indicator-global-surface-temperature-2021
  in_library: ~
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points: \r\n\r\nSince the 1880s, the average global temperature has increased by 1.8°F. Since the 1980s, average temperatures have exceeded the last century's average every year.\r\n\r\nAbout the Indicator:\r\n\r\nGlobal average temperatures include air temperatures measured on land and sea surface temperatures measured from ships and buoys worldwide. The data shown in the graph were drawn from the National Oceanic and Atmospheric Administration (NOAA) Global Historical Climatology Network (GHCN) and International Comprehensive Ocean-Atmosphere Data Set (ICOADS).\r\n\r\nWhy It's Important:\r\n\r\nChanges in global temperatures over the past century provide one important line of evidence for the effects of increasing greenhouse gas emissions. Such evidence can inform national and international policy discussions."
  title: 'Indicator: Global Surface Temperatures'
  topic: ~
  uri: /report/indicator-global-surface-temperature-2021
  url: http://www.globalchange.gov/browse/indicators/global-surface-temperatures
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-heating-and-cooling-degree-days-2021.yaml
  identifier: indicator-heating-and-cooling-degree-days-2021
  in_library: ~
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points: \r\n\r\nDegree days reflect changes in climate and are used as an indicator for the energy demand for heating or cooling buildings (generally, fossil fuel demand for heating and electricity demand for cooling).  Since around 1980, the number of heating degree days has decreased and the number of cooling degree days has increased relative to the 20th-century average. The recent increase in cooling degree days is driven by more frequent days above 65°F and more frequent extreme high temperatures.\r\n\r\nAbout the Indicator:\r\n\r\nHeating and cooling degree days are calculated by the National Oceanic and Atmospheric Administration (NOAA). Daily temperature values for each region of the United States are used to calculate departures from the 65°F baseline. These values are population-weighted using United States Census Bureau data, such that, for example, the same temperature produces more degree days in New York City than in rural Nebraska.\r\n\r\nWhy It's Important:\r\n\r\nThis indicator is used in utility planning and can support construction decisions. It provides information on the relationship between climate and energy use that can inform mitigation strategies.\r\n\r\nAs temperatures continue to rise, combined changes in heating and cooling degree days are projected to change patterns of energy use and increase net electricity demand nationwide."
  title: 'Indicator: Heating and Cooling Degree Days'
  topic: ~
  uri: /report/indicator-heating-and-cooling-degree-days-2021
  url: http://www.globalchange.gov/browse/indicators/heating-and-cooling-degree-days
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-us-heat-waves-2021.yaml
  identifier: indicator-us-heat-waves-2021
  in_library: ~
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points:\r\n\r\nHeat waves are occurring more often than they used to in major cities across the United States, from an average of two heat waves per year during the 1960s to more than six per year during the 2010s. The average heat wave season across 50 major cities is 47 days longer than it was in the 1960s. Of the 50 metropolitan areas in this indicator, 46 experienced a statistically significant increase in heat wave frequency between the 1960s and 2010s. The increase in the length of the heat wave season was significant in 44 locations.\r\n\r\nAbout the Indicator:\r\n\r\nUnusually hot days and multi-day heat waves are a natural part of day-to-day variation in weather. As the Earth’s climate warms, however, hotter-than-usual days and nights are becoming more common and heat waves are expected to become more frequent and intense (Climate Science Special Report Executive Summary) <tbib>21f65069-74b3-4bf7-bc09-0f359b825aad</tbib>. Increases in these extreme heat events can lead to more heat-related illnesses and deaths, especially if people and communities are not prepared and do not take steps to adapt <tbib>f0640d95-a845-40e6-a442-88eeff3127dc</tbib>.\r\n\r\nLarge urban areas already face challenges related to heat.  Surface air temperatures are often higher in urban areas than in surrounding rural areas for a number of reasons, including the concentrated release of heat from buildings, vehicles, and industry. This urban heat island effect, is expected to strengthen in the future as the structure, spatial extent, and population density of urban areas change and grow (Climate Science Special Report, Chapter 10) <tbib>1b0ce605-0f6c-4e1f-8fea-71e87cb4304f</tbib>.\r\n\r\nThis indicator examines trends over time in two characteristics of heat waves in the United States: \r\n- Frequency: the number of heat waves that occur every year.\r\n- Season length: the number of days between the first heat wave of the year and the last.\r\n\r\nHeat waves can be defined in many ways. For consistency across the country, this indicator defines a heat wave as a period of two or more consecutive days where the daily minimum apparent temperature (actual temperature adjusted for humidity) in a particular city exceeds the 85th percentile of historical July and August temperatures (1981–2010) for that city. This approach is useful for several reasons:\r\n\r\n- The most serious health impacts of a heat wave are often associated with high temperatures at night, which is when the daily minimum usually occurs. If the air temperature stays too warm at night, the body faces extra strain as the heart pumps harder to try to regulate body temperature.\r\n- Adjusting for humidity is important because when humidity is high, water does not evaporate as easily, so it is harder for the human body to cool off by sweating. That is why health warnings about extreme heat are often based on the “heat index,” which combines temperature and humidity.\r\n- By using the 85th percentile for each individual city, this indicator defines “unusual” in terms of local conditions. A specific temperature like 95°F might be considered unusually hot in one city but perfectly normal in another city. Plus, people in relatively warm regions (such as the Southwest) may be better acclimated and adapted to hot weather.\r\n\r\nData for this indicator are based on temperature and humidity measurements between 1961 and 2019 from long-term weather stations, which are generally located at airports. This indicator focuses on the 50 most populous U.S. metropolitan areas that have available weather data from a consistent location. The year 1961 was chosen as the starting point because most major cities have collected consistent data since at least that time. The methodology for this indicator is based on Habeeb et al. 2015. \r\n\r\nWhy It’s Important:\r\n\r\n- Heat waves can lead to illness and death, particularly among older adults, the very young, economically disadvantaged groups, and other vulnerable populations such as those in outdoor occupations.\r\n- Prolonged exposure to excessive heat can lead to other impacts—for example, damaging crops and injuring or killing livestock.\r\n- Extreme heat events can lead to power outages as heavy demands for air conditioning strain the power grid."
  title: 'Indicator: Heat Waves'
  topic: ~
  uri: /report/indicator-us-heat-waves-2021
  url: https://www.globalchange.gov/browse/indicators/us-heat-waves
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-ocean-chlorophyll-concentrations-2020.yaml
  identifier: indicator-ocean-chlorophyll-concentrations-2020
  in_library: ~
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points:\r\n\r\n  - Some of the highest average chlorophyll concentrations are located near continental coasts of the Pacific and Atlantic Oceans.  \r\n\r\nAbout the Indicator:  \r\n\r\nPhytoplankton are microscopic, floating, plant-like organisms that live in oceans, lakes, and rivers. Phytoplankton form the base of the marine food web, converting solar energy into organic matter (primary production). This process ultimately feeds the world’s fish, sea birds, marine mammals, and humans. Because phytoplankton use photosynthetic pigments like chlorophyll to convert solar energy into organic matter, the amount of phytoplankton present in the ocean can be assessed by measuring chlorophyll concentrations. When phytoplankton populations are large, the color of the water appears greener because of high concentrations of chlorophyll.  \r\n\r\nPhytoplankton populations, as indicated by chlorophyll concentrations, respond to both seasonal (short-term) and climatic (long-term) changes. Primary production by phytoplankton can be affected indirectly by climatic factors, such as changes in water temperatures and surface winds, which affect mixing within the water column and the availability of nutrients. Changes in cloud cover, which can reduce or increase solar energy available for photosynthesis, can also affect primary production.  \r\n\r\nThe chlorophyll concentration data shown here were obtained from global satellite measurements by the SeaWiFS and MODIS-Aqua projects of the National Aeronautics and Space Administration (NASA). Satellite data collection allows for large spatial coverage and frequent measurements over time, which is useful for assessing long-term changes. One limitation, however, is that satellites can only measure near-surface chlorophyll concentrations, thus potentially underestimating the total amount of phytoplankton present at all water depths. Chlorophyll concentrations also do not provide information on the composition of phytoplankton communities (for example, the abundance of larger versus smaller species).  \r\n\r\nWhy It’s Important:  \r\n\r\n- Changes in phytoplankton populations may impact fish and other marine life, which can affect economic productivity and food availability. \r\n- Decision makers can use this indicator to understand the health and productivity of marine ecosystems that depend on phytoplankton."
  title: 'Indicator: Ocean Chlorophyll Concentrations'
  topic: ~
  uri: /report/indicator-ocean-chlorophyll-concentrations-2020
  url: https://www.globalchange.gov/browse/indicators/ocean-chlorophyll-concentrations
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-sea-level-rise-2021.yaml
  identifier: indicator-sea-level-rise-2021
  in_library: ~
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points:\r\n\r\nGlobal sea level has risen by about 8 inches since scientific record keeping began in 1880. The rate of global sea level rise has increased in recent decades. The current rate is a little more than an inch per decade.\r\n\r\nAbout the Indicator:\r\n\r\nRising global sea level is a critical consequence of climate change. As ocean waters warm, they expand. Also, as air temperatures warm, water from melting ice sheets, polar ice caps, and glaciers enters into our ocean basins.\r\n\r\nSea level rise is not uniform across the globe. Coastal communities are affected by their local sea level rise, which reflects global sea level rise, changes in local land elevation, tides and winds. In Louisiana, for example, local sea level is rising about 4 inches per decade because the land is sinking and sea level is rising.\r\nGlobal average sea level has risen by about 8 inches (about 21 cm) since 1900, with about 3 of those inches (about 7.5 cm) occurring since 1993. Human-caused climate change has made a substantial contribution to sea level rise since 1900, contributing to a rate of rise greater than during any preceding century in at least 2,800 years. In addition to the global average sea level rise, local sea level rise – sometimes called “relative sea level rise” – happens at different rates in different places. Local sea level rise is affected by the global sea level rise, but also by local land motions, and the effects of tides, currents, and winds. Many places along the United States coast have seen their local sea levels rise faster than the average global rate. As sea levels have risen, the number of tidal floods each year that cause minor impacts, often called “nuisance floods,” have increased 5- to 10-fold since the 1960s in several U.S. coastal cities (very high confidence). Rates of increase are accelerating in over 25 Atlantic and Gulf Coast cities (very high confidence).\r\n\r\nWhy It’s Important:\r\n\r\n- Sea level rise and climate change-related threats like high tide and storm-surge flooding affects social, economic, and ecological systems along the U.S. coasts.\r\n- Sea level rise affects local infrastructure and economies in U.S. coastal communities as more areas are affected by tidal flooding and the effects of increasing storm surge during extreme weather events."
  title: 'Indicator: Sea Level Rise'
  topic: ~
  uri: /report/indicator-sea-level-rise-2021
  url: https://www.globalchange.gov/browse/indicators/global-sea-level-rise
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-sea-surface-temperature-2021.yaml
  identifier: indicator-sea-surface-temperature-2021
  in_library: ~
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points:    \r\n\r\nDuring the past four decades, sea surface temperatures have exceeded the 20th century average every year and are now higher than at any other time since records began.  \r\n\r\nAbout the Indicator:  \r\n\r\nThe data shown represent temperatures in the upper 10 meters of the ocean and were drawn from the National Oceanic and Atmospheric Administration (NOAA) NOAAGlobalTemp dataset.   \r\n\r\nWhy It’s Important:  - \r\n\r\nChanges in sea surface temperatures reflect the overall warming trend in the climate system and, in turn, influence weather and climate patterns worldwide.  - Sea surface temperature data can be used to understand the response of the ocean to global warming and, in turn, how that response may influence other changes in climate."
  title: 'Indicator: Sea Surface Temperatures'
  topic: ~
  uri: /report/indicator-sea-surface-temperature-2021
  url: https://www.globalchange.gov/browse/indicators/sea-surface-temperatures
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-start-of-spring-2021.yaml
  identifier: indicator-start-of-spring-2021
  in_library: ~
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points:   \r\n\r\nOn average, the start of spring has occurred earlier in the contiguous United States since 1984. A trend toward earlier springs  could have significant implications for agriculture, natural resource and hazard management, and recreation.  \r\n\r\nAbout the Indicator:  \r\n\r\nThis indicator estimates the annual start of spring on the basis of when growth can begin for temperature-sensitive native and cultivated plants. It can be used to monitor, assess, and predict variations and trends in spring timing at the national scale.   \r\n\r\nThe annual start of spring can be estimated for any location where daily minimum and maximum temperatures are recorded. The modeled values correlate well with observed leafing and flowering in a number of native and cultivated species, such as winter wheat, pear, and peach varieties.   \r\n\r\nThese values are calculated from a numerical model that simulates the accumulation of heat needed to bring plants out of winter dormancy and into vegetative and reproductive growth. The model is based on:  \r\n- Long-term observations of lilac and honeysuckle first-leaf and first-bloom, collected by citizen science volunteers at hundreds of sites across the contiguous United States \r\n- Daily minimum and maximum temperatures measured at weather stations  \r\n\r\nWhy It’s Important:  \r\n\r\n- The earlier arrival of the start of spring has been linked to recent warming trends in global climate. \r\n- This indicator can help decision makers understand and anticipate climate impacts on:  \r\n\r\n-  habitats and species \r\n-  agricultural production \r\n-  recreation \r\n-  the management of natural hazards such as wildfires"
  title: 'Indicator: Start of Spring'
  topic: ~
  uri: /report/indicator-start-of-spring-2021
  url: https://www.globalchange.gov/browse/indicators/start-spring
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-terrestrial-carbon-storage-2020.yaml
  identifier: indicator-terrestrial-carbon-storage-2020
  in_library: ~
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points:\r\n\r\n- Terrestrial ecosystems store large amounts of carbon dioxide each year: for example, net annual carbon dioxide storage by forests, urban forests, croplands, and grasslands totaled 773.8 million metric tons in 2018.  \r\n\r\n- Forests (not including urban forests) annually store the majority of terrestrial carbon dioxide in the United States. In recent years, croplands and grasslands have become net carbon dioxide sources. With the exception of one year since 2009, more carbon dioxide has been released annually than stored in croplands and grasslands.\r\n\r\nAbout the Indicator:\r\n\r\n- The data shown in the graph were drawn from the U.S. Environmental Protection Agency (EPA) Inventory of Greenhouse Gas Emissions and Sinks, in which annual carbon dioxide storage is estimated using three complementary datasets: the U.S. Department of Agriculture (USDA) National Resources Inventory, the USDA Forest Service Forest Inventory and Analysis, and the Multi-Resolution Land Characteristics Consortium National Land Cover Dataset. These datasets represent a combination of statistical survey approaches and satellite data. Changes to terrestrial carbon storage reflect the impacts of many factors.\r\n\r\nWhy it's Important:\r\n\r\n- Changes affecting these ecosystems—such as alterations in climate or land use—can contribute to changes in carbon storage, which in turn can affect the climate system through the release of greenhouse gases.\r\n\r\n- This indicator can help decision makers understand how climate change, land management, natural disturbances, and ecosystem dynamics affect annual terrestrial carbon storage in the United States."
  title: 'Indicator: Terrestrial Carbon Storage'
  topic: ~
  uri: /report/indicator-terrestrial-carbon-storage-2020
  url: https://www.globalchange.gov/browse/indicators/terrestrial-carbon-storage
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-us-surface-temperature-2021.yaml
  identifier: indicator-us-surface-temperature-2021
  in_library: ~
  publication_year: 2021
  report_type_identifier: indicator
  summary: "Key Points:  \r\n\r\nRising temperatures in the United States are indicative of warming in the global climate system. In the contiguous United States, temperatures during this century have been, on average, 1.5°F warmer than during the last century. Human activities have contributed to this increase in temperature through the addition of carbon dioxide and other heat-trapping greenhouse gases into the atmosphere.  \r\n\r\nAbout the Indicator:  \r\n\r\nThese data were obtained from the National Oceanic and Atmospheric Administration (NOAA) nClimDiv dataset. \r\n\r\nThe nClimDiv is based on daily data from the Global Historical Climatology Network (GHCN), which includes temperature and other climatic measurements from stations located around the world.  \r\n\r\nWhy It’s Important:  \r\n\r\n- This Indicator can inform preparedness decisions in a wide variety of sectors, such as energy production, agriculture, and human health."
  title: 'Indicator: U.S. Surface Temperatures'
  topic: ~
  uri: /report/indicator-us-surface-temperature-2021
  url: https://www.globalchange.gov/browse/indicators/us-surface-temperatures
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-annual-greenhouse-gas-index-2020.yaml
  identifier: indicator-annual-greenhouse-gas-index-2020
  in_library: ~
  publication_year: 2020
  report_type_identifier: indicator
  summary: "Key Points: \r\n\r\nThe warming influence of greenhouse gases in the atmosphere has increased substantially over the last several decades. In 2019, the AGGI was 1.45, which represents an increase of 45% since 1990. Carbon dioxide remains the largest contributor to radiative forcing.\r\n\r\n\r\nAbout the Indicator:\r\n\r\nThis indicator demonstrates the change in radiative forcing resulting from changing concentrations of twenty greenhouse gases:\r\n- carbon dioxide (CO₂)\r\n- methane (CH₄)\r\n- nitrous oxide (N₂O)\r\n- chlorofluorocarbons (CFC-11 and CFC-12)\r\n- a set of 15 minor, long-lived halogenated gases\r\n\r\nThis 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 (NOAA) 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. \r\n\r\nNOAA’s Global Monitoring Division provides high-precision measurements of the abundance and distribution of long-lived greenhouse gases that are used to calculate global average concentrations. Radiative forcing for each gas is computed from these concentrations, and total radiative forcing for all gases is used to calculate the AGGI. \r\n\r\nRadiative forcing from methane has steadily increased since 2007, after having been nearly constant from 1999 to 2006. Owing to the Montreal Protocol, an international agreement signed in 1987, CFCs have been decreasing since the mid- to late 1990s after a long period of increase. However, CFC replacements (many of the “other halogenated gases” in the graph) have been increasing since the phase-out of CFCs.\r\n\r\nWhy It’s Important:\r\n\r\n- The warming influence of greenhouse gases in the atmosphere has increased substantially over the last several decades.\r\n- AGGI is a measure of what human activity has already done to affect the climate system through greenhouse gas emissions.\r\n- Decision makers can use this indicator to inform mitigation strategies."
  title: 'Indicator: Annual Greenhouse Gas Index'
  topic: ~
  uri: /report/indicator-annual-greenhouse-gas-index-2020
  url: ~
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-arctic-sea-ice-extent-2020.yaml
  identifier: indicator-arctic-sea-ice-extent-2020
  in_library: ~
  publication_year: 2020
  report_type_identifier: indicator
  summary: "Key Points:  \r\n\r\nThe September minimum sea ice extent in the Arctic has continued to decrease over the past four decades. Some projections suggest that the Arctic will be virtually ice-free during summers by the middle of this century.\r\n\r\n\r\nAbout the Indicator:  \r\n\r\nSea ice extent is estimated using daily satellite images to calculate the total ocean area that has an ice concentration of 15% or more. Trends in sea ice extent are calculated from average values measured during the month of September, which is typically when sea ice extent reaches its annual minimum. Minimum sea ice extent in the Arctic has decreased by about 39% since 1979 (the first full year of satellite data). At this rate, some projections suggest that the Arctic will be virtually ice-free during summers by the middle of this century. \r\n\r\nThe melting of sea ice reduces the area of white surface that reflects the sun’s radiation, simultaneously increasing the area of dark ocean surface that absorbs it. This albedo affect results in a cycle of further sea ice melt and more warming of the ocean. Before melting begins, snow-covered sea ice absorbs only about 20% of the solar radiation that reaches it, whereas the ice-free ocean surface absorbs over 90%. A warmer ocean may melt ice from below, or may release heat back into the atmosphere before the ocean refreezes in the winter—leading over time to less sea ice and a warmer climate.\r\n\r\n  \r\nWhy It’s Important:  \r\n\r\n- As sea ice cover declines and the Arctic atmosphere warms, wind patterns in the northern hemisphere may shift.\r\n- The loss of ice increases the risk of erosion along coastlines and changes the presence of marine species in certain areas, affecting commercial fish stocks and the economies of some coastal towns.\r\n- Decision makers can use this indicator to understand the magnitude and rate of sea ice loss and prepare for the associated impacts on coastlines and commercial industries."
  title: 'Indicator: Arctic Sea Ice Extent'
  topic: ~
  uri: /report/indicator-arctic-sea-ice-extent-2020
  url: ~
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-atmospheric-carbon-dioxide-2020.yaml
  identifier: indicator-atmospheric-carbon-dioxide-2020
  in_library: ~
  publication_year: 2020
  report_type_identifier: indicator
  summary: "Key Points:\r\n\r\nThe amount of CO2 in the atmosphere has increased more than 20% in less than 40 years, owing largely to human activities, and representing well over 50% of the total increase in atmospheric carbon dioxide since the onset of the industrial revolution (1750).\r\n\r\nAbout the Indicator: \r\n\r\nGreenhouse gases such as carbon dioxide trap heat in the atmosphere. Increasing concentrations of these gases have driven an increase in global temperatures. The Annual Greenhouse Gas Index (AGGI) shows that over the past decade, increases in carbon dioxide are responsible for about 84% of the increase in the heat-trapping capacity of the atmosphere. Although the atmospheric concentration of carbon dioxide fluctuates over seasonal cycles, as illustrated by the saw-tooth pattern in the graph, the overall trend has been a steady increase since data collection began. Global monthly average concentrations of carbon dioxide have risen from around 339 parts per million in 1980 (averaged over the year) to 410 parts per million in 2019, an increase of more than 20%.\r\n\r\nThe National Oceanic and Atmospheric Administration (NOAA) Global Monitoring Division has measured carbon dioxide and other greenhouse gases for several decades through a globally distributed network of about 70 air sampling sites, including the Mauna Loa Observatory in Hawai’i. The data for this indicator come from a subset of about 40 of these sites located in isolated regions of the ocean.\r\n\r\nWhy it's Important:\r\n\r\nCarbon dioxide concentration is an important measure of how human activity has increased the heat-trapping capacity of the atmosphere.\r\n\r\nThis indicator can inform carbon emissions policies at national and international levels."
  title: 'Indicator: Atmospheric Carbon Dioxide'
  topic: ~
  uri: /report/indicator-atmospheric-carbon-dioxide-2020
  url: ~
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-billion-dollar-disasters-2020.yaml
  identifier: indicator-billion-dollar-disasters-2020
  in_library: ~
  publication_year: 2020
  report_type_identifier: indicator
  summary: "Key Points:\r\n\r\n1. The number of weather and climate-related disasters exceeding 1 billion dollars has increased in the United States since 1980.  \r\n2. The increase in Billion Dollar Disasters over time represents a combination of factors, including an increase the magnitude and frequency of some kinds of hazards (flooding, extreme heat, a driving component of drought and wildfire hazards) and changes in the value and placement of assets and property. \r\n3. From January 1980 through June 2019, the U.S. experienced 263 weather and climate disasters with overall damage costs reaching or exceeding $1 billion, including Consumer Price Index (CPI) adjustments, for each individual event. The cumulative costs for these 263 events exceed $1.775 trillion.\r\n\r\n\r\nAbout the Indicator:\r\nhe Billion Dollar Disaster indicator provides insight into the frequency and the total estimated costs of major weather and climate events that occur in the United States. This indicator compiles the annual number of weather and climate-related disasters across seven event types. Events are included if they are estimated to cause more than one billion U.S. dollars in direct losses. The cost estimates of these events are adjusted for inflation using the Consumer Price Index (CPI) and are based on costs documented in several Federal and private-sector databases.\r\nIn recent decades, the U.S. has experienced a rising number of weather and climate disasters that cause significant economic damages and societal losses. From 1980 to 2019, the annual average number of billion-dollar events was 6.6, including CPI adjustments. For the most recent 5 years (2015–2019), the annual average was 13.8 events.\r\nThe distribution of damage from U.S. Billion-dollar disaster events from 1980 to 2019 is dominated by tropical cyclone losses. Tropical cyclones have caused the most damage ($954.4 billion) and also have the highest average event cost ($21.2 billion per event). Hurricanes are responsible for slightly more than half (53.8%) of the total losses for all the U.S. billion-dollar disasters but represent less than one-fifth (17.1%) of all the billion-dollar events we have assessed since 1980. \r\nThe increase in population and material wealth over the last several decades are important factors for the increased damage potential. Climate change is also playing an increasing role in the increasing frequency of some types of extreme weather that lead to billion-dollar disasters. Most notably, the rise in vulnerability to drought, lengthening wildfire seasons and the potential for extremely heavy rainfall and inland flooding events are most acutely related to the influence of climate change (Melillo et al. 2014).\r\n\r\nWhy It’s Important:\r\n\r\n- In addition to direct threats to life and safety, major weather and climate disasters claim property, disrupt business, and affect daily life.\r\n- All U.S. states, Puerto Rico, and the U.S. Virgin Islands have been impacted by at least one billion-dollar disaster since 1980.\r\n- Climate change is playing a role in the increasing frequency of some types of extreme weather that lead to billion-dollar disasters."
  title: 'Indicator: Billion Dollar Disasters'
  topic: ~
  uri: /report/indicator-billion-dollar-disasters-2020
  url: ~
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-frost-free-season-2020.yaml
  identifier: indicator-frost-free-season-2020
  in_library: ~
  publication_year: 2020
  report_type_identifier: indicator
  summary: "Key Points: \r\n\r\nDuring the past 30 years, there has been an increase in the length of the frost-free season over the contiguous United States and Alaska, relative to the 1979–2019 average.\r\n\r\nAbout the Indicator:\r\n\r\nGlobal daily freeze-thaw data are provided by the National Aeronautics and Space Administration (NASA) Freeze-Thaw Earth Systems Data Record, which represents one of the longest continuous global records from satellite-based observations. Satellite microwave sensors are used to determine the frozen or thawed status of water on the land surface at a given time. Measurements are taken over the contiguous United States and Alaska and include all vegetated land areas where seasonal frozen temperatures are a major constraint to plant growth. Collecting these data over time provides information on the number of frost-free days in a given year.\r\n\r\nWhy It’s Important:\r\n\r\n- Observed changes in the length of the frost-free season reflect the overall warming trend in the climate system.\r\n- The frost-free season can be an important factor in determining the potential growing season for vegetation. For instance, some pests and pathogens affecting forests and crops are projected to benefit from warmer temperatures and longer frost-free seasons.\r\n- This indicator can help decision makers understand and anticipate climate impacts on:\r\n\r\n- Agriculture, including crop planning\r\n- Natural resource management\r\n- Wildfire risk management"
  title: 'Indicator: Frost Free Season'
  topic: ~
  uri: /report/indicator-frost-free-season-2020
  url: http://www.globalchange.gov/browse/indicators/frost-free-season
- _public: 1
  contact_email: ~
  contact_note: ~
  doi: ~
  frequency: ~
  href: https://data.globalchange.gov/report/indicator-global-surface-temperature-2020.yaml
  identifier: indicator-global-surface-temperature-2020
  in_library: ~
  publication_year: 2020
  report_type_identifier: indicator
  summary: "Key Points:\r\n\r\nSince the 1880s, the average global temperature has increased by more than 1.7°F. Since the 1980s, average temperatures have exceeded the last century's average every year.\r\n\r\nAbout the Indicator:\r\n\r\nGlobal average temperatures include air temperatures measured on land and sea surface temperatures measured from ships and buoys worldwide. The data shown in the graph were drawn from the National Oceanic and Atmospheric Administration (NOAA) Global Historical Climatology Network (GHCN) and International Comprehensive Ocean-Atmosphere Data Set (ICOADS).\r\n\r\nWhy It's Important:\r\n\r\nChanges in global temperatures over the past century provide one important line of evidence for the effects of increasing greenhouse gas emissions. Such evidence can inform national and international policy discussions."
  title: 'Indicator: Global Surface Temperatures'
  topic: ~
  uri: /report/indicator-global-surface-temperature-2020
  url: ~