--- attributes: ~ caption: "Long-term observations demonstrate the warming trend in the climate system and the effects of increasing atmospheric greenhouse gas concentrations (Ch. 2: Climate, Box 2.2). This figure shows climate-relevant indicators of change based on data collected across the United States. Upward-pointing arrows indicate an increasing trend; downward-pointing arrows indicate a decreasing trend. Bidirectional arrows (e.g., for drought conditions) indicate a lack of a definitive national trend.

Atmosphere (a–c): (a) Annual average temperatures have increased by 1.8°F across the contiguous United States since the beginning of the 20th century; this figure shows observed change for 1986–2016 (relative to 1901–1960 for the contiguous United States and 1925–1960 for Alaska, Hawai‘i, Puerto Rico, and the U.S. Virgin Islands). Alaska is warming faster than any other state and has warmed twice as fast as the global average since the mid-20th century (Ch. 2: Climate, KM 5; Ch. 26: Alaska, Background). (b) The season length of heat waves in many U.S. cities has increased by over 40 days since the 1960s. Hatched bars indicate partially complete decadal data. \\(c) The relative amount of annual rainfall that comes from large, single-day precipitation events has changed over the past century; since 1910, a larger percentage of land area in the contiguous United States receives precipitation in the form of these intense single-day events.

Ice, snow, and water (d–f): (d) Large declines in snowpack in the western United States occurred from 1955 to 2016. (e) While there are a number of ways to measure drought, there is currently no detectable change in long-term U.S. drought statistics using the Palmer Drought Severity Index. (f) Since the early 1980s, the annual minimum sea ice extent (observed in September each year) in the Arctic Ocean has decreased at a rate of 11%–16% per decade (Ch. 2: Climate, KM 7).

Oceans and coasts (g–i): (g) Annual median sea level along the U.S. coast (with land motion removed) has increased by about 9 inches since the early 20th century as oceans have warmed and land ice has melted (Ch. 2: Climate, KM 4). (h) Fish, shellfish, and other marine species along the Northeast coast and in the eastern Bering Sea have, on average, moved northward and to greater depths toward cooler waters since the early 1980s (records start in 1982). (i) Oceans are also currently absorbing more than a quarter of the carbon dioxide emitted to the atmosphere annually by human activities, increasing their acidity (measured by lower pH values; Ch. 2: Climate, KM 3).

Land and ecosystems (j–l): (j) The average length of the growing season has increased across the contiguous United States since the early 20th century, meaning that, on average, the last spring frost occurs earlier and the first fall frost arrives later; this map shows changes in growing season length at the state level from 1895 to 2016. (k) Warmer and drier conditions have contributed to an increase in large forest fires in the western United States and Interior Alaska over the past several decades (CSSR, Ch. 8.3). (l) Degree days are defined as the number of degrees by which the average daily temperature is higher than 65°F (cooling degree days) or lower than 65°F (heating degree days) and are used as a proxy for energy demands for cooling or heating buildings. Changes in temperatures indicate that heating needs have decreased and cooling needs have increased in the contiguous United States over the past century.

Sources: (a) adapted from Vose et al. 2017, (b) EPA, (c–f and h–l) adapted from EPA 2016, (g and center infographic) EPA and NOAA.
The interactive version of this figure was revised in June 2019. See Errata for details: https://nca2018.globalchange.gov/downloads

" chapter: doi: 10.7930/NCA4.2018.CH1 identifier: overview-executive-summary number: 1 report_identifier: nca4 sort_key: 101 title: Overview url: https://nca2018.globalchange.gov/chapter/1 chapter_identifier: overview-executive-summary cited_by: [] contributors: - href: https://data.globalchange.gov/contributor/25228.yaml id: 25228 organization: country_code: US identifier: us-environmental-protection-agency international: ~ name: U.S. Environmental Protection Agency organization_type_identifier: federal url: http://www.epa.gov/ organization_uri: /organization/us-environmental-protection-agency person: first_name: Michael id: 2200 last_name: Kolian middle_name: ~ orcid: 0000-0002-7134-8317 url: https://www.researchgate.net/profile/Mike_Kolian person_id: 2200 person_uri: /person/2200 role_type_identifier: point_of_contact uri: /contributor/25228 create_dt: 2017-07-20T19:02:07 files: - file: 75/31/1d63ea0d3dcc09205301caa36bfe/Overview_indicators_print_v15.jpg href: https://data.globalchange.gov/assets/75/31/1d63ea0d3dcc09205301caa36bfe/Overview_indicators_print_v15.jpg identifier: 4788c740-b1c2-4b2b-a286-d252a963b8e9 landing_page: ~ location: ~ mime_type: image/jpeg sha1: a0b015df100003edecc81de616163057976920a4 size: 2037203 thumbnail: 75/31/1d63ea0d3dcc09205301caa36bfe/.thumb-4788c740-b1c2-4b2b-a286-d252a963b8e9.png thumbnail_href: https://data.globalchange.gov/assets/75/31/1d63ea0d3dcc09205301caa36bfe/.thumb-4788c740-b1c2-4b2b-a286-d252a963b8e9.png uri: /file/4788c740-b1c2-4b2b-a286-d252a963b8e9 url: /assets/75/31/1d63ea0d3dcc09205301caa36bfe/Overview_indicators_print_v15.jpg gcmd_keywords: - definition: |- Planning refers to the formulation of a course of action to be taken in the event of a hazard emergency. href: https://data.globalchange.gov/gcmd_keyword/5c14b001-518f-460b-90fe-139bf192d1f2.yaml identifier: 5c14b001-518f-460b-90fe-139bf192d1f2 label: HAZARDS PLANNING parent_identifier: 464de0a5-2bb9-4172-9fd3-1634cbc4e739 uri: /gcmd_keyword/5c14b001-518f-460b-90fe-139bf192d1f2 - definition: ~ href: https://data.globalchange.gov/gcmd_keyword/23703b6b-ee15-4512-b5b2-f441547e2edf.yaml identifier: 23703b6b-ee15-4512-b5b2-f441547e2edf label: CLIMATE INDICATORS parent_identifier: e9f67a66-e9fc-435c-b720-ae32a2c3d8f5 uri: /gcmd_keyword/23703b6b-ee15-4512-b5b2-f441547e2edf - definition: A measure of temperature at different levels of the Earth's atmosphere. href: https://data.globalchange.gov/gcmd_keyword/35e1f93b-99b3-4430-b477-0ecafa80d67a.yaml identifier: 35e1f93b-99b3-4430-b477-0ecafa80d67a label: ATMOSPHERIC TEMPERATURE parent_identifier: c47f6052-634e-40ef-a5ac-13f69f6f4c2a uri: /gcmd_keyword/35e1f93b-99b3-4430-b477-0ecafa80d67a - definition: A period of abnormally dry weather sufficiently long enough to cause a serious hydrological imbalance. href: https://data.globalchange.gov/gcmd_keyword/12a896f3-993d-49f6-aafc-17378ffa3998.yaml identifier: 12a896f3-993d-49f6-aafc-17378ffa3998 label: DROUGHTS parent_identifier: b7d562cf-9b9b-4461-900b-50423a8c4d29 uri: /gcmd_keyword/12a896f3-993d-49f6-aafc-17378ffa3998 - definition: '(Also called hot wave, warm wave.) A period of abnormally and uncomfortably hot and usually humid weather. To be a heat wave such a period should last at least one day, but conventionally it lasts from several days to several weeks. In 1900, A. T. Burrows more rigidly defined a "hot wave" as a spell of three or more days on each of which the maximum shade temperature reaches or exceeds 90°F. More realistically, the comfort criteria for any one region are dependent upon the normal conditions of that region. In the eastern United States, heat waves generally build up with southerly winds on the western flank of an anticyclone centered over the southeastern states, the air being warmed by passage over a land surface heated by the sun.' href: https://data.globalchange.gov/gcmd_keyword/ca820557-401e-4e5e-ac32-29fdbc0628b3.yaml identifier: ca820557-401e-4e5e-ac32-29fdbc0628b3 label: HEAT WAVE parent_identifier: b7d562cf-9b9b-4461-900b-50423a8c4d29 uri: /gcmd_keyword/ca820557-401e-4e5e-ac32-29fdbc0628b3 - definition: 'Extreme precipitation events in the form of high amounts of rainfall can contribute to flooding, landslides and mud flows. Effects of extreme precipitation on the natural environment can often be disproportionally larger than the cumulative effect of normal precipitation patterns. The magnitude of societal impacts of extremes depends upon a variety of factors such geographic location, population density, infrastructure design standards and emergency response systems (Parry et al., 2007)' href: https://data.globalchange.gov/gcmd_keyword/fc5a1b7a-5ee8-4d67-80f5-a57e3f1734ab.yaml identifier: fc5a1b7a-5ee8-4d67-80f5-a57e3f1734ab label: EXTREME PRECIPITATION parent_identifier: b29b46ad-f05f-4144-b965-5f606ce96963 uri: /gcmd_keyword/fc5a1b7a-5ee8-4d67-80f5-a57e3f1734ab - definition: An increase in the average height of the sea surface over a vertical datum. href: https://data.globalchange.gov/gcmd_keyword/536a86bd-3dd1-4f4a-9b4a-222a12746db5.yaml identifier: 536a86bd-3dd1-4f4a-9b4a-222a12746db5 label: SEA LEVEL RISE parent_identifier: 5273c8c2-d30b-4666-b2d5-0388ce2741d0 uri: /gcmd_keyword/536a86bd-3dd1-4f4a-9b4a-222a12746db5 - definition: |- Degree days are based on the assumption that when the outside temperature is 65°F, we don't need heating or cooling to be comfortable. Degree days are the difference between the daily temperature mean, (high temperature plus low temperature divided by two) and 65°F. If the temperature mean is above 65°F, we subtract 65 from the mean and the result is Cooling Degree Days. If the temperature mean is below 65°F, we subtract the mean from 65 and the result is Heating Degree Days. -------------------------------------------------------------------------- Example 1: The high temperature for a particular day was 90°F and the low temperature was 66°F. The temperature mean for that day was: ( 90°F + 66°F ) / 2 = 78°F Because the result is above 65°F: 78°F - 65°F = 13 Cooling Degree Days Example 2: The high temperature for a particular day was 33°F and the low temperature was 25°F. The temperature mean for that day was: ( 33°F + 25°F ) / 2 = 29°F Because the result is below 65°F: 65°F - 29°F = 36 Heating Degree Days. The calculations shown in the two examples above are performed for each day of the year and the daily degree days are accumulated so that we can compare months and seasons. href: https://data.globalchange.gov/gcmd_keyword/db0d03d7-1d08-42fb-b212-0da35b88e656.yaml identifier: db0d03d7-1d08-42fb-b212-0da35b88e656 label: COOLING DEGREE DAYS parent_identifier: e8580cbb-701a-4ab1-a40f-5fae4ae1ea24 uri: /gcmd_keyword/db0d03d7-1d08-42fb-b212-0da35b88e656 - definition: |- Degree days are based on the assumption that when the outside temperature is 65°F, we don't need heating or cooling to be comfortable. Degree days are the difference between the daily temperature mean, (high temperature plus low temperature divided by two) and 65°F. If the temperature mean is above 65°F, we subtract 65 from the mean and the result is Cooling Degree Days. If the temperature mean is below 65°F, we subtract the mean from 65 and the result is Heating Degree Days. -------------------------------------------------------------------------- Example 1: The high temperature for a particular day was 90°F and the low temperature was 66°F. The temperature mean for that day was: ( 90°F + 66°F ) / 2 = 78°F Because the result is above 65°F: 78°F - 65°F = 13 Cooling Degree Days Example 2: The high temperature for a particular day was 33°F and the low temperature was 25°F. The temperature mean for that day was: ( 33°F + 25°F ) / 2 = 29°F Because the result is below 65°F: 65°F - 29°F = 36 Heating Degree Days. The calculations shown in the two examples above are performed for each day of the year and the daily degree days are accumulated so that we can compare months and seasons. href: https://data.globalchange.gov/gcmd_keyword/fe2bc223-e503-4ca1-924c-d3fd5876721c.yaml identifier: fe2bc223-e503-4ca1-924c-d3fd5876721c label: HEATING DEGREE DAYS parent_identifier: e8580cbb-701a-4ab1-a40f-5fae4ae1ea24 uri: /gcmd_keyword/fe2bc223-e503-4ca1-924c-d3fd5876721c - definition: 'Migration is the relatively long-distance movement of individuals, usually on a seasonal basis. It is a ubiquitous phenomenon, found in all major animal groups, including birds, mammals, fish, reptiles, amphibians, insects, and crustaceans. The trigger for the migration may be local climate, local availability of food, the season of the year or for mating reasons.' href: https://data.globalchange.gov/gcmd_keyword/0de668aa-cc97-482d-a0eb-cddcb1a705b6.yaml identifier: 0de668aa-cc97-482d-a0eb-cddcb1a705b6 label: SPECIES MIGRATION parent_identifier: 76943142-e5a9-4ecf-b496-050dd3d97101 uri: /gcmd_keyword/0de668aa-cc97-482d-a0eb-cddcb1a705b6 - definition: ~ href: https://data.globalchange.gov/gcmd_keyword/ed8797be-661a-48c9-a7fe-2600b6c7c067.yaml identifier: ed8797be-661a-48c9-a7fe-2600b6c7c067 label: LENGTH OF GROWING SEASON parent_identifier: 112e71ec-c0a1-49a8-82d7-bcb317b45860 uri: /gcmd_keyword/ed8797be-661a-48c9-a7fe-2600b6c7c067 - definition: 'An uncontrolled fire in combustible vegetation that occurs in the countryside or a wilderness area. Other names such as brush fire, bushfire, forest fire, desert fire, grass fire, hill fire, peat fire, vegetation fire, and veldfire may be used to describe the same phenomenon depending on the type of vegetation being burned. A wildfire differs from other fires by its extensive size, the speed at which it can spread out from its original source, its potential to change direction unexpectedly, and its ability to jump gaps such as roads, rivers and fire breaks. Wildfires are characterized in terms of the cause of ignition, their physical properties such as speed of propagation, the combustible material present, and the effect of weather on the fire.' href: https://data.globalchange.gov/gcmd_keyword/868b87a1-d8c2-49b3-8bbd-9cbbed115271.yaml identifier: 868b87a1-d8c2-49b3-8bbd-9cbbed115271 label: WILDFIRES parent_identifier: ec0e2762-f57a-4fdc-b395-c8d7d5590d18 uri: /gcmd_keyword/868b87a1-d8c2-49b3-8bbd-9cbbed115271 - definition: |- A measure of the alkaline or acid strength of a substance. pH is defined as the logarithm of the reciprocal of the hydrogen ion concentration of a solution. href: https://data.globalchange.gov/gcmd_keyword/4433600b-f323-458a-b295-352f939aab6b.yaml identifier: 4433600b-f323-458a-b295-352f939aab6b label: PH parent_identifier: 6eb3919b-85ce-4988-8b78-9d0018fd8089 uri: /gcmd_keyword/4433600b-f323-458a-b295-352f939aab6b - definition: Pertaining to the study of frozen seawater over the ocean surface. href: https://data.globalchange.gov/gcmd_keyword/d73e969a-4b66-4713-8d63-fa3cbb1e25e3.yaml identifier: d73e969a-4b66-4713-8d63-fa3cbb1e25e3 label: SEA ICE parent_identifier: 91697b7d-8f2b-4954-850e-61d5f61c867d uri: /gcmd_keyword/d73e969a-4b66-4713-8d63-fa3cbb1e25e3 - definition: |- Pertaining to the measurement of the amount of water in a given snow pack. href: https://data.globalchange.gov/gcmd_keyword/47d8d3db-9aea-49f3-8edd-5216736a85ef.yaml identifier: 47d8d3db-9aea-49f3-8edd-5216736a85ef label: SNOW WATER EQUIVALENT parent_identifier: 50b8fe04-9149-4b7f-a8b2-b33b1e3aa192 uri: /gcmd_keyword/47d8d3db-9aea-49f3-8edd-5216736a85ef href: https://data.globalchange.gov/report/nca4/chapter/overview-executive-summary/figure/indicators-nca3-image.yaml identifier: indicators-nca3-image images: - attributes: ~ create_dt: 2017-10-05T13:34:02 description: ~ identifier: a7304d90-a2fa-494b-b6f1-68e219de37a5 lat_max: ~ lat_min: ~ lon_max: ~ lon_min: ~ position: 11 submission_dt: 2018-11-16T23:05:21 time_end: ~ time_start: ~ title: U.S. Heating and Cooling Degree Days url: ~ usage_limits: Figure may be copyright protected and permission may be required. Contact original figure source for information - attributes: ~ create_dt: 2018-07-25T14:32:29 description: ~ identifier: 4081b164-6a98-48a8-9fea-73296b8e1f54 lat_max: ~ lat_min: ~ lon_max: ~ lon_min: ~ position: 12 submission_dt: 2019-06-10T18:50:56 time_end: ~ time_start: ~ title: Indicators of Change Infographic url: ~ usage_limits: Figure may be copyright protected and permission may be required. Contact original figure source for information - attributes: ~ create_dt: 2017-10-05T13:31:02 description: ~ identifier: 9eabcfff-3285-4da6-bd3c-f14fb201f5ea lat_max: ~ lat_min: ~ lon_max: ~ lon_min: ~ position: 3 submission_dt: 2018-11-16T23:04:10 time_end: ~ time_start: ~ title: Western U.S. Snowpack url: ~ usage_limits: Figure may be copyright protected and permission may be required. Contact original figure source for information - attributes: ~ create_dt: 2017-10-05T13:32:05 description: ~ identifier: 680e175c-5683-4911-b232-c187fa274cf4 lat_max: ~ lat_min: ~ lon_max: ~ lon_min: ~ position: 5 submission_dt: 2018-11-16T23:04:32 time_end: ~ time_start: ~ title: Arctic Sea Ice Extent url: ~ usage_limits: Figure may be copyright protected and permission may be required. Contact original figure source for information - attributes: ~ create_dt: 2017-10-05T13:35:19 description: ~ identifier: 4a264057-671b-43b4-9869-dae71d90f9bd lat_max: 71.38 lat_min: 16.92 lon_max: -66.09 lon_min: 173.00 position: 6 submission_dt: 2019-06-10T18:50:55 time_end: 2017-12-31T00:00:00 time_start: 1920-01-01T00:00:00 title: U.S. Sea Level url: ~ usage_limits: Figure may be copyright protected and permission may be required. Contact original figure source for information - attributes: ~ create_dt: 2017-10-05T13:39:30 description: ~ identifier: 598fc444-e18f-4f0c-8d08-3d68f4885181 lat_max: ~ lat_min: ~ lon_max: ~ lon_min: ~ position: 7 submission_dt: 2018-11-16T23:04:59 time_end: ~ time_start: ~ title: U.S. Marine Species Distribution url: ~ usage_limits: Figure may be copyright protected and permission may be required. Contact original figure source for information - attributes: ~ create_dt: 2017-10-05T13:36:49 description: ~ identifier: 9eeb6894-6c9d-4e9c-8993-c40106f758ab lat_max: ~ lat_min: ~ lon_max: ~ lon_min: ~ position: 8 submission_dt: 2018-11-16T23:05:05 time_end: ~ time_start: ~ title: Hawai'i Ocean Acidity url: ~ usage_limits: Figure may be copyright protected and permission may be required. Contact original figure source for information - attributes: ~ create_dt: 2017-10-05T13:26:43 description: ~ identifier: a9a21ade-8322-47fd-aa12-3af66dd29110 lat_max: ~ lat_min: ~ lon_max: ~ lon_min: ~ position: 9 submission_dt: 2018-11-16T23:05:11 time_end: ~ time_start: ~ title: Growing Season Length url: ~ usage_limits: Figure may be copyright protected and permission may be required. Contact original figure source for information - attributes: ~ create_dt: 2017-10-05T13:28:13 description: ~ identifier: b3101e2e-f6f9-4c8b-90c6-27715d60d57d lat_max: ~ lat_min: ~ lon_max: ~ lon_min: ~ position: 10 submission_dt: 2018-11-16T23:05:17 time_end: ~ time_start: ~ title: U.S. Wildfires url: ~ usage_limits: Figure may be copyright protected and permission may be required. 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Contact original figure source for information - attributes: ~ create_dt: 2017-10-05T13:25:45 description: ~ identifier: 22e68ddd-8df0-4a1a-8cf0-9ae56f7caf18 lat_max: ~ lat_min: ~ lon_max: ~ lon_min: ~ position: 2 submission_dt: 2018-11-16T23:03:58 time_end: ~ time_start: ~ title: U.S. Heavy Precipitation url: ~ usage_limits: Figure may be copyright protected and permission may be required. Contact original figure source for information - attributes: ~ create_dt: 2017-10-05T13:29:02 description: ~ identifier: 3e58bcba-9bd0-4693-8721-c6080517ed7a lat_max: ~ lat_min: ~ lon_max: ~ lon_min: ~ position: 4 submission_dt: 2018-11-16T23:04:18 time_end: ~ time_start: ~ title: U.S. Drought Conditions url: ~ usage_limits: Figure may be copyright protected and permission may be required. Contact original figure source for information kindred_figures: [] lat_max: ~ lat_min: ~ lon_max: ~ lon_min: ~ ordinal: 2 parents: [] references: [] regions: - description: The complete territory of the United States of America href: https://data.globalchange.gov/region/united-states.yaml identifier: united-states label: Entire US uri: /region/united-states report_identifier: nca4 source_citation: ~ submission_dt: 2019-06-10T18:50:54 time_end: ~ time_start: ~ title: Indicators of Change uri: /report/nca4/chapter/overview-executive-summary/figure/indicators-nca3-image url: ~ usage_limits: Figure may be copyright protected and permission may be required. Contact original figure source for information