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TitleUnderstanding observed global climate change
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LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorBush, E; Gillett, N; Watson, E; Fyfe, J; Vogel, F; Swart, N
SourceCanada's changing climate report; by Bush, E (ed.); Lemmen, D S (ed.); 2019 p. 26-72, https://doi.org/10.4095/327803 (Open Access)
LinksOnline - En ligne (interactive - interactif)
LinksCanada's Changing Climate Report - Additional Information
Year2019
PublisherGovernment of Canada
Documentbook
Lang.English
Mediapaper; on-line; digital
RelatedThis publication is contained in Bush, E; Lemmen, D S; (2019). Canada's changing climate report
RelatedThis publication is a translation of Bush, E; Bush, E; Gillett, N; Gillett, N; Watson, E; Watson, E; Fyfe, J; Fyfe, J; Vogel, F; Vogel, F; Swart, N; Swart, N; (2019). Comprendre les changements climatiques mondiaux observés, Rapport sur le climat changeant du Canada
File formatpdf
ProvinceBritish Columbia; Alberta; Saskatchewan; Manitoba; Ontario; Quebec; New Brunswick; Nova Scotia; Prince Edward Island; Newfoundland and Labrador; Northwest Territories; Yukon; Nunavut; Northern offshore region; Eastern offshore region; Western offshore region
NTS1; 2; 3; 10; 11; 12; 13; 14; 15; 16; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 52; 53; 54; 55; 56; 57; 58; 59; 62; 63; 64; 65; 66; 67; 68; 69; 72; 73; 74; 75; 76; 77; 78; 79; 82; 83; 84; 85; 86; 87; 88; 89; 92; 93; 94; 95; 96; 97; 98; 99; 102; 103; 104; 105; 106; 107; 114O; 114P; 115; 116; 117; 120; 340; 560
Lat/Long WENS-141.0000 -50.0000 90.0000 41.7500
SubjectsNature and Environment; surficial geology/geomorphology; environmental geology; hydrogeology; climate; climatology; climate effects; snow; ice; permafrost; ground ice; sea ice; glaciers; surface waters; rivers; lakes; temperature; precipitation; ground temperatures; oceanography; climate, arctic; Canadian Cordillera; climate change; ice caps; fresh water; cumulative effects
Illustrationslocation maps; photographs; graphs; sketches; figures; plots; charts
ProgramClimate Change Impacts and Adaptation Program, Canada in a Changing Climate
Released2019 04 02; 2020 12 08
Abstract(Summary)
The Earth's climate system comprises interacting physical components - the atmosphere, the hydrosphere (liquid water on Earth), the cryosphere (frozen elements), the land surface, and the biosphere, which encompasses all living things on land and in water. Measurements of variables within all of these systems provide independent lines of evidence that the global climate system is warming. The consistency of the signals across multiple components of the climate system provides a compelling story of unequivocal change. The best-known indicator for tracking climate change is global mean surface temperature (GMST), estimated as the average (or mean) temperature for the world from measurements of sea surface temperatures and of near-surface air temperatures above the land. This measure has risen an estimated 0.85ºC (90% uncertainty range between 0.65ºC and 1.06ºC) over the period 1880-2012. Each of the last three full decades (1980s, 1990s, and 2000s) has broken successive records for average 10-year temperatures. A warming slowdown occurred in the early 21st century, even though decadal temperature for the 2000s was higher than that for the 1990s. Natural climate variability influences GMST on a variety of timescales; therefore, periods of reduced or enhanced warming on decadal timescales are expected. The causes of the early 21st century warming slowdown are now better understood, and it appears to have ended, with the years 2015, 2016, and 2017 being the warmest on record, with GMST more than 1ºC above the pre-industrial average level. Signals of climate warming are also evident in other components of the climate system. The shift toward a warmer global climate on average has been accompanied by an increase in warm extremes and a decrease in cold extremes. The amount of water vapour (atmospheric humidity) in the atmosphere has very likely increased, consistent with the capacity of warmer air to hold more moisture. Not only has the ocean warmed at the surface, it is virtually certain that the whole upper ocean (t o a depth of 700 m) has warmed. Global mean sea level has risen an estimated 0.19 m o ver the period 1901?2010 (90% uncer tainty range between 0.17 m and 0.21 m) as a consequence of the expansion of ocean waters d ue to warming (warmer water tak es up more volume) and the addition of new meltwater from shrinking glaciers and ice sheets worldwide. The extent of Arctic sea ice has also been shrinking in all seasons, with declines most evident in summer and autumn. Understanding how much human activity has contributed to the observed warming of the climate system also draws from multiple lines of evidence. This includes evidence from observations, from improved understanding of processes and feedbacks within the system that determine how the climate system responds to both natural and human-induced perturbations, and from climate models (see Chapter 3.3.1). The ability of greenhouse gases (GHGs) in Earth's atmosphere to absorb heat energy radiated from the Earth is well understood. Emissions of GHGs from human activities have led to a build-up of atmospheric GHG levels. This rise in atmospheric GHG levels, predominantly carbon dioxide, has been the main driver of climate warming during the Industrial Era. The strong warming effect of increases in GHGs has been offset to some extent by increases in levels of atmospheric aerosols, which have climate-cooling effects. Variations in the brightness of the sun during the Industrial Era have had a warming effect on climate that is at least 10 times smaller than that from human activity and cannot explain the observed rise in global temperature. Volcanic eruptions have cooling effects on global climate that can last several years but cannot explain the observed long-term change in global temperature. Determining how much of the observed climate warming and other climatic changes are due to these drivers is a complex task, as the climate system does not respond to these drivers in a straightforward way. To accomplish this task, climate (or Earth system) models are essential tools for identifying the causes of observed climate changes. Experiments with these models simulate how the climate system responds to real-world changes, including the impacts of human activities, and compare this with idealized experiments without human interference. On the basis of analysis of observations and such experiments, it is extremely likely that human influences, primarily emissions of GHGs, have been the dominant cause of the observed global warming since the mid-20th century. Studies have confirmed that there is a human contribution to observed changes in the lower atmosphere, the cryosphere, and the ocean, on a global scale.
Summary(Plain Language Summary, not published)
This chapter provides a synopsis of the evidence that the Earth's climate system is warming, that other aspects of climate are changing consistent with this warming, and that human activities are the main cause of these changes.
GEOSCAN ID327803