The science of climate change

This illustration shows the climate system, its subsystems and relevant processes and interactions. It depicts how energy from the sun is absorbed and re-radiated as the atmosphere interacts with other components of the Earth system, such as the hydrosphere (oceans), the cryosphere (snow, sea ice, and glaciers), the biosphere (animals and plants), the pedosphere (soil) and the lithosphere (rocks). Two-way arrows depict air-ice, ice-ocean, air-ocean, and land air interactions. One-way arrows show incoming solar radiation from the sun and outgoing terrestrial radiation.

This bar graph is from the the United States’ National Oceanic and Atmospheric Administration. It depicts global land and ocean temperature anomalies between 1880 and 2014, relative to the 20^th century average. Whereas temperatures were colder than average between 1880 and 1940, they have been warmer than average since the late 1970s. This trend illustrates that global temperature has been increasing over the 20^th century. The figure shows that 2014 is the warmest year on record, with temperatures at 0.74 degrees Celsius (°C) above average. The coldest years on record are in the early 1900s, with temperatures around 0.49°C below average.

There are two graphs from the Intergovernmental Panel on Climate Change’s (IPCC) Fifth Assessment Report (AR5) that show observed indicators of a changing climate. The first graph shows the Arctic summer sea ice extent (measured in million square kilometers (km²)) from 1900 to present. This graph shows that amounts of ice have diminished over time, with extent ranging from over 10 million km² in 1990 to around 6 million km² in recent years. The second graph shows global average sea level (measured in millimetres (mm)) from 1900 to present. It illustrates that the global mean sea level has risen about 20 centimeters (cm) since 1900.

This figure is from the IPCC’s AR5. It illustrates the widespread impacts that have been attributed to climate change across the globe. Three categories of impacts are depicted:

1. Physical systems: includes glaciers, snow, ice and/or permafrost; rivers, lakes, floods and/or drought; and coastal erosion and/or sea level effects
2. Biological systems: includes terrestrial ecosystems, wildfire and marine ecosystems
3. Human and managed systems: includes food production and livelihoods, health and/or economics

This figure illustrates the relative contribution of climate change (major or minor) to the observed impact, the confidence in attribution and regional scale impacts. Evidence is strongest in the natural systems, i.e., the physical and biological systems. For North America, climate change has had a major contribution to impacts on glaciers, snow, ice and/or permafrost and terrestrial ecosystems. Climate change has had a minor contribution to impacts on wildfires.

This image shows a colour-coded map of Canada depicting temperature trends from 1948 to 2012. It illustrates that temperatures are warming across the country. Temperature increases range from up to 3°C warmer in Canada’s North to around 1°C warmer on Canada’s eastern coast.

This image shows current examples of how a changing climate can impact across Canada. In Canada’s North, there is a picture of a lopsided building, which illustrates how warming permafrost is affecting building foundations. From West to East, other images depict forest fires, drought, infrastructure failure, heat waves and storm surges.

This image shows examples of the longer-term impacts of a changing climate across Canada. In Canada’s North, there is a picture of a polar bear, which illustrates how climate change is affecting ecosystems. From West to East, other images depict forests, agriculture, water quality, water availability and aquatic resources.

The purpose of this slide is to show what is causing climate change. In particular, this slide depicts long-term greenhouse gas (GHG) records, which show a rapid increase since the Industrial Age. The top quadrant of the graph depicts increases in Carbon dioxide (CO₂), with the explanation that these increases are due primarily to fossil fuel use, with additional contribution from land use change. The middle and bottom quadrants of the graph depict increases in methane (CH₄) and Nitrous oxide (N₂O), which are primarily due to agriculture. The slide also explains that GHGs like CO₂ are well mixed and long-lived, and their effects are global. The data in these graphs has been obtained from atmospheric concentrations of GHGs from direct measurements starting in the mid-20^th century, and from air bubbles trapped in glacial ice prior to that. This figure is from the IPCC AR5 report.

Making projections about future climate requires projections of future greenhouse gas concentrations or emissions. On this slide, a graph depicts four different scenarios of CO₂ concentration (measured in parts per million (ppm)) from the year 2000 - 2100, spanning a range from low to high emission (intensive mitigation to limited mitigation). The first scenario shows rapidly increasing concentrations to ~ 950 ppm by 2100. The middle two scenarios show a stabilizing CO₂ concentration. The final scenario shows a peak in CO₂ concentrations around 2050, followed by a modest decline to around 400 ppm CO₂, by the end of the century. These scenarios, which are taken from Van Vuuren et al. (2011), are used as input to global climate models.

The magnitude of future climate change depends directly on future emissions. The graphics on the slide show results for scenarios in 2081-2100 of annual mean surface temperature change (Figure a) and average percent change in annual mean precipitation (Figure b). Changes are shown relative to 1986-2005. The figures on the left hand side are representative of low emissions and high mitigation, while the figures on the right hand side are representative of high emissions and limited mitigation. Changes in average surface temperature and average precipitation are higher in the figures showing high emissions and limited mitigation.

There are two graphs from the IPCC’s AR5 on other indicators that are projected to change. The graph on the left shows Northern Hemisphere September sea ice extent (measured in millions of km²) between 1950 and 2100 under low and high emission scenarios. With low emissions, sea ice extent is projected at around 3 million km² by 2100, whereas it hits the zero mark around 2080 with high emissions. The graph on the right shows global mean sea level rise (measured in meters) between 2000 and 2100 under low and high emission scenarios. With low emissions, global mean sea level rise is projected around 0.45m by 2100, whereas it is close to 0.75m with high emissions.

This figure is from IPCC’s AR5 Synthesis Report. It shows a combined graph that represents the higher adapted risks to various categories of impacts depending on future cumulative CO₂ emissions and the potential changes in global temperature. The right side of the image is a graph showing the potential range of temperatures that are possible with a given level of CO₂ emissions. For example, a range of 530-580 cumulative anthropogenic CO₂ emissions (GtCO₂) could raise the global temperature above the 2°C threshold. The left side of the image shows the risk associated with various temperatures within five categories of impacts: Unique & threatened systems; Extreme weather events; Distribution of impacts; Global aggregate impacts; Large-scale singular events. Each category of impacts has its own scale of risk level as related to changes in temperature.

This image from globalcarbonproject.org is a line graph depicting observed and future scenarios of global emissions for the period 1980 to 2100. The observed emissions start at around 5 gigatons of carbon (GtC) and increase to almost 10 GtC by 2013. The limited mitigation curve increases the emissions to just under 30 GtC by 2100, which could result in a temperature increase of 3.2 to 5.4ºC. At the other end of the spectrum, the high mitigation scenario drops to 0 GtC by 2070, but still has a potential temperature increase ranging from 0.9 to 2.3ºC. Two intermediate scenarios are also shown.

This image is a line graph, from a paper published in the journal Nature Climate Change. The graph shows historic CO₂ emissions from 1990 to 2010 for developed and developing countries. There are two lines for both developed and developing countries representing consumption and production trends. For developed countries, production starts at about 3.8 petagrams of carbon (PgC), and falls to about 3.5 PgC by 2010. The Consumption line starts at about 3.9 PgC, peaks at about 4.2 PgC in 2008, and falls to around 4.0 by 2010. The developing countries production line starts at 2.1 PgC in 1990, and increases to 5.0 PgC by 2010. The developing countries consumption line starts at below 2 PgC and ends in 2010 at about 4.4 PgC.

This image shows a line graph, from Environment Canada’s National Inventory Report, depicting trends (in percentage change) in Canada’s GHG emissions, nationally and by key sectors, for the period 2005 to 2013. Emissions from the mining and upstream oil and gas production sector increase by nearly 40% over the period. Emissions from transportation increase by about 5% over the period. The national total decreases by about 4%.  The category “all other sections” decreases by about 6% over the 8-year period. Public electricity and heat production decrease by about 30% by 2013.

There are four images on this slide showing the covers of the IPCC AR5 reports (The Physical Science Basis; Impacts, Adaptation and Venerability; Mitigation of Climate Change; and the Synthesis Report)

This image shows two line graphs from the IPCC AR5 with multiple lines of model and observations data depicting temperature changes over the 1860 to 2010. The first graph shows model data with natural and anthropogenic forcings, which match closely with the observed data. The second graph shows model data with natural forcings only, which continue to hover around the 0°C mark up until the 1960s, whereas the observations continued to increase.

The first image on this page is a line graph from the National Snow and Data Center that shows the decreasing Arctic sea ice cover extent for the period 1979 to 2012. The graph shows that at the beginning of the period the ice extent was about 7.5 million km², and by 2012 the extent of ice had dropped to below 4 million km². The second two images from the National Aeronautics and Space Administration (NASA) Earth Observatory show satellite images of the extent of Arctic sea ice. In the image from 1984, the ice fills the Arctic basin almost completely, with only some open water along Russia’s north coast. In the image from 2012, the Arctic ice coverage is much reduced, only covering the North Pole over to Greenland and Canada’s Arctic Archipelago.

These figures are from the British Columbia Forestry and the Canadian Forest Service. There are two maps showing circles representing the number and magnitude of wildfires. The first map depicts the conditions in 1999, where there are wild fires throughout BC, with none being very large. The second map depicts conditions in 2012 and shows several concentrations of large fires in the northeast and southern areas of British Colombia.

Two pie charts show the proportions of GHG emissions by sector in 2012, one for the world, and one for Canada. The pie charts break emission sources down into 7 sectors: Agriculture; industrial processes; waste, energy - transportation; energy - electricity/heat; energy - other fuel consumption; energy - manufacturing/construction; energy - fugitive emissions. Canada and the world have similar proportions for emissions, except for Energy - transportation (world 16%, Canada 24%); Energy -electricity/heat (world 33%, Canada 22%) and energy - other fuel consumption (world 9%, Canada 16%).