The Science of Climate Change

November 23, 2015

Image of Moraine Lake in Banff National Park, Alberta

Image of Moraine Lake
in Banff National Park, Alberta

Overview

Key Messages

  • Warming over the 20th century is indisputable and largely due to human activities.
  • Canada’s rate of warming is about twice the global rate: a 2ºC increase globally means a 3 to 4ºC increase for Canada.
  • Effects will persist for centuries because greenhouse gases (GHGs) are long-lived and the oceans are warming.
  • Cumulative CO2 emissions largely determine ultimate warming. A 2ºC warming target may still be attainable, but we are already 65% of the way to the associated carbon limit or budget and global emissions must peak before mid-century.
  • GHG emissions need to become net zero in order to stabilize climate at any temperature.

The Climate System

World Ocean Review

Image: World Ocean Review

Long description

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.

 

  • Energy from the sun is absorbed and re-radiated. The atmosphere acts like an insulator, keeping the surface warm both day and night, providing a life-supporting average temperature of approximately 14ºC.
  • Increases to the amount of GHGs in the atmosphere alter the energy balance (increasing energy absorbed) and lead to climate warming.

Evidence of Climate Change

“Warming is unequivocal”Note *

Global Land and Ocean Temperature Anomalies, January - December
(Annual anomalies relative to 20th century)

Global Land and Ocean Temperature Anomalies, January-December

Long description

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 20th 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 20th 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.

 

  • Global temperature continues to rise; each of the last three decades has been successively warmer than any preceding decade since the 1850s.
  • Warming is not uniform; temperature in Canada has been increasing at roughly double the global mean rate. The Arctic is warming even faster.

Other indicators of a warming planet

Arctic summer sea ice extent

Arctic summer sea ice extent

  • Snow, sea ice, glaciers and permafrost are in decline, consistent with observed warming.

Global average sea level

Global average sea level

IPCC AR5, Summary for Policymakers (WG1), Fig. SPM.3

Long description

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.

 

  • Global average sea level has risen about 20 cm since 1900 due to expansion of warming ocean waters and the addition of water to the ocean from melting land ice.

Impacts have been observed globally - climate change will amplify existing risks and create new ones

  • Evidence is strongest in natural systems (blue and green).
  • Impacts on human systems (red) include food production, local livelihoods and health.

Map of world showing observed impacts attributed to physical, biological, human and managed systems

Bars represent quantity of evidence

IPCC AR5, Synthesis Report, Summary for Policymakers, Fig. SPM.4

Long description

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.

 

Observed changes in Canada: Consistent with global changes

  • Longer growing season
  • More heat waves and fewer cold spells
  • Thawing permafrost
  • Earlier river ice break-up
  • Increase in precipitation over large parts of Canada, more snowfall in northwest Arctic
  • Earlier spring runoff
  • Earlier budding of trees
  • Indigenous people of the Arctic are no longer able to predict the weather as their forefathers did (Society for Ecological Restoration).

Canadian Temperature Trends - 1948 to 2012

Canadian temperature trends - 1948-2012

Long description

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.

 

Canada is already warmer, wetter and stormier

image shows current examples of how a changing climate can impact across Canada

Photos: AP Photo, AlaskaPhotoWorld, F. Prevel/AP

Long description

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.

 

Longer-term impacts of a changing climate in Canada

Image shows examples of the longer-term impacts of a changing climate across Canada

Photos: Parks Canada, T. Archer, Hydro-Quebec, Le Soleil, J-M. Dorion

Long description

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.

 

What is Causing Climate Change?

Long-term GHG records show rapid increase since the Industrial Age.

Graphs showing rapid increase in Co2, CH4 and N2O since the Industrial Age

IPCC AR5, WGI, Fig. 6.11

Long description

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-20th century, and from air bubbles trapped in glacial ice prior to that. This figure is from the IPCC AR5 report.

 

  • Increases in CO2 are due primarily to fossil fuel use, with additional contribution from land use change.
  • Those of CH4 and N2O are primarily due to agriculture.
  • GHGs like CO2 are well mixed and long-lived; effects are global.
  • Atmospheric concentrations of GHGs from direct measurements starting in the mid – 20th century, and from air bubbles trapped in glacial ice prior to that.

Projecting Future Climate Change

x

Van Vuuren et al., Climatic Change, 2011

Long description

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.

 

  • Making projections about future climate requires projections of future greenhouse gas concentrations or emissions.
  • Four different scenarios have been used; they span a range from low to high emissions (intensive mitigation to limited mitigation).
  • These scenarios are used as input to global climate models.

Magnitude of future climate change depends directly on future emissions

(a) Change in average surface temperature (1986-2005 to 2081-2100)

Change in average surface temperature (1986-2005 to 2081-2100)

IPCC AR5, WGI, Summary for Policymakers, Fig. SPM.8

(b) Change in average precipitation (1986-2005 to 2081-2100)

Change in average precipitation (1986-2005 to 2081-2100)

IPCC AR5, WGI, Summary for Policymakers, Fig. SPM.8

Long description

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.

 

Other indicators are also projected to change

Arctic Summer sea ice extent

Arctic summer sea ice extent

IPCC AR5, WGI, Summary for Policymakers, Fig. 2.1.

Global mean sea level rise

Global mean sea level rise

IPCC AR5, WGI, Summary for Policymakers, Fig. 2.1.

Long description

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.

 

Risks from climate change depend on cumulative CO2emissions

image shows a combined graph that represents the higher adapted risks to various categories of impacts

Adapted from IPCC, AR5, Synthesis Report, Fig. 3.1

Long description

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.

 

  • Above 2°C, the United Nations Framework Convention on Climate Change (UNFCCC) target, risks of severe, widespread and irreversible impacts increase.
  • We are already about 65% of the way to the cumulative emissions limit consistent with 2°C.

Keeping warming below the 2ºC target will require rapid global emissions reductions

Observed Emissions and Future Scenarios

Observed Emissions and Future Scenarios

globalcarbonproject.org; IPCC, AR5

Long description

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.

 

  • The high mitigation scenario is the only one assessed as maintaining temperature change below 2ºC. It requires net zero, or even negative, emissions before the end of the century.

Historical CO2 emissions from 1990 to 2010 of developed and developing countries

Nature Climate Change, Volume 2, Jan 2012. Figure 2.

Long description

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.

 

2005-2013 trends in Canada’s GHG emissions (National total and key sectors)

2005-2013 trends in Canada GHG emissions (National total and key sectors)

Environment Canada, National Inventory Report: Greenhouse Gas Sources and Sinks in Canada 1990-2013

Long description

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.

 

Summary

  • The science is conclusive: Warming is unequivocal and human influence on the climate system is clear.
  • Impacts of a changing climate are already being felt, and they will increase with further warming. Adaptation will be needed to manage the risks.
  • The cumulative total emissions is what determines the ultimate level of warming. To avoid exceeding 2°C, global GHG emissions need to decrease rapidly.
  • GHG emissions need to become net zero in order to stabilize climate at any temperature.

Annex 1: Intergovernmental Panel on Climate Change

four images on this slide showing the covers of the IPCC AR5 reports

Long description

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)

 

“Human influence on the climate system is clear” (IPCC AR5)

  • This headline statement is supported by increasing GHG concentrations, observed warming and related changes, and scientific understanding based on modelling the climate system.
  • Climate models are able to reproduce many of the observed changes when forced with observed GHG concentrations.
    • Natural processes alone cannot explain observed warming.
  • Climate model simulations of global mean temperature change, compared with observations. Left: with natural and human forcing; right: with natural forcing only.

image shows two line graphs from the IPCC AR5 with multiple lines of model and observations data

IPCC AR5, WGI, Chapter 10, FAQ 10.1

Long description

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.

 

Annex 2: Changes Observed in Canada

Average September arctic sea ice extent

Average Monthly Arctic Sea Ice Extent
August 1979-2015

Average Monthly Arctic Sea Ice Extent August 1979-2015

National Snow and Ice Data Centre

1979–2012
Note that 2012 had the lowest sea ice extent on record (records updated to 2014).

Average September Arctic Sea Ice Extent 1984

Average September Arctic Sea Ice Extent 1984

Average September Arctic Sea Ice Extent 2012

Average September Arctic Sea Ice Extent 2012

Long description

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.

 

Summary of number and magnitude of wildfires in British Columbia

Summary of number and magnitude of wildfires in British Columbia

BC Forestry and the Canadian Forest Service

Long description

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.

 

Proportion of GHG emissions by sector (2012)

  • Emissions from electricity generation account for significantly less of Canada’s total national emissions, compared with the global average.
  • In addition, emissions from transportation in Canada contribute more to Canada’s total national emissions, compared with the global average.

World (2012)

CAIT Climate Data Explorer. 2015. Washington, DC: World Resources Institute. Available online at: http://cait.wri.org.

Canada (2012)

CAIT Climate Data Explorer. 2015. Washington, DC: World Resources Institute. Available online at: http://cait.wri.org.

Long description

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%).

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