Page 370 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

334 part II The Water, Weather, and Climate Systems
3.0 2.5 2.0 1.5 1.0 0.5
1.4 1.2 1.0 0.8 0.6 0.4 0.2
papers from professional organizations (for example, the Association of American Geographers, the Ameri- can Meteorological Society, the Geological Society of America, and the American Geophysical Union) also support this consensus. Bringing together leading scientists from an array of disciplines to assess Earth’s climate system, the IPCC is the world’s foremost sci- entific entity reporting on climate change. The 2013–2014 IPCC Fifth As- sessment Report describes as 95%–100% certain that human activities are the primary cause of present climate change. Specifi- cally, the Fifth Assessment Report concludes with at least 95% certainty that the observed warming from 1951 to 2010 matches the estimated human contribu- tion to warming; in other words, the IPCC found that scientists are 95%–100% certain that humans are responsible for the tem- perature increase. The Fifth Assessment Report is avail- able at www.ipcc.ch/index.htm# .UiDyVj_pxfk.
The IPCC, formed in 1988 and operating under sponsorship of the United Nations Environment Pro- gramme (UNEP) and the World Meteorological Or- ganization (WMO), is the international scientific orga- nization coordinating global climate change research, climate forecasts, and policy formulation—truly a global collaboration of scientists and policy experts from many disciplines. Its reports represent peer-reviewed, consensus opinions among experts in the scientific community concerning the causes of climate change as well as the uncertainties
00 1980 1985 1990 1995 2000 2005 2010
Year
▲Figure 11.23 Greenhouse gases: relative percentages of radiative forcing. The coloured areas indicate the amount of radiative forcing accounted for by each gas, based on the concentrations present in earth’s atmosphere. note that CO2 accounts for the largest amount of radiative forcing. The right side of the graph shows radiative forcing converted to the annual greenhouse gas index (aggi), set to a value of 1.0 in 1990. in 2012, the aggi was 1.32, an increase of 30% in 22 years. [From the NOAA Annual Greenhouse Gas Index (AGGI), nOaa, updated summer 2013, available at www.esrl.noaa.gov/gmd/aggi/aggi.html.]
RF Factors
LOSU
Long-lived greenhouse gases
Stratospheric water vapour from CH4
Surface albedo
Direct effect
Total
aerosol Cloud-albedo effect
Linear contrails
Solar irradiance
Total net anthropogenic
Ozone
AGGI (2012) = 1.32 1990 = 1.0
Stra
tospheric
Land use
Halocarbons
Tropospheric
Black carbon on snow
High
Med
Low
Med–Low
Med–Low
Low
Low
Low
–2 –1 0 1 2 Radiative Forcing (W · m–2)
▲Figure 11.24 Analysis of radiative forcing (rF) of temperatures. The top group of items in the table (for example, long-lived greenhouse gases) represent anthropogenic radiative forcing. The only long-term natural climate forcing included is solar irradiance. note that the overall direction of forcing is positive (raising temperatures), caused mainly by atmospheric CO2. in the preliminary 2013 iPCC Fifth Assessment Report from Working group i, total net anthropogenic forcing is increased to 2.3 W·m−2 from the 1.6 W·m−2 calculated in 2006 and shown above. [Based on iPCC, Working group i, Fourth Assess- ment Report: Climate Change 2007: The Physical Science Basis, Figure SPM-2, p. 4, and Figure 2.20, p. 203.]
N2O CH4
Carbon dioxide Methane Nitrous oxide CFC-12 CFC-11
15 minor halogenated gases
CO2
High
Natural Anthropogenic Parts per billion (ppb)
Annual Greenhouse Gas Index