Page 371 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 11 Climate Change 335
Three-dimensional grid boxes interact vertically and horizontally with one another.
Atmospheric grid boxes include elements of terrain and vegetation, and local climate factors.
motions of Earth–atmosphere systems. They can be pro- grammed to model the effects of linkages between specific cli- matic components over different time frames and at various scales. Submodel programs for the atmo- sphere, ocean, land surface, cryo- sphere, and biosphere may be used within the GCMs. The most sophisticated models couple at- mosphere and ocean submodels and are known as Atmosphere– Ocean General Circulation Models (AOGCMs). At least a dozen established GCMs are now in operation around the world.
Radiative Forcing
Scenarios
Scientists can use GCMs to de- termine the relative effects of various climate forcings on tem- perature (remember that a cli- mate forcing is a perturbation in
Earth’s radiation budget that causes warming or cooling). One question that scientists have sought to answer is, “Does positive radiative forcing have natural or anthropo- genic causes?”
Figure 11.26 compares results from two sets of climate simulations as compared to actual global average tempera- ture observations for land and ocean (black line) made from 1906 to 2010. In the graph, the actual temperature data are compared with simulations in which both natural and anthropogenic forcings were included (shaded pink area and black line). These data are compared with simu- lations that included natural forcing only, modeled from
Land and Ocean Surface 2
1
0 –1
Oceanic grid boxes include currents, salinity, and temperature.
▲Figure 11.25 Grid boxes and layers in a general circulation model.
and areas where further research is needed. In 2007, the IPCC shared the Nobel Peace Prize for its two decades of work raising understanding and awareness of global cli- mate change science.
Climate Models and Forecasts
In addition to using paleoclimatic records and actual mea- surements of present-day climatic elements, scientists use computer models of climate to assess past trends and forecast future changes. A climate model is a mathemati- cal representation of the interacting factors that make up Earth’s climate systems, including the atmosphere and oceans, and all land and ice. Some of the most complex computer climate models are general circulation models (GCMs), based on mathematical models originally estab- lished for forecasting weather.
The starting point for such a climate model is a three- dimensional “grid box” for a particular location on or above Earth’s surface (Figure 11.25). The atmosphere is divided vertically and horizontally into such boxes, each having distinct characteristics regarding the movement of energy, air, and water. Within each grid box, physi- cal, chemical, geological, and biological characteristics are represented in equations based on physical laws. All these climatic components are translated into computer codes so that they can “talk” to each other, as well as in- teract with the components of grid boxes on all sides.
GCMs incorporate all climatic components, includ- ing climate forcings, to calculate the three-dimensional
1910 1900 2010
▲Figure 11.26 Climate models showing relative effects of natural and anthropogenic forcing. Computer models track the agreement between observed temperature anomalies (black line) with two forcing scenarios: combined natural and anthropogenic forcings (pink shading) and natural forcing only (blue shading). The natural forcing factors include solar activity and volcanic activity, which alone do not explain the temperature increases. [Based on Climate Change 2013: The Physical Science Basis, Working group i, iPCC Fifth Assessment Report, September 27, 2013: Fig. SPM-6, p. 32.]
Temperature change (C°)