As climate change is a complex puzzle of interacting systems that scientists are still working to clearly grasp, predictions of future climate change are never definite. Forecast of climate changes are predicted by means of computer models that mathematically simulate the interactions of the land, sea, and air, which together determine the Earth's climate. Computer simulation is a software program that runs on any size computer that attempts to simulate some phenomenon based on a scientist's conceptual and mathematical understanding of the phenomenon. Climate models are based on a wealth of scientific observations and well established laws of physics, including the laws of gravity and fluid motion, and the conservation of energy, momentum, mass, and water. It is this dependence on basic physical laws that lends high confidence to the prediction that a buildup of greenhouse gases will eventually lead to a significant alteration in the Earth's climate. In order to predict the behavior of the atmosphere for only a few days ahead, an atmosphere-only model, with no simulation of the ocean, can be used. This is the method employed in making short-term weather forecasts, whose relative accuracy demonstrates the ability of this sort of model to reproduce some of the important details of the atmosphere's behavior.
A General Circulation Model (GCM) is a mathematical model of the general circulation of a planetary atmosphere or ocean and based on the Navier–Stokes equations on a rotating sphere with thermodynamic terms for various energy sources (radiation, latent heat). Navier–Stokes equations describe the motion of fluid substances. A fluid is a substance that continually deforms (flows) under an applied stress, no matter how small. These equations are the basis for complex computer programs commonly used for simulating the atmosphere or ocean of the Earth. Atmospheric and Oceanic GCMs (AGCM and OGCM) are key components of Global Climate Models along with sea ice and land-surface components. GCMs and global climate models are widely applied for weather forecasting, understanding the climate, and projecting climate change. Sea ice is largely formed from seawater that freezes. Because the oceans consist of saltwater, this occurs below the freezing point of pure water, at about -1.8 °C (28.8 °F). These computationally intensive numerical models are based on the integration of a variety of fluid dynamical, chemical, and sometimes biological equations.
All of the published estimates of how the climate could change in the future are created by computer models of the Earth’s climate system, the General Circulation Models (GCMs). These Models have proven to be extremely vital tools for simulating and understanding climate, and there is considerable confidence and trust that they are able to provide believable estimates of future climate change, particularly at larger scales. However, these models persists to have significant limitations, such as in their representation of clouds, which lead to uncertainties in the magnitude and timing, as well as regional details, of predicted climate change. On the other hand, over several decades of model development, they have consistently provided a robust and unambiguous picture of significant climate warming in response to increasing greenhouse gases. It is important to recognize that predictions of climate change in specific areas are not forecasts comparable to tomorrow’s weather forecast. Rather, they are hypothetical examples of how the climate might change and usually contain a range of possibilities as opposed to one specific high likelihood outcome