A climate model is a simplified numerical simulation of the climate.
Climate scientists attempt to validate or prove the skill of the models by tuning them to match observations of the climate.
All the models are claimed to have good agreement with the 20th century temperature trends, yet are acknowledged to have significant errors.
Currently the most advanced climate models, still disagree by more than a factor of two in their sensitivity to greenhouse gas forcing, and have significant disagreements with observed climate behavior at high latitudes.
They are, therefore, utterly unable to project the change of climate in response to future greenhouse gas scenarios.
The climate is generally not considered predictable, because not all the internal processes of the climate are well understood.
Dr. Roy Spencer wrote:
- "All leading climate models forecast that as the atmosphere warms there should be an increase in high altitude cirrus clouds, which would amplify any warming caused by manmade greenhouse gases. That amplification is a positive feedback. What we found in month-to-month fluctuations of the tropical climate system was a strongly negative feedback. As the tropical atmosphere warms, cirrus clouds decrease. That allows more infrared heat to escape from the atmosphere to outer space."