Two sayings come to mind relative to this entire topic of human impact on the Earth's climate ... "figures don't lie but liars do figure" ... and ... "we are all entitled to our own opinions, but not to our own facts".
My question deals with the robustness of the computer models. We are told they are based on thousands of years of data taken from tree rings and ice cores and other sources. If that is the case, then why can't the data be modified to exclude all climate input between 1909 and 2009 and then rerun the program to project global temperature for the last 100 years?
If the models correctly predict the warming and cooling patterns the world "experienced" over the last 100 years, maybe we ought to get serious about what they say for the next 20-100 years. Likewise, if the output does not reasonably correlate to the patterns we have experienced since 1909, why should be believe they can predict the next several decades?
Can anyone answer my question as to why the above cannot be done?
The models are adjusted until they successfully 'hindcast' .
The trouble with that is that it cannot be known whether the correct variables were adjusted to achieve the desired result. An adjustment in a wide range of variables woud create an accurate hindcast but it does not necessarily reflect reality.
The only test is if one then runs it forward and compares the result with the real world.
Unfortunately the models start to diverge from reality every time as soon as they are run forward in parallel with the real world.