An uncalibrated sim will typically give crazy results like 'increasing atmospheric CO2 by 1% raises surface temperatures by 300 degrees' or 'one large forest fire will trigger a permanent ice age'. If you see an uncalibrated sim giving results that seem even vaguely plausible, this means the programmer has tinkered with its internal mechanisms to make it give those results. Doing that is basically equivalent to just typing up the desired output by hand - it provides evidence about the beliefs of the programmer, but nothing else.