The reason of course, is the huge amount of averaging that is done to obtain global temperature estimates, this averaging essentially averages out most of the human induced noise. (realclimate.org)
The first problem is that the proxy - based global temperature estimates do not actually agree with the thermometer - based estimates very well. (globalwarmingsolved.com)
But, we found that it occurs for most of the proxy - based global temperature estimates. (globalwarmingsolved.com)