First off- global temps are difficult to measure, adding up readings from different areas of the land and sea is a complex job. Second- it doesn't matter that much what the number actually is (accuracy) as long as we can measure how much it is changing (precision). My problem with totally believing the figures that we are getting about global warming is the adjustments that are being made to the measurements. These adjustments are made for many reasons, such as changing from one type of instrument to another or filling in missing areas. But they almost always step up. By step up I mean that the accuracy figure (actual temperature) is raised step and then precision measurements are based on that new increased baseline. But the new higher baseline is compared to older lower baselines. Why does this matter and how are biases introduced? Take satellites, when one generation is replaced by the next there is an overlap and they try to calibrate them together but often the first satellite is badly degraded. The people who manage the satellites often disagree with the adjustments made to their instruments' readings but they can't really do anything about it. And the baseline always goes up. The diving buoys for measuring ocean temps originally produced data that showed substantial cooling for the early 00's. They were checked, scrutinized and recalibrated until the readings were more in line. Would this have happened if the data had shown higher temps? The surface station readings have been a total travesty. Poor placement, massive loss of individual stations, poor data collection methodologies and of course temperature adjustments that often are the majority of the trend. I am not saying there has been no temperature increase. But I am saying that biased adjustments in just about every area have had a significant effect on the overall trend of increasing temps.