While these adjustments don't have a big effect on the global temperature record, they are needed to obtain consistent local records from equipment which has changed over time. (skepticalscience.com)
The amount of energy difference is huge and I don't think that many people would argue that they don't have a significant impact on the global temperature in the short run. (realclimate.org)
Back then, natural causes were the dominant forcings on global temperature trends. (realclimate.org)