Aging weather stations contribute to high temperature records
...A paper published in the International Journal of Climatology finds that aging of the solar radiation screens on weather stations is causing a large positive bias in measured temperatures of 1.63°C, which by way of comparison is more than twice the global warming of 0.7°C recorded since the end of the Little Ice Age in 1850.

According to the authors, “During the comparison [of the new vs. 5 year old] and 1 to 3-year-old screens, significant temperature differences were recorded at different times of the day. The differences, wider than the uncertainty amplitude, demonstrate a systematic effect. The temperature measured with the older screen is larger, and the maximum instantaneous difference was 1.63 °C (for 0–5 years comparison) in daytime hours....