William Michael Connolley is a climate modeller. Connolley is a Senior Scientific Officer in the Physical Sciences Division in the Antarctic Climate and the Earth System project at the British Antarctic Survey.

Connolley holds a Bachelor of Arts in mathematics and Doctor of Philosophy. from the University of Oxford for his work on numerical analysis. Connolley has authored and co-authored many articles in the field of climatological research, and it is his view that there is a consensus in the scientific community about climate change topics such as global warming; and believes that the various reports from the Intergovernmental Panel on Climate Change (IPCC) summarise this consensus.

One of Connolley's current research interests is sea ice, its observations and modelling, in global climate models (GCM), especially the HadCM3 GCM. Around Antarctica, direct observations of sea ice are sparse, and even the most easily observable quantity, ice fraction, is not directly available; satellite Special Sensor Microwave/Imager (SSMI) based observations are used instead. However, different algorithms produce somewhat different results, sufficiently so that verification of GCM output becomes difficult. Hence Connolley has studied the validation of the SSMI products against more direct observations from upward looking sonar observations in the Weddell Sea area. In his investigation, the results indicate the Bootstrap product appears to "fit better" than the NASA Team product, and is it indicated by Connolley that the GCM results are more realistic than previous results.

Connolley has long had an interest in confronting the notion that "all scientists were predicting an ice age in the 1970s" (known as global cooling). Connolley maintains a webpage analysing papers relevant to this issue. Connolley actively posts to newsgroups such as sci.environment, writes for RealClimate, maintains a personal blog, and contributes to Wikipedia. According to Connolley, his activities in various outlets are to support his belief that scientists can and should participate in the public understanding of science.

In 2005, the journal Nature wrote a comparison of the relative reliability of Wikipedia and Brittanica, in which Connolley was discussed as an example of an expert who regularly contributes to Wikipedia.