To "take the temperature" of a group is to obtain opinions from various members and determine the level of support, or opposition, in the group for a particular action or policy.
A group can be warm or cold to an action or policy.
Example: "Democratic insiders are taking the temperature of some top party donors about the possibility of naming White House press secretary Robert Gibbs as chairman of the Democratic National Committee heading into President Barack Obama’s reelection campaign in 2012, senior officials tell POLITICO."
This means, the insiders are measuring the support, or lack thereof, for placing outgoing press secretary Robert Gibbs as chairman of the Democratic National Committee. According to the article (link below), reaction is positive, so we may say members are warm to the possibility.