The warming of the planet is most evident by direct temperature measurements obtained by respected international scientific institutions, i.e. NASA, NOAA (national oceanic and atmospheric administration) and many others around the globe. There are also complex mathematical models that are used to represent both the historical and future behavior of global average temperatures. Since of the complexity of measurement and volatility of global temperatures, the most commonly accepted representation is the global combined average temperature anomaly,(change) of land and sea surface. This is expressed against a baseline value calculated to represent the pre industrial era (1951-1980). This anomaly is now hovering around 0.6C with highest observations of 0.63 - 0.66C.

The majority consensus by all is that the global temperatures are steadily rising in co relation to the industrial revolution.

Graph sources,

http://data.giss.nasa.gov/gistemp/graphs/

http://www.climate.gov/#climateWatch

http://en.wikipedia.org/wiki/File:Satellite_Temperatures.png