Step 1 - we humans discover that the Arctic accumulates more heat on a summer's day then the equatorial regions.
Step 2 - we realise that our atmosphere is heated not so much directly by the sun but by heat from the surface.
George Best not the footballer circa 1580
Step 3 - we discover that heat and light are two separate forms of radiant energy
Émilie Du Châtelet - An Essay On Heat - 1739
Step 4 - we discover proof of ice ages
Ignaz Venetz - Climate Change Pioneer
Step 5 - we prove that George Best was correct - we demonstrate experimentally the absorption of Émilie Du Châtelet's solar heat by soil, plants etc. on Earth and its re-radiation at longer wave-lengths.
Step 6 - we measure what is now called the greenhouse gas effect by measuring the heat re-radiated by the moon.
The Moon And The Telephone
Step 7 - we calculate the amount of industrially produced CO2 that humans put into the atmosphere as compared with natural geological processes.
Arvid G Högbom (article in Swedish)
image source - sok.riksarkivet.se
Step 8 - we discover that industrially produced CO2 is warming the planet.
Svante Arrhenius 1896
And the rest, as they say, is history.
But if you need more persuading that global warming is a scientific fact, please follow the many links to reliable sources in "In post-election media, colorful thread develops on science—mainly climate science".
It bears repeating that the truth can only flourish where error has been plucked out by the roots.