It makes me very suspicious that actual scientists could consider this settled... I'm just a layman and have been pointing out these variables for years. These are ones I can think of right off the top of my head.
Atmospheric particle dynamics: volcanic activity, aerosols, dust, water vapor, moist convection, cloud building.
Solar cycles (certainly some we have no way of knowing): sun spots, solar wind, magnetic flux, major eruptions and their direction.
Universe interactions: asteroids, cosmic radiation, pulsars, position in the galaxy.
Earth: magnetosphere, gravity waves, continental shift, mountain building, wind patterns, ocean currents, earth tilt, orbit, vegetation adaptation, animal cultivation, deforestation.
Top those variations off with data collection inconsistencies and outright manipulations... and I don't see how anyone can draw conclusions except con men and their marks.