"Until the Industrial Revolution, melting of snow and ice at the end of cyclical glacial periods was driven by changes in the Earth’s orbit. As snow and ice melted on the planet, the albedo, or reflectivity, of the earth declined, with land and ocean absorbing more heat from the sun. As the planet slowly warmed, a warmer and better-mixed ocean released CO2 into the atmosphere, which amplified the warming that was already in progress. In all, temperature typically increased by 6°C (11° F) over thousands of years during these interglacial periods, and one third of this increase was a result of the CO2 that outgassed from the ocean once warming began. Therefore, CO2 was not the initial cause of melting ice on the planet. It merely amplified a signal that was already in progress."
"By contrast, as humans burn fossil fuels, we are creating a new driver of snow and ice melt and accompanying sea-level rise. [Note that the current rate of temperature increase is far too dramatic to be natural.] This time, additional CO2 entering the atmosphere is coming from sources of carbon that had previously been safely sequestered for millions of years in fuels such as oil and gas. This increased carbonization will remain in play for many thousands of years.
We know from basic physics that CO2 traps heat. The phenomenon is perhaps best demonstrated by Earth’s neighbor Venus... Venus has 100,000 times the amount of CO2 in its atmosphere as Earth does" [and, even when you take into account that Venus is 72% the distance from the sun as Earth is and receives more sun light, this increased factor does not on its own account for the fact that Venus' average temperature is 462° C (863° F), high enough to melt lead].
"Thus, while the past sea-level rises were the result of melting glaciers and the thermal expansion was driven by changes in Earth’s orbit and amplified by oceanic CO2 released after initial warming, today's anthropogenic CO2 releases are directly driving this."
What Sun Looks Like From Other Planets: