There are geological records going back millions of years.
The fact is, decades ago, climate scientists projected a startling increase in global temperatures would occur based on increasing carbon dioxide levels. It is is happening.
For years, climate change denialists argued that there was no change happening until it became impossible to dismiss. Then they moved to claiming it was part of a natural cycle. Scientists have shown a very thorough understanding of the factors involved in cycles and none of them can be attributed as a cause of the temperature increase.
Scientists said it would happen and it did. Why do you find it so hard to accept they have got it right?
Some denialists have now accepted it is being caused by human activity and started arguing that it will improve the planet.