Sure, just like there's convincing evidence of the Bermuda Triangle. The same sorts of high-CO2 + warmer temps events happened before the rise of human civilizations, if you ask anyone who studies the prehistorical climate. What were those spikes caused by, cavemen in SUVs? What caused the most recent warming trend that produced bumper crops in Europe? What caused the Little Ice Age that followed? Was it cow flatulence? Knights on dirt bikes?
Ignorant people are gullible people, and gullible people fall for the man-caused-global-warming scenario because they are ignorant of basic earth science. It's disturbing how many people are surprised to learn that the polar ice caps have melted and refrozen many times in the earth's history, or that there is pretty strong evidence of mass global-wide extinctions happening many times, or that a look at ice core drillings that date 10,000 years or even 200,000 years represent a time span that is nothing -- less than the blink of an eye in the context of earth's past.
More folks should grab geology and paleontology books and read them for kicks just for a basic education -- and then do what I did, read Gore's "Earth in the Balance" and see how many BLATANLY false statements he makes in the book that you may not have known were false if you hadn't just read some of the latest books on paleontology and geology.
Milankovitch cycle-forced climate variability, actually.
What caused the most recent warming trend that produced bumper crops in Europe? What caused the Little Ice Age that followed? Was it cow flatulence? Knights on dirt bikes?
The Little Ice Age has been explained primarily due to a period of lower solar activity, called the Maunder Minimum of decreased sunspot numbers. At the end of the LIA, a couple of large volcanic eruptions also had a brief effect.