Who claims that?
The real experts are well aware of the variables.

read this... (Google it).

Proc. Natl. Acad. Sci. USA
Vol. 94, pp. 8350–8353, August 1997
Colloquium Paper
This paper was presented at a colloquium entitled ''Carbon Dioxide and Climate Change,'' organized by Charles D.
Keeling, held November 13–15, 1995, at the National Academy of Sciences, Irvine, CA.
Tree rings, carbon dioxide, and climatic change
GORDON C. JACOBY* AND ROSANNE D. D'ARRIGO
Tree-Ring Laboratory, Lamont–Doherty Earth Observatory, Palisades, NY 10964

Only the Dunning-Kroger effect crowd ever claims that anyone claims that. Those outside the science constantly think they have found the big flaw, the obvious thing that the experts overlooked. They think this only because they are so darn far behind in the science that they don't know how much they don't know.