Green iguanas are ectotherms adapted to lowland tropics. Below roughly 10 degrees Celsius their metabolism slows sharply; near 4 to 7 degrees the muscles that keep an iguana clamped to a branch simply stop responding, and gravity does the rest. The animal is not dead, and handling one is unwise because it may recover its temper before it recovers its coordination.
South Florida hosts a large introduced population descended from escaped and released pets, concentrated along canals and in suburban trees. Cold events in 2010, 2018, 2020 and 2022 produced widespread falls, and forecast offices have issued plain-language warnings about the hazard.
Severe cold does kill iguanas, and hard freezes have measurably knocked back the Florida population, though it has recovered each time. There is an open question about selection: repeated cold events could favour individuals with slightly greater cold tolerance, which would matter for how far north the species can eventually establish. The evidence for such a shift is suggestive rather than settled.