University of Michigan geophysicist Shaopeng Huang has found that even layers deep in the Earth have felt the increased heat from global warming, terming the change “rocky fever.”
“Not to feel global warming, one would need to hide beneath 600 feet of rocks,” Huang said. “Although its causes are debatable, recent global warming is indisputable.”
Huang was part of a 2000 study, cited in the National Research Council report on global warming, which showed that the 20th century was the warmest of the last five centuries. Now, the temperature increase has been found to permeate subsurface rock.
Here’s the paper describing the data (PDF, subscription required). Abstract here, open access.