Global Warming: correlation or causality?

Carl Berkowitz
Pacific Northwest National Laboratory

A number of direct measures will be presented showing that climate is changing, including a graph of variations in the Earth's surface temperature. Also to be presented will be indicators of the human influence on the atmosphere such as large changes in the atmospheric concentrations of CO2, CH4 and N2O. This information, without causal links, establishes a strong correlation between climate change and measures of human activity. Several causal relations will be then be given, including the role of 'greenhouse gases', that move these observations from correlation to causality.

Despite both correlation and causality, there is still room for uncertainty. A number of changes expected with the causal link between observations and global change have not been observed, e.g., there have been no significant trends of Antarctic sea-ice extent during the period of reliable satellite measurements (although this may be seen in the future since it takes time to warm the southern ocean). And climate models still have many areas of known uncertainty, most notably in their treatment of clouds which affect the amount of planetary scale warming, though not its direction. But although complex physically-based models cannot yet simulate all aspects of climate, the consensus of the scientific community is that climate change is real, and that human activities have contributed a significant amount to these changes.