PowerPoint Presentation - Presentation at Yale University

The scientific evidence for a human ÒfingerprintÓ on global climate has strengthened over time

ÒThe balance of evidence suggests a discernible human influence on global climateÓ

ÒThere is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activitiesÓ

ÒMost of the observed increase in globally averaged temperatures since the mid-20th century is very likely* due to the observed increase in anthropogenic greenhouse gas concentrationsÓ


	I havenÕt shown you this, but the Earth is warming. We know this from detailed analyses of thermometric temperature records.
	The best information we have indicates that the EarthÕs mean near-surface temperature has increased by around 0.5^oC over the last 100 years.
	Analyses of ÒreconstructedÓ temperature data from tree rings, ice cores, corals and boreholes indicate that the Earth is now warmer than at any time since at least 1400 A.D.
	I have shown you one example of a ÒfingerprintÓ study, in which model-predicted and observed patterns of temperature change have significant similarities.
	These similarities generally increase with time, and they canÕt be fully explained by the ÒnoiseÓ of natural climate fluctuations (assuming that model estimates of this noise are realistic).
	Here, IÕve shown you results for vertical cross-sections of temperature change. We and others have obtained rather similar results from analyses of geographical patterns of temperature change at the EarthÕs surface.