Detection of an Emerging Anthropogenic Warming Signal at Regional Scales

Previous studies have shown that observed significant warming trends over the period of 1950 and 1999 in surface air temperature consistent with the response to anthropogenic forcing are detected at scales on the order of 500 km in many regions of the globe. In this study, we investigate the emerging anthropogenic warming signals in the scenario future runs simulated by six AR4 models at regional scales. Simulated trends in surface temperature over different periods starting from the year of 2000 at individual 5x5 latitude and longitude grid boxes are compared with model estimates of the natural internal variability of these trends. It is found that an emerging anthropogenic warming signal is detected as early as the year of 2015 at continental scales, and the year of 2020 at large fractions of the grid boxes over the globe. Detection results here are likely to be of considerable practical importance, as natural and human systems are more likely to be affected by regional temperature changes when these changes are outside the range normally experienced by the systems.