[show abstract][hide abstract] ABSTRACT: Significant changes in physical and biological systems are occurring on all continents and in most oceans, with a concentration of available data in Europe and North America. Most of these changes are in the direction expected with warming temperature. Here we show that these changes in natural systems since at least 1970 are occurring in regions of observed temperature increases, and that these temperature increases at continental scales cannot be explained by natural climate variations alone. Given the conclusions from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report that most of the observed increase in global average temperatures since the mid-twentieth century is very likely to be due to the observed increase in anthropogenic greenhouse gas concentrations, and furthermore that it is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent except Antarctica, we conclude that anthropogenic climate change is having a significant impact on physical and biological systems globally and in some continents.
[show abstract][hide abstract] ABSTRACT: We have analyzed the seasonal variations of global mean surface air temperature (SAT) and surface energy budgets of 17 AR4 models. Considerable differences in the amplitude of seasonal cycle (A) in the global mean SAT in the pre-industrial control simulations among the models have been traced, to a large degree, to differences in their simulated clear-sky downward longwave radiation (LW "«) and latent heat flux (LH). We suggest that water vapor feedback process influence the seasonal changes of SAT through its roles on the seasonal variations of LW "« and LH. This implies that the simulated seasonal change of global mean SAT might contain a clue about the sensitivity of water vapor feedback and the A of in SAT thus provides some constraint on climate sensitivity since both are subject to the same feedback process.
Geophysical Research Letters - GEOPHYS RES LETT. 01/2008; 35(8).
[show abstract][hide abstract] ABSTRACT: Trends in surface temperature over the last 100, 50, and 30 yr at individual grid boxes in a 5° latitude longitude grid are compared with model estimates of the natural internal variability of these trends and with the model response to increasing greenhouse gases and sulfate aerosols. Three different climate models are used to provide estimates of the internal variability of trends, one of which appears to overestimate the observed variability of surface temperature at interannual and 5-yr time scales. Significant warming trends are found at a large fraction of the individual grid boxes over the globe, a much larger fraction than can be explained by internal climate variations. The observed warming trends over the last 50 and 30 yr are consistent with the modeled response to increasing greenhouse gases and sulfate aerosols in most of the models. However, in some regions, the observed century-scale trends are significantly larger than the modeled response to increasing greenhouse gases and sulfate aerosols in the atmosphere. Warming trends consistent with the response to anthropogenic forcing are detected at scales on the order of 500 km in many regions of the globe.
Journal of Climate - J CLIMATE. 01/2005; 18(21):4337-4343.