Daily Archives: May 16, 2013

Are climate models improving?

Kyle L. Swanson. Emerging selection bias in large-scale climate change simulations. Geophysical Research Letters. DOI: 10.1002/grl.50562

Climate change simulations are the output of enormously complicated models containing resolved and parameterized physical processes ranging in scale from microns to the size of the Earth itself. Given this complexity, the application of subjective criteria in model development is inevitable. Here we show one danger of the use of such criteria in the construction of these simulations, namely the apparent emergence of a selection bias between generations of these simulations. Earlier generation ensembles of model simulations are shown to possess sufficient diversity to capture recent observed shifts in both the mean surface air temperature as well as the frequency of extreme monthly mean temperature events due to climate warming. However, current generation ensembles of model simulations are statistically inconsistent with these observed shifts, despite a marked reduction in the spread among ensemble members that by itself suggests convergence towards some common solution. This convergence indicates the possibility of a selection bias based upon warming rate. It is hypothesized that this bias is driven by the desire to more accurately capture the observed recent acceleration of warming in the Arctic and corresponding decline in Arctic sea ice. However, this convergence is difficult to justify given the significant and widening discrepancy between the modeled and observed warming rates outside of the Arctic.

Click here for the full paper (fee).

Atmospheric methane concentrations less than IPCC predictions

Almost all climate models project atmospheric methane levels to increase over the next 3 decades. Some IPCC scenarios assume a large increase throughout the 21st century. Actual observations are well below these model predictions. Click here or images below for a full report.