Climate models often exhibit spurious long-term changes independent of either internal variability or changes to external forcing. Such changes, referred to as model “drift,” may distort the estimate of forced change in transient climate simulations. The importance of drift is examined in comparison to historical trends over recent decades in the Coupled Model Intercomparison Project (CMIP). Comparison based on a selection of metrics suggests a significant overall reduction in the magnitude of drift from phase 3 of CMIP (CMIP3) to phase 5 of CMIP (CMIP5). The direction of both ocean and atmospheric drift is systematically biased in some models introducing statistically significant drift in globally averaged metrics. Nevertheless, for most models globally averaged drift remains weak compared to the associated forced trends and is often smaller than the difference between trends derived from different ensemble members or the error introduced by the aliasing of natural variability. An exception to this is metrics that include the deep ocean (e.g., steric sea level) where drift can dominate in forced simulations. In such circumstances drift must be corrected for using information from concurrent control experiments. Many CMIP5 models now include ocean biogeochemistry. Like physical models, biogeochemical models generally undergo long spinup integrations to minimize drift. Nevertheless, based on a limited subset of models, it is found that drift is an important consideration and must be accounted for. For properties or regions where drift is important, the drift correction method must be carefully considered. The use of a drift estimate based on the full control time series is recommended to minimize the contamination of the drift estimate by internal variability.

Climate models consistently project a substantial decrease in the Indonesian Throughflow (ITF) in response to enhanced greenhouse warming. On interannual timescales ITF changes are largely related to tropical Pacific wind variability. However, on the multidecadal timescales investigated here we demonstrate that regional winds and associated changes in the upper ocean circulation cannot explain the projected ITF decrease. Instead, the decrease is related to a weakening in the northward flow of deep waters entering the Pacific basin at ~40°S and an associated reduction in the net basin‐wide upwelling to the north of the southern tip of Australia. This can be traced back to consistent changes in the Antarctic Circumpolar Current and Southern Ocean overturning, although questions still remain as to the ultimate drivers. In contrast to the ITF decrease, substantial projected changes to the upper ocean circulation of the Pacific basin are well explained by robust changes in the surface winds.

Even in the absence of external forcing, climate models often exhibit long-term trends that cannot 2 be attributed to natural variability. This so called "climate drift" arises for various reasons including: 3 perturbations to the climate system on coupling component models together and deficiencies in 4 model physics and numerics. When examining trends in historical or future climate simulations, it is 5 important to know the error introduced by drift so that action can be taken where necessary. This 6 study assesses the importance of drift for a number of climate properties at global and local scales. 7To illustrate this we have focussed on simulated trends over the second half of the 20 th century. 8While drift in globally-averaged surface properties is generally considerably smaller than observed 9 and simulated 20th century trends, it can still introduce non-trivial errors in some models. 10 Furthermore, errors become increasingly important at smaller scales. The direction of drift is not 11 systematic across different models or variables; as such drift is considerably reduced in the multi-12 model mean. Despite drift being primarily associated with ocean adjustment, it is also apparent in 13 atmospheric variables. For example, most models have local drift magnitudes that are typically 14 between 15 and 35% of the 20 th century simulation trend magnitudes for 1950-2000. Below depths 15 of 1000 to 2000m, drift dominates over any forced trend in most regions. As such steric sea-level is 16 strongly affected and for some models and regions the sea-level trend direction is reversed. Thus

While the practice of reporting multi-model ensemble climate projections is well established, there is much debate regarding the most appropriate methods of evaluating model performance, for the purpose of eliminating and/or weighting models based on skill. The CMIP3 model evaluation undertaken by the Pacific Climate Change Science Program (PCCSP) is presented here. This includes a quantitative assessment of the ability of the models to simulate 3 climate variables: (1) surface air temperature, (2) precipitation and (3) surface wind); 3 climate features: (4) the South Pacific Convergence Zone, (5) the Intertropical Convergence Zone and (6) the West Pacific Monsoon; as well as (7) the El Niño Southern Oscillation, (8) spurious model drift and (9) the long term warming signal. For each of 1 to 9, it is difficult to identify a clearly superior subset of models, but it is generally possible to isolate particularly poor performing models. Based on this analysis, we recommend that the following models be eliminated from the multi-model ensemble, for the purposes of calculating PCCSP climate projections: INM-CM3.0, PCM and GISS-EH (consistently poor performance on 1 to 9); INGV-SXG (strong model drift); GISS-AOM and GISS-ER (poor ENSO simulation, which was considered a critical aspect of the tropical Pacific climate). Since there are relatively few studies in the peer reviewed literature that have attempted to combine metrics of model performance pertaining to such a wide variety of climate processes and phenomena, we propose that the approach of the PCCSP could be adapted to any region and set of climate model simulations. KEY WORDS: Climate model evaluation · Regional climate projections · CMIP3 · PacificResale or republication not permitted without written consent of the publisher

Continuous long-term delivery of experimental drugs to the cochlea of a small animal, such as a young guinea pig, presents several technical problems. A method of placing and securing a cannula-osmotic pump system is described in this paper. Guinea pigs (225-410 g) were unilaterally implanted with an Alzet micro-pump and cannula for delivery of 20 mM tetrodotoxin (TTX) (six animals) or saline (three animals) for three days (1 microliter/h). Auditory brainstem responses (ABRs) were recorded under light anesthesia on post-implant day 1 and day 3 and compared with pre-implant baseline values. In all six cochleas infused with TTX, most frequencies showed a 30-60dB decrease in sensitivity within 24 h. Saline control animals showed little or no change from baseline sensitivity for most frequencies. In three TTX-infused animals, the cannula-pump unit was removed on day 3, and ABRs were followed during recovery. Most frequencies returned to, or near, pre-implant levels after pump removal but recovery times varied. By day 6, all animals had recovered post-surgical weight loss and showed a gain of 10-40 g. Brains and cochleas were removed and processed for sectioning. Assessment of the cochlear nucleus of non-recovery TTX-treated animals showed a deafness-related flattening of auditory nerve active zones on the treated side.