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The circulation system of the North Atlantic Ocean has weakened and is predicted to weaken further in the coming decades. An analysis suggests that this decline could lead to accelerated global surface warming. The circulation system of the North Atlantic Ocean has weakened and is predicted to weaken further in the coming decades. An analysis suggests that this decline could lead to accelerated global surface warming.

Arising from: R. G. Graversen, T. Mauritsen, M. Tjernstrom, E. Kallen & G. Svensson , 53–56 (2008)10.1038/nature06502 ; Graversen et al. reply Relative rates of temperature change between the troposphere and surface, and the mechanisms that produce these changes, have long been a contentious issue. Graversen et al.1, predicated upon the ERA-40 reanalysis2, report polar tropospheric amplification of surface warming and attempt to explain this finding dynamically. Here we show (1) that data from satellites3,4 and weather balloons5 indicate that the ERA-40 trends are increasingly unrealistic polewards of 62° N; (2) that the two other reanalyses considered1 exhibit very different polar trends; and (3) that the vertical profile of polar trends in ERA-40 is unrealistic, particularly above the troposphere. These quasi-independent strands of evidence imply that the pattern of warming in the Arctic troposphere is highly unlikely to be as given in ERA-40 and as reported by Graversen et al.1.

Uncertainty over tropical tropospheric temperature change has loomed large over the last two decades. Use of wind data to infer temperature change offers a new avenue of investigation.

Our plan to create a suite of surface-temperature data sets for analysis by the international climate community (Nature465,158–159; 2010) is now under way. In the interest of transparency, we announce the publication of 12 white papers that are available until 1 September for public comment through a moderated blog(www.surfacetemperatures.org)

Arising from: Q. Fu et al. Nature 429, 55–58 (2004); see also communication from Gillett et al.; Fu et al. reply There has been considerable debate about changes in the temperature of the troposphere1 measured using the Microwave Sounding Unit (MSU) instrument2,3 or radiosondes4,5. Fu et al.6 linearly combine time series from two MSU channels to estimate vertically integrated 850–300-hPa temperatures and claim consistency between surface and free-troposphere warming for one MSU record. We believe that their approach overfits the data, produces trends that overestimate warming and gives overly optimistic uncertainty estimates. There still remain large differences between observed tropospheric temperature trends and those simulated by a climate model.

Words, Meanings, and Messages Theory and Experiments in Psycholinguistics. By Ragnar Rommetveit. Pp. viii + 328. (Academic Press: New York and London; Universitetsforlaget: Oslo, 1968.) n.p.