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Ka-Kit Tung and Jiansong Zhou

Abstract

Using a modified method of multiple linear regression on instrumented sea surface temperature (SST) in the two longest historical datasets [the Extended Reconstructed SST dataset (ERSST) and the Met Office Hadley Centre Sea Ice and SST dataset (HadISST)], it is found that the response to increased greenhouse forcing is a warm SST in the mid- to eastern Pacific Ocean in the equatorial region in the annual or seasonal mean. The warming is robustly statistically significant at the 95% confidence level. Consistent with this, the smaller radiative heating from solar forcing produces a weak warming also in this region, and the spatial pattern of the response is neither La Niña–like nor El Niño–like. It is noted that previous reports of a cold-tongue (La Niña–like) response to increased greenhouse or to solar-cycle heating were likely caused by contaminations due to the dominant mode of natural response in the equatorial Pacific. The present result has implications on whether the Walker circulation is weakened or strengthened in a warmer climate and on coupled atmosphere–ocean climate model validation.

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Jiansong Zhou and Ka-Kit Tung

Abstract

Using 54 yr of NCEP reanalysis global data from 1000 to 10 hPa, this study establishes the existence and the statistical significance of the zonal-mean temperature response to the 11-yr solar cycle throughout the troposphere and parts of the lower stratosphere. Two types of statistical analysis are used: the composite-mean difference projection method, which tests the existence of the solar cycle signal level by level, and the adaptive AR(p)-t test, which tells if a particular local feature is statistically significant at the 95% confidence level. A larger area of statistical significance than that in previous published work is obtained, due to the longer record and a better trend removal process. It reveals a spatial pattern consistent with a “bottom up” mechanism, involving evaporative feedback near the tropical ocean surface and tropical vertical convection, latent heating of the tropical upper troposphere, and poleward large-scale heat transport to the polar regions. It provides an alternative to the currently favored “top down” mechanism involving stratospheric ozone heating.

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Jiansong Zhou and Ka-Kit Tung

Abstract

To unmask the anthropogenic global warming trend imbedded in the climate data, multiple linear regression analysis is often employed to filter out short-term fluctuations caused by El Niño–Southern Oscillation (ENSO), volcano aerosols, and solar forcing. These fluctuations are unimportant as far as their impact on the deduced multidecadal anthropogenic trends is concerned: ENSO and volcano aerosols have very little multidecadal trend. Solar variations do have a secular trend, but it is very small and uncertain. What is important, but is left out of all multiple regression analysis of global warming so far, is a long-period oscillation called the Atlantic multidecadal oscillation (AMO). When the AMO index is included as a regressor (i.e., explanatory variable), the deduced multidecadal anthropogenic global warming trend is so impacted that previously deduced anthropogenic warming rates need to be substantially revised. The deduced net anthropogenic global warming trend has been remarkably steady and statistically significant for the past 100 yr.

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Jiansong Zhou and Ka-Kit Tung

Abstract

The purpose of the present work is to demonstrate that a solar cycle response exists in surface temperature using the longest global dataset available, which is in the form of 1854–2007 sea surface temperature (SST), with an emphasis on methods and procedures, data quality, and statistical tests and the removal of deterministic signals, such as volcano aerosol forcing and greenhouse gas warming. Using the method of composite-mean difference (CMD) projection, signals of warming during solar maximum and cooling during solar minimum years are found in the global SST over the 14 cycles, dispelling previous claims that the solar cycle response before 1920 is opposite to that of the modern era. The magnitude of the solar cycle response averaged over the oceans between 60°S and 60°N is about 0.1°C of warming for each W m−2 variation of the solar constant (but is slightly lower, at ~0.085°C, when periods of suspected bad data are averaged in, which is consistent with previous work). The signal is robust provided that the years near the Second World War are excluded, during which transitions from British ships to U.S. ships introduced warm bias in the SST, as recently pointed out by D. Thompson and his colleagues. Monte Carlo tests show that the extracted signal has less than 0.02% chance of being a random occurrence. This establishes the existence of a solar cycle response at the earth’s surface at high statistical confidence. Contamination of the signal by volcano aerosols is estimated using the multiple CMD inversion method and found to be small over this long record, although ENSO contamination varies depending on the period chosen but is also small.

The multidecadal trend of response to solar forcing is found to account for no more than a quarter of the observed warming in SST during the past 150 yr, under a reasonable but unproven assumption that the climate response to secular solar forcing and to solar cycle forcing has the same spatial pattern.

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