Showing papers by "Sallie L. Baliunas published in 2002"

A False Planet around HD 192263

Abstract: We present new high-precision Stromgren photometry and Ca II H and K spectrophotometry of HD 192263. Based on radial velocity variations detected previously by two groups, this K2 V star was thought to host a 0.75 MJup (minimum mass) planetary companion in a 24 day orbit. Our photometric observations reveal periodic variations that match the purported planetary orbital period, while the Ca II H and K emission fluxes are modulated on half the planetary period. This suggests that rotational modulation of the visibility of stellar surface activity is the source of the observed radial velocity variations. Therefore, HD 192263 should be removed from lists of stars with well-established planetary companions unless further observations and analysis can support the existence of the planet in spite of the star's intrinsic variations.

Modeling climatic effects of anthropogenic carbon dioxide emissions: unknowns and uncertainties. Reply to Karoly et al. (2003)

Abstract: We encourage the readers of this Comment/Reply exchange to read our original paper (Soon et al. 2001) in its entirety because of the way Karoly et al. have portrayed the content and the context of our research paper. For example, when we referred to our reviews concerning the weaknesses of GCMs as being ‘biased’, we said that ‘we are biased in favor of results deduced from observations.’ Karoly et al.’s reference to this is a quote out of context that, if read alone, mischaracterizes our meaning. In passing, we are surprised by Karoly et al.’s apparent reference to the popular meaning of the word ‘biased’. It appears that they are treating our reference to bias as though greater confidence would be warranted in work where systematic biases are not acknowledged, as in the IPCC Third Assessment Report they recommend (IPCC 2001). They do not follow up with any rejection of the analyses, or of the discussion of observational and modelling difficulties in our original article. Three points form the substance of the Comment. The first is a discussion of our statement that unique attribution of climate change to increasing atmospheric CO2 is not possible. Despite the promise of controversy in pre-emptive staking of theirs and IPCC’s authority on climate science, in substance their discussion concludes that we are correct. Second is a discussion of our statement that modelling studies have not substantiated the attribution of climate change to rises in CO2. Karoly et al. respond that ‘modelling studies have helped to substantiate that CO2 added to the air is likely to have caused significant global warming’. This is cautious wording. Modelling studies may have helped—especially as the notion of ‘ help’ is subjective; nevertheless, the attribution of climate change to CO2 is not substantiated, and Karoly et al. have not affirmed that it is substantiated. They are right to be careful. The Comment offers a discussion of precisely how modelling studies are or can be used, or be ‘ helpful’, even if falling short of substantiation. Karoly et al. are overly optimistic, in our view, in not acknowledging the importance of what is unknown and unquantifiable in our current limited knowledge of the climate system, and in turn the major uncertainty in use of these models to interpret observational variables. The burden of our paper was to demonstrate these gaps, leading to the conclusion we summarized in our abstract, ‘[U]ncritical application of climate models has led to the commonly held but erroneous impression that modeling has proven or substantiated the hypothesis that CO2 added to the air has caused or will cause significant global warming.’ Karoly et al. sketch the application of a formal method for detection/attribution of greenhouse gas forcing and climate change response. However, to outline the existence of a formal method is not to demonstrate the meaningfulness of its application. Quantification of the effects of anthropogenic greenhouse gases is confounded by numerous unresolved climate issues—both anthropogenic issues, such as the direct and indirect role of multi-component aerosols, deforestation and land-use changes, and also natural issues, such as volcanic forcing and the influence of solar forcing. Yet one readily finds such assumptions in current detection/attribution literature as: ‘[E]stimates of natural internal variability and the forced climate change signal required to apply standard detection tech-

Gauging the Sun: Comparative photometric and magnetic activity measurements of sunlike stars, 1984-2001

Abstract: Visible light photometric observations of a small sample of sunlike stars with mean chromospheric activity levels similar to or slightly lower than the Sun's suggest that total solar irradiance variations on activity cycle timescales may be comparatively small (Lockwood et al. 1992, Nature 360, 653; Radick et al. 1998, ApJS 118, 239). The Sun's irradiance variation over the past two cycles is 0.04% rms compared with 0.1% rms for the stellar sample measured at Lowell from 1984 to 1995. This assertion can now be tested using new photometric measurements from Fairborn Observatory automated telescopes (1993-2001) that extend the duration of stellar observations to 17 years. Chromospheric activity measurements for these stars come from the Mount Wilson HK program (1966-2001) and the Lowell Observatory Solar Stellar Spectrograph program (1993-2001). In this presentation we will describe efforts to merge the overlapping Lowell and Fairborn photometry and the Mt. Wilson and Lowell HK measurements with the goal of reducing the uncertainties in previous efforts to characterize stellar photometric variations near the limit of detection.