The TSI Instruments – What’s Old, What’s New, and What’s Next

<p>What is the Earth&#8217;s incoming energy, that is, the value of the total solar irradiance (TSI) powering the entire Earth&#8217;s climate system on an absolute scale? How accurate are the instruments providing these data? How stable are they on climate-relevant timescales? How well can the 43-year spaceborne TSI measurement record from over a dozen instruments be put into a single time-series composite for the climate- and solar-research communities? How can that composite be extrapolated to historical times using other solar-activity proxies via reconstructions? How do these historical-reconstruction models differ from each other, and how well do they agree with the current measurements? And what is the future of those measurements?</p>