by Peter Pilewskie, University of Colorado Boulder
The Sun—seemingly a constant in our lives—actually swings from sleepy to animated and back to sleepy every eleven years or so. When the Sun moves into the active part of its cycle, storms roil across its surface, spinning bursts of radiation toward the Earth and creating “spots” on the Sun that are visible from Earth.
How changes in the solar cycle affect Earth’s climate—for example, whether relatively quiet cycles with fewer sunspots have a slight cooling effect—is a question we’ve just begun to answer. Researchers have gazed up at sunspots for hundreds of years, but we have only recently started to chip away at the Sun-climate connection using sophisticated instruments that can observe the Sun from space and models that can simulate how the atmosphere responds to small changes in the Sun’s output.
By 2034, we will have observed the Sun from space for about five solar cycles. Three of the five cycles will have been measured with climate-quality accuracy—right now we’ve just measured one—meaning that in two decades time we will know with much great accuracy how relatively small changes in the Sun have impacted climate.
Now we have the ability to accurately measure the total radiation across all wavelengths over which the Earth is bathed in sunlight, a measure known as total solar irradiance. By 2034, we will have an equally accurate measure at each individual wavelength, a quantity called solar spectral irradiance. Teasing apart how the Sun’s output at different wavelengths are increasing or decreasing with time, we will be able to better understand Earth’s atmospheric response to subtle changes in the Sun. We will know how much of that response depends on ozone, water vapor, clouds, the oceans, and ice caps, and other elements of the Earth system. Twenty years from now, solar irradiance observations, specifically in the ultraviolet, will be used in weather forecast models and will lead to improved seven-day forecasts.
Improved forecasts are of great value, but more significantly, we will have vastly expanded our knowledge of the Sun’s impact on climate. Research at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder is already revolutionizing our knowledge in these areas with cutting-edge instrumentation like the Total and Spectral Solar Irradiance Sensor (TSIS), which provides unprecedented measurement accuracy and stability. By 2034, we will have put into context the current anomalously quiet behavior of the Sun: Is this a “once in a century” behavior or did we enter a Grand Minimum, similar to that which may have caused the “Little Ice Age” of the 17th century?
Currently, we have only one instrument at a time measuring the Sun’s irradiance, which leaves our record of the Sun’s activity vulnerable to gaps if a satellite malfunctions or if the launch of the scheduled replacement instrument is delayed or disrupted.
By 2034, technological advances that will enable smaller instruments to be deployed in constellations of micro-satellites will have eliminated the threat of data gaps in our record of solar irradiance. CU-Boulder is at the forefront in the development of small yet highly capable instruments and spacecraft, poised for these new challenges in the coming decades. Earth-observing instruments will have undergone an evolution of their own: smaller, lighter, and with more wavelength coverage. With enhanced on-board processing capabilities, these “smart” sensors will make observing decisions on their own, responding to extreme weather and climate events and capturing their time evolution, all of which will enhance our predictive capabilities. Rather than transmitting raw data, high-level information relating to weather and climate will be transmitted to “decision makers” on the ground. It is likely that climate observations will be more valuable than ever, and we will have that information at our fingertips.
It is hard to make predictions of the Sun’s impact on climate without putting it into the context of anthropogenic climate change: It is safe to guess that we will better understand the human influence on climate change by 2034 because we will have quantified solar variability with exceedingly high accuracy. We will have a detailed record of the Sun’s effect on climate from 1980-2034.
I can’t today predict the climate of 2034, but since it is only 20 years out—not long by climate standards—the safest guess is to extrapolate current trends: rising surface temperatures and sea level, and quite likely, a seasonally ice-free Arctic sea. If indeed the Sun has entered a new Grand Minimum, its impact on the current trends in Earth climate will be uncertain. It may slow or delay current trends, but probably not eliminate them entirely.
Peter Pilewskie joined the University of Colorado in 2004 with a joint appointment in the Laboratory for Atmospheric and Space Physics and in the in the Department of Atmospheric and Oceanic Sciences. He teaches courses in radiative transfer, remote sensing, and environmental instrumentation. Peter is a co-Investigator for the NASA Solar Radiation and Climate Experiment (SORCE), the current NASA mission measuring the total and spectral solar irradiance from space, and he is Principal Investigator for the Total and Spectral Solar Irradiance Sensor (TSIS), the future mission to insure the continuity of those same climate data records. His research interests include solar spectral variability and its effects on terrestrial climate; quantifying the Earth-atmosphere radiative energy budget; surface, airborne, and satellite remote sensing of clouds and aerosols; and theoretical atmospheric radiative transfer. Prior to his arrival at the University of Colorado, Peter spent 15 years at the NASA Ames Research Center where his research centered on airborne measurements of atmospheric radiation, cloud and aerosol remote sensing, and analysis of the atmospheric radiative energy budget. His work has been supported by the National Oceanic and Atmospheric Administration, Department of Energy, Naval Research Laboratory, National Science Foundation and NASA.