Speaker: Martin Mlynczak, NASA Langley Research Center
Abstract: The concentration of carbon dioxide, CO2, has been increasing in Earth’s atmosphere since the beginnings of the Industrial Revolution in the late 1700’s. Largely due to the burning of fossil fuels, the amount of CO2 in the atmosphere as measured by its volume mixing ratio has increased from 280 parts per million (ppm) around the year 1800 to over 400 ppm today. CO2 strongly absorbs infrared radiation near the peak of Earth’s emission spectrum. Increases in CO2 result in additional capture of energy emitted by Earth’s surface, and ultimately lead to a warming of the Earth’s surface and lower atmosphere. A key estimate as to the degree to which increasing CO2 causes climate change is expressed in the concept of “radiative forcing”, which is defined as the change in net radiative energy within the climate system associated with the buildup of CO2. The concept of radiative forcing (RF), and its accurate computation, are the benchmarks upon which all of climate change science rests. In this talk we will examine the computation of RF and discuss some fundamental physical principles (including the first law of thermodynamics; the Heisenberg uncertainty principle; and the harmonic oscillator) underlying these calculations. We will progress through some rather complex calculations conducted at high spectral resolution to elucidate the uncertainty associated with our understanding and knowledge of RF. Lastly, we will discuss the radiative effects of increased CO2 on Earth’s high atmosphere (above 100 km altitude), which leads to cooling aloft, with long-term consequences for space flight operations.