The scientific press is hyping research by Lawrence Berkeley National Laboratory that claims to have, for the first time, measured radiative forcing by carbon dioxide. Even if they have, it’s no big deal because such forcing is assumed from basic physics. They also claim that their measurement provides proof of anthropogenic global warming. But, as we shall see, they may be putting effect before cause.
Seth Borenstein, the Associated Press’ chief climate alarmist, writes “Scientists have witnessed carbon dioxide trapping heat in the atmosphere above the United States, chronicling human-made climate change in action.”
The Berkeley press release is titled “First direct observation of carbon dioxide’s increasing greenhouse effect at the Earth’s surface.” The paper, published in Nature, is somewhat more modest in its claim: “Observational determination of surface radiative forcing by CO2 from 2000 to 2010.”
Within the press release, one of the scientists is quoted as saying, “”We see, for the first time in the field, the amplification of the greenhouse effect because there’s more CO2 in the atmosphere to absorb what the Earth emits in response to incoming solar radiation.”
First, some background on what was done.
The scientists measured down-welling infrared radiation using Atmospheric Emitted Radiance Interferometer spectra from two stations located in Oklahoma and Alaska over the period from 2000 to 2010 during which atmospheric carbon dioxide increased by 22 parts per million. They claim to have 3300 measurements from Alaska and 8300 measurements from Oklahoma. Keep those numbers in mind.
They found that the down-welling radiation increased during that period and attribute that increase to the rise of carbon dioxide.
Some possible problems:
I wonder why the specific time period was chosen. In 2010 a strong La Nina produced a relatively cool tropospheric temperature, while in 2010 a strong El Nino produced a relatively warm tropospheric temperature. The difference was about half a degree Centigrade. A warmer atmosphere will intrinsically produce more down-welling infrared radiation regardless of its composition. So, was the increased down-welling radiation due to increased CO2 or increased temperature? I think they may be confusing cause and effect.
Also curious is that another study (See Evidence that CO2 emissions do not intensify the greenhouse effect ), using the same type of instruments, made 800,000 measurements during the period 1996 to 2010 and found a significant decrease in down-welling infrared radiation.
The Berkeley researchers claim that only about 10 percent of their increased down-welling radiation came from carbon dioxide. As far as I can tell, however, the emissions from carbon dioxide fall within the spectra emitted by water vapor, but the researchers claim a mathematical manipulation allows them to distinguish the 10 percent of radiation from carbon dioxide versus the 90 percent from water vapor and other gases in the atmosphere.
The Berkeley researchers claim to have found a radiation increase of “0.2 Watts per square meter per decade.” How much is that? German physical chemist Dr. Siegfried Dittrich notes:
“The number for the increase in CO2-dependent back radiation given by Nature of 0.2 watt/m2 per decade is indeed in reality nothing more than trifle. Why would the earth be shocked when 1367 watts per square meter strikes the surface at noon along the equator? The ever-changing deviations from this so-called solar constant mean value are in fact considerably greater than the above given 0.2 watts/m2.” An additional complication is that the measurements by Berkeley researchers was for only cloud-free areas.
Another paper in Geophysical Research Letters: “On the Incident Solar Radiation in CMIP5 Models” finds sampling errors much larger than the 0.2 Watts per square meter that the Berkeley researchers claim to have measured. Here is the paper abstract:
“Annual incident solar radiation at the top of atmosphere (TOA) should be independent of longitudes. However, in many Coupled Model Intercomparison Project phase 5 (CMIP5) models, we find that the incident radiation exhibited zonal oscillations, with up to 30 W/m2 of spurious variations. This feature can affect the interpretation of regional climate and diurnal variation of CMIP5 results. This oscillation is also found in the Community Earth System Model (CESM). We show that this feature is caused by temporal sampling errors in the calculation of the solar zenith angle. The sampling error can cause zonal oscillations of surface clear-sky net shortwave radiation of about 3 W/m2 when an hourly radiation time step is used, and 24 W/m2 when a 3-hour radiation time step is used.”
The alleged measurement could easily be instrument error.
There is still a question about whether they saw what they claimed to have seen. This may be an example of confirmation bias, they saw what they wanted to see based on equivocal evidence.
But in the end, to paraphrase a prominent politician: what difference does it make at this point in time?