The unprecendented Pacific Northwest heat wave reached 108oF on June 26, 112oF the next day, and then the new record temperature of 116oF on June 28 in Portland. The usual opportunists jumped in with their typical cries of “rising CO2 levels,” “blaming greenhouse gas emissions,” “stop all fossil fuels,” “need state carbon taxes,” and “the world as we know it will end in 10 years if we don’t act quickly.”
But — scientifically — what really caused this unique heat wave?
Several days beforehand, we saw atmospheric pressure patterns that were virtually identical to those of Portland’s previous all-time historic highs of 107oF — which occurred 30 July 1965, and 8 and 10 August 1981. However, why did we reach 116oF this time?
Let’s consider “greenhouse gases.” Water vapor optical depths of the 1981 and 2021 heat waves were virtually identical — as found in atmospheric records from Salem, OR. Thus, differences in water vapor cannot explain this 9oF higher record.
Atmospheric CO2 levels in August 1981 were ~340 ppmv (parts-per-mllion by volume), compared with ~415 ppmv in June 2021. Calculating the change in radiative forcing (∆F) from CO2 — as a stand-alone constituent — the difference is 1.07 Wm2 (watts per square meter). Taking the mean daily temperature deviation (∆T = ~90oF), and plugging that into the derivative of the Stefan-Boltzmann equation, dF/dT, we get 6.45 Wm2-K1 (watts per square meter per degree Kelvin).
Using this relationship, if CO2 acted as the sole cause, this would contribute +0.27oF to the heating total. Thus, CO2’s contribution to the 2021 heat wave would not even increase temperatures from the previous 107oF record to 108oF. We conclude that the difference in atmospheric CO2 levels cannot be the culprit.
Comparing solar-radiation dynamics in 1965 and 1981, versus 2021, the potential temperatures of Earth’s surface began the same. However, considering the solar angle, 46o latitude for Portland, declination angle of Earth to the solar ecliptic plane, and 15 degrees per hour from solar noon as the hour angle — the sum integral of solar radiation to Earth’s surface on June 28 was 461 Wm2 — compared to 415 Wm2 on August 8th, a difference of 46 Wm2.
Taking into account solar insolation [i.e., flux of solar radiation per unit of horizontal area for Portland, which depends on the solar zenith angle (between the sun’s angle and the vertical) and the distance of Earth from the sun], and the variance in elliptical orbit of earth around the sun — between June 28 and August 8 — adds an additional 8 Wm2 of solar insolation to the extra-terrestrial solar radiation of 6 Wm2, relative to earth’s surface at a perpendicular angle to the atmosphere. These further considerations decrease the difference in solar radiation from 46 Wm2 to 36.7 Wm2, which is still enormously substantial.
If we divide this variance into the rate of change of flux with respect to temperatures of 6.45 Wm2-K1 — the difference is +10.2oF — compared to the heat waves in 1965 and 1981. Adding 10.2oF to 107oF gives you 117.2oF, which is within 1.2o F of the new record-high temperature of 116oF. Given the microclimates in and around the Portland area, 117.2oF is not statistically different from 116oF.
Many meteorologists ascribed the heat wave to an “upper air heat dome.” These are not created by greenhouse gases, but rather are associated with the dynamic westerly wind belt surrounding the planet, and the jet stream winds contained within. Creation of a heat dome is directly proportional to the strength of low-pressure systems upstream or downstream (or both) — which are also called “cold areas” of low pressure aloft. It is generation of these low-pressure systems that cause the strength of the high-pressure system; its residing subsidence thus creates the heat dome within the high pressure.
The preceding heat dome was necessary, because the jet stream pushed all clouds far away to the north. Absence of clouds obviously increases the level of solar radiation striking the surface below. Hence, the heat dome sets the table for temperature extremes; this was necessary at the onset, because the temperature inversion subsidence associated with it — inhibited the vertical mixing of air and allowed rapid solar heating of the surface, such that temperatures did climb to 105oF on June 25. Then solar radiation took over and set the potential temperature higher for the next two days until the maximum of 116oF was reached.
Natural causes of “climate change” (cooling and warming) include: [a] solar activity; [b] radiative forcing and insolation (amount of sunlight absorbed vs amount radiated back into space); [c] cloud type and amount; [d] Earth’s rotation and interplay between its atmosphere and oceans; [e] variations in Earth’s precession, eccentricity and axial tilt; [f] gravitational pull of other planets of substantial mass (especially Jupiter); and [g] volcanic eruptions both on land and underwater.
“Climate alarmists” attribute Earth’s warming to rising CO2 levels — with no proof except computer-modeling predictions. Comparing Portland’s previous record highs of 107oF in 1965 and 1981 with the 2021 high of 116oF, we determined [see above] that CO2 could contribute no more than +0.27oF to the 9oF difference.
In conclusion, by blocking all clouds, the heat dome alone would only have allowed us to approach the previous records of 107oF. The timing of these heat waves, relative to the sun’s angle with Portland, therefore explains virtually everything. In 1981, the heat waves occurred the first week of August; in 1965, end of July. In 2021, Portland was within one week of the summer solstice. This difference — when combined with upper-air dynamics (“heat dome” over the northeastern Pacific) — is the basis for the severity of the 2021 heat wave. We conclude that solar radiation — which is a major “natural cause” of climate change — was virtually the sole reason for Portland’s new all-time record high.
— Chuck Wiese, Meteorologist
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