The 2019-2020 Australian wildfires burned 186,000 square kilometers. The 2022 Hunga Tonga eruption injected material into the stratosphere with more force than any volcanic event in decades. Both were massive perturbations to the atmosphere. Both injected aerosols, particles, and gases into the upper atmosphere. Both had measurable effects on stratospheric temperature: the wildfires warmed the stratosphere by approximately 0.77 degrees Celsius (smoke particles absorb radiation); Hunga Tonga cooled the middle-to-upper stratosphere by approximately 0.5 degrees Celsius.
Published in PNAS, Yaowei Li and Susan Solomon at MIT applied a signal-to-noise technique to satellite measurements — subtracting long-term greenhouse gas trends, El Nino/La Nina variability, and solar cycles to isolate each event's specific temperature fingerprint. The stratospheric effects were clear and distinct. The surface warming effect of both events was undetectable. Zero.
The structural insight is about the asymmetry between large perturbation and large effect. Both events were enormous by any physical measure. Both measurably altered the stratosphere. Neither produced detectable warming at the surface where people live, crops grow, and ice melts. The stratosphere and the surface are coupled but not proportionally — perturbations that dominate one layer can be invisible in the other.
The implication cuts in one direction: if events of this magnitude produce no detectable surface warming, then the surface warming that is occurring cannot be attributed to natural events of this kind. The null result constrains the explanation space. Every candidate cause that operates through stratospheric aerosol injection — wildfires, eruptions, other natural sources — has been tested at maximum plausible intensity and found insufficient. What remains is what was already there: the slower, steadier, structurally different forcing from greenhouse gas accumulation.