"What has come to be known as 'weather attribution,' research assigning causation to observed weather events, is fraught with methodological problems. Veteran climate scientist Roger A. Pielke Jr. in his Substack publication The Honest Broker calls it 'weather attribution alchemy'."

Last year was hot, unusually so. The global temperature was almost 0.3°C above 2022 levels, so much higher that even conventional analyses of global warming didn't appear to explain it. As a recent article in Science magazine notes, iconic climate scientist James Hansen was suggesting that a new, air-pollution-driven warming mechanism might be at work. NASA's Gavin Schmidt posited that a novel, unknown force could be involved.

Wrong, says a team of six climate scientists led by Shiv Priyam Raghuraman (University of Illinois, Champaign-Urbana). The culprit is more likely the familiar climate confounder, El Niño (technically, the El Niño-Southern Oscillation or ENSO).

Writing in the journal Atmospheric Chemistry and Physics, published by the European Geosciences Union, the scientific team writes,

our results underscore the importance of the El Niño-Southern Oscillation in driving the occurrence of global warming spikes such as the one in 2023, without needing to invoke anthropogenic forcing, such as changes in atmospheric concentrations of greenhouse gases or aerosols, as an explanation.

They add:

Global-mean surface temperature rapidly increased 0.29 ± 0.04 K from 2022 to 2023. Such a large interannual global warming spike is not unprecedented in the observational record, with a previous instance occurring in 1976-1977. However, why such large global warming spikes occur is unknown, and the rapid global warming of 2023 has led to concerns that it could have been externally driven.

And:

Here we show that climate models that are subject only to internal variability can generate such spikes, but they are an uncommon occurrence (p = 1.6 % ± 0.1 %). However, when a prolonged La Niña immediately precedes an El Niño in the simulations, as occurred in nature in 1976-1977 and 2022-2023, such spikes become much more common (p = 10.3 % ± 0.4 %). Furthermore, we find that nearly all simulated spikes (p = 88.5 % ± 0.3 %) are associated with El Niño occurring that year.

The University of Illinois research fits with an August paper by four researchers from CICERO Center for International Climate Research in Oslo, Norway. Published in the Communications Earth & Environment journal, Bjørn H. Samset et al. wrote:

2023 was the warmest year on record, influenced by multiple warm ocean basins. This has prompted speculation of an acceleration in surface warming, or a stronger than expected influence from loss of aerosol induced cooling.... We show that the strong deviation from recent warming trends is consistent with previously observed sea surface temperature influences, and regional forcing.

"Weather Attribution" Alchemy

What has come to be known as "weather attribution," research assigning causation to observed weather events, is fraught with methodological problems. Veteran climate scientist Roger A. Pielke Jr. in his Substack publication The Honest Broker calls it "weather attribution alchemy."

Pielke notes that the U.N.'s Intergovernmental Panel on Climate Change (IPPC) describes weather attribution research as seeking "to attribute aspects of specific extreme weather and climate events to certain causes." The IPCC adds:

Scientists cannot answer directly whether a particular event was caused by climate change, as extremes do occur naturally, and any specific weather and climate event is the result of a complex mix of human and natural factors. Instead, scientists quantify the relative importance of human and natural influences on the magnitude and/or probability of specific extreme weather events.

Pielke offers three important aspects of weather attribution.

Pielke writes that "some dismiss entirely the possibility of human-caused changes in climate while others quickly claim that every weather event is more extreme or more common due to climate change. These extreme positions are roughly aligned with the far right and far left respectively -- and discussion of climate science and policy has long been dominated by these extremes."