metmike: Something, likely natural happened in 2023 that was NOT from the increase in CO2 that caused a much different warming pattern and extreme warming that can't be explained by the previous explanations for much of the previous warmings.

Hunga Tonga volcano: impact on record warming

https://wattsupwiththat.com/2024/07/09/hunga-tonga-volcano-impact-on-record-warming/

2. Uncharted territory 

In June 2023, the North Atlantic experienced a heat wave unprecedented in 40 years, with temperatures 5°C warmer than usual. Carlo Buontempo, the director of Copernicus, said the world was “entering uncharted territory. We have never seen anything like this in our life”.[ii] To understand what has puzzled scientists so much, it is necessary to look at the evolution of the temperature of the Earth’s oceans throughout the year since 1979.

Figure 5. 60°N-60°S global ocean surface temperature by year since 1979. 

On average, the Earth’s oceans are warmest in February-March and coldest in October-November, with an intermediate maximum in August. This is an annual cycle caused by the tilt of the Earth’s axis, the arrangement of the continents, and seasonal changes in atmospheric circulation and albedo. A cycle that has never been broken as long as measurements have been kept until 2023. This year shows an accentuated warming since January, leading to daily temperature records since the beginning of April. But what is absolutely astonishing is that the ocean continued to warm in June and July and reached an annual maximum in August, something that has never happened before. And the warming through August is staggering, about 0.33°C above the 2016 record, which is huge for the ocean. After that, the annual cycle begins to behave normally, but at a much higher temperature, which is slowly falling. In June 2024, after 415 days of record temperatures, the ocean is still about 0.2°C warmer than it should be.

4. Sulfate aerosols are not responsible 

Another possibility that is under consideration is the reduction of sulfate aerosols as a result of the change in marine fuel regulations in 2020.

 Figure 9. Global sulfur emissions for the past 64 years 

The reduction in sulfur emissions since the late 1970s is considered a significant warming factor by reducing emissions of shortwave radiation reflected from the atmosphere. However, the reduction in sulfur dioxide emissions from marine fuels since 2020 is estimated at 14% of total emissions.

5. CO₂ increase didn’t do it 

The amount of CO₂ in the atmosphere has increased slightly by about 2.5 parts per million in 2023.

Figure 11. Monthly (red) and 12-month (black) CO₂ levels at Mauna Loa. 

The increase from 418.5 to 421 ppm represents an increase of 0.6% and is similar to the increase that has occurred each year for the past several decades. Nothing in our knowledge of the effect of CO₂ increases on climate suggests that such a small increase could have led to such a large and abrupt warming. There is no study to suggest that the gradual increase in CO₂ could lead to a sudden increase in climate variability. Therefore, all model predictions are long-term and affect the statistics of weather phenomena. The proof is that scientists and models cannot explain what happened in 2023.

6. Tonga volcano prime suspect 

Just over a year before the abrupt warming, in January 2022, an extremely unusual volcanic eruption took place in Tonga. How unusual? It was an eruption of VEI 5 explosivity, capable of reaching the stratosphere, which occurs on average every 10 years.

 Figure 12. Time and cone elevation of VEI ≥5 volcanic eruptions of the past 200 years, their distribution by altitude (yellow bars), and the suggested depth for a submarine eruption capable of projecting a large amount of water to the stratosphere (red line).

 There have been a number of eruptions with VEI 5 or higher in the last 200 years, although not all of them have affected the global climate. This figure shows with dots the date they occurred and the elevation at which the volcanic cone was located. The yellow bars show the distribution of eruptions in 500 m elevation bins. The Tonga eruption was a submarine explosion at very shallow depths, about 150 m below the sea surface. It ejected 150 million tons of water into the stratosphere. 

In our 200 years of records there is only one other submarine eruption with VEI 5, which occurred in 1924 off the Japanese island of Iriomote at a depth of 200 m and did not affect the atmosphere. Only surface effects were observed. NASA scientists believe that the Tonga explosion occurred at the right depth to project a lot of water into the stratosphere.[vi] This depth is indicated by the red line. So, the Tonga eruption is a once in 200-year event, probably less than once in a millennium. Science was very lucky. We are not so lucky. 

We know that strong volcanic eruptions, capable of reaching the stratosphere, can have a very strong effect on the climate for a few years, and that this effect can be delayed by more than a year. The eruption of Mount Tambora in April 1815 had a global effect on the climate, but it took 15 months for the effect to develop, during the year without a summer of 1816. These delayed effects coincided with the appearance of a veil of sulfate aerosols in the Northern Hemisphere atmosphere due to seasonal changes in the global stratospheric circulation. 

Figure 13. Stratospheric water vapor anomaly at 45°N. 

In this image on the vertical axis, we observe the water vapor anomaly in the stratosphere between 15 and 40 km altitude with ocher tones for negative values and greenish for positive ones. The measurement takes place at 45° latitude in the northern hemisphere. On the horizontal axis is the date, and we can see that the large anomaly created by the Tonga eruption does not appear in the Northern Hemisphere until one year later, in 2023, when the warming occurred. Thus, there are dynamical events in the stratosphere that have the appropriate time lag to coincide with the abrupt warming in 2023.

 Because the Tonga eruption is unprecedented, there is much about its effects that we do not understand. But we do know that the planetary greenhouse effect is very sensitive to changes in stratospheric water vapor because, unlike the troposphere, the stratosphere is very dry and far from greenhouse saturation. 

As a group of scientists showed in 2010, the effect of changes in stratospheric water vapor is so important that the warming between 2000 and 2009 was reduced by 25% because it decreased by 10%.[vii] And after the Tonga eruption, it increased by 10% because of the 150 million tons of water released into the stratosphere, so we could have experienced much of the warming of an entire decade in a single year. 

 Figure 14. Global water vapor anomaly above 68hPa. 

The stratosphere has already begun to dry out again, but it is a slow process that will take many years. In 2023 only 20 million tons of water returned to the troposphere, 13%.[viii] 

7. Dismissing natural warming 

On the one hand, we have an absolutely unprecedented abrupt warming that the models cannot explain and that has scientists scratching their heads. Such anomalous warming cannot logically respond to the usual suspects, El Niño, reduced sulfur emissions, or increased CO₂, which have been going on for many decades. 

On the other hand, we have an absolutely unprecedented volcanic eruption, the effects of which we cannot know, but which, according to what we know about the greenhouse effect, should cause significant and abrupt warming. 

Of course, we cannot conclude that the warming was caused by the volcano, but it is clear that it is by far the most likely suspect, and any other candidate should have to demonstrate its ability to act abruptly with such magnitude before being seriously considered.