Climate Risk at a Tipping Point?

Air Temperature, Sea Surface Temperature, and Tropical Storms

Schrödinger’s cat plays peek-a-boo

Air and Sea Surface Temperature (SST) records have been broken.

Is this due to

  1. an extreme tail event within slowly evolving climatic change?
  2. a mid-tail event within gradually accelerating climatic change?
  3. a typical event within rapidly accelerating (tipping-point) climate change?

According to Copernicus Climate Change Service (C3S), January 2024 was the warmest on record, pushing the 12-month mean global temperature (Feb 2023 – Jan 2024) to exceed the 1850-1900 pre-industrial average by more than 1.5°C. (See summary here.)

In February, the daily Sea Surface Temperature (SST) for 60°S–60°N reached a new absolute record level. The previous highest values were reached on the 23rd and 24th of August 2023.

**Figure 1.** Daily sea surface temperature (°C) averaged over the extra-polar global ocean (60°S–60°N) 
for 2015 (blue), 2016 (yellow), 2023 (red), and 2024 (black line). All other years between 1979 and 2022 
are shown with grey lines. Data source: ERA5. Credit: Copernicus Climate Change Service/ECMWF. [Download
pdf version](https://climate.copernicus.eu/sites/default/files/custom-uploads/Page%20Uploads/2401%20CB/PR_Fig2_era5_daily_sst_60S-60N.pdf).
Figure 1. Daily sea surface temperature (°C) averaged over the extra-polar global ocean (60°S–60°N) for 2015 (blue), 2016 (yellow), 2023 (red), and 2024 (black line). All other years between 1979 and 2022 are shown with grey lines. Data source: ERA5. Credit: Copernicus Climate Change Service/ECMWF. Download pdf version.

According to the latest ENSO update and prediction by NOAA National Weather Service, “transition from El Niño to ENSO-neutral1 is likely by April-June 2024 (79% chance), with increasing odds of La Niña developing in June-August 2024 (55% chance).”

**Figure 2.** NOAA Climate Prediction Center Probabilistic El Niño Southern Oscillation (ENSO) Outlook (8 Feb 2024).
Figure 2. NOAA Climate Prediction Center Probabilistic El Niño Southern Oscillation (ENSO) Outlook (8 Feb 2024).

El Niño is declared when SST in the tropical eastern Pacific rise to at least 0.5°C above the long-term average, while La Niña is declared when SST in the tropical eastern Pacific falls to at least 0.5°C below the long-term average. Moreover, these thresholds must be exceeded for a period of at least 5 consecutive overlapping 3-month seasons.

During El Niño there are typically more tropical storms in the tropical Pacific, but fewer in the tropical Atlantic.

During La Niña, the opposite pattern typically holds: there are more tropical storms in the tropical Atlantic than in the tropical Pacific.

**Figure 3.** Annual counts of Atlantic Tropical Storms and Hurricanes 1851--2022. Prior to 1950, the detection 
of storms and hurricanes relied on observation from ships and land. Post-1950, aircraft became much more involved in the 
detection of storms and hurricanes. Satellite observation was brought online at the end of the 1960s. Post-1970, satellite
observation was much more involved in the detection of storms and hurricanes. Hence the comprehensiveness of observation
undergoes changes in 1950 and 1970. Data source: [NOAA National Hurricane Center](https://www.nhc.noaa.gov/climo/)
Figure 3. Annual counts of Atlantic Tropical Storms and Hurricanes 1851–2022. Prior to 1950, the detection of storms and hurricanes relied on observation from ships and land. Post-1950, aircraft became much more involved in the detection of storms and hurricanes. Satellite observation was brought online at the end of the 1960s. Post-1970, satellite observation was much more involved in the detection of storms and hurricanes. Hence the comprehensiveness of observation undergoes changes in 1950 and 1970. Data source: NOAA National Hurricane Center

The annual counts of Tropical Storms and Hurricanes illustrated in Figure 3 show an increase over the post-1950 period.

However, there is substantial variability. To simplify the visual representation, consider the 10-year Trailing Averages plotted below.

**Figure 4.** 10-year Trailing Averages of Atlantic Tropical Storms and Hurricanes 1860--2022.
Figure 4. 10-year Trailing Averages of Atlantic Tropical Storms and Hurricanes 1860–2022.

In the post-2000 period the 10-year Trailing Average of Atlantic Tropical Storms rises above and remains above previous highs.

During this period, the 10-year Trailing Average of Atlantic Hurricanes also rises above previous historical highs.

These post-2000 highs were achieved along with increased volatility in the annual count, but the volatility is comparable with the volatility of previous peaks in storm and hurricane activity.

**Figure 5.** 10-year Trailing Standard Deviation of Atlantic Tropical Storms and Hurricanes 1860–2022.
Figure 5. 10-year Trailing Standard Deviation of Atlantic Tropical Storms and Hurricanes 1860–2022.

So for Atlantic Storms and Hurricanes, there is a change in mean activity without a substantial increase in volatility over previous records.

Of the three conjectures introduced at the top, this post-2000 level change doesn’t fit the archetype of #1. an extreme tail event within slowly evolving climatic change.

The post-2000 Atlantic storm data could still be consistent with either #2. a mid-tail event within gradually accelerating climatic change or #3. a typical event within rapidly accelerating (tipping-point) climate change.

Epicurus’ (c. 342–270 BCE) Principle of Multiple Explanations offers guidance here: If more than one theory is consistent with the observations, keep all of these theories.

Current data are consistent with a radical tipping-point explantion, but not exclusively so.

Like Schrödinger’s cat, we both are and are not at a tipping point in climate change.




  1. “ENSO-neutral” refers to the El Niño Southern Oscillation (ENSO) being neither in the (warmer SST) “El Niño” state nor in the (cooler SST) “La Niña” state, whereby the SST in the tropical eastern Pacific falls within +/- 0.5°C of the long-term average. ↩︎