September 2023 was the month with the highest temperature anomaly on record. What contributed to this?
The temperature rose about 0.5°C from November 2022 to March 2023, and this occurred at a time when we were not even in an El Niño yet, as illustrated by the above image, from an earlier post. Below is an updated image, from January 1950 to September 2023, adapted from NOAA
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Further contributors
There are further reasons why the temperature can be expected to keep rising beyond September 2023.
Aerosols that have a cooling effect, such as dust and sulfates (SO₄), are also important. As fossil fuel is burned, sulfates are co-emitted. Since they pollute the air, measures have been taken and are being taken to reduce them, e.g. in shipping, and this has pushed up the temperature rise. Meanwhile, cooling aerosols such as sulfates are still high. As illustrated by the image below, adapted from nullschool.net, SO₄ was as high as 8.621 τ at the green circle on October 6, 2023, at 07:00 UTC. In future, SO₄ could fall dramatically, e.g. in case of a sudden economic collapse, reducing the aerosol masking effect rapidly and abruptly causing a substantial rise in temperature.
The above image was created by Zach Labe with NSIDC data (Arctic + Antarctic) for each year from 1979 to 2023 (satellite-era; NSIDC, DMSP SSM/I-SSMIS). The image illustrates that global sea ice extent recently reached the largest anomaly in the satellite record. Anomalies are calculated using a 5-day running mean from a climatological baseline of 1981-2010. 2016 is shown with a yellow line. 2023 is shown using a red line (updated 10/16/2023).
As said, there are many factors behind the temperature increase around latitude -60° (South). As Paul mentions, this latitude receives a lot of sunlight around the year. Therefore, it is not surprising that, as oceans continue to heat up, there is huge loss of sea ice at this latitude, as well as loss of lower clouds, while open oceans are additionally less efficient than sea ice when it comes to emitting in the far-infrared region of the spectrum. The image below, adapted from NASA, shows a white band around -60° (South), indicating that the Southern Ocean has long been colder there than elsewhere, but has recently started to catch up with the global temperature rise.
The above image also illustrates that anomalies are highest in the Arctic, narrowing the temperature difference between the Arctic and the Tropics, with the air flow slowing down accordingly.
This in turn changes the Jet Stream and the Polar Vortex, resulting in blocking patterns that can, in combination with rising temperatures, strongly increase the frequency, intensity, duration and area coverage of extreme weather events such as storms and lightning, heatwaves and forest fires.
Forest fires in Canada have been releasing massive amounts of emissions that push up the temperature, including greenhouse gases such as carbon dioxide, warming aerosols such as black carbon & brown carbon and NMVOC (non-methane volatile organic carbon) and carbon monoxide that reduce the availability of hydroxyl, resulting in more methane and ozone in the atmosphere.
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| [ NH sea surface temperature anomaly ] |
As temperatures rise, increased meltwater runoff from Greenland and more icebergs moving south, in combination with stronger ocean stratification and stronger storms over the North Atlantic, can also cause a freshwater lid to form at the surface of North Atlantic that can at times enable a lot of hot water to get pushed abruptly underneath this lid toward the Arctic Ocean. The danger is that more heat will reach the seafloor and destabilize methane hydrates contained in sediments at the seafloor of the Arctic ocean.
The next danger is that the thin Arctic sea ice will rapidly retreat early next year as a warming Arctic Ocean will transfer more heat to the atmosphere over the Arctic, resulting in more rain and more clouds in the atmosphere over the Arctic, speeding up sea ice loss and further pushing up the temperature rise over the Arctic, as discussed at the feedbacks page, which also discusses how less Arctic sea ice can push up temperatures through the emissivity feedback. As temperatures rise over the Arctic, permafrost on land also threatens to thaw faster, threatening to cause huge releases of greenhouse gases, including carbon dioxide, methane and nitrous oxide.
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| [ Global energy-related greenhouse gas emissions 2000-2022, adapted from EIA ] |
There are numerous further feedbacks that can accelerate the temperature rise and tipping points that can get crossed and cause even more abrupt rise of the temperature. One of these is the clouds tipping point that in itself can cause a temperature rise of 8°C, as discussed here.
Further feedbacks are also discussed at the Extinction page. One further feedback is water vapor. A warmer atmosphere holds more water vapor, at a rate of 7% for each Degree Celsius the temperature rises. As temperatures keep rising, ever more water vapor will be sucked up by the atmosphere. This will also cause more droughts, reducing the ability of land to sustain vegetation and provide soil cooling through shading and through evaporation and formation of lower clouds, as discussed here. More water vapor in the atmosphere will also speed up the temperature rise because water vapor is a potent greenhouse gas.
The fact that such tipping points and feedbacks occur as greenhouse gas levels reach certain levels and as the temperature rise makes it critical to assess how fast greenhouse gas levels could rise and by how much the temperature has already risen.
NASA data up through September 2023
The image below, adapted from NASA, shows that the September 2023 NASA Land+Ocean temperature was 1.78°C higher than it was in September 1923. The anomaly is 1.74°C when compared to a base centered around the year 1900 (1885-1915). The 1.74°C anomaly can be adjusted by 0.99°C to reflect a pre-industrial base, air temperature and higher polar anomalies (as shown in the box on the bottom right of the image), adding up to a potential anomaly of 2.73°C.
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Indeed, earlier analysis such as discussed here, points out that the temperature may already have risen by more than 2°C (compared to pre-industrial) in 2015, when politicians pledged at the Paris Agreement to take action to combat the temperature rise to prevent this from happening.
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Blue: Polynomial trend based on Jan.1880-Sep.2023 data. Magenta: Polynomial trend based on Jan.2010-Sep.2023 data. |
Seafloor methane is one of many elements that could jointly cause a temperature rise of over 10°C, in the process causing the clouds tipping point to get crossed that can push up the temperature rise by a further 8°C, as illustrated by the image on the right, from the extinction page.
Conclusion
The precautionary principle should prevail and the looming dangers should prompt people into demanding comprehensive and effective action to reduce the damage and to improve the situation.
Links
• NASA – global maps
• NOAA – ENSO and Temperature bars
• The International Research Institute for Climate and Society, Columbia University Climate School
https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/?enso_tab=enso-sst_table
• Nullschool.net
• NSIDC – sea ice graph
• Zach Labe – Global sea ice – extent, concentration, etc.
• NASA – zonal means
• Guy McPherson – College of Complexes Presentation (with Improved Audio)
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