Cooler global temperatures in 2021

2021 will be the coolest year since 2018, ending up between 0.7C and 0.8C warmer than the  baseline climate of 1961 to 1990. This spread mainly depends on which SST dataset you  use.

There are two versions of HadSST namely version 3 and version 4. My calculations of temperature to date were always based on Version 3. Version 4 gives higher 21st century temperature anomalies than Version 3 but is said to be more accurately aligned to floating buoys. Neither dataset had been updated since September until 2 days ago. Version 3  was updated just for October while  HadSST4 was updated for October and November. Consequently I calculated two sets of results using my spherical triangulation method. The monthly comparisons are shown below.

Global monthly temperature anomalies using GHCNV4 and HadSST3/4

The overall effect is a systematic increase in recent global temperatures by ~ 0.05C . The H4 global temperature for October is 0.97C and the H3 temperature is 0.92. The November temperature is only available for H4 and is 0.88C.

The annual temperatures for 2021 (11 months for H4 and 10 months H3) are shown below.

Annual global temperatures based on GHCN-V4C and a) HadSST3/4

Using H3 results in 2021 being the 6th equal warmest year, while using H4  2021 becomes the 4th warmest year.

Here is a spatial comparison between the two results

Spatial difference between HadSST3(left) and HadSST4(right) in the Arctic Ocean.

Here is an animation for November 2021 V4S4 (HadSST4)


Australia looks much cooler than normal!

I will probably use HadSST4 in future as it seems to be better accepted and supported. Here are the arguments as to why many climate scientists believe it is better.


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Home Climate Analysis

There is a  remarkable one man blog which set out to understand the earth’s climate 2 years ago. The author is Kevan Hashemi  who is a lecturer at Brandeis University and has worked on the Atlas experiment at CERN.  see:  He seems to have more or less followed the same path as me to understand the greenhouse effect from basic physics  and determine by just how much increasing CO2 will change the earth’s temperature. His value of 1.5C warming for a doubling of CO2 levels agrees with mine. He also produced a nice plot of the 350 year HADCET temperature  data which I have updated to 2021. This demonstrated that climate change has had a rather small effect on UK temperatures. Of course the slight rise since ~1990 looks a little worse if you plot “anomalies”.

Average temperatures for HadCET over 365 years.

Here is  his decadal trend analysis for the full HadCET. Basically he takes a rolling ten year gradient. There is little evidence of any rapid warming since 1850.

Decadal trends.

However it is his study of the carbon cycle that is particularly interesting because he has correctly explained the CO2 level variations over recent glacial cycles.

The last post on the site summarises his findings which seriously irked some mainstream climate scientists. He replied gallantly  but eventually fell silent and this was his last post. Yet I have not seen any carbon cycle model that is able to describe  the CO2 response to Ice Age cycles as well as his does.

His model was based on a fixed C14 proportion  dispersed in the atmosphere and the deep ocean.

Each year, cosmic rays create 8 kg of carbon-14 in the upper atmosphere. If carbon-14 were a stable atom, all carbon in the Earth’s atmosphere would be carbon-14. But carbon-14 is not stable. One in eight thousand carbon-14 atoms decays each year. The rate at which the Earth’s inventory of carbon-14 decays must be equal to the rate at which it is created. There must be 64,000 kg of carbon-14 on Earth.

The Earth’s atmosphere contains 800 Pg of carbon (1 Pg = 1 Petagram = 1012 kg) bound up in gaseous CO2. Therefore the oceans contain 80,000 Pg.

His argument is that the exchange of CO2 with the deep ocean remains in balance as more CO2 is added to the atmosphere. So to double the CO2 in the atmosphere you need to also double the CO2 contained in the deep oceans. This will take thousands of years of anthropogenic emissions instead of say 100 years. I suspect one possible  problem with his logic is that we are constantly adding CO2 to the atmosphere from fossil fuels which are devoid of  C14 because they have been buried for millions of years. So the C14 accounting  begins to unwind as more of our annual emissions dilute the atmospheric C14 content.

The global carbon cycle is immensely complicated because it depends on life, plate tectonics  and volcanism, all working on different timescales. Yet each year ~50% of our annual carbon emissions are absorbed by rapid oceans/biosphere processes and this ratio is unchanged in 50 years.

AR4 plot: The fraction of Anthropogenic CO2 retained in the atmosphere is unchanged in over 50 years, despite increasing emissions.

Today the global net flux of fossil fuel CO2 into the ocean is ~ 2Gtons C per year, amid exchange fluxes of 90 Gtons/year. This implies that if we simply kept emissions stable then the oceans would fairly soon also stabilise CO2 levels in the atmosphere. However there is a complication – the so called buffering or Revelle factor.

“The Revelle factor (buffer factor) is the ratio of instantaneous change in carbon dioxide (CO2) to the change in total dissolved inorganic carbon (DIC), and is a measure of the resistance to atmospheric CO2 being absorbed by the ocean surface layer.”

The Revelle effect describes how only a small fraction of pCO2 is present in ocean water when much larger amounts are added to the atmosphere. Depending on the alkalinity of the water, DIC is either present as CO3, HCO3, or CO2. When the pH is high (basic) the Revelle factor is greatest, causing much of the DIC to exist as HCO3 or CO3, and not CO2. So, the greater the buffering effect (low Revelle Factor) the more DIC occurs as CO3 or HCO3, effectively lowering the pCO2 levels in both the atmosphere and ocean.

This statement has taken on mythical proportions and is embedded in carbon cycle models like the BERN model. It implies there is a long tail on carbon levels in the atmosphere

My knowledge of chemistry is pretty minimal but I find it a far more descriptive than quantitive science.     Kevan argues that :

“When a gas and liquid are at equilibrium, there is as much gas entering the liquid per unit time as there is leaving it. Because gaseous CO2 has only one species, its probability of absorption into the ocean does not vary with its concentration. ”

This must be true. It is just a question of timescales. David Archer’s book is mostly descriptive with no firm predictions so I suspect we don’t really know how fast the Earth recovers from a sudden release of CO2. The BERN model is basically a parameterised guess.

The fact that 50% of CO2 emissions have been  absorbed by the oceans for the last 70 years needs to be explained first.

The carbon cycle mixes  physics, chemistry, biology  and geology all up into one complex imbroglio. My gut feeling is that stabilising our carbon emissions must also  stabilise CO2 levels within a decade. Of course I could be wrong as could everyone else.

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Global Temperature for September 2021 is 0.81C

The average temperature was 0.81 C in September. This was up a little from August (0.76C). However 2021 is turning out to cooler than recent years with an average annual temperature with 3 months remaining of 0.69C. This makes it on track to be the coolest year since 2014.

Annual average temperatures (2021 first 9 months)

The monthly data show the effects of the 2021 La Nina.

Monthly average temperatures updated to September 2021

This strong La Nina is evident in the latest SST data.

Over land areas cold spots in Siberia, Greenland and Alaska/Kamchatka are evident.

With just 3 months to go and a continuing la Nina,  it looks almost certain that 2021 will either be the coldest or the next coldest of the last 7 years.

You can download the monthly and annual data here and these are updated regularly.

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