Finest climatic temperatures – watts with that?

By Andy May

I just gave an informal zoom talk to a small group about measuring climate change through temperatures. The moderator, Dave Siegel, recorded it and posted the presentation here if you’d like to view it. It’s about 15 minutes plus a few afterwords for discussion.

The PowerPoint slides can be downloaded here, and the slides with my notes can be downloaded here.

The main points of the conversation are::

• The IPCC and I agree that temperature is a key indicator of the changing state of the climate system.

• The IPCC has traditionally used global mean surface temperature (GMST) to estimate global temperature change. It has an organized database, but the atmospheric temperatures are very chaotic so they may not be meaningful from a climatic point of view.

• The new measure of warming based on the Global Surface Air Temperature (GSAT) model is extremely problematic when introduced into AR6 as planned. It is calculated using a model from GMST and increases the rate of warming by 4%. Models suggest that GSAT is warming faster than GMST, but the data available does not support this additional warming. The data we have is mainly measurements of the night air temperature of ships.

• The mixed ocean layer is in constant contact with the surface and has 27 times the heat capacity of the entire atmosphere. It covers 71% of the earth’s surface and does not respond to short-term chaotic fluctuations in atmospheric temperature. As a result, it’s a more stable long-term record of climate change.

• The deeper ocean below the mixed layer is a record of past temperatures.

• A model is needed to create a good temperature record from current deep sea temperatures as well as proxies from seabed sediments.

• The term “climate change” is redundant, the climate has always changed and always will, we should just say “climate”.

The last slide of the presentation shows what can be done. It uses data from Yair Rosenthal, 2013, Science.

The graphic on the left shows a temperature reconstruction by Yair Rosenthal and colleagues in their work in Science from 2013. On the right we see a location map and a temperature profile for Makassarstrasse from the University of Hamburg’s database.

The graphic on the left shows a temperature reconstruction by Yair Rosenthal and colleagues in their work in Science from 2013. They use foraminifera in the Makassar Strait between Sulawesi and Borneo in Indonesia. The water at about 500 meters above sea level in which the forams live comes from the Southern Ocean near Antarctica, the southern Indian Ocean and the North Pacific. This place is ideal for checking the water temperature of 500 meters for much of the southern hemisphere and part of the northern hemisphere.

Deeper water is more isolated from the surface and the trends reflect longer-term climate changes that are not contaminated by atmospheric variability.

On the right we see a map and a temperature profile for Makassarstrasse from the University of Hamburg’s database. The database is a high resolution monthly series (0.25 degrees latitude and longitude) using all available data from many years. This profile receives most of the data from 2004 to 2016. It shows an average temperature of around 7.7 ° C at 500 meters. Thus, this area warms up to 500 m about 0.5 ° C from the depths of the Little Ice Age. Here the low temperature was 7.2 ° C in 1810.

The Holocene climatic optimum is shown in the graphic, and in this strait the temperature was often above 10 degrees, the medieval warm period was around 8.5 ° C, much warmer than today.

In summary, the data we need to reconstruct the Holocene and older temperatures in the oceans and in ocean sediments. Sea temperature reconstructions represent much more of the earth’s surface (defined as from the sea floor to the top of the atmosphere) than any land or oceanic measurements in the atmosphere. The atmosphere is too chaotic and unstable to give us representative climate trends. Sea temperatures are more stable, more usable and easier to compare with paleo temperatures.

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