Site icon Andy May Petrophysicist

Best Climate Change Temperatures

By Andy May

I just gave an informal Zoom talk to a small group on measuring climate change through temperatures. The host, Dave Siegel, recorded it and has posted the presentation here, if you want to view it. It is about 15 minutes, plus some discussion afterword.

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

The key points of the talk are:

The final slide of the presentation illustrates what can be done, it uses data from Yair Rosenthal, 2013, Science.

The left-hand graph shows a temperature reconstruction by Yair Rosenthal and colleagues in their 2013 paper in Science. On the right we see a location map and a temperature profile for the Makassar Strait from the University of Hamburg database.

The left-hand graph shows a temperature reconstruction by Yair Rosenthal and colleagues in their 2013 paper in Science. They use bottom-dwelling foraminifera in the Makassar Strait, between Sulawesi and Borneo in Indonesia. The water at about 500-meters, where the forams live, is sourced from the Southern Ocean near Antarctica, the southern Indian Ocean and the North Pacific. This location is ideal for checking the 500-meter water temperature for much of the Southern Hemisphere and a portion of the Northern Hemisphere.

Deeper water is more insulated from the surface and the trends reflect longer-term climatic changes, uncontaminated with atmospheric variability.

On the right we see a location map and a temperature profile for the Makassar Strait from the University of Hamburg database. The database is a high resolution (0.25° latitude and longitude) monthly series that uses all available data from many years. This profile gets most of its data from 2004-2016. It shows an average temperature, at 500 meters, of about 7.7°C. Thus, this area, at 500 m, warms 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 identified on the graph, and in this strait, the temperature was often over 10 degrees, the Medieval Warm Period was about 8.5°C, much warmer than today.

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

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