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Pro: Climate Models Have Been Demonstrated to be Accurate.

From NASA

By Alan Buis,
NASA’s Jet Propulsion Laboratory

An animation of a GISS (Goddard Institute for Space Studies) climate model simulation made for the United Nations’ Intergovernmental Panel on Climate Change Fourth Assessment Report, showing five-year averaged surface air temperature anomalies in degrees Celsius from 1880 to 2100. The temperature anomaly is a measure of how much warmer or colder it is at a particular place and time than the long-term mean temperature, defined as the average temperature over the 30-year base period from 1951 to 1980. Blue areas represent cool areas and yellow and red areas represent warmer areas. The number in the upper right corner represents the global mean anomaly.

Credit: NASA’s Goddard Institute for Space Studies

There’s an old saying that “the proof is in the pudding,” meaning that you can only truly gauge the quality of something once it’s been put to a test. Such is the case with climate models: mathematical computer simulations of the various factors that interact to affect Earth’s climate, such as our atmosphere, ocean, ice, land surface and the Sun.

For decades, people have legitimately wondered how well climate models perform in predicting future climate conditions. Based on solid physics and the best understanding of the Earth system available, they skillfully reproduce observed data. Nevertheless, they have a wide response to increasing carbon dioxide levels, and many uncertainties remain in the details. The hallmark of good science, however, is the ability to make testable predictions, and climate models have been making predictions since the 1970s. How reliable have they been?

Now a new evaluation of global climate models used to project Earth’s future global average surface temperatures over the past half-century answers that question: most of the models have been quite accurate.

In a study accepted for publication in the journal Geophysical Research Letters, a research team led by Zeke Hausfather of the University of California, Berkeley, conducted a systematic evaluation of the performance of past climate models. The team compared 17 increasingly sophisticated model projections of global average temperature developed between 1970 and 2007, including some originally developed by NASA, with actual changes in global temperature observed through the end of 2017. The observational temperature data came from multiple sources, including NASA’s Goddard Institute for Space Studies Surface Temperature Analysis (GISTEMP) time series, an estimate of global surface temperature change.

The results: 10 of the model projections closely matched observations. Moreover, after accounting for differences between modeled and actual changes in atmospheric carbon dioxide and other factors that drive climate, the number increased to 14. The authors found no evidence that the climate models evaluated either systematically overestimated or underestimated warming over the period of their projections.

“The results of this study of past climate models bolster scientists’ confidence that both they as well as today’s more advanced climate models are skillfully projecting global warming,” said study co-author Gavin Schmidt, director of NASA’s Goddard Institute of Space Studies in New York. “This research could help resolve public confusion around the performance of past climate modeling efforts.”

Models that were used in the IPCC 4th Assessment Report can be evaluated by comparing their approximately 20-year predictions with what actually happened. In this figure, the multi-model ensemble and the average of all the models are plotted alongside the NASA Goddard Institute for Space Studies (GISS) Surface Temperature Index (GISTEMP). Climate drivers were known for the ‘hindcast’ period (before 2000) and forecast for the period beyond. The temperatures are plotted with respect to a 1980-1999 baseline. Credit: Gavin Schmidt

Con: Global Ocean Temperatures are Warming at Only ~50% the Rate of Climate Model Projections

Dr. Roy Spencer, a climate scientist from the University of Alabama, Hunstville examined the claims of accuracy of climate models by comparing them to actual measured temperatures.

From Dr. Roy Spencer’s Blog

The plot below (Fig. 1) shows the monthly global (60N-60S) average ocean surface temperature variations since 1979 for 68 model simulations from 13 different climate models. The 42 years of observations we now have since 1979 (bold black line) shows that warming is occurring much more slowly than the average climate model says it should have.

Fig. 1. 68 CMIP6 climate model simulations of global average sea surface temperature (relative to the 5 year average, 1979-1983), and compared to observations from the ERSSTv5 dataset.

In terms of the linear temperature trends since 1979, Fig. 2 shows that 2 of the top-cited ocean temperature datasets have warming trends near the bottom of the range of climate model simulations.

Fig. 2. Linear temperature trends, 1979-2020, for the various model and observational datasets in Fig. 1, plus the HadSST3 observational record.

Deep Ocean Warming Could Be Mostly Natural

A related issue is how much the deep oceans are warming. As I have mentioned before, the (inarguable) energy imbalance associated with deep-ocean warming in recent decades is only about 1 part (less than 1 Watt per sq. m) in 300 of the natural energy flows in the climate system.

This is a very tiny energy imbalance in the climate system. We know NONE of the natural energy flows to that level of accuracy.

What that means is that global warming could be mostly natural, and we would not even know it.

I’m not claiming that is the case. I am merely pointing out the level of faith that is involved in the adjustments made to climate models, which necessarily produce warming due to increasing CO2 because those models simply assume that there is no other source of warming.

Yes, more CO2 must produce some warming. But the amount of warming makes all the difference to global energy policies.

Seldom is the public ever informed of these glaring discrepancies between basic science and what politicians and pop-scientists tell us.

Why does it matter?

It matters because there is no Climate Crisis. There is no Climate Emergency.

Yes, irregular warming is occurring. Yes, it is at least partly due to human greenhouse gas emissions. But seldom are the benefits of a somewhat warmer climate system mentioned, or the benefits of more CO2 in the atmosphere (which is required for life on Earth to exist).

But if we waste trillions of dollars (that’s just here in the U.S. — meanwhile, China will always do what is in the best interests of China) then that is trillions of dollars not available for the real necessities of life.

Prosperity will suffer, and for no good reason.

via Watts Up With That?

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May 5, 2021