Global climate models have been used by climate scientists since the 1970s. They have been refined over the years as more data have accumulated and computers have become faster and more powerful. Yet, even the relatively simple models from the 1970s have proved to be quite accurate at predicting future climate. Most have predicted a 3° Celsius (5.4° Fahrenheit) rise in global temperature by 2100 under “business-as-usual” greenhouse gas emissions conditions. Yet over the past year, the predictions of many of the climate models are “running hot,” predicting roughly a 5° Celsius (9° Fahrenheit) rise by the end of the century. The scientists who develop and run the models are baffled; they are not sure why their predictions are spiking.
One possible reason is a recently improved module to measure the effects on global temperature of clouds and aerosols in the atmosphere. The question the modelers are scrambling to answer is whether the new module is wrong, overweighting cloud impact on temperature, or if it is accurate, which could mean that previous models understated that impact, an unlikely outcome given the general accuracy of past models.
The predicted temperature spike may be unrelated to the refined cloud module. Some other sensitivity or combination of sensitivities may be responsible for the jump. Scientists have identified almost a dozen “tipping points,” any one of which, if passed, would have cascading impacts on other parts of the hugely complex climate system. The observed anomalous spikes in the latest climate models could be telling us that one or more of those tipping points has been reached, with the anticipated calamitous implications for our climate future.Bad news for the human race and indeed all life on Earth if that is the case.
 https://www.bloomberg.com/news/features/2020-02-03/climate-models-are-running-red-hot-and-scientists-don-t-know-why, “Climate Models Are Running Red Hot, and Scientists Don’t Know Why,” Eric Roston, Bloomberg, February 3, 2020.