More Blown Assumptions in Climate Theory
Climate change is a consensus of global experts, except when they stand on assumptions of quicksand.
Speleothems of South American and Asian Monsoons Influenced by a Green Sahara (Geophysical Research Letters). When building models of past climactic trends, climate scientists have relied on the levels of greenhouse gases and on orbital cycles (Milankovitch theory; see 22 June 2018, “Why Milankovitch Cycle Theory Is Like Astrology”). Now, three scientists took a look at cave formations in Africa and South America, and a light bulb went off; they realized that the Sahara was green about 6,000 years ago. That changes the models. Look at their conclusions:
The mid‐Holocene (6,000‐years ago) had slightly lower greenhouse gas concentrations and significantly higher Northern Hemisphere summer sunlight than preindustrial (1850 CE). There is also evidence for vegetation changes during the mid‐Holocene, most notably increased vegetation over the now arid Sahara. Most climate model simulations of the mid‐Holocene account for the greenhouse gas and orbital changes but frequently neglect the vegetation changes. Here, we use a climate model to separate the effects of a vegetated Sahara from those due to greenhouse gases and orbit during the mid‐Holocene. Our mid‐Holocene simulation with the addition of a vegetated Sahara better represents measurement‐based climate reconstructions of the period than our mid‐Holocene simulation that only includes greenhouse gas and orbital changes. These simulated improvements are particularly pronounced in the South American and Asian monsoon regions, despite their distance from the Sahara. Our results emphasize the importance of vegetation feedbacks when simulating past and future climate change.
If the models don’t capture historical climate well, how well can they model future climate trends?
Past is Key to Predicting Future Climate, Scientists Say (University of Arizona). This press release is remarkable for its juxtaposition of confidence in the consensus with doubt about the particulars.
“Models become more complex and, in theory, they get better, but what does that mean?” Tierney said. “You want to know what happens in the future, so you want to be able to trust the model with regard to what happens in response to higher levels of carbon dioxide.”
While there is no debate in the climate science community about human fossil fuel consumption pushing Earth toward a warmer state for which there is no historical precedent, different models generate varying predictions. Some forecast an increase as large as 6 degrees Celsius by the end of the century.
These U of A researchers apparently did not read the previous paper about a green Sahara’s influence on models. “The key is CO2,” they say. But what of the unknown unknowns that remain?
“We urge the climate community to test models on paleoclimates early on, while the models are being developed, rather than afterwards, which tends to be the current practice,” Tierney said. “Seemingly small things like clouds affect the Earth’s energy balance in major ways and can affect the temperatures your model produces for the year 2100.”
Overkill, glacial history, and the extinction of North America’s Ice Age megafauna (PNAS). David Meltzer tackles the difficult question of the extinction of American megafauna during the Pleistocene. There has been a long-standing debate between those who say that changing climate caused the extinction and those who believe early humans drove the large mammals extinct. While Meltzer argues for the first view, he recognizes the complexities of the available evidence. He thinks his view is better, but the “Climate Challenge” leaves difficult questions as well, like why didn’t all the animals disappear at the same time? Why didn’t it happen in previous periods of climate change?
Accordingly, there will be no single climate “theory”—comparable to overkill’s one size fits all approach—that explains the disappearance of those 38 genera of mammals, along with all of the other extinctions and evolutionary and biotic changes that took place. Climate change may have been the ultimate driver, but the proximate factors that led, for example, to the demise of the mastodon in the midwestern forests are likely to have been quite distinct from those that caused horses and camels to vanish from western grasslands, or the glyptodont to disappear from southeastern swamps.
If scientists cannot link climate to the disappearance of large mammals in the past, how can they assert with confidence what will happen in the future?
Meltzer could always appeal to the Stuff Happens Law, but he wouldn’t dare, because that will offend AOC and Greta, who need the world to end in twelve years. For globalism to work, it needs a crisis, and man must be blamed for everything wrong.