reading on the non-linear solar activity (solar minimum waves) and global warming from times of settlement - one of the earliest I've read based on history of population is an era that lasted until 1600s, followed by the little ice age due to a combination of low solar activity and volcanic aerosol as a possible cause of wiping the trace of Norse from Greenland.

Another possible cause is greenhouse gasses. This is an excerpt from the book "How Iceland Changed the World" by Egill Bjarnason evaluating pieces of history based on William Ruddiman's theory.

“Many people think greenhouse gases were mainly released into the atmosphere after the industrial revolution. Ice cores in fact show that carbon dioxide began to appear at greater rates in the atmosphere around eight thousand years ago, parallel to the invention of agriculture and resulting deforestation. Likewise, methane spiked around four thousand years ago, when farmers in East Asia began to use wetlands to grow rice. The agricultural revolution caused massive population growth, and thus the cycle of change grew greater and greater until the world experienced a series of pandemics. The black death and other plagues hit Europe in the fourteenth and fifteenth centuries, and shortly afterward, native people in North and South America were exposed by European settlers to germs completely foreign to their immune systems. Modern research indicates that these plagues claimed more lives than early documentation suggests. By Ruddiman’s theory, these deaths wiped out much of the existing agriculture, reversing the climate trend and eventually causing a temperature decline. By then the Greenland colonies were already struggling, and the sudden shift in climatic conditions delivered the final blow. The black death reached Iceland in 1402 and wiped out nearly two-thirds of the population. The pandemic is not believed to have reached Greenland because no mass graves from the time have been found. And yet the disease still managed to kill off the Norse population"