The Climate Change Deniers' Cult will bob and weave; and sometimes espouse the commonness of rapid change in the past. They fail to grasp that this works against their position. Yes, dramatic climate transitions have occurred in the past
but very rarely on the time scale of human civilization. 53 million years ago, for example, temperature fell sharply due to a sudden increase in duckweed population.
If duckweed could induce a sharp temperature change, imagine what
Homo technologis can do.
I tried to explain this earlier and will excerpt from that post.
. . . It is not known with certainty what caused the Earth to cool about 3 million years ago, leading to glaciation and a climate where hominids thrived. One possible cause is the closing of the Central American Seaway as plate tectonics pushed the South and North America landmasses together. Separating the cold water in the Eastern Pacific from the warm Caribbean increased ocean heat in the North Atlantic which (paradoxically?) increased ice production in Greenland.
Anyway, as we examine past fluctuation it is interesting to see how often the level of greenhouse gases, especially CO2, correlates strongly with temperature. With CO2 both cause and effect of warming, positive feedback means that small changes can have a big effect on global temperatures.
This is a key point that deniers of anthropogenic climate change overlook. They take exactly the WRONG conclusion from the FACT that there have been frequent temperature fluctuations in the past. The sharp fluctuations of the past demonstrate that, due to positive feedbacks, the Earth's climate is FRAGILE. Two trillion tons of CO2 may seem like a tiny amount, but scientists understand that it has had a huge effect, and will continue to heat the Earth in coming decades.
Two specific changes may illustrate climate fragility. About 56 million years ago, methane hydrates in ocean sediments became warm enough to be released. This happened quite suddenly, and -- because methane is a greenhouse gas -- there was an EXTREMELY rapid rise in Earth's temperature, even bigger than the anthropogenic warming we currently enjoy. This sudden temperature rise caused massive extinctions.
Just a few million years later there was sharp temperature change in the opposite direction. With the extinctions, higher temperatures, and high concentration of CO2, multitudes of oceanic duckweeds (mosquito-ferns) thrived., sequestering carbon as dead duckweeds dropped to the ocean floor. This carbon sequestration caused temperatures to fall sharply.
These examples show that tiny causes, e.g. a rise in duckweed population, can have big effect. CO2 levels in the atmosphere are higher than they've been in a million years; and are still growing. Temperature records are being over-turned (though not in Santa Monica!). Large glaciers are on the verge of collapse. Habitats on land and ocean undergo profound changes.
By now the nay-sayers, embarrassed by their own wilful ignorance, are unwelcome at Faux News and turn to Newsmax and Infowars!