What do these scientists say is the cause of the increase in temperature throughout the 20th century?

What do these scientists say is the cause of the increase in temperature throughout the 20th century? natural climatic variability.

Scientists attribute the global warming trend observed since the mid-20th century to the human expansion of the "greenhouse effect"1 — warming that results when the atmosphere traps heat radiating from Earth toward space.

the only plants classified as non-seed producers are b) moss, fern, and liverwort!

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