5.2. Summer insolation values 8 percent higher than today produced summer monsoons stronger than today nearly 10,000 years ago across North Africa and southern Eurasia. This connection is supported by model simulations (A) and by evidence from Earth's surface (B).
concluded that a major source of the methane changes measured in Antarctic ice must be changes in the strength of the tropical monsoons.
The reason for the connection between monsoons and methane is shown in figures 5.1 and 5.2. When strong monsoon rains fall on tropical wetlands, they flood them with water during the summer season when plants grow. As plants die, they decompose in stagnant water lacking oxygen. Bacteria attack the decaying plant matter and convert its carbon to several products, including methane gas (CH4). The methane bubbles off from the wetlands into the atmosphere where it stays for an average of 10 years before being oxidized to other gases. This physical connection builds directly on John Kutzbach's orbital monsoon theory: stronger summer radiation causes a stronger monsoon circulation that produces
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