Background

Greenhouse gas warming simulations generally predict an increased intensity of Asian summer monsoonal circulations and, therefore, more monsoonal rainfall (Meehl and Washington, 1993; Hirakuchi and Giorgi, 1995; Li et al., 1995; Zwiers and Kharin, 1998; Chakraborty and Lal, 1994; Suppiah, 1995; Zhao and Kellog, 1988; Hulme et al., 1998; Wang, 1994).

What was done

In a study germane to this subject, Fleitmann et al. developed high-resolution stable isotope records from three contemporaneously-deposited stalagmites located in a shallow cave in Southern Oman that provide an annually-resolved record of Indian Ocean monsoon rainfall over the past 780 years.

What was learned

Over the last eight decades of the 20th century, when global temperatures rose at a rate described by climate alarmists as "unprecedented," Indian Ocean monsoon rainfall declined dramatically, in stark contrast to what has historically been predicted by most climate models. In addition, the other single most substantial decline in monsoon rainfall coincided with a major temperature spike identified by Loehle (2004) in the temperature records of Keigwin (1996) and Holmgren et al. (1999, 2001) that began sometime in the early 1400s. This abrupt warming, which has also been identified by McIntyre and McKitrick (2003), pushed temperatures above the peak warmth of the 20th century before they fell back to pre-spike levels in the mid-1500s, a trend that produced just the opposite trend in the monsoon rainfall record of Fleitmann et al., i.e., an initial dramatic decline in monsoon rainfall followed by a subsequent dramatic increase.

What it means

These real-world observations provide a strong double-barreled confirmation that global temperature variations elicit just the opposite variations in Indian Ocean monsoon rainfall than what is predicted by global climate models.

References

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