One of my favorite moments in An Inconvenient Truth (AIT) is when Al Gore blames global warming for a record-breaking downpour in Mumbai, India.
“July 2005, Mumbai, India, received 37 inches of rain in 24 hours—the largest downpour any Indian city has received in one day,” Gore wrote in the book version of the film (p. 110). Clear evidence (in his mind) that the world’s weather was going crazy and fossil fuel emissions were the culprit.
I looked into this back in 2007. Since it is unscientific to attribute any particular weather event to a gradual increase in global average atmospheric temperatures, I reasoned that if global warming were influencing rainfall in Mumbai, we would see it in long-term precipitation records. Through a quick Web search I found that Mumbai had not one but two weather stations, and each had a program allowing site visitors to access and plot historic weather data.
So for each station, I directed the program to plot rainfall in Mumbai for the month of July as far back as data were available (1959). In neither case was there any discernible precipitation trend over the previous 45 years.
Why rehash this ancient history now? Over at the Center for the Study of Carbon Dioxide and Global Change, those amazing Idsos, Craig and Sherwood, review a new study of rainfall in Northeast India. Okay, Mumbai is on India’s West coast, but the study also examines rainfall records over the entire country, and the data for the Northeast go back to the 1870s.
Is there any evidence of long-term trends in precipitation that might be correlated with global warming?
Here’s how the Idsos describe what the researchers learned:
Jain et al. report that, overall, no clear pattern for rainfall for the Northeast Region of India has emerged, either spatially or temporally; and they thus say that “one can conclude that the rainfall series for this region for the period 1871-2008 does not have any significant trend.” In addition, they report that “several studies relating to [the] changing pattern of rainfall over India observed that there is no clear trend of increase or decrease in average rainfall over the [entire] country,” citing the studies of Mooley and Parthasarathy (1984), Thapliyal and Kulshrestha (1991), Lal (2001) and Kumar et al. (2010).
So there you have it: No long-term change in July rainfall in Mumbai, and none in rainfall generally in India. To borrow some favorite phrases from the alarm camp, the record-breaking July 2005 dowpour in Mumbai is “consistent with” natural variability and exactly what natural variability “looks like.”