All together now: climate change means more extreme rainfall. “It is likely that there have been statistically significant increases in the number of heavy precipitation events”. Yep, that’s what the IPCC said in 2012. And if it’s all we quoted, you would probably join the ranks of people believing scientists have long been warning that global warming means heavier rain and worsening storms. But the original sentence doesn’t end there. It goes on to read: “...in more regions than there have been statistically significant decreases, but there are strong regional and subregional variations in the trends.” Rather changes the meaning doesn’t it? And when we look more closely, the uncertainty deepens.
The sentence quoted above was from the IPCC Special Report on Weather Extremes, or SREX. It was a follow up to the 4th Assessment Report or AR4, and it was followed a year later by the 5th Assessment Report or AR5. The AR5 also surveyed evidence on extreme weather and its conclusions regarding extreme precipitation echoed the SREX:
In summary, further analyses continue to support the AR4 and SREX conclusions that it is likely that since 1951 there have been statistically significant increases in the number of heavy precipitation events (e.g., above the 95th percentile) in more regions than there have been statistically significant decreases, but there are strong regional and subregional variations in the trends. In particular, many regions present statistically non-significant or negative trends, and, where seasonal changes have been assessed, there are also variations between seasons (e.g., more consistent trends in winter than in summer in Europe).
So there isn’t one clear pattern and it varies depending on where you live. Often exactly where. The AR5 did go on to say “The overall most consistent trends towards heavier precipitation events are found in central North America (very likely increase) but assessment for Europe shows likely increases in more regions than decreases.”
From that remark, a Canadian might think that we’re in the part of the world where scientists are warning that extreme precipitation is on the rise. Except that our federal government scientists don’t agree:
the observational record has not yet shown evidence of consistent changes in short-duration precipitation extremes across the country.