A new satellite study of rainfall suggests that in the last 20 years the intensity of rainfall has mysteriously declined a little in most places. This is despite predictions it would increase, and CO2 itself rising by 41ppm globally during the same period.
By 2001 humans had cumulatively produced 291,000 Mt of carbon from fossil fuels, and cement production, but by 2020 our total cumulative emissions amounted to 470,000 Mt. (CDIAC data). So from 2001-2020, mankind produced 179,000 Mt of carbon or 38% of all-time homo sapiens emissions. Converting pure carbon to CO2 that means humans have emitted 656,000 Mt of CO2 yet seen either a decline or no trend at all in rainfall intensity.
Global CO2 rose from 371ppm in 2001 all the way to 414ppm in 2020. All the scare stories we are shown daily of floods across the world are simply part of the weather we have always experienced and always will.
THe picture below shows a trend of increasing rainfall intensity. Not only will there be mmore intense rainfalls, there will also be more intense snowfalls.
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We saw earlier in the course that climate change already appears to have influenced the frequency and intensity of various types of extreme weather events. The observed warming so far amounts to less than a 1°C relative to pre-industrial time. Given projected warming of several more degrees C over the next century (depending on the precise emissions scenario), the future increases in extreme weather events can be expected to be far larger than what we have observed thus far.
A large increase in the incidence of extreme precipitation events is expected. As we know, warmer oceans evaporate water into the atmosphere at a faster rate, and a warmer atmosphere can hold more water vapor. These features imply a more vigorous hydrological cycle, and heavier individual events when conditions are conducive to precipitation. Basic atmospheric physics tells us that 1°C warming we have seen already implies roughly 2% higher concentration of water vapor in the atmosphere on average, and correspondingly, roughly 2% more precipitable water during any particular precipitation event. Depending on the particular emissions scenario, we can expect a several fold larger increase over the next century. Since flooding is associated with large accumulations of rainfall over short periods of time, this increase in precipitation intensity implies greater potential for flood conditions—ironically, even for regions that on average see greater drought, i.e., more dry days (something we alluded in our discussion of general precipitation trends in the previous lesson).