Action Can’t Wait for More Scientific Results on Climate Change

Written by Frank Lowenstein on . Posted in Learn

The rising Mississippi has captured national headlines, as the flood crest now moving toward Louisiana and Mississippi breaks records dating back to 1927. This closes out a remarkable 12 months of global deluge, with dramatic and often unprecedented floods in Tennessee, Australia, Pakistan, Brazil, Colombia and now back to the U.S. again.

News reports periodically raise the question of whether climate change contributes to the recent record water levels in the Mississippi – or the Magdalena or the Indus. But teasing out the climate signature of any one weather event in one place is a difficult task, much like the dilemma facing parents if they try to determine how much of any given episode of teenage moodiness is due to hormonal change.

As with teenage behavior, there is lots of natural variability to weather, and the underlying trends, while clear, are slow enough to make specific attribution difficult. So typically climate scientists respond that they can’t definitively attribute a given weather event to climate change – an accurate if unsatisfying lack of a villain. We all want to solve the mystery. Just as in the board game Clue, we want to know that the flood was caused by Colonel Mustard with the candlestick in the library.

In February 2011, two articles in the prestigious journal Nature finally made the link between past weather events and climate change in a scientifically rigorous way. One documents the role of greenhouse gas emissions in producing more frequent severe precipitation events that afflicted much of the northern hemisphere during the last half of the 20th century. The other paper is perhaps even more impressive, looking at a specific flood in England and Wales in 2000 that was the worst since record-keeping began there in 1766. The authors used 10,000 model runs to compare the likelihood of the observed flooding with and without greenhouse gas emissions. The results suggest that there is a better than two-thirds chance that greenhouse gas emissions increased the risk of flooding by at least 90 percent, and a much higher probability that greenhouse gases increased the risk of flooding by at least 20 percent. Since the floods damaged nearly 10,000 homes and caused more than $2 billion in damage, the change in risk has real meaning – both economically and in human suffering.

Climate models predict that severe weather events becoming more common will be the mantra of our lives, and even more so of our children’s lives. The Mississippi basin, for example, is experiencing a “500-year flood” for the second time in less than 20 years. (A 500 year flood is one of such severity that it has a only an 0.2 percent chance of occurring in any given year, so that it should occur on average once every 500 years). This could be a sign that climate change combined with other human modifications of the Mississippi’s water cycle have already reset the odds, or it could simply be extraordinary bad luck. But we shouldn’t expect climate scientists to definitively tell us which anytime soon. As the analysis of England’s millennial floods shows, scientific results will come too late for the news cycle, and too late for the people now losing their livelihoods and homes.

Even in a climate change world, however, Mother Nature doesn’t need to be the enemy. Restoring floodplains or reforestation in steep watersheds could help reduce the impact of future floods, while providing benefits for people in the form of more open space and in many cases more reliable water supplies through the heat of the summer.

Frank Lowenstein is the climate adaptation strategy leader at The Nature Conservancy

Photo courtesy of NASA (Residents in Illinois make their way through the Great Mississippi River Flood of 1927, similar to the current floods we’re seeing, which should be a very rare event that happens only once every 500 years.)

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Comments (1)

  • Jimbo


    “A 500 year flood is one of such severity that it has a only an 0.2 percent chance of occurring in any given year, so that it should occur on average once every 500 years.”

    Based on what? Did you ever think that this is a flawed assumption? That would be another explanation of why there are so many “500 year floods”.


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