We Need to Remember Our Multiplication Tables

09/02/2010 05:38 pm ET | Updated May 25, 2011

San Francisco -- Five years ago, not one but two calamitous floods struck major cities, each taking more than a thousand lives. One, of course, was Katrina, but only a month earlier, 37 inches struck the city of Mumbai, India, wiping out entire neighborhoods. Both of these catastrophes followed truly extreme weather events. Katrina wasn't the biggest hurricane ever to hit the Gulf of Mexico, but it was up there, and 37 inches of rain was unprecedented in Mumbai.

This month a much greater flood catastrophe has engulfed Pakistan, engulfing a quarter of the country, flooding an area the size of England, killing about 2000 people, and swelling the Indus River to 40 times its normal size. Tens of millions of people have been displaced. It's not clear how much of this disaster can be attributed to extreme weather.

Yes, the monsoon was heavy this year. In certain areas, like Peshawar, it was extraordinarily heavy, so the localized flooding that devastated Swat and other areas in the Northwest can be viewed as an extreme weather event. And heavy monsoons in the region feeding into the Indus from the Punjab in the east, including catchments across the border in India, meant that the Chenab, Sutlet, and Jhelum were already very high when late-month cloudbursts hit the Northwest part of the Indus basin in Pakistan.

But why were localized cloudbursts over areas like Swat and Peshawar able to generate not only localized tragedy but a national catastrophe? Why was there no equivalent damage across the border in India, where weather charts show the monsoon was even higher?

Some commentators are arguing that the catastrophic floods in Pakistan have as much to do with deforestation as they do with weather. Pakistan's "timber mafia" have, in the past several years, achieved unprecedented freedom to log at will.

"But this month the mud and water deluge cascaded off the tree-bare mountains and hills with exceptional force and barrelled down towards the plains in mammoth fury. In a trade-off, the timber mafia had allowed the mountain poor to raid the logs stacked in the nullahs to make doors, window frames and furniture for their homes. But, propelled by the force of the run-off, the logs turned into instruments of destruction, smashing all in their wake. Rivers and dams turned black with timber. Relief workers said bridges, homes, and people were destroyed and swept away by the hurtling and swirling logs before the waters spread on to the plains below, engulfing an area of more than 60,000 square miles, more than twice the land area of Scotland."

The logging in the mountains has simply been the final act in the gradual deforestation of Pakistan -- the entire river corridor was once girded by, and protected by, dense forest cover which could absorb water, break the force of floods, and capture the silt that comes down from the geologically unstable Karakorum range as fertile soil.

Now all of the natural safeguards and systems that created Pakistan's productive and densely populated plains have been removed. Rainfall even slightly above average can overtax the Indus system which, in effect, has been turned from a meandering stream into a drainpipe -- a drainpipe too small for heavy rains.

We see similar patterns here in the US. The most damaging floods in American history were the Mississippi River floods of 1993. Again, there was very heavy precipitation, but the river had handled larger volumes of water before, with far less destruction, because natural systems -- flood plains, wetlands, riverine forests -- were still intact and able to absorb much of the impact of the heavy flow.

There is more than one lesson from the Indus floods. We should worry, tremendously, about the impact of a disrupted climate and more extreme rainfall events. Pakistan cannot handle them. But we should worry just as much about the need to restore the natural biological dampers to the system -- the barriers which historically protected Pakistanis from heavy monsoons (and stored their water for drier years.) After all, when causes multiply, the results get larger very fast. 2+2 and 2 x 2 both equal 4. But make that 2 a 3 and the impact soards from 6 to 9. Make it 5, and 10 becomes 25. Preventing further climate chaos OR rebuilding the natural systems that protect us from weather -- we can't focus on just one. We must do both.

I wonder if this realization has finally sunk in for Bjorn Lomborg. Lomborg announced this week that he was abandoning the "climate change is no big deal" camp where he made his reservation, and was instead publishing a new book stating that global warming is one of the world's "chief concerns" and calling for a global carbon tax and the expenditure of $100 billion.

When I debated Lomborg at Harvard back in 2002, Lomborg conceded the reality that more carbon pollution meant higher sea levels and more flooding in countries like Bangladesh. His response: "Build dikes." Perhaps as he's watched natural catastrophes like the one in Pakistan unfold, Lomborg has come to his senses and realized that the human capacity to manage extreme weather is simply much smaller than the climate cynics would like us to believe.