Weird Weather in a Warming World

Given the weather of late, extremes seem to have become the norm.

New York City just had its hottest June-to-August stretch on record. Moscow, suffering from a once-in-a-millennium heat wave, tallied thousands of deaths, a toll that included hundreds of inebriated, overheated citizens who stumbled into rivers and lakes and didn’t come out. Pakistan is reeling from flooding that inundated close to a fifth of the country.

For decades, scientists have predicted that disastrous weather, including heat, drought and deluges, would occur with increasing frequency in a world heated by the rising concentrations of greenhouse gases. While some may be tempted to label this summer’s extremes the manifestation of our climate meddling, there’s just not a clear-cut link — yet.

Martin Hoerling, a research meteorologist who investigates extreme weather for the National Oceanic and Atmospheric Administration, calls any such impression “subjective validation.” He and other climate scientists insist there’s still no way to point to any particular meteorological calamity and firmly finger human-caused global warming, despite high confidence that such warming is already well under way.

One reason is that extreme weather, while by definition rare, is almost never truly unprecedented. Oklahoma City and Nashville had astonishing downpours this year, but a large area of Vermont was devastated by a 36-hour deluge in November 1927. The late-season tropical storm killed more than 80 people, including the state’s lieutenant governor, drowned thousands of dairy cows and destroyed 1,200 bridges.

A 2002 study of lake sediments in and around Vermont found that the 1927 flood was mild compared with some in the pre-Columbian past. In fact, since the end of the last ice age, there were four periods — each about 1,000 years long and peaking roughly every 3,000 years — that saw a substantial number of much more intense, scouring floods. (The researchers found hints in the mud that a fifth such period is beginning.)

Many scientists believe that sub-Saharan Africa will be particularly vulnerable in the coming decades to climate-related dangers like heat waves and flash-flooding. But global warming is the murkiest of the factors increasing the risks there. Persistent poverty, a lack of governance and high rates of population growth have left African countries with scant capacity to manage too much or too little water.

As in Vermont, the climate history of Africa’s tropical belt also makes it incredibly difficult to attribute shifts in extreme weather to any one cause. A recent study of layered sediment in a Ghanaian lake revealed that the region has been periodically beset by centuries-long super-droughts, more potent and prolonged than any in modern times. The most recent lasted from 1400 to 1750.

Though today’s extremes can’t be reliably attributed to the greenhouse effect, they do give us the feel, sweat and all, of what’s to come if emissions are not reined in. Martin Hoerling told me that by the end of the century, this summer’s heat may be the status quo in parts of Russia, not a devastating fluke. Similar projections exist for Washington, the American Southwest, much of India and many other spots.

With the global population cresting in the coming decades, our exposure to extreme events will only worsen. So whatever nations decide to do about greenhouse gas emissions, there is an urgent need to “climate proof” human endeavors. That means building roads in Pakistan and reservoirs in Malawi that can withstand flooding. And it means no longer encouraging construction in flood plains, as we have been doing in areas around St. Louis that were submerged in the great 1993 Mississippi deluge.

In the end, there are two climate threats: one created by increasing human vulnerability to calamitous weather, the other by human actions, particularly emissions of warming gases, that relentlessly shift the odds toward making today’s weather extremes tomorrow’s norm. Without addressing both dangers, there’ll be lots of regrets. But conflating them is likely to add to confusion, not produce solutions.

Andrew C. Revkin, a former environment reporter for The Times who writes the blog Dot Earth for