Sweltering Pittsburgh residents protesting the heat now have history supporting them: Federal climate scientists announced Monday that the first half of the year has been Pittsburgh's warmest on record.
Pittsburgh's average temperature from January to June was 51.3 degrees, 4.7 degrees above average and the highest since recordings began in 1948, according to data from a National Climatic Data Center report. Pittsburgh joins more than 100 cities and 28 states that have posted their hottest first six months on record. The national temperature so far this year of 52.9 degrees, 4.5 degrees above average, has never been reached in 118 years of recordings.
Between June 21 and June 30, 81 regional recording stations broke all-time temperature records. In Pittsburgh, the thermostat reached 90 degrees on seven out of nine days so far in July, pushing this month's average temperature 7.9 degrees above normal, according to Lee Hendricks of Pittsburgh's National Weather Service forecast office. A cold front is expected to roll back temperatures gradually over the next week.
NCDC climate scientist Jake Crouch explained that the jet stream, an air current above Earth's surface that affects storms and weather, has been farther north than usual since December, allowing warm, subtropical air to invade the U.S. That contributed to the fourth-warmest winter on record and the warmest-ever spring on record.
The jet stream's position has also limited precipitation, Mr. Crouch said, driving up temperatures and creating the conditions for drought and wildfires. Tens of thousands of people have been forced to flee their homes in Colorado to avoid blazes scientists say are connected to the conditions.
"Much of the dryness we've been seeing has been in the Mountain West," Mr. Crouch said. "Dry hot conditions are ideal for wildfires."
Farmers are also suffering. Just less than 56 percent of the country is in a drought, the most extensive area since the U.S. Drought Monitor started studying conditions in 2000. Over 40 percent of the nation's pastures and rangelands are in "poor" or "very poor" condition, according to the monitor. Mr. Crouch said the dry conditions are "wreaking havoc on crops across the country," hitting farms in the Midwest and Ohio Valley especially hard.
The Pittsburgh region has begun feeling the effects. Mr. Hendricks of the National Weather Service said Allegheny County's average rainfall is 4.6 inches below normal so far this year, while Beaver County's is 7.3 inches below normal.
Water deficits in local reservoirs have been building since this winter's abnormally low snowfall, and this summer's drought and heat are accelerating the problems.
"It's a perfect storm of events happening that put us in this position," said Dan Jones of the Pittsburgh Army Corps of Engineers. Mr. Jones said the Berlin Lake near Youngstown, Ohio, is 71/4 feet below its normal summer pool levels. The nearby Michael Kirwan Reservoir is 6 feet below normal, while southwestern Pennsylvania's Youghiogheny Lake is 81/2 feet below normal.
Mr. Jones said the conditions are among the worst the Army Corps has seen in 40 years.
The Army Corps has responded by warning boaters and swimmers to beware of hazards that now rise close to lake surfaces. Mr. Jones said boat launch ramps will close earlier this year as lake and reservoir water is diverted for use maintaining navigation channels in parched rivers. A 26-year-old man died Saturday trying to swim to a sand bar in Berlin Lake that appeared only once water levels fell.
Community drinking water intake "could be impacted," too, Mr. Jones said.
Mr. Crouch of NCDC said the national trends "are all consistent with what we'd expect of climate change," but stopped short of pinpointing climate change as the driving factor.
A separate study released Tuesday by the National Oceanic and Atmospheric Administration, however, linked global warming to a 2011 Texas drought that caused $10 billion in damages. La Nina, which causes milder temperatures and drought in the South, was part of the problem. But scientists also found that heat waves associated with La Nina events are now 20 times more likely than they were in the 1960s because of climate change, which the scientists said is thought to be attributable to human influence.
"Man-made climate change makes Texas climate drought more likely," said Peter Stott, one of the authors of the study.
The scientists said 2011 flooding that killed hundreds in Bangkok could not be explained directly by global warming. The study also found that carbon dioxide levels steadily increased in 2011, reaching a yearly global average above 390 parts per million (ppm) for the first time since instrument records began.
Benjamin Mueller: firstname.lastname@example.org, 412-263-4903.