Human-caused climate change has triggered heavier deluges, more frequent floods and more extreme heat events in Pennsylvania and across the northeast United States in a trend likely to worsen with the current rate of global greenhouse gas emissions, according to a draft federal climate report released late last week.
The draft National Climate Assessment, in its first revision since 2009, finds clearer evidence than ever of a changing climate and its recognizable impacts.
"Climate change, once considered an issue for a distant future, has moved firmly into the present," the report begins.
The national assessment was assembled from published scientific reports and written by more than 240 experts.
In a section devoted to the current and expected climate impact on the northeast U.S., the report describes a future where increased flooding and heavier precipitation in Pennsylvania will challenge riverbank communities and overwhelm infrastructure built with an outdated sense of a "normal" climate in mind.
"Because of the influence of human activities, the past climate is no longer a sufficient indicator of future conditions," the report notes.
The region already has seen the greatest increase in extreme rain and snow events in recent decades of any area of the country. The amount of precipitation falling in "very heavy events" increased 74 percent in the Northeast over the past 55 years, the report finds.
"Hurricanes such as Irene and Sandy provided a 'teachable moment,'â" the report says, "by demonstrating the region's vulnerability to extreme weather events" and the efficacy of plans to respond to them.
Warmer weather will extend the region's growing season, but the report notes that the potential benefit to farmers will likely be tempered by an increased risk of intense rainfall, wet springs, heat stress, invasive pests, aggressive weeds and damaging cycles of frost and freeze.
In a conference call Tuesday to discuss the new assessment, Raymond Najjar, Ph.D., a Penn State oceanographer who studies climate change impacts and contributed to the report, said "future warming is inevitable" because of carbon's long life in the atmosphere from past emissions.
But he added that "over the long term - 50 or 100 years into the future - our current emissions and the emissions over the coming decades can have a big difference."
The national assessment describes likely future impacts based on several scenarios, ranging from a rapid reduction in emissions to continued emissions growth.
So far, global emissions are on track to be even higher than the report's high-emissions scenario.
And the analysis notes that while voluntary efforts, government actions and a recent shift from coal to natural gas to generate electricity have reduced U.S. emissions in recent years, those changes "are not close to sufficient" to reduce U.S. emissions to the level necessary to avoid some of the worst impacts of climate change.
Contact the writer: llegere@timesshamrock.com