EXPLAINER | Climate Change
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Climate Change

Matt Rourke / Associated Press

Floodwaters partly submerge a van in Darby, Pa., Aug. 13, 2018. Climate models predict the Northeastern U.S. will experience more precipitation going forward. 2018 was Pennsylvania’s wettest year on record.

There is overwhelming scientific evidence that the earth is warming at an unprecedented rate and human activities are the main driver. Global leaders have been meeting for decades to address this issue, which threatens both human and natural systems.

The most recent major effort — the 2015 Paris climate agreement — sought to strengthen the global response and avoid the worst effects of climate change, by limiting a global temperature rise in this century well below 2 degrees Celsius above pre-industrial levels.

Why is a few degrees of warming such a big deal?

Richard Alley, a professor of geosciences at Penn State University, explains why the world is more sensitive to climate change than we like to think:

A stark United Nations report issued in 2018 calls on governments to do even more — and try to keep the warming below 1.5 Celsius. The scientists who authored it concede that there is “no documented historic precedent” for such a rapid transformation of the global economy, but say the world faces myriad crises as early as 2040—including food shortages, extreme weather, wildfires, and a mass die-off of coral reefs — unless greenhouse gas emissions are sharply cut.

According to the United Nations Intergovernmental Panel on Climate Change, the “human influence on the climate system is clear.” The National Oceanic and Atmospheric Administration writes, “human activities have increased the abundance of heat-trapping gases in the atmosphere, which a large majority of climate scientists agree is the main reason for the 1.5°F (0.85°C) rise in average global temperature since 1880.” Major greenhouse gases emitted by human activities include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), Hydrofluorocarbons (HFCs), perfluorocarbons(PFCs), sulfur hexafluoride(SF6) and nitrogen triflouride (NF3).

Scientists can also look far back into the past and see how the earth’s climate has changed by examining natural time capsules, such as ice cores, layers of glaciers, ocean sediments, tree rings, and coral reefs. Tiny pockets of air left in ice show scientists a “paleoclimate” record, stretching back more than 800,000 years. It reveals “the current climatic warming is occurring much more rapidly than past warming events,” according to NASA’s Earth Observatory.

What’s in store for Pennsylvania?

Although it has a relatively small share of the global population, Pennsylvania is an energy powerhouse and a major contributor of greenhouse gases.

Pennsylvania is the fifth-largest carbon polluter among states, according to EIA data. Over the past 110 years, Pennsylvania has seen a long-term warming of more than 1 °C (1.8°F), interrupted by a brief cooling period in the mid-20th century, according to the state’s latest climate impact assessment.

Pennsylvania’s latest Climate Action Plan was released in April 2019 by the state Department of Environmental Protection. It calls for an 80 percent reduction of greenhouse gas emissions by 2050, from 2005 levels. It outlines 19 strategies for addressing climate change, including promoting clean energy, energy efficiency, monitoring ecosystems vulnerabilities, and providing resources to help farmers and the outdoor tourism industry adapt.

Climate-related risks to Pennsylvanians include frequent extreme weather events, injury and death from those events, and threats to human health through air pollution, diminished water quality, and heat stress. The warming will also affect farmers as it presents changing pest, weed, and disease management challenges.

Climate models predict the region will experience more precipitation as temperatures continue to rise. The state’s Climate Action Plan says annual precipitation in Pennsylvania has increased by about 10 percent since the early 20th century and is expected to increase by another 8 percent by 2050.

Putting a price on carbon

Pennsylvania is currently reviewing a citizen-led petition to place a price on carbon through an economy wide cap-and-trade program.

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