Government Report Provides Most Recent Evidence of Climate Change

Parts of the U.S. are particularly vulnerable to sea level rise, factors that are exacerbated by storms producing extreme flood surges and increases in tidal flooding. | Air Force/Tech. Sgt. Larry E. Reid Jr.

A new federal report strengthens our understanding of global climate change, providing policymakers with scientific evidence to develop responses, said Rush Holt, CEO of the American Association for the Advancement of Science, following the release of the Climate Science Special Report on Friday.

The report, written and reviewed by leading U.S. scientists as part of the National Climate Assessment, reinforces that warming temperatures and extreme weather around the globe are “extremely likely” to be the result of carbon pollution from human activities.

“The overwhelming scientific evidence of our changing climate cannot be ignored,” Holt said in a statement. “Scientists at federal agencies, national labs and academic institutions worked to summarize what we know about climate change in the United States and around the world. The Climate Science Special Report lays out the most recent scientific evidence of climate change, once again confirming that climate change is real, it’s happening now, and human activity is the primary cause.”

Holt stressed that the report “provides scientific evidence to decision-makers at all levels – local, state, regional and national – to help inform how society can respond to climate change.”

In its executive summary, the report concludes “it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence.”

Greenhouse gas emissions that trap heat in the atmosphere, widespread clearing of forests and agricultural activities are major factors driving temperature increases since 1951, the report states.

The burning of fossil fuels also is highlighted as having an unparalleled impact on the Earth’s climate, and continued emissions have the potential to accelerate human-induced climate change and contribute to unanticipated changes that may be difficult or impossible to manage.

Limiting increases in global average temperatures to a 3.6 F target would require significant reductions in carbon pollution levels and ultimately eliminating net greenhouse gas emissions altogether, the report says. Yet, such a shift will be particularly difficult to achieve in light of President Donald Trump’s decision in June to withdraw from the Paris Agreement.

“This report underscores the vast body of evidence that firmly establishes how climate is changing, humans are responsible, the risks are real, and the window of time to prevent serious and even dangerous impacts is closing,” said Katharine Hayhoe, one of the report authors and a professor and director of Texas Tech University Climate Science Center in Lubbock.

Extreme weather events such as excessive precipitation and heat waves are on the rise, the report finds. Warming temperatures and high precipitation levels contribute to destructive wildfires, extensive property damage and costly flooding, as was recently seen in northern California and in the aftermath of the rain and resulting flooding from Hurricane Harvey in Houston.

The report finds that the U.S. is particularly vulnerable to projected sea level rise; areas such as the Northeast and western Gulf of Mexico could face rates that exceed global average sea level rise. As sea levels have risen, many coastal areas have seen increased flooding during high tides and extreme flooding during coastal storms; these trends are projected to continue in the coming century.

Hurricanes are exhibiting some changes that have been linked to climate change, including increases in intensity and precipitation rates, but additional studies are still needed to understand these trends and how they may continue in the future, the report says.

“The further we push the Earth’s climate away from its natural state, the greater the risks of dangerous and even potentially unforeseen consequences,” said Robert Kopp, a report author and professor in the Department of Earth and Planetary Sciences at Rutgers University in New Jersey.

Kopp noted recent findings have revealed the possibility of even more serious impacts including “ice sheet melt in Greenland and Antarctica to compound extremes, where events occurring simultaneously or in rapid sequence can amplify the risks to both human and natural systems.”

The U.S. Global Change Research Program, which coordinates the National Climate Assessment report process, also released draft versions of two other reports for public comment: the Second State of the Carbon Cycle Report and the Fourth National Climate Assessment. The National Academy of Sciences will conduct a peer review of these reports. 

“Providing these reports for public comment is a key step toward ensuring that the reports and the larger National Climate Assessment process are transparent and maintain standards for scientific integrity,” said Emily Cloyd, AAAS public engagement project director.

Four authors of the Climate Science Special Report – Hayhoe, Kopp, Radley Horton and Sarah Doherty – will discuss the report’s key findings and recent developments in climate science during a AAAS Facebook Live discussion on Nov. 8 at 3:00 p.m. Eastern. In addition, Victoria Keener will discuss the draft National Climate Assessment and Anna Michalak will discuss the draft Second State of the Carbon Cycle Report. 

The National Oceanic and Atmospheric Administration is the lead federal agency on the report for the U.S. Global Change Research Program, which produced Volume 1 of the 4th National Climate Assessment. The full National Climate Assessment is expected to be completed and published in 2018. A 1990 law, known as the Global Change Research Act, requires federal agencies to provide an overview of the latest climate science and a thorough review of the impact of climate change throughout the U.S. to the president and the Congress every four years.

[Associated image: The aftermath of flooding in North Charleston, South Carolina caused by over 15 inches of rainfall resulting from a fall 2015 storm. | Ryan Johnson/North Charleston CC BY-SA 2.0]