Federal Agencies Report that Humans are the Dominant Cause of Climate Change

 

Directly contradicting the Trump administration position on climate change, 13 federal agencies released an extensive scientific report that says humans are the dominant cause of the global temperature rise that has occurred since 1901, creating the warmest period in human history.

Over the past 115 years, global average temperatures have increased 1.8 degrees Fahrenheit (1 degree Celsius), leading to record breaking weather events and temperature extremes. According to the report, the global, long-term warming trend is “unambiguous” and there is “no convincing alternative explanation” that anything other than humans are to blame because of the cars we drive, the power plants we operate, and the forests we destroy.
 

Surprisingly, the report was approved for release by the White House. However, the findings come as the Trump administration is defending its climate change policies on several fronts. 

Public drafts of the report have circulated for months, making it politically perilous to tinker with the findings. So, with editing a high-risk affair and the report required by Congress, the administration may have just decided to downplay it, said John Holdren, who ran the Office of Science and Technology Policy under President Barack Obama.

"It would do more harm to block this report than to let it out," Holdren, now a Harvard University environmental policy professor, said in an interview. "They’re letting it out on a Friday afternoon, which is pretty much the standard approach for letting out something that you don’t want to get a lot of attention." 

The government is required to produce the national assessment every four years. This time, the report is split into two documents, one that lays out the fundamental science of climate change and the other that shows how the United States is being affected on a regional basis. Combined, the two documents total over 2,000 pages.

The first document, called the Climate Science Special Report, is a finalized report, having been peer-reviewed by the National Academy of Sciences and vetted by experts across government agencies.

 

The climate of the United States is strongly connected to the changing global climate. The short statements listed below highlight past, current, and projected climate changes for the United States and the globe:

• Global annually averaged surface air temperature has increased by about 1.8°F (1.0°C) over the last 115 years (1901–2016). This period is now the warmest in the history of modern civilization. 

• Human activities, especially emissions of greenhouse gases, are 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. 

• Thousands of studies conducted by researchers around the world have documented changes in surface, atmospheric, and oceanic temperatures; melting glaciers; diminishing snow cover; shrinking sea ice; rising sea levels; ocean acidification; and increasing atmospheric water vapor. 

• Global average sea level has risen by about 7–8 inches since 1900. Global sea level rise has already affected the United States; the incidence of daily tidal flooding is accelerating in more than 25 Atlantic and Gulf Coast cities. 

• Global average sea levels are expected to continue to rise—by at least several inches in the next 15 years and by 1–4 feet by 2100. A rise of as much as 8 feet by 2100 cannot be ruled out. Sea level rise will be higher than the global average on the East and Gulf Coasts of the United States. 

• Changes in the characteristics of extreme events are particularly important for human safety, infrastructure, agriculture, water quality and quantity, and natural ecosystems. Heavy rainfall is increasing in intensity and frequency across the United States and globally and is expected to continue to increase. The largest observed changes in the United States have occurred in the Northeast.

• Heatwaves have become more frequent in the United States since the 1960s, while extreme cold temperatures and cold waves are less frequent. Recent record-setting hot years are projected to become common in the near future for the United States, as annual average temperatures continue to rise.

• The incidence of large forest fires in the western United States and Alaska has increased since the early 1980s and is projected to further increase in those regions as the climate changes, with profound changes to regional ecosystems.
   
• Annual trends toward earlier spring melt and reduced snowpack are already affecting water resources in the western United States and these trends are expected to continue. 

• The magnitude of climate change beyond the next few decades will depend primarily on the amount of greenhouse gases (especially carbon dioxide) emitted globally. Without major reductions in emissions, the increase in annual average global temperature relative to pre-industrial times could reach 9°F (5°C) or more by the end of this century. With significant reductions in emissions, the increase in annual average global temperature could be limited to 3.6°F (2°C) or less. 

• The global atmospheric carbon dioxide (CO2) concentration has now passed 400 parts per million (ppm), a level that last occurred about 3 million years ago, when both global average temperature and sea level were significantly higher than today.

• In 2014 and 2015, emission growth rates slowed as economic growth became less carbon-intensive. Even if this slowing trend continues, however, it is not yet at a rate that would limit global average temperature change to well below 3.6°F (2°C) above pre-industrial levels.

To view the entire statements contained in the Executive Summary of the report (36 pages), click here

To view the full National Climate Assessment, Volume 1 (477 pages), click here