Human Activity Will Determine Climate Change

Human Activity Will Determine Climate Change.

A new U.S. government report drew a direct line between human activity and the quickening pace of climate change, saying the future emissions of greenhouse gasses would determine how warm the earth gets and how quickly sea levels rise. “The last three years have been the warmest years on record for the globe,” according to National Climate Assessment. “Many lines of evidence demonstrate that it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.” The report was produced by the Global Change Research Program, which is mandated by federal law to produce a comprehensive climate assessment. The report was crafted by scientists from 13 federal agencies, including the National Oceanic and Atmospheric Administration, the National Aeronautics and Space Administration, the Energy Department and the Environmental Protection Agency. The findings are based on scientific, peer-reviewed research, plus publicly available data sets and assessments of previous reports written by federal agencies, according to the report.

The report’s statement that reductions in greenhouse-gas emissions could mitigate the expected rise in global temperatures comes as the Trump administration has rolled back U.S. efforts to limit emissions. Most notably, President Donald Trump moved to pull the country from the Paris climate accord, the global push to slow carbon emissions, saying it stepped on U.S. sovereignty and constrained American industry. Without major reductions in greenhouse-gas emissions, global temperatures could stand at 9°F (5°C) or above preindustrial levels by the end of the century, according to the new Climate Science Special Report. With deep cuts in emissions, the change could be limited to 3.6°F (2°C) or less, the report said. It noted that in 2014 and 2015, the pace of carbon-emissions growth did slow, but not at a fast-enough rate to significantly slow future temperature rises. The report doesn’t make policy recommendations. “The magnitude of climate change beyond the next few decades will depend primarily on the amount of greenhouse gases (especially carbon dioxide) emitted globally,” the report said. Among its findings was that the global average sea level has risen by about seven to eight inches since 1900, but nearly half of that increase has happened in the past 25 years or so. That is already affecting cities in the U.S. along the Atlantic and Gulf coasts, where tidal flooding is becoming more commonplace, according to the report. Looking ahead, the report says sea levels are expected to rise by at least several inches in the next 15 years and by one to four feet by 2100.

Average surface air temperature has increased by about 1.8°F over the past 115 years, with recent years serving “record-breaking, climate-related extremes,” according to the report. Heavy rains, heat waves, and forest fires are becoming more frequent, the report said. Last month, California experienced some of the most savage fires on record, leaving many without homes and dozens dead. Scientists have also observed changes in ocean temperatures, plus melting glaciers and diminishing snow cover and sea ice, according to the report, which was released Friday. Wednesday, NASA published maps showing that two to four times as many of Greenland’s coastal glaciers are at risk of accelerated melting as previously thought. This summer, a massive iceberg broke off from Antarctica. Scientists disagree over the role of climate change in that event. The change in climate will also affect human health and productivity, according to the report and other studies. In its Countdown 2017, the medical journal The Lancet published data showing rising temperatures have resulted in a 5.3% decrease in the global labor capacity of rural workers between 2000 and 2016. The capacity of mosquitoes to spread dengue fever has increased globally by almost 10% since 1950 and in Southeast Asia, air pollution contributed to more than 1.9 million deaths in 2015. The Lancet also reported that 125 million more people over the age of 65—an already vulnerable population—were exposed to heat waves in 2016 than in 2000.

In the federal report, scientists say they expect the number of days with temperatures above 90°F (32°C) will rise, while the number with below-freezing temperatures will decline. President Trump was an outspoken skeptic of climate change before he entered politics, calling it an “expensive hoax” and a concept invented by the Chinese. Since entering the Oval Office, Mr. Trump has backed steps to reverse policies meant to combat climate change, but largely has avoided stating his position on the science. In June, Mr. Trump announced that the U.S. would exit the Paris climate accord, while leaving open the possibility of negotiating the deal or crafting a new one on better terms. The U.S. has the world’s second highest level of greenhouse-gas emissions, behind China. Under the Paris agreement, the U.S. aimed to cut carbon-dioxide emissions by 26% to 28% below 2005 levels by the year 2025. United Nations Ambassador Nikki Haley subsequently said Mr. Trump “believes the climate is changing. And he believes pollutants are part of the equation.” She added: “Just because we got out of a club doesn’t mean that we don’t care about the environment.” This week, the EPA barred scientists receiving agency grants from serving on its scientific advisory boards, a move critics charged was unnecessary and aimed at eroding the influence of scientists in general.

Credit: Daniela Hernandez for The Wall Street Journal, 3 November 2017.