(left) Global annual average temperature has increased by more than 1.2°F (0.7°C) for the period 1986–2016 relative to 1901–1960. Red bars show temperatures that were above the 1901–1960 average, and blue bars indicate temperatures below the average. (right) Surface temperature change (in °F) for the period 1986–2016 relative to 1901–1960. Gray indicates missing data. Graphic: Wuebbles, et al., 2017 / Climate Science Special Report: Fourth National Climate Assessment, Volume I

By Chris Mooney, Juliet Eilperin, and Brady Dennis
3 November 2017

(The Washington Post) – The Trump administration released a dire scientific report Friday detailing the growing threats of climate change. The report stands in stark contrast to the administration’s efforts to downplay humans’ role in global warming, withdraw from an international climate accord and reverse Obama-era policies aimed at curbing U.S. greenhouse-gas output.

The White House did not seek to prevent the release of the government’s National Climate Assessment, which is mandated by law, despite the fact that its findings sharply contradict the administration’s policies. The report affirms that climate change is driven almost entirely by human action, warns of potential sea-level rise as high as eight feet by the year 2100, and enumerates climate-related damage across the United States that is already occurring as a result of 1.8 degrees Fahrenheit of global warming since 1900.

“It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century,” the document reports. “For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence.”

The report’s release underscores the extent to which the machinery of the federal scientific establishment, operating in multiple agencies across the government, continues to grind on even as top administration officials have minimized or disparaged its findings. Federal scientists have continued to author papers and issue reports on climate change, for example, even as political appointees have altered the wording of news releases or blocked civil servants from speaking about their conclusions in public forums. The climate assessment process is dictated by a 1990 law that Democratic and Republican administrations have followed.

Environmental Protection Agency Administrator Scott Pruitt, Energy Secretary Rick Perry and President Trump have all questioned the extent of humans’ contribution to climate change. One of the EPA’s Web pages posted scientific conclusions similar to those in the new report until earlier this year, when Pruitt’s deputies ordered it removed.

The report comes as Trump and members of his Cabinet are working to promote U.S. fossil-fuel production and repeal several federal rules aimed at curbing the nation’s carbon output, including ones limiting greenhouse-gas emissions from existing power plants, oil and gas operations on federal land and carbon emissions from cars and trucks. Trump has also announced he will exit the Paris climate agreement, under which the United States has pledged to cut its overall greenhouse-gas emissions between 26 percent and 28 percent compared with 2005 levels by 2025.

The report could have considerable legal and policy significance, providing new and stronger support for the EPA’s greenhouse-gas “endangerment finding” under the Clean Air Act, which lays the foundation for regulations on emissions.

“This is a federal government report whose contents completely undercut their policies, completely undercut the statements made by senior members of the administration,” said Phil Duffy, director of the Woods Hole Research Center. [more]

Trump administration releases report finding ‘no convincing alternative explanation’ for climate change


Observed changes in the occurrence of record-setting daily temperatures in the contiguous United States. Red bars indicate a year with more daily record highs than daily record lows, while blue bars indicate a year with more record lows than highs. The height of the bar indicates the ratio of record highs to lows (red) or of record lows to highs (blue). For example, a ratio of 2:1 for a blue bar means that there were twice as many record daily lows as daily record highs that year. (Figure source: NOAA/NCEI). Graphic: Vose, et al., 2017 / Climate Science Special Report: Fourth National Climate Assessment, Volume I

3 November 2017 (U.S. Global Change Research Program) – The climate of the United States is strongly connected to the changing global climate. The statements 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. The last few years have also seen record-breaking, climate-related weather extremes, and the last three years have been the warmest years on record for the globe. These trends are expected to continue over climate timescales.

This assessment concludes, based on extensive evidence, that it is extremely likely that 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.

In addition to warming, many other aspects of global climate are changing, primarily in response to human activities. 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.

For example, global average sea level has risen by about 7–8 inches since 1900, with almost half (about 3 inches) of that rise occurring since 1993. Human-caused climate change has made a substantial contribution to this rise since 1900, contributing to a rate of rise that is greater than during any preceding century in at least 2,800 years. 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. Annual average temperature over the contiguous United States has increased by 1.8°F (1.0°C) for the period 1901–2016; over the next few decades (2021–2050), annual average temperatures are expected to rise by about 2.5°F for the United States, relative to the recent past (average from 1976–2005), under all plausible future climate scenarios.

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. Under higher scenarios, and assuming no change to current water resources management, chronic, long-durationhydrological drought is increasingly possible before the end of this century.

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 preindustrial 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. Continued growth in CO2 emissions over this century and beyond would lead to an atmospheric concentration not experienced in tens to hundreds of millions of years. There is broad consensus that the further and the faster the Earth system is pushed towards warming, the greater the risk of unanticipated changes and impacts, some of which are potentially large and irreversible.

The observed increase in carbon emissions over the past 15–20 years has been consistent with higher emissions pathways. 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 preindustrial levels.

Climate Science Special Report Fourth National Climate Assessment (NCA4), Volume I

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