In early November, the Trump administration released a “Climate Science Special Report.” Contrary to many of the administration’s environmental officials, the report finds that the Earth’s climate is changing due to a multitude of human actions.
“Human activities continue to significantly affect Earth’s climate by altering factors that change its radiative balance … In the industrial era, human activities have been, and are increasingly, the dominant cause of climate warming,” said one of the key findings on physical causes of the climate change.
The “Climate Science Special Report: Fourth National Climate Assessment” was prepared with a large cadre of dozens of authors and contributors. They work at many federal agencies and universities throughout the country.
Its purpose, according to the authors, is “to be an authoritative assessment of the science of climate change, with a focus on the United States, to serve as the foundation for efforts to assess climate-related risks and inform decision-making about responses.”
In the summary, they began, “The global warming of the past 50 years is primarily due to human activities, predominantly the burning of fossil fuels.”
The report acknowledges there are natural contributors to the evolution of climate change. These include solar radiation, volcano eruptions, as well as El Niño. However, the conclusion is that these natural events have not been significant contributors to the increasing surface temperatures.
The most important contributor to the climate change is the substantial increase in atmospheric carbon dioxide, CO2. According to the report, “In the industrial era, the CO2 atmospheric growth rate has been exponential with the increase in atmospheric CO2 approximately twice that absorbed by the oceans … The global average CO2 concentration has increased by 40% over the industrial era.”
Methane and nitrous oxide also are significant gaseous contributors to the effective transformation of the planet’s climate. “The atmospheric concentrations
of CO2, CH4, and N2O are higher now than they have been in at least the past 800,000
years,” the report concluded.
The result of the concentration of these gases in the atmosphere is that the average annual temperature over the U.S. has increased 1.2 degrees in the past 30 years compared to the first 60 years of the 20th century. Cold waves have declined in frequency while heat waves are occurring more often.
Based on climate models, the report projects the average annual temperature over the U.S. will increase 2.5 degrees in the next 35 years and may increase even more before the 21st century ends. The models also predict that extreme temperatures are likely to increase more than the average temperatures. This includes cold days as well as hot days.
There is a very high confidence from the models that, “The number of days below freezing is projected to decline while the number above 90°F will rise.”
The authors examined regions within the U.S., as well as the entire North American continent. The largest change in warming occurred in the western U.S. The change in the annual average and annual maximum average temperatures was half a degree greater in the Southwest region (Arizona, California, Colorado, Nevada, New Mexico and Utah).
Even for the annual average minimum temperature, the Southwest increase was 1.6 degrees compared to 1.4 degrees for the contiguous U.S.
Warm temperatures and water availability already are characteristics of the region and their importance will be exacerbated in the future.
Water in the Southwest will decline, according to the report, which forecasts diminishing snowpack and resulting less stream flow. Droughts will become more frequent.
Less water and warmer temperatures will have a negative effect on the region’s agricultural production, which supports the whole country.
Residents in the rural and forested areas of the region can expect “more wildfire and increased risks to communities across extensive areas,” according to the report.
The report suggested that the region might mitigate the worst of these changes with a migration to greater use of geothermal, wind and solar-energy resources. A greater consumption of renewal energy resources could substantially reduce heat-trapping gases.
While the report’s conclusions were pessimistic, the authors praised several regional efforts to reverse the emission of threatening gases. Ten northeast and mid-Atlantic states have formed the Regional Greenhouse Gas Initiative. Five Southwest states have adopted new goals for using renewable energy.
California was singled out for Assembly Bill 32, “Global Warming Solution Act,” with the goal to reduce greenhouse emissions to 1990 levels by 2020. AB 32 was enacted in 2006.