Courtesy : wikipedia.org

Climate change

Climate change in the United States has led to the country warming by 2.6 °F (1.4 °C) since 1970. Due to climate change, the climate of the United States is shifting in ways that are widespread and varied between regions.From 2010 to 2019, the United States experienced its hottest decade on record. Extreme weather events, invasive species, floods and droughts are increasing.Climate change’s impacts on tropical cyclones and sea level rise also affects regions of the country.

Cumulatively since 1850, the U.S. has emitted a larger share than any country of the greenhouse gases causing current climate change, with some 20% of the global total of carbon dioxide alone. Current US emissions per person are among the largest in the world.Various state and federal climate change policies have been introduced, and the US has ratified the Paris Agreement despite temporarily withdrawing. In 2021, the country set a target of halving its annual greenhouse gas emissions by 2030.

Climate change is having considerable impacts on the environment and society of the United States. This includes implications for agriculture, the economy, human health and indigenous peoples, and it is seen as a national security threat. States that emit more carbon dioxide per person and introduce policies to oppose climate action are generally experiencing greater impacts.^[2020 was a historic year for billion-dollar weather and climate disasters in U.S.

Although historically a non-partisan issue, climate change has become controversial and politically divisive in the country in recent decades. Oil companies have known since the 1970s that burning oil and gas could cause global warming but nevertheless funded deniers for years.Despite the support of a clear scientific consensus, as of 2021 one third of Americans deny that human-caused climate change exists although the majority are concerned or alarmed about the issue.

Greenhouse gas emissions

The U.S. has higher annual per capita emissions than China, which has more total annual emissions.

Cumulatively over time, U.S. emissions have caused more economic damage globally than any other nation.

This section is an excerpt from Greenhouse gas emissions by the United States.

US greenhouse gas emissions by economic sector

  Transportation (28.6%)

  Electricity generation (25.1%)

  Industry (22.9%)

  Agriculture (10.2%)

  Commercial (6.9%)

  Residential (5.8%)

  U.S. territories (0.4%)

The United States produced 5.2 billion metric tons of carbon dioxide equivalent greenhouse gas (GHG) emissions in 2020,the second largest in the world after greenhouse gas emissions by China and among the countries with the highest greenhouse gas emissions per person. In 2019 China is estimated to have emitted 27% of world GHG, followed by the United States with 11%, then India with 6.6%. In total the United States has emitted a quarter of world GHG, more than any other country.Annual emissions are over 15 tons per person and, amongst the top eight emitters, is the highest country by greenhouse gas emissions per person.Because coal-fired power stations are gradually shutting down, in the 2010s emissions from electricity generation fell to second place behind transportation which is now the largest single source. In 2020, 27% of the GHG emissions of the United States were from transportation, 25% from electricity, 24% from industry, 13% from commercial and residential buildings and 11% from agriculture.These greenhouse gas emissions are contributing to climate change in the United States, as well as worldwide.

Impact on the natural environment

See also: Tropical cyclones and climate change

Temperature and weather changes

Human-induced climate change has the potential to alter the prevalence and severity of extreme weather events such as heat waves, cold waves, storms, floods and droughts.A 2012 Intergovernmental Panel on Climate Change (IPCC) report confirmed that a strong body of evidence links global warming to an increase in heat waves, a rise in episodes of heavy rainfall and other precipitation, and more frequent March 2020 placed second to 2016 for being the second-hottest March on record with an average of 2.09 Fahrenheit (1.16 Celsius) above that of the 20th-century.

According to the American government’s Climate Change Science Program, “With continued global warming, heat waves and heavy downpours are very likely to further increase in frequency and intensity. Substantial areas of North America are likely to have more frequent droughts of greater severity. Hurricane wind speeds, rainfall intensity, and storm surge levels are likely to increase. The strongest cold season storms are likely to become more frequent, with stronger winds and more extreme wave heights.”

In 2022, Climate Central reported that, since 1970, the U.S. is 2.6 °F (1.4 °C) warmer, all 49 states analyzed^{(Hawaii data not available)} warmed by at least 1.8 °F (1.0 °C), and 244 of 246 U.S. cities analyzed warmed.Many of the fastest-warming locations were in the drought-prone Southwest, with Reno, Nevada, warming by +7.7 °F (4.3 °C).Alaska warmed by 4.3° F (2.4 °C), where melting glaciers contribute to sea level rise, and permafrost melt releases greenhouse gases.Ninety percent of U.S. counties experienced a federal climate disaster between 2011-2021, with some having as many as 12 disasters during that time.

Current/past Köppen climate classification map for the United States for 1980–2016

Predicted Köppen climate classification map for the United States for 2071–2100

The number of $1 billion Atlantic hurricanes almost doubled from the 1980s to the 2010s, and inflation-adjusted costs have increased more than elevenfold.The increases have been attributed to climate change and to greater numbers of people moving to coastal areas.

Extreme precipitation events have become more common over recent decades.

The number and severity of high-cost extreme weather events has increased in the 21st century in the United States, and some of these are because of global warming. By August 2011 alone, the NOAA had registered nine distinct extreme weather disasters for that year, each totalling $1 billion or more in economic losses. Total losses for 2011 were evaluated as more than $35 billion before Hurricane Irene.

Though the costs and frequency of cyclones have increased on the east coast, it remains unclear whether these effects have been driven primarily by climate change. When correcting for this, a comprehensive 2006 article in Geophysical Research Letters found “no significant change in global net tropical cyclone activity” during past decades, a period when considerable warming of ocean water temperatures occurred. However, the study found major regional shifts, including a general rise of activity in the North Atlantic area, including on the U.S. eastern coast.

From 1898 through 1913, there have been 27 cold waves which totalled 58 days. Between 1970 and 1989, there were about 12 such events. From 1989 until January 6, 2014, there were none. The one on the latter date caused consternation because of decreased frequency of such experiences.

Looking at the lack of certainty as to the causes of the 1995 to present increase in Atlantic extreme storm activity, a 2007 article in Nature used proxy records of vertical wind shear and sea surface temperature to create a long-term model. The authors found that “the average frequency of major hurricanes decreased gradually from the 1760s until the early 1990s, reaching anomalously low values during the 1970s and 1980s.” As well, they also found that “hurricane activity since 1995 is not unusual compared to other periods of high hurricane activity in the record and thus appears to represent a recovery to normal hurricane activity, rather than a direct response to increasing sea surface temperature.” The researches stated that future evaluations of climate change effects should focus on the magnitude of vertical wind shear for answers.

The frequency of tornadoes in the U.S. has increased, and some of this trend takes place due to climatological changes though other factors such as better detection technologies also play large roles. According to a 2003 study in Climate Research, the total tornado hazards resulting in injury, death, or economic loss “shows a steady decline since the 1980s.” The authors reported that tornado “deaths and injuries decreased over the past fifty years.” They state that additional research must look into regional and temporal variability in the future.

Heat waves

In recent decades in the U.S., the percentage of record high daily temperatures has predominated over record daily low temperatures, with record daily highs now more than twice that of record daily lows.

From the 1960s the amount and longevity of heat waves have increased in the contiguous United States. The general effect of climate changes has been found in the journal Nature Climate Change to have caused increased likelihood of heat waves and extensive downpours.Concerns exist that, as stated by a National Institutes of Health (NIH) study in 2003, increasing “heat and humidity, at least partially related to anthropogenic climate change, suggest that a long-term increase in heat-related mortality could occur.” However, the report found that, in general, “over the past 35 years, the U.S. populace has become systematically less affected by hot and humid weather conditions” while “mortality during heat stress events has declined despite increasingly stressful weather conditions in many urban and suburban areas.” Thus, as stated in the study, “there is no simple association between increased heat wave duration or intensity and higher mortality rates” with current death rates being largely preventable, the NIH deeply urging American public health officials and physicians to inform patients about mitigating heat-related weather and climate effects on their bodies.

Hotter temperatures and drier weather due to climate change has been linked to wildfires, such as those in California in 2020.

In 2021 an unprecedented heat wave occurred in the northwest linked to climate change.The heatwave brought temperatures close to 50 °C to many areas that generally do not experience such heat like Portland and Seattle, killed 500 people and caused 180 wildfires in British Columbia in Canada. The heat wave was made 150 times more likely by climate change.According to World Weather Attribution such events occur every 1,000 years in today climate but if the temperature will rise by 2 degrees above preindustrial levels, such events will occur each 5–10 years. However, it was more severe than predicted climate models. Significant impacts in that area were expected in the Pacific Northwest only by the middle of the 21st century.Currently, scientists search ways to make the predictions more accurate because: “researchers need to assess whether places such as North America or Germany will face extremes like the heat dome and the floods every 20 years, 10 years, five years – or maybe even every year. This level of accuracy currently isn’t possible”.

The leading cause of animal extinction rates within the United States is due to rising temperatures and heat waves. Science writer Mark C. Urban states, “Species must disperse into newly suitable habitats as fast as climate shifts across landscapes.”The risk of extinction among species isn’t as detrimental in the United States as compared to other countries such as, “South America, Australia, and New Zealand.” Due to these species needing to adapt as fast as rising temperature, Urban stresses the idea of countries who are at great risk, and even those who aren’t to adapt strategies to limit further advances in rising temperatures and climate change.

Droughts

EPA-reported drought conditions for the 48 contiguous states. The curve is a nine-year weighted average. Wet and rainy conditions versus moments of drought in the U.S. have varied significantly over the past several decades.

A dry lakebed in California in its worst megadrought in 1,200 years, intensified by climate change, causing water rationing in the state.

Further information: Droughts in the United States, Southwestern North American megadrought, and 2020–21 North American drought

A 2006 study suggested that drought conditions appear to be worsening in the southwest while improving in the northeast. In the years 2000–2021 the southwestern North American megadrought persisted. Climate change increased temperature, reduced the amount of precipitation, decreased snowpack and increased the ability of air to soak humidity, helping to create arid conditions. As of 2021 the drought was the most severe in the last 500 years.As of 30 June 2021 61% of continental USA were in drought conditions. Demand for water and cooling rose. In June 2021 water restrictions entered into force in California. Climate change is responsible for 50% of the severity of the drought in California. Water restrictions are expected to expand on many states in the US west, farmers are already affected. In San Francisco a hydropower plant can stop work due to lack of water.

A study published in Nature Climate Change concluded that 2000–2021 was the driest 22-year period in southwestern North America since at least 800 CE. One of the study’s researchers said that, without climate change, the drought would probably have ended in 2005.42% of the megadrought’s severity is said to be attributable to temperature rise as a result of climate change, with 88% of the area being drought-stricken. n 2020-2021, the Colorado River, feeding seven states, shrank to the lowest two-year average in more than a century of record keeping.