98% of all scientists agree that climate change is real and happening now.
In the last 650,000 years there have been seven cycles of glacial advance and retreat, with the end of the last ice age about 7,000 years ago, beginning the modern climate era. Most of these previous climate changes are attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives.
The current warming trend is of particular significance because it’s a result of human activity for the past 12,000 years. However, since the mid-20th century and proceeding at a rate that is unprecedented, humans are releasing carbon dioxide and other gases into the atmosphere that is making drastic changes to our climate.
- Global Temperature Rise: Most of the warming occurred in the past 35 years, with the six warmest years on record taking place since 2010.
- Warming Oceans: The oceans have absorbed much of this increased heat, with the top 700 meters (about 2,300 feet) of ocean showing warming of 0.302 degrees Fahrenheit since 1969.
- Shrinking Ice Sheets: The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA’s Gravity Recovery and Climate Experiment show Greenland lost and average of 281 billion tons of ice per year between 1993 and 2016, while Antarctica lost about 119 billion tons during the same time period. The rate of Antarctica ice mass loss has tripled in the last decade.
- Glacial Retreat: Glaciers are retreating almost everywhere around the world — including in the Alps, Himalayas, Andes, Rockies, Alaska and Africa.
- Decreased Snow Cover: Satellite observations reveal that the amount of spring snow cover in the Northern Hemisphere has decreased over the past five decades and that the snow is melting earlier.
- Sea Level Rise: Global sea level rose about 8 inches in the last century. The rate in the last two decades, however, is nearly double that of the last century.
- Declining Arctic Sea Ice: Both the extent and thickness of Arctic sea ice has declined rapidly over the last several decades.
- Extreme Events: The number of record high temperature events in the United States has been increasing, while the number of record low temperature events has been decreasing, since 1950. The U.S. has also witnessed increasing numbers of intense rainfall events.
- Ocean Acidification: Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30 percent. This increase is the result of humans emitting more carbon dioxide into the atmosphere and hence more being absorbed into the oceans. The amount of carbon dioxide absorbed by the upper layer of the oceans is increasing by about 2 billion tons per year.
The Consequences of Climate Change
Effects that scientists had predicted in the past would result from global climate change are now occurring: loss of sea ice, accelerated sea level rise and longer, more intense heat waves.
Change will Continue through this Century and Beyond: Global climate is projected to continue to change over this century and beyond. The magnitude of climate change beyond the next few decades depends primarily on the amount of heat-trapping gases emitted globally, and how sensitive the Earth’s climate is to those emissions.
- Temperatures will Continue to Rise: Because human-induced warming is superimposed on a naturally varying climate, the temperature rise has not been, and will not be, uniform or smooth across the country or over time.
- Frost-Free Season will Lengthen: The length of the frost-free season has been increasing nationally since the 1980s, with the largest increases occurring in the western United States, affecting ecosystems and agriculture.
- Changes in Precipitation Patterns: Projections of future climate suggest that the recent trend towards increased heavy precipitation events will continue. This trend is projected to occur even in regions where total precipitation is expected to decrease.
- More Droughts and Heat Waves: Droughts and heat waves (periods of abnormally hot weather lasting days to weeks) everywhere are projected to become more intense, and cold waves less intense everywhere.
- Hurricanes will become Stronger and more Intense: The intensity, frequency and duration of North Atlantic hurricanes, as well as the frequency of the strongest (Category 4 and 5) hurricanes, have all increased since the early 1980s. Hurricane-associated storm intensity and rainfall rates are projected to increase as the climate continues to warm.
- Sea Level will Rise 1-4 Feet by 2100: Global sea level has risen by about 8 inches since reliable record keeping began in 1880. It is projected to rise another 1 to 4 feet by 2100. This is the result of added water from melting land ice and the expansion of seawater as it warms. Also storm surges and high tides could combine with sea level rise and land subsidence to further increase flooding in many regions. Sea level rise will continue past 2100 because the oceans take a very long time to respond to warmer conditions at the Earth’s surface. Ocean waters will therefore continue to warm and sea level will continue to rise for many centuries at rates equal to or higher than those of the current century.
- Arctic is Becoming Ice-Free: The Arctic Ocean is expected to become essentially ice-free in summer before mid-century.
Effects in the USA
- Northeast: Heat waves, heavy downpours and sea level rise pose growing challenges to many aspects of life in the Northeast. Infrastructure, agriculture, fisheries and ecosystems will be increasingly compromised. Many states and cities are beginning to incorporate climate change into their planning.
- Northwest: Changes in the timing of streamflow reduce water supplies for competing demands. Sea level rise, erosion, inundation, risks to infrastructure and increasing ocean acidity pose major threats. Increasing wildfire, insect outbreaks and tree diseases are causing widespread tree die-off.
- Southeast: Sea level rise poses widespread and continuing threats to the region’s economy and environment. Extreme heat will affect health, energy, agriculture and more. Decreased water availability will have economic and environmental impacts.
- Midwest: Extreme heat, heavy downpours and flooding will affect infrastructure, health, agriculture, forestry, transportation, air and water quality, and more. Climate change will also exacerbate a range of risks to the Great Lakes.
- Southwest: Increased heat, drought and insect outbreaks, all linked to climate change, have increased wildfires. Declining water supplies, reduced agricultural yields, health impacts in cities due to heat, and flooding and erosion in coastal areas are additional concerns.