Climate Change

Climate change refers to long-term shifts in global or regional climate patterns, including temperature, precipitation, and wind patterns. Since the mid-20th century, human activities, particularly the burning of fossil fuels, have become the dominant cause of observed warming. The scientific consensus confirms that these changes are leading to widespread and often severe impacts on ecosystems, human societies, and the global economy.

Last updated September 3, 2025

Definition and Terminology

Climate change encompasses significant and lasting changes in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or in the distribution of weather around the average conditions. While Earth's climate has changed throughout history, the current warming trend is of particular significance because it is unequivocally the result of human activity since the mid-19th century and proceeding at a rate unprecedented over millennia, according to the Intergovernmental Panel on Climate Change. The term is often used interchangeably with Global Warming, which refers specifically to the long-term heating of Earth's climate system observed since the pre-industrial period (between 1850 and 1900) due to human activities.

Causes of Recent Climate Change

The primary driver of recent climate change is the enhanced Greenhouse Effect. This effect is a natural process where certain gases in the atmosphere, known as Greenhouse Gases (GHGs), trap heat from the sun. Human activities have significantly increased the concentration of these gases, intensifying the effect. According to NASA, the main sources of anthropogenic GHGs include:

–Fossil Fuels: The burning of Fossil Fuels like coal, oil, and natural gas for electricity, heat, and transportation is the largest source of global emissions, primarily of carbon dioxide (CO₂).
–Deforestation: Forests act as carbon sinks, absorbing CO₂ from the atmosphere. Clearing forests for agriculture, logging, or other land uses releases this stored carbon and reduces the planet's capacity to absorb future emissions.
–Industrial Processes: Certain manufacturing processes, such as cement production, release large amounts of CO₂.
–Agriculture: Agricultural practices release significant quantities of methane (CH₄) from livestock digestion and rice paddies, as well as nitrous oxide (N₂O) from the use of nitrogen-based fertilizers.

Evidence and Observed Effects

Evidence for rapid climate change is compelling and has been documented by numerous scientific institutions worldwide. Key observations reported by NOAA include:

–Global Temperature Rise: The planet's average surface temperature has risen about 1.18° Celsius (2.12° Fahrenheit) since the late 19th century, with most of the warming occurring in the past 40 years.
–Warming Oceans: The ocean has absorbed much of this increased heat, with the top 100 meters showing warming of more than 0.33° Celsius (0.6° Fahrenheit) since 1969.
–Shrinking Ice Sheets and Glaciers: The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA's Gravity Recovery and Climate Experiment show Greenland lost an average of 279 billion tons of ice per year between 1993 and 2019, while Antarctica lost about 148 billion tons per year, as detailed by the National Snow and Ice Data Center.
–Sea Level Rise: Global Sea Level Rise has accelerated, rising about 8 inches (20 centimeters) in the last century. The rate in the last two decades, however, is nearly double that of the last century and is accelerating slightly every year.
–Extreme Weather Events: The frequency and intensity of extreme weather events such as heatwaves, droughts, heavy precipitation, and tropical cyclones have increased in many regions.
–Ocean Acidification: The CO₂ content of the Earth’s oceans has been increasing, leading to a rise in acidity by about 30% since the beginning of the Industrial Revolution. This process, known as Ocean Acidification, threatens marine ecosystems, particularly coral reefs.

International Response and Policy

The international community has sought to address climate change through various agreements and frameworks. The primary international body for assessing the science related to climate change is the Intergovernmental Panel on Climate Change (IPCC). The United Nations Framework Convention on Climate Change (UNFCCC), established in 1992, provides the overall framework for intergovernmental efforts. A major milestone under the UNFCCC was the adoption of the Paris Agreement in 2015. According to the United Nations, its central aim is to strengthen the global response to the threat of climate change by keeping a global temperature rise this century well below 2 degrees Celsius above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5 degrees Celsius.