Climate change

Climate change refers to long-term shifts and changes in global temperatures and weather patterns. While climate variations are natural, scientific evidence shows that human activities have been the main driver of climate change since the mid-20th century, primarily through the emission of greenhouse gases from burning fossil fuels.^[1]

The largest driver of warming is the emission of greenhouse gases, of which more than 90% are carbon dioxide (CO₂) and methane. Fossil fuel burning for electricity, heat, and transportation is the largest source of greenhouse gas emissions. Additional causes include agriculture, deforestation, and manufacturing.^[2]

Temperature rise is accelerating feedback loops. For example, as Arctic sea ice melts, less sunlight is reflected and more is absorbed by the ocean. Climate change has resulted in expanding deserts, heat waves and wildfires more frequently, the sea level rising, and mass migration of species as their environment changes.

Observed changes

Temperature changes

Multiple independent temperature measurements show Earth has warmed since 1880. According to NASA and NOAA, the global average temperature has increased by about 1.1°C (2°F) since the late 19th century. Most of the warming occurred in the past 40 years, with the six warmest years on record occurring since 2014.

Arctic changes

The Arctic is warming nearly twice as fast as the global average in a phenomenon known as Arctic amplification. Arctic sea ice is declining at a rate of 13% per decade, and the thickness of sea ice has also decreased. The Greenland ice sheet is losing mass six times faster than it was in the 1980s.

Sea level rise

Global sea level has risen about 21–24 centimeters (8.2–9.4 inches) since 1880, with about a third of that rise occurring since 1993. The rise is due to thermal expansion of seawater and melting of glaciers and ice sheets. Current projections suggest sea levels could rise by 0.43 to 2.84 meters (1.4 to 9.3 feet) by 2100.

Causes

Greenhouse gases

The greenhouse effect occurs when greenhouse gases in a planet's atmosphere insulate the planet from losing heat to space, raising its temperature. Human activities since the Industrial Revolution have increased atmospheric concentrations of carbon dioxide by over 40%, with levels now at their highest in over 3 million years.

The main greenhouse gases responsible for human-caused climate change include:

• Carbon dioxide (CO₂) - accounts for about 76% of emissions
• Methane (CH₄) - accounts for about 16% of emissions
• Nitrous oxide (N₂O) - accounts for about 6% of emissions
• Fluorinated gases - account for about 2% of emissions

Human activities

The primary human activities contributing to climate change include:

• Burning fossil fuels - for electricity, heat, and transportation
• Deforestation - reducing Earth's capacity to absorb CO₂
• Industrial processes - manufacturing, cement production, chemical processes
• Agriculture - livestock farming and rice cultivation produce methane
• Transportation - cars, planes, ships, and trains burning fossil fuels

Impacts

Environmental impacts

Climate change is affecting natural systems worldwide. Biodiversity loss is accelerating as species struggle to adapt to changing conditions. Coral reefs are experiencing widespread bleaching due to rising ocean temperatures. Permafrost is thawing, releasing stored carbon and methane.

Human impacts

Climate change affects human health through heat waves, air pollution, extreme weather events, and disease vectors. Food security is threatened by changing precipitation patterns and increasing temperatures. Water scarcity affects billions of people as glaciers melt and droughts become more frequent.

Economic impacts

The economic costs of climate change include damage from extreme weather events, reduced agricultural productivity, health care costs, and infrastructure damage. The Stern Review estimated that without action, climate change could cost between 5-20% of global GDP annually.

Mitigation and adaptation

Mitigation

Climate change mitigation involves reducing greenhouse gas emissions and enhancing carbon sinks. Key strategies include transitioning to renewable energy, improving energy efficiency, protecting forests, and developing carbon capture technologies.

Adaptation

Climate adaptation involves adjusting to actual or expected climate change effects. This includes building sea walls, developing drought-resistant crops, improving water management, and creating early warning systems for extreme weather.

International response

The international community has responded through agreements such as the Paris Agreement, which aims to limit global warming to well below 2°C above pre-industrial levels. The Intergovernmental Panel on Climate Change (IPCC) provides scientific assessments on climate change for policymakers worldwide.