Are humans responsible for climate change?

Yes, the overwhelming scientific consensus is that human activities are the primary driver of the climate change observed since the mid-20th century. Here's why scientists have reached this conclusion:

Key Evidence

Greenhouse gas emissions
Human activities—primarily burning fossil fuels (coal, oil, and natural gas), deforestation, and industrial processes—have significantly increased the concentration of greenhouse gases in the atmosphere, especially carbon dioxide (CO₂) and methane (CH₄). CO₂ levels have risen from about 280 parts per million (ppm) before the Industrial Revolution to over 420 ppm today, a level not seen in at least 800,000 years based on ice core data.

The greenhouse effect
These gases trap heat in the atmosphere that would otherwise radiate into space. This is basic, well-understood physics (the same principle used in satellite instruments and demonstrated in laboratory settings), and increasing concentrations of these gases logically leads to more heat retention.

Attribution studies
Climate scientists use sophisticated models to compare observed warming with what would be expected from natural factors alone (solar activity, volcanic eruptions, natural climate cycles) versus natural + human factors. These models consistently show that natural factors alone cannot explain the rate and pattern of warming observed since the 1950s—human emissions are needed to account for it.

Scientific consensus
Major scientific organizations worldwide—including NASA, NOAA, the IPCC (Intergovernmental Panel on Climate Change), national academies of science from numerous countries, and virtually every major scientific body studying climate—agree that human activity is the dominant cause of recent warming. This consensus is based on decades of peer-reviewed research across multiple independent lines of evidence.

What This Means

While natural climate variability exists and has always been part of Earth's history, the current rate and magnitude of warming is unusual and best explained by human-caused increases in greenhouse gases. This is one of the most thoroughly studied and well-supported conclusions in modern science.