Are humans responsible for climate change?

Are humans responsible for climate change? I'll gather the latest scientific evidence on our role.

Yes — according to the overwhelming scientific evidence, humans are the principal cause of recent climate change, though natural factors also influence climate.

Scientific Consensus

> There is unequivocal evidence that Earth is warming at an unprecedented rate. Human activity is the principal cause.

> The global warming trend observed on Earth since the mid-20th century is caused by human activities.

Multiple independent analyses of the peer-reviewed literature and surveys of climate experts put agreement that humans are causing recent warming at roughly 97% or higher, with authoritative bodies treating the evidence as beyond reasonable scientific dispute.

The Intergovernmental Panel on Climate Change (IPCC), the UN body that assesses climate science, stated in its Sixth Assessment Report (AR6, 2021):

> "It is unequivocal that human influence has warmed the atmosphere, ocean, and land."

The report reinforces earlier assessments:

> The AR6 report reinforces earlier IPCC scientific assessments that human activities are the primary driver of many of these observed changes.

Why scientists attribute warming to humans

1. Greenhouse gas emissions from human activities:

Human-made emissions in the atmosphere, rapid, unsustainable deforestation, and the increases in non-reflective surfaces, like asphalt, are all examples of human activities amplifying the greenhouse effect, trapping and slowing heat loss to space

The IPCC found:

> Observed increases in well-mixed greenhouse gas (GHG) concentrations since around 1750 are unequivocally caused by human activities.

Since the Industrial Revolution, concentrations of greenhouse gases such as carbon dioxide, methane and nitrous oxide have risen, with CO2 rising from about 280 parts per million to over 410 ppm — and isotopic fingerprinting shows the source is fossil fuels, not natural sources like volcanoes or forest fires.

Analysis of IPCC findings summarized as:

> Humans emissions and activities have caused around 100% of the warming observed since 1950

2. Ruling out natural causes alone:

> We know this warming is largely caused by human activities because the key role that carbon dioxide plays in maintaining Earth’s natural greenhouse effect has been understood since the mid-1800s.

> Finally, no other known climate influences have changed enough to account for the observed warming trend. Taken together, these and other lines of evidence point squarely to human activities as the cause of recent global warming.

In particular, solar activity cannot explain current warming:

> The amount of solar energy Earth receives has followed the Sun's natural 11-year cycle of small ups and downs, with no net increase since the 1950s. Over the same period, global temperature has risen markedly. It is therefore extremely unlikely that the Sun has caused the observed global temperature warming trend over the past half-century.

Does natural climate change also happen?

Yes. Earth's climate has always varied due to natural factors including volcanic eruptions, changes in solar output, orbital variations (Milankovitch cycles), and internal variability. However, the current rate and magnitude of warming - about 1.0°C above 1850-1900 for 2011-2020, and 1.1°C when including more recent years - is occurring at an unprecedented rate in at least the last 2,000 years, and climate models can only reproduce it when human-caused greenhouse gas forcing is included.

In summary, while natural processes contribute to climate variability, the unequivocal dominant driver of warming since the mid-20th century is human activity, primarily through burning of fossil fuels (coal, oil, gas), deforestation, and agriculture that increase heat-trapping greenhouse gases.