Are humans responsible for climate change?

Humans and climate change — I'll gather the latest scientific consensus on our role.

Yes — according to the overwhelming scientific consensus, humans are responsible for modern climate change.

1. What the major scientific bodies say

> Scientific evidence continues to show that human activities (primarily the human burning of fossil fuels) have warmed Earth's surface and its ocean basins, which in turn have continued to impact Earth's climate.

•Multiple studies published in peer-reviewed scientific journals show that climate-warming trends over the past century are extremely likely due to human activities.

•Joint statement from 18 scientific associations: "Observations throughout the world make it clear that climate change is occurring, and rigorous scientific research demonstrates that the greenhouse gases emitted by human activities are the primary driver."

•American Association for the Advancement of Science: "Based on well-established evidence, about 97% of climate scientists have concluded that human-caused climate change is happening."

•American Geophysical Union: "Based on extensive scientific evidence, it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century."

•The Intergovernmental Panel on Climate Change (IPCC) — the UN body that synthesizes climate science from thousands of experts worldwide — states:

> “It is unequivocal that the increase of CO2, methane, and nitrous oxide in the atmosphere over the industrial era is the result of human activities and that human influence is the principal driver of many changes observed across the atmosphere, ocean, cryosphere, and biosphere.”

The same conclusion is repeated in NASA's summary of the IPCC Sixth Assessment Report: it is unequivocal that the increase of CO2, methane, and nitrous oxide in the atmosphere over the industrial era is the result of human activities and that human influence is the principal driver.

In its Sixth Assessment Report the IPCC concluded that human activities, principally through greenhouse gas emissions, have unequivocally caused global warming.

2. How scientists know it is human-caused

a) The greenhouse effect expanded by humans:
Scientists attribute the global warming trend observed since the mid-20th century to the human expansion of the "greenhouse effect" — warming that results when the atmosphere traps heat radiating from Earth toward space.

The five key greenhouse gases are carbon dioxide, nitrous oxide, methane, chlorofluorocarbons, and water vapor. Human activities, especially burning fossil fuels and deforestation, have increased their concentrations.

b) Measurable human fingerprint:
The industrial activities that our modern civilization depends upon have raised atmospheric carbon dioxide levels by nearly 50% since 1750. Scientists can see a distinctive isotopic fingerprint in the atmosphere confirming the increase is due to human activities.

c) Natural causes ruled out:
While the Sun has played a role in past climate changes, the evidence shows the current warming cannot be explained by the Sun.

Specifically:

•Since 1750, the average amount of energy from the Sun either remained constant or decreased slightly.

•Studies show solar variability has played a role in past climate changes, but several lines of evidence show that current global warming cannot be explained by changes in energy from the Sun.

Climate models that include solar changes can't reproduce the observed temperature trend over the past century without including a rise in greenhouse gases.

3. How strong is the consensus?

Multiple methods — surveys of experts and massive literature reviews — converge on an overwhelming consensus that humans are the main cause of contemporary climate change: classic estimates cluster around 97%, recent multi-country studies and literature audits report agreement rates from ~97% to >99.9%.

This is not just one study. NASA lists nearly 200 worldwide scientific organizations that hold the position that climate change has been caused by human action, and notes that most leading scientific organizations worldwide have issued public statements endorsing this position.

In short: Natural climate variability exists, but the rapid warming observed since the mid-20th century is dominantly — and unequivocally in the language of the IPCC — caused by human emissions of greenhouse gases, primarily from burning coal, oil and gas, deforestation, agriculture and industrial processes.

Citations (1)

1nasa.govGovernment
Scientific Consensus - NASA Science
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