“Human greenhouse-gas emissions have driven most global warming since the mid-20th century, while solar variability has contributed only a small amount.”

• IPCC AR6 WG1 (2021) Summary for Policymakers concludes it is 'unequivocal that human influence has warmed the atmosphere, ocean and land,' and attributes a best estimate of 1.07 °C of the ~1.09 °C of observed warming (1850–1900 to 2010–2019) to human-caused greenhouse gases plus aerosols — i.e., essentially all of it, which comfortably satisfies 'most'.
• IPCC AR6 gives the best estimate of solar and volcanic (natural) forcing contribution to 1850–2019 surface warming as about -0.1 to +0.1 °C — effectively negligible compared with ~1.0–2.0 °C of warming from well-mixed greenhouse gases (partly offset by aerosol cooling).
• Direct satellite measurements of total solar irradiance since 1978 show a flat-to-slightly-declining trend across solar cycles, while global surface temperature rose roughly 0.2 °C per decade — the two have diverged for over four decades, ruling out the Sun as the dominant driver of recent warming.
• Fingerprint evidence is inconsistent with solar forcing and consistent with greenhouse forcing: the stratosphere has cooled while the troposphere and surface warmed, nights have warmed faster than days, and winters faster than summers. Increased solar output would warm the stratosphere as well.
• Radiative-transfer physics plus measured CO2 rise (~280 ppm pre-industrial to >420 ppm today) yields a forcing of roughly 2.2 W/m² from CO2 alone, versus ~0.0–0.1 W/m² from solar changes since 1750 (IPCC AR6 Chapter 7). Satellite spectroscopy has directly measured the increase in downward longwave radiation at CO2 and CH4 wavelengths.
• Isotopic (declining 13C/12C and 14C ratios) and oxygen-depletion evidence confirms the atmospheric CO2 increase is from fossil fuel combustion, tying the forcing unambiguously to human emissions.
• Independent national and international assessments converge: the U.S. Fourth National Climate Assessment / Climate Science Special Report states there is 'no convincing alternative explanation' and that human activities caused the 'substantial majority' (likely 93–123%) of observed 1951–2010 warming; the Royal Society–U.S. National Academy of Sciences joint report reaches the same conclusion.
• Carbon Brief's review of multiple independent attribution studies finds human forcings account for ~100% (and in several analyses slightly more than 100%, offset by natural cooling factors) of observed warming since 1950.

• The word 'most' is technically an understatement rather than an error: the mainstream estimate is that humans caused essentially 100% of post-1950 warming, with natural factors near zero or slightly negative. A pedant could call 'most' imprecise, but it is not false.
• Attribution carries real uncertainty, dominated by poorly constrained aerosol cooling (AR6 best estimate about -1.1 W/m², with a wide range) and by estimates of internal variability (e.g., Atlantic and Pacific multidecadal variability), which some researchers argue could account for a modest fraction of multidecadal trends.
• Reconstructions of pre-satellite solar irradiance differ: some older reconstructions imply a larger solar increase over the early 20th century, so the solar share of warming before ~1950 is larger than it is after 1950. The claim is correctly limited to the mid-20th century onward, but solar forcing is not trivial over the full industrial period.
• A minority of researchers (e.g., Svensmark and colleagues on cosmic-ray/cloud coupling, or Scafetta's solar-cycle analyses) argue for amplified indirect solar effects. These mechanisms have not held up in CERN CLOUD experiments or in observational cloud records and are rejected by the assessment literature, but they are a nonzero dissenting line of work.
• 'Greenhouse-gas emissions' is a slight simplification: human-caused warming also includes land-use change and black carbon, and is partly masked by human-caused aerosol cooling, so the net human contribution involves several forcings rather than greenhouse gases alone.

97/100 — the lab’s own confidence in the score above, not a second reading of the claim.

IPCC (AR6 Working Group I, Summary for Policymakers)journal · 99 · IPCC AR6 WG1 Ch.3: Human Influence on the Climate Systemjournal · 98 · IPCC AR6 WG1 Ch.7: The Earth's Energy Budget, Climate Feedbacks and Climate Sensitivityjournal · 98 · NASA Global Climate Change — Causesgov · 96 · USGCRP Climate Science Special Report (NCA4 Vol. I), Executive Summarygov · 96 · U.S. Fourth National Climate Assessment, Ch.2 Our Changing Climategov · 95 · Royal Society & U.S. National Academy of Sciences, 'Climate Change: Evidence and Causes'edu · 97 · NOAA Climate.gov — Climate Change: Incoming Sunlightgov · 94 · Carbon Briefnews · 85 · Skeptical Scienceother · 75 · U.S. Environmental Protection Agency — Causes of Climate Changegov · 92

• IPCC AR6 finds it is unequivocal that human influence has warmed the climate system and estimates that greenhouse gases caused substantial warming, while aerosols offset some of it; the assessed contribution from solar and volcanic drivers to 2010-2019 warming relative to 1850-1900 is near zero, with a small uncertainty range.
• Satellite-era solar observations show no sustained upward trend in the Sun's energy output since the late 1970s, while global surface temperature has continued to rise sharply; this timing supports greenhouse gases rather than solar variability as the dominant driver.
• Attribution studies using observations and climate models find that greenhouse gases account for most or more than all of the observed warming since the mid-20th century, with human aerosol pollution masking part of that warming and natural forcings, including solar, contributing little.
• The vertical pattern of warming also supports greenhouse forcing: the lower atmosphere and surface have warmed while the stratosphere has cooled, a fingerprint expected from greenhouse-gas increases and not from a brighter Sun.

• Solar variability is not literally zero: the 11-year solar cycle and longer-term changes can produce small climate effects, especially on short timescales or regionally, so the claim is strongest when interpreted as global, multi-decadal warming since the mid-20th century.
• Attribution has uncertainty because aerosols, volcanic eruptions, ocean variability, and measurement differences complicate the exact partition of warming. However, those uncertainties do not overturn the conclusion that greenhouse gases dominate and solar variability is small.
• Some researchers have proposed larger solar contributions, especially for earlier 20th-century warming, but these claims are not the mainstream assessment for warming since the mid-20th century and are outweighed by IPCC assessments, satellite solar records, and detection-attribution studies.

96/100 — the lab’s own confidence in the score above, not a second reading of the claim.

Intergovernmental Panel on Climate Changeother · 98 · NASAgov · 93 · U.S. Global Change Research Programgov · 95 · Nature Geosciencejournal · 92 · Geophysical Research Lettersjournal · 88

• The Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6) states that it is 'unequivocal that human influence has warmed the atmosphere, ocean and land,' identifying human-emitted greenhouse gases as the primary driver of global warming since the mid-20th century.
• NASA and the Royal Society report that satellite measurements since the late 1970s show no net increase in the Sun's energy output. In fact, solar irradiance has slightly declined over the last few decades, a period that coincides with the most rapid increase in global temperatures.
• Comparisons of radiative forcing (the difference between incoming and outgoing energy in the Earth's system) show that the warming effect of human-produced greenhouse gases is magnitudes larger than the negligible influence of variations in solar irradiance since 1750.

• A small minority of researchers (such as Henrik Svensmark) have proposed the 'cosmic ray hypothesis,' suggesting that solar variability indirectly affects the climate by modulating galactic cosmic rays, which could theoretically influence cloud formation and reflect sunlight.
• A handful of contrarian studies published outside the mainstream consensus argue for higher solar climate sensitivity, asserting that natural cycles play a larger role. However, these hypotheses have been repeatedly tested and largely dismissed by the broader scientific community because they cannot account for the observed rapid warming and atmospheric patterns (like stratospheric cooling) seen over the past 70 years.

99/100 — the lab’s own confidence in the score above, not a second reading of the claim.

Intergovernmental Panel on Climate Change (IPCC)gov · 99 · NASAgov · 98 · The Royal Societyedu · 95

• IPCC Sixth Assessment findings summarized by the U.S. Congressional Research Service estimate that well-mixed human greenhouse gases contributed 1.0–2.0°C of warming, while natural drivers contributed only −0.1 to +0.1°C over the relevant period. This supports the wording “most global warming.”[https://www.congress.gov/crs_external_products/R/PDF/R47082/R47082.3.pdf]
• NASA reports that climate simulations including only solar variability and volcanic aerosols reproduce observed temperatures only until about 1950; thereafter they cannot reproduce the warming without human greenhouse-gas increases.[https://science.nasa.gov/earth/climate-change/global-warming/]
• NASA states that solar energy received by Earth has shown no net increase since the 1950s while global temperature has risen substantially, and that observed surface warming combined with stratospheric cooling is inconsistent with increased solar output as the main cause.[https://science.nasa.gov/climate-change/faq/is-the-sun-causing-global-warming/]
• The National Academies conclude that rigorous analysis shows most observed global warming over roughly the past 50 years cannot be explained by natural causes and requires a significant human influence.[https://nap.nationalacademies.org/read/25733/chapter/5]
• The National Academies report that recent solar forcing is estimated at about +0.01 W/m², roughly 300 times smaller than anthropogenic forcing.[https://www.nationalacademies.org/read/29239/chapter/4]

• Solar variability is a real climate influence and can affect temperatures from decade to decade; therefore “only a small amount” should not be interpreted as zero contribution.[https://science.nasa.gov/earth/climate-change/global-warming/]
• The statement does not specify a quantitative period or warming metric. Attribution estimates vary somewhat depending on whether the comparison begins in the mid-20th century, uses surface temperature or another metric, and accounts for aerosols and internal variability.[https://www.congress.gov/crs_external_products/R/PDF/R47082/R47082.3.pdf]
• Human greenhouse gases are not the only human climate influence: anthropogenic aerosols have exerted a substantial cooling effect, so the claim is accurate about the dominant driver but simplifies the full human attribution of observed warming.[https://www.congress.gov/crs_external_products/R/PDF/R47082/R47082.3.pdf]

98/100 — the lab’s own confidence in the score above, not a second reading of the claim.

U.S. Congressional Research Service, summarizing IPCC AR6gov · 98 · NASA Sciencegov · 97 · NASA Sciencegov · 97 · NASA Sciencegov · 97 · National Academies of Sciences, Engineering, and Medicineedu · 98 · National Academies of Sciences, Engineering, and Medicineedu · 98

• IPCC AR6 finds it unequivocal that human influence warmed the climate system; well-mixed greenhouse gases are the dominant driver of the observed rise since the mid-20th century, with best-estimate human-caused warming (~1.07°C from 1850–1900 to 2010–2019) matching observed warming.
• Satellite total solar irradiance records since 1978 show no rising trend; solar output has been flat to slightly declining while surface temperatures rose sharply.
• CMIP detection-and-attribution experiments: natural-only (solar + volcanic) simulations do not reproduce post-1950 warming; adding anthropogenic GHG (and aerosol) forcings does.
• Observed vertical fingerprint—tropospheric warming plus stratospheric cooling—matches greenhouse-gas forcing and is inconsistent with increased solar output, which would warm the stratosphere.
• AR6 effective radiative forcing from anthropogenic well-mixed GHGs far exceeds estimated solar ERF (near zero over 1750–2019, and not positive since the mid-20th century).

• A minority of TSI reconstructions that imply a larger secular 20th-century solar increase have been used to argue solar variability explains more of the early- and mid-century warming (though they do not account for post-1980 warming under declining or flat TSI).
• Residual uncertainty in aerosol cooling and internal variability (e.g., Atlantic Multidecadal Oscillation) means the exact GHG share has a range, so a few papers assign a larger natural fraction to recent decades.
• Unconfirmed amplifying mechanisms (cosmic-ray/cloud hypotheses) have been proposed; they remain unsupported by the bulk of observational and experimental evidence (including CERN CLOUD results) and are not adopted in IPCC assessments.

92/100 — the lab’s own confidence in the score above, not a second reading of the claim.

IPCCother · 97 · NASAgov · 95 · NOAAgov · 94 · U.S. Global Change Research Programgov · 93 · UK Met Officegov · 92