What are Human-Induced Global Warming and Observed Global Warming?

Human-induced and observed global warming are two related indicators of global warming for comparing the observed (actual) warming to the warming attributed to human activities.

What is the difference between observed and human-induced warming?

Observed warming is the measured temperature of the planet, and is directly related to the impacts of climate-related events in a given year; it is therefore useful for planning climate adaptation. However, this value fluctuates quite a lot each year due to natural processes such as solar variation, volcanic eruptions, and El Niño oscillations; these yearly fluctuations mean that it can be difficult to see how close the current climate is to long-term average temperatures such as the 1.5 °C (2.7 °F) and 2 °C (3.6 °F) stabilization targets set out in the Paris Agreement.

Scientists, therefore, use techniques called “Detection and Attribution” to separate the “noise” of these naturally caused fluctuations from the “signal” of human-induced warming (sometimes also called anthropogenic warming). Human contributions to warming come from well-mixed greenhouse gases (consisting of CO2, CH4, N2O, and F-gases) and other human forcings (consisting of aerosol radiation interaction, aerosol-cloud interaction, black carbon on snow, contrails, ozone, stratospheric H₂O, and land use). Human-induced warming is directly related to human activities and changes predictably and smoothly each year, making it useful for planning climate mitigation.

What is the difference between decade-average and single-year warming?

Two definitions were used to report recent levels of human-induced warming in the IPCC' latest 6th Assessment Cycle: the decade-average and single-year values. The decade-average definition was used in the IPCC's 6th Assessment Report, and the single-year definition was used in its Special Report on Global Warming of 1.5 °C. The results for both definitions were updated in the Indicators of Global Climate Change 2023 paper using identical datasets and methods, which means that the two definitions are fully consistent with each other.

Since climate change is defined as the change in average conditions (such as temperature) over a long period of time, the benefit of calculating human-induced warming by removing natural fluctuations is that it "live" tracks the signal of climate change over time, avoiding potential misconceptions resulting from short-term fluctuations due to natural processes that don't contribute to the longer-term climate average.

Observed warming is therefore often reported using the decade-average value as a measure of how the overall climate has changed. Calculating the decade-average value of human-induced warming is, therefore, useful to compare how much of the observed long-term climate trend results from human activities. In 2023, the 2014-2023 averages for observed and human-induced warming were both at 1.19 °C (2.14 °F), demonstrating that almost all observed changes are a result of human activity.

While the single-year observed warming isn't as useful as an indicator of overall long-term climate change due to natural fluctuations each year, the human-induced warming level in a single year remains a good indicator of the level of climate change because these fluctuations have been filtered out. However, the single-year observed warming remains a useful indicator of expected climate impacts in a given year. In 2023, the observed and human-induced warming were 1.43 °C (2.57 °F) and 1.31 °C (2.36 °F), respectively, demonstrating the higher relative significance of natural fluctuations in a single year compared to the decade average.

Note that the decade-average warming is calculated for the most recent decade and the single-year warming is calculated for the most recent year; this results in a “lag” of around 5 years between them. For example, for the 2023 calculations, the 2014-2023 decade average is centered around 2018, whereas the 2023 single-year is centered on 2023.

Units and measures

Degrees Celsius (°C) or degrees Fahrenheit (°F). Numerical ranges of confidence are presented in this text using square [ ] brackets.

Insights from this chart

The chart emphasizes the difference between the steadily increasing human-induced temperature and the fluctuating increase in the observed warming. The constant fluctuations of increases and decreases in the observed temperature are very visible for the yearly values. Long-term climate change mitigation efforts should not be based on these yearly fluctuations, but should instead be based on the steady human-induced warming.

Despite the difference, both temperature indicators are linked and are continuing to increase without showing any signs of slowing down.

About the data

Climate Change Tracker is part of the Indicators of Global Climate Change (IGCC) initiative to spread indicators of climate change that are consistent with the IPCC Assessment Report 6. The IGCC produces estimates for key climate indicators: emissions of greenhouse gases and short-lived climate forcers, greenhouse gas concentrations, radiative forcing, surface temperature changes, the Earth’s energy imbalance, warming attributed to human activities, the remaining carbon budget, and estimates of global temperature extremes.

Comparison with IPCC Assessment Report 6

In IPCC AR6 (WG1 Chap. 3 Sect. 3.3.1.1.2) for the 2010–2019 period, human-induced warming averaged 1.07 [0.8 to 1.3] °C (1.94 [1.4 to 2.3] °F). The newly repeated calculation for the same period resulted in the same numbers, and since then the warming has increased to 1.19[1.06 to 1.30] °C (2.14[1.91 to 2.34] °F) for the currently most up-to-date period of 2014-2023.

Regarding the observed warming in IPCC AR6 (Chap. 3 Sect. 3.3.1.1.2) for the 2010–2019 period, human-induced warming averaged 1.06 [0.88 to 1.21] °C (1.91 [1.58 to 2.18] °F). The newly repeated calculation for the same period resulted in 1.07 [0.89 to 1.22] °C (1.93 [1.60 to 2.20] °F), and since then the warming has increased to 1.19[1.06 to 1.30] °C (2.14[1.91 to 2.34] °F) for the currently most up-to-date period of 2014-2023.

Comparison with the IPCC Special Report Global Warming of 1.5 °C

The IPCC Special Report 1.5 (Chap. 1 Sect. 1.2.1.3) originally reported the human-induced warming per year, and for 2017 it reported 1.0 [0.8 to 1.2] °C (1.8 [1.4 to 2.2] °F). Based on the new recalculation, it is now projected that in 2017 human-induced warming was 1.15 [0.9 to 1.4] °C (2.07 [1.6 to 2.5] °F) with values for 2023 having risen to 1.31 [1.1 to 1.7] °C (2.36 [2.0 to 3.1] °F).

Data sources

IGCC Indicators of Global Climate Change 2023: annual update of key indicators of the state of the climate system and human influence, Piers M. Forster et al.
Credits: Credits: Smith, C., Walsh, T., Gillett, N., Hall, B., Hauser, M., Krummel, P., Lamb, W., Lamboll, R., Lan, X., Muhle, J., Palmer, M., Ribes, A., Schumacher, D., Seneviratne, S., Trewin, B., von Schuckmann, K., & Forster, P. (2024). ClimateIndicator/data: Indicators of Global Climate Change 2023 revision (v2024.05.29a) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.8000192Update cycle: yearlyDelay: mixed