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This number shows an up-to-the-second assessment of human-induced global warming since the second half of the 19^th century. In the 2015 Paris Agreement countries around the world agreed to work towards keeping global warming below 2 degrees – and ideally at 1.5 degrees – in order to avoid the worst impacts of climate change.

Natural Contribution shows the estimated contribution to Earth's temperature change from natural causes, such as changes in solar activity and volcanic eruptions. These account for some of the variation in global temperatures, but they cannot explain the overall warming.

Human-Induced Contribution shows the estimated contribution from all human activities, including the burning of fossil fuels, other forms of pollution, and our changing uses of land. Since this line closely follows the temperatures observed in the real world, it shows that the observed warming can largely be attributed to human activity. However, it is not an exact match for observed temperatures.

Combined Response shows the combined impacts of human-induced and natural changes - this is the "signal". This line more closely matches the observed temperatures, and shows that human-induced changes, plus some natural forcing, has caused the global warming trend we see today.

Observations show real-world observations of global mean temperature. The Earths temperature has been steadily increasing since the 1960s, very close to the combined forced warming. Today, essentially all of the observed warming is human-induced. The uncertainty has decreased significantly since the 1950s, due to a huge increase in the quantity and quality of data.

Internal Variability is the "noise" contribution from natural fluctuations in the climate system, such as from El Niño and La Niña events, which cause the short-term fluctuations of the Observations above and below the Combined Response line. Internal Variability does not cause the long-term global warming trend, but does meaningfully contribute to annual extreme events.

Attribution science is used to separate out the various "signal" and "noise" contributions to global temperature change, using multiple lines of evidence, including observed temperature records, radiative forcing data, climate model simulations, and statistical methods. The results are consistent across these many different approaches, providing robust evidence for the human influence on global temperatures. Find out more about attribution science in this video from Dr Friederike Otto, one of the pioneers of attribution science.

See here for further details about the numbers, graphics, and methods used above, and an animation showing how the GWI attribution method works.

What contributes to human-induced global warming?

This number shows an up-to-the second assessment of cumulative carbon dioxide (CO₂) emissions. CO₂ emissions are the biggest contributor to human-induced climate change.

This number shows an up-to-the second estimate of all other non-CO₂ human influences on energy coming in and out of the Earth's atmosphere, measured in W/m². Depending on the specific activity and its history, these influences can either contribute to cooling and/or warming . While the specific warming and cooling profile of these other human influences vary, collectively they caused a slight masking of the warming from CO₂ emissions prior to the 1980s, and following then caused additional warming on top of the warming from CO₂ emisisons.

Why do net CO₂ emissions matter?

CO₂ emissions account for the majority of global warming. Warming from CO₂ emissions will continue to increase as long as the total amount of CO₂ cumulatively emitted continues to rise. When cumulative emissions stop increasing, the cumulative emissions line in the graph above flattens out, and so does the warming from CO₂.

The only way to stop additional warming from CO₂ emissions is to stop the increase in their cumulative emissions, which means reaching a state where net annual emissions of CO₂ (emissions minus removals) are zero: this is known as a state of 'net zero' carbon dioxide emissions.

In the 2015 Paris Agreement countries around the world agreed to work towards achieving 'net zero' carbon dioxide emissions. First and foremost, this means reducing CO₂ emissions. In order to meet climate targets, it will also be necessary to remove some CO₂ from the atmosphere. This could be done by through biological pathways such as forest restoration, or through technologies such as carbon capture and storage.

How do CO₂ emissions and other climate drivers contribute to global warming?

In the second figure above, the total human-induced global warming estimated from observed temperatures is given almost exactly by simply adding the warming caused cumulative CO₂ emissions to the temperature changes caused by other human activities: all lines of evidence agree on what is driving the global temperature change that we directly observe.

Human-induced warming (ΔT) over a time-interval ranging from seconds to decades is

• proportional to total cumulative carbon dioxide emissions over that time-interval (E)
• plus the impact of any change in global energy imbalance due to other human influences on climate (ΔF).

This relationship captures the main drivers of human-induced global warming, which can be written as a very approximate first-order equation:

where

• \( \kappa_E \) is the "Transient Climate Response to Emissions", about 0.45 (±0.18) °C per trillion tonnes of CO₂ (Arias et al., 2021: Technical Summary in IPCC AR6 WGI) .
• \( \kappa_F \) is the "Transient Climate Response to Forcing", about 0.42 (±0.10)°C per W/m² (Allen et al., 2022: Net Zero Science, Origins, and Implications) .

While the full scientific calculation of the Global Warming Index involves more accurate calculations, this simple equation is a good approximation of the main drivers of human-induced global warming.

See here for further details about the numbers, graphics, and methods used above, and an animation showing how the GWI attribution method works.