A Temperature Rise Of 18 Degrees Celsius

When looking only at carbon dioxide (CO₂) and methane (CH₄), how much temperature rise could they cause?

Above image shows methane in ppm CO₂e (carbon dioxide equivalent), using a Global Warming Potential (GWP) of 150. The image shows how carbon dioxide and methane could jointly cross 1200 ppm CO₂e in 2040. The image uses IPCC and WMO data up to 2018 to display three lines:
1. Black line: CO₂ in parts per million (ppm);
2. Red line: CH₄ in ppm CO₂e, using a GWP of 150;
3. Purple line: CO₂ and CH₄ in ppm CO₂e.
Trends are added, with a trend selected for methane to reflect a steep rise due to methane hydrate destabilization.

How likely is it that such a high CO₂e will be crossed? In the screenshot below, the high-end of the A1F1 scenario used by the IPCC reaches a CO₂e level of 1550 ppm by the year 2100. 

Temperature rise for February 2016 versus 1951-1980.
Next to carbon dioxide and methane, there are further warming elements such as aerosol changes, albedo changes, water vapor and nitrous oxide that come on top of the temperature rise that had already occurred.

How much warming has already occurred? In the NASA image on the right, the February 2016 anomaly compared to 1951-1980 is 1.36°C, but when going back to the year 1900, the February 2016 anomaly compared to 1900 (i.e. 1885-1914) is 1.70°C, as illustrated by the image underneath that uses a baseline of 1885-1914.  

Temperature rise for February 2016 versus 1900.
In the 2016 analysis, the February 2016 rise from 1900 was given a value of 1.62°C, a figure that is easier to use in forward projections up to 2026, given that February 2016 was a peak. 

Furthermore, an additional 0.3°C was added for temperature rise from pre-industrial to 1900.  Later analyses such as this one also added a further 0.2°C to the temperature rise, to reflect ocean air temperatures (rather than water temperatures) and higher polar anomalies (note the grey areas on the image in the right).

Anyway, a value of 1.62°C was used in the initial analysis for the February 2016 rise from 1900. The image on the right illustrates the potential for a global temperature rise of more than 10°C (18°F) by 2026, based on February 2016 data by making a 10-year projection using a relatively high temperature rise scenario resulting from progressive growth in warming elements, as discussed in posts of March 11 and March 13, 2016.  

The image on the right features at the extinction page and updates an earlier image by adding in the text that aerosol changes include both loss of cooling aerosols (e.g. sulfates) and a rise in heating aerosols (e.g. black carbon and brown carbon), as also discussed at the aerosols page

The image below, from a 2017 post, spreads out the temperature rise with the stacked bars flipped upside down, to get the rise that has already occurred at the bottom. Bars are centred around February for each year. 

[ from a 2017 post ]

As it turned out later (in 2020), the above projections for the rises in February 2018, 2019 and 2020 were too high. Feedbacks did not start to kick in as much yet, fortunately, while the temperature rise in 2020 also turned out to be suppressed by an El Nino and low sunspots. 

In a February 2019 analysis, an 8°C rise for the clouds feedback was added, which would come on top of the warming that would already have occurred in 2026 due to other warming elements, resulting in a total rise of as 18°C or 32.4°F from preindustrial, as shown on the image below. The analysis used a value of 1.85°C for the 1750-2019 rise, a value that was maintained for the other years. The image is below. 

A 2020 analysis for the post There is no time to lose resulted in the update for the 10°C temperature rise image, displayed below, a rise that could go well beyond 10°C, as discussed below. 

[ from the post There is no time to lose ]

Importantly, growth in warming elements can occur in several ways and still result in the cloud tipping point getting crossed.

As an example, even when just adding up carbon dioxide and methane, the 1200 ppm CO₂e tipping point could be crossed very quickly in case of large, abrupt methane releases from hydrates, as warned about by Shakhova et al. and as discussed in an earlier post

On May 15, 2019, scripps.ucsd.edu recorded a carbon dioxide level of 415.7 ppm at Mauna Loa, Hawaii. NOAA recorded a methane level of 1.867 ppm for December 2018.

As shown at the FAQ page, methane is 150 times as potent as a greenhouse gas over the next ten years compared to carbon dioxide. Accordingly, this 1.867 ppm of methane causes global heating of 280.05 ppm CO₂e. 

[ from earlier post ]
Imagine a burst of methane erupting from the seafloor of the Arctic Ocean that would add an amount of methane to the atmosphere equal to twice the methane that is already there. 

Twice the 1.867 ppm of methane is 3.734 ppm, which at 150 times the potency of carbon dioxide translates into a CO₂e of 560.1 ppm. 

Adding this to recent levels of carbon dioxide and methane results in a level of 1255.85 ppm CO₂e, well exceeding the 1,200 ppm CO₂e tipping point and thus triggering an extra 8°C rise.

How likely is such a huge methane release? Seafloor methane releases could be triggered by strong winds causing an influx of warm, salty water into the Arctic ocean, as described in an earlier post. A study published in 2012 calculates that 1000-fold methane increase could occur resulting in a rise of as much as 6°C within 80 years, with more to follow after that.

In conclusion, when adding further warming elements, the 1,200 ppm CO₂e tipping point could be reached in one decade, and a 8°C clouds feedback could come on top of a rise of 10°C by 2026, resulting in a total 18°C rise, as illustrated by the image on the right, from an earlier post.

The situation is dire and calls for immediate, comprehensive and effective action, as described in the Climate Plan.



• WMO Greenhouse GasBulletin

• Understanding the Permafrost–Hydrate System and Associated Methane Releases in the East Siberian Arctic Shelf, by Natalia Shakhova, Igor Semiletov and Evgeny Chuvilin (2019)

• Possible climate transitions from breakup of stratocumulus decks under greenhouse warming, by Tapio Schneider et al. (2019)

• Ten Degrees Warmer In A Decade?

• February Temperature

• A Global Temperature Rise Of More than Ten Degrees Celsius By 2026?

• How Much Warming Have Humans Caused?

• Temperature Rise

• A rise of 18°C or 32.4°F by 2026?

• Aerosols

• When will we die?

• There is no time to lose

• Climate Plan