Over the past 400,000 years, temperatures went up and down between 16°C and 6°C. The image below, from an earlier post, shows that temperatures moved up and down by roughly 10°C (18°F) between glacial and inter-glacial phases of ice ages, in line with Milankovitch cycles.

As the image also shows, a 100 ppm rise of carbon dioxide and 300 ppb rise of methane go hand in hand with a 10°C temperature rise. In other words, it looks like high levels of greenhouse gases in the atmosphere have already locked us in for a future temperature rise of 10°C.

Currently, we are at the peak of a Milankovitch cycle, or just passed the most recent peak. If temperatures were to rise by some 8.1°C, they would reach a level virtually unprecedented in the history of Earth (image right).

The extinction page describes the elements of a potential temperature rise of 8.1°C. Note that this 8.1°C rise comes on top of the temperature rise that has already occurred from preindustrial to 2016.

Below follows some further background on the figures used in above image.

In 1951-1980, NASA's default baseline, the temperature was 14°C (57.20°F).

In 1900, it was 13.72°C (56.70°F), assuming that temperatures had risen by 0.28°C from 1900 to the baseline of 1951-1980, as the trend line below indicates (from an earlier post).

In 1750, it was 13.42°C (56.16°F), assuming temperatures were 0.58°C below the baseline of 1951-1980, i.e. some 0.3°C lower than in 1900, as discussed in an earlier post.

In 2015 (Jan-Dec), the temperature was 0.85°C above baseline (see top image on the right), so it was 14.85°C (58.73°F) in 2015.

In 2016 (Jan-Dec), it was 1.00°C above baseline (see bottom image on the right), so it was 15.00°C (59.00°F) in 2016.

In 2026, it will be 23.10°C (73.62°F) if temperatures were to rise by 8.10°C from 2016 to 2026. A monthly peak could take the temperature up to 23.44°C (more than 10°C above preindustrial). Such temperatures would be hotter than it has been for 500 million years. Note also that the high temperatures during mass extinctions were reached gradually over many years, whereas the current rise threatens to reach such a peak in just ten years time. Up to 96% of all marine species and 70% of terrestrial vertebrate species became extinct when temperatures rose by 8 °C (14 °F) during the Permian-Triassic extinction, or the Great Dying, 252 million years ago. During the Paleocene/Eocene Thermal Maximum (PETM), which occurred 55 million years ago, global temperatures rose by 5°C in ~13 years.

In the video below, Guy McPherson discusses the situation.


• Climate Plan

• Extinction page

• How much warming have humans caused?

• Mean methane levels reach 1800 ppb

• NASA, The Elusive Absolute Surface Air Temperature (SAT)

• NASA, decadal temperature

• Horizontal graph by Chris Scotese

• The original vertical graph by Chris Scotese from the wayback machine

• August 2016 another month above Paris Agreement guardrail

• The Paleocene-Eocene Thermal Maximum (PETM)

• Permian-Triassic extinction, or the Great Dyinghttps://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extinction_event

• Abrupt Climate Change

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