The Threat of Global Warming causing Near-Term Human Extinction

The Potential For Huge Abrupt Temperature Rise

How much could temperatures rise?

The image below shows that temperatures typically moved up and down by roughly 10°C (ten degrees Celsius, or eighteen degrees Fahrenheit, i.e. 18°F) between a glacial and interglacial phase of the ice ages, suggesting that 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.

[ from the post What Does Runaway Warming Look Like? ]

How fast could temperatures rise?

How fast could such a rise eventuate? There a number of reasons why - despite the high levels of greenhouse gases in the atmosphere - a huge temperature rise has until now unfolded only slowly, including:
  • Carbon dioxide emissions reach their greatest warming impact ten years after release. In other words, the full wrath of the carbon dioxide emitted over the past decade is yet to come.
  • A rapid temperature rise is held off by the temporary masking effect of aerosols emitted when burning fuel (especially sulfur dioxide from coal-fired power plants). Once this masking effect falls away, a huge sudden rise in temperature can be expected.
  • A rapid temperature rise is further held off by the fact that some feedbacks can take time to kick in. There is a huge (but decreasing) capacity of oceans, ice sheets and glaciers to act as a buffer for heat. Demise of the ice and snow cover in the Arctic and methane releases from the seabed of the Arctic Ocean can take time to eventuate and much sunlight is still reflected back into space by the snow and ice cover in the Arctic. However, even though their impact may now look only minimal, one or more feedbacks can cause a dramatic non-linear rise, speeding up the way one or more feedbacks kick in, not only in terms of progression of a non-linear rise, but also due to interaction between feedbacks.
[ Created by Sam Carana, part of AGU 2011 poster ]
As an example of a non-linear temperature rise, Arctic sea ice demise is causing more heat to be absorbed in the Arctic, resulting in further decline of the snow and ice cover, in turn causing more sunlight to be absorbed (rather than reflected back into space as before). This self-reinforcing feedback loop accelerates warming in the Arctic.

Much carbon is stored in large and vulnerable pools (see image below) that have until now been kept stable by low temperatures. A rapid temperature rise would hit vulnerable carbon pools hard, making them release huge amounts of greenhouse gases, further contributing to the acceleration of the temperature rise.

Image is from Monthly CO₂ not under 400 ppm in 2016.
1 Gigatonne (Gt) = 1 billion tonnes = 1 Petagram (Pg).
1 PgC = 3.664 Gt of CO₂. Oceans have absorbed some
40% of CO₂ emissions since the start of the industrial era.
Recent annual CO₂ take up by oceans is about 26%
(annual global average over 2006 - 2015).
The huge amounts of carbon at risk of getting into the atmosphere in the form of carbon dioxide and methane from above-mentioned vulnerable carbon pools comes on top of emissions caused by people such as the loss of 116 Gt of organic carbon from the top 2 m of soil to the atmosphere due to agriculture over the past 12,000 years, with the rate of loss increasing dramatically in the past 200 years.

study by Crowther et al. (2017) suggests that some 30 ± 30 Gt C could be lost from the top 10 cm surface soil for a 1°C, and some 55 ± 50 Gt C for a 2°C rise of global average soil surface temperatures, which would increase CO₂ levels in the atmosphere by some 25 ppm.

The study adds that, since high-latitude regions have the largest standing soil C stocks and the fastest expected rates of warming, the overwhelming majority of warming-induced soil C losses are likely to occur in Arctic and subarctic regions.

A study by Del Vecchi et al. (2024) suggests that a gradual thawing of Artic permafrost could release between 22 billion and 432 billion tons of carbon dioxide by 2100 if current greenhouse gas emissions are reined in — and as much as 550 billion tons if they are not.

The scenario of a rapid 10°C temperature rise thus becomes a distinct possibility when considering the size and vulnerability of some of the terrestrial and marine carbon pools and the combined warming impact of:
  • Carbon dioxide emitted over the past decade reaching their peak impact soon
  • Falling away of the masking effect that aerosols currently exercise over global warming; and
  • Feedbacks causing even higher levels of greenhouse gases (carbon dioxide, methane, water vapor, ozone, etc.), resulting in less heat being radiated from Earth, while increasingly less sunlight is getting reflected back into space (albedo decline).

The Potential For Huge Methane Releases

The methane feedback deserves some further attention. Note that the above Unesco image gives an estimate of 10x10³ or 10,000 Gt C for ocean methane hydrates, but that several studies give even higher estimates, as illustrated by the image below, from Pinero et al.

The amount of carbon stored in hydrates globally was in 1992 estimated to be 10,000 Gt (USGS), while a later source gives a figure of 63,400 Gt C for the Klauda & Sandler (2005) estimate of marine hydrates. 

Natalia Shakhova et al. in 2010 estimated the accumulated potential for the East Siberian Arctic Shelf (ESAS) region alone (image on the right) as follows:
• organic carbon in permafrost of about 500 Gt
• about 1000 Gt in hydrate deposits
• about 700 Gt in free gas beneath the gas hydrate stability zone.

Methane hydrates are present at many locations. Further warming of the Gulf Stream is causing methane eruptions off the North American coast. Methane eruptions from marine sediments have also been reported off the coast of New Zealand and in many further locations. 

[ click on images to enlarge ]
The map on the right shows the thickness of Northern Hemisphere permafrost below the seabed. Methane hydrates in marine sediments aren't the only type of hydrates that should be considered. Methane also appears to be erupting from hydrates on land in Siberia, on Antarctica, on the Qinghai-Tibetan Plateau and on Greenland. The hydrates are kept stable by the pressure of large volumes of snow and ice, but wild weather swings could cause cracks and the resulting pressure changes could destabilize such hydrates. Methane is also present in large quantities in lakes, such as at the bottom of Lake Baikal.

Methane contained in hydrates in sediments below the seabed isn't the only type of methane that should be regarded as a threat. Sediments at the seafloor can also contain methane in the form of free gas, typically below the permafrost, and this can be released due to rising temperatures that weaken the permafrost. Permafrost itself can also contain large amounts of carbon that could be transformed by microbes into methane as temperatures rise.

Methane underneath the permafrost and carbon contained in frozen sediments often has an organic origin. Additionally, there is mantel methane, which has a geological origin and can rise through the sediment in the form of free gas or can be sealed off by permafrost, unable to rise further until the permafrost thaws. Mantel methane can also form hydrates in marine sediments at the bottom edge of the permafrost.

The sheer size of the above carbon pools makes that there is a huge danger that methane levels in the atmosphere will grow rapidly, due to releases from methane hydrates and from terrestrial permafrost. What adds to the danger of such methane releases is that levels of greenhouse gasses in the atmosphere currently are very high and rising rapidly.

Abrupt Warming - How Much and How Fast?

How much could temperatures rise? The above 2017 image shows how a rapid rise of more than 10°C (18°F) could take place within a few years, resulting in mass extinction of many species, including humans.

How fast could temperatures rise? The trend in above image is based on NASA January 2012-February 2017 anomalies from 1951-1980, adjusted by +0.59°C to cater for the rise from 1750 to 1951-1980. The trend points at a 3°C rise in the course of 2018, which would be devastating. Moreover, the rise doesn't stop there and the trend points at a 10°C rise as early as the year 2021.

Is this polynomial trend the most appropriate one? This has been discussed for years, e.g. at the Controversy Page, and more recently at Which Trend Is best?

The bottom part of the above image shows the warming elements that add up to the 10°C (18°F) temperature rise. Figures for five elements may be overestimated (as indicated by the ⇦ symbol) or underestimated (⇨ symbol), while figures in two elements could be either under- or overestimated depending on developments in other elements. Interaction between warming elements is included, i.e. where applicable, figures on the image include interaction based on initial figures and subsequently apportioned over the relevant elements.

A closer look at each of these warming elements further explains why abrupt warming could take place in a matter of years. As far as the first two elements are concerned, i.e. the rise from 1900 and the rise from 1750 to 1900, this has already eventuated. The speed at which further warming elements can strike is depicted in the image below, i.e. the rise could for a large part occur within years and in some cases within days and even immediately.

Assessing the Danger

The danger can be looked at on three dimensions: timescale, probability and severity. On the severity dimension, a 10°C temperature rise is beyond catastrophic, i.e. we're talking about extinction of species at massive scale, including humans. On the probability dimension, the danger appears to be progressing inevitably toward certainty if no comprehensive and effective action is taken.

In terms of timescale, a 10°C temperature rise could eventuate within a matter of years, which makes the danger imminent, adding further weight to the need to start taking comprehensive and effective action, as described in the Climate Plan.

The Threat

With little or no action taken on global warming, it appears that the Anthropocene will lead to extinction of the very human beings after which the era is named, due to anthropogenic warming, with the Anthropocene possibly running from 1952 to 2021, i.e. a mere 69 years and much too short to constitute a geological era. Given the importance of the Paris Agreement and given that pre-industrial refers to a period prior to the Industrial Revolution, it makes more sense to move the start of the Antropocene back at least to 1750, which would extend its duration by about 200 years, but since anthropogenic warming had already started with earlier agriculture and deforestation, it makes even more sense to change the start of the Antropocene to an even earlier year. The importance of an early base as pre-industrial reference is that a larger temperature rise comes with stronger feedbacks and with the danger that emissions alone are no longer the dominant driver of the temperature rise, but that feedbacks have taken over as the main driver to further accelerate a runaway temperature rise.

Anyway, to highlight that the threat that extinction of humans and many other species could occur soon, it would be better to talk about the Sixth Extiction Event, or at least the threat thereof, as also illustrated by the image below.

[ See: Feedbacks in the Arctic and the Extinction page ]
In conclusion, it's high time that homo sapiens starts acting as genuinely wise modern human beings and commit to comprehensive and effective action as discussed at the Climate Plan.

Have warnings been given about this threat? 

Many posts have warned about this, e.g. Abrupt Warming - How Much And How Fast?Will humans be extinct by 2026? and Warning of mass extinction of species, including humans, within one decade

The danger was described back in 2007: Total Extinction.
The mechanism was depicted back in 2011: Runaway Global Warming.

Mechanisms behind a huge temperature rise have been discussed repeatedly, e.g. in this 2024 post

The IPCC keeps downplaying how dire the situation is we're in

As discussed in this 2024 post, the IPCC keeps giving the impression that the temperature rise is small, e.g. by using the period 1850-1900 as "reference", despite mounting evidence that the temperature rise is much larger, especially when calculated from a genuinely pre-industrial base. The IPCC also keeps giving the impression that there was a carbon budget to divide among polluters, a carbon budget large enough for polluters to keep polluting for decades to come, whereas there is just a huge carbon debt for which there is no short-term remedy.

A 2024 analysis concludes that Arctic terrestrial permafrost now emits more greenhouse gases than it stores, and the trend is likely to accelerate as temperatures keep rising in the Arctic. The highest carbon dioxide emissions over the 2000-2020 period came from inland rivers and wildfires. The non-permafrost wetlands exhaled the most methane, and dry tundra released the most nitrous oxide.

The joint CO₂e of emissions in this analysis only cover part of global emissions, e.g. the analysis excludes emissions from Arctic subsea permafrost and from oceans in general, from many mountain areas and from the Southern Hemisphere. The study also appears to have excluded emissions caused by anthropogenic disturbances such as clear-cutting, logging and fracking activities in the region, while calculations typically use a low global warming potential (GWP) for methane (100-year horizon).

The prospect of further releases looks dire. The analysis gives estimates that the upper three meters of permafrost region soils store 1,000 Gt of soil organic carbon, while deeper deposits could store an additional amount of as much as 1,000 Gt C. The analysis concludes that the permafrost region is the largest terrestrial carbon and nitrogen pool on Earth. Miesner et al. (2023) warn that an additional 2822 Gt of organic carbon is stored in subsea Arctic shelf permafrost and Huang et al. (2024) warn that the top two meters of soil globally holds about 2300 Gt of inorganic carbon, which has been left out of environmental models, and 23 Gt of this carbon may be released over the next 30 years.

The transition from sink to source of the region is an important feedback of the temperature rise that is not fully reflected in many climate models. According to the IPCC, 14–175 Gt CO₂e (in carbon dioxide and methane) gets released per 1°C of global warming, which is likely to underestimate the situation by downplaying many feedbacks. Despite the dire situation, the IPCC keeps promoting less effective policies such as support for biofuel and fuel efficiency standards, as discussed in earlier posts such as this 2022 one.

Climate Emergency Declaration

The situation is dire and the precautionary principle calls for rapid, comprehensive and effective action to reduce the damage and to improve the situation, as described in this 2022 post, where needed in combination with a Climate Emergency Declaration, as discussed at this group.


• Will the Anthropocene last for only 100 years?

• How much time is there left to act?

• The Mechanism leading to Collapse of Civilization and Runaway Global Warming

• Permafrost extent sets drainage density in the Arctic - by Joanmarie Del Vecchi et al (2024)
Discussed at Facebook at:

• Extinction

• Pre-industrial

• Feedbacks

• Potential for methane release (2011 post)

• Warning of mass extinction of species, including humans, within one decade

• Climate Plan

• Transforming Society

• Climate Emergency Declaration

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