Could Earth go the same way as Venus?

A 2°C, 3°C, 4°C or 5°C RISE?

The rise that has already unfolded may have already crossed 2°C above pre-industrial, according to this analysis that shows that the temperature may have risen as much as 2.3°C from pre-industrial to 2020. Furthermore, the temperature rise is accelerating. In other words, the world is already in the danger zone and the question remains what the implications will be of a 3°C, 4°C and 5°C rise.
[ from an earlier post ]

What would be the impact of a 3°C, a 4°C, or a 5°C rise?

At a 3°C rise, humans will likely go extinct, as habitat for humans (and many other species) will disappear. Such a rise will cause a rapid decline of the snow and ice cover around the globe, in turn making that less sunlight gets reflected back into space. Associated changes are discussed in more detail at this page and this page, and include that the jet stream will further get out of shape, resulting in more extreme weather events such as droughts, heatwaves and firestorms. Changes to the jet stream will also contribute to a further strengthening of storms, which threatens to at times push large amounts of hot, salty water into the Arctic Ocean, triggering eruptions of more and more seafloor methane, as discussed in an earlier post.

[ from an earlier post  ]
From a 4°C rise, Earth will experience a moist-greenhouse scenario. As the temperature rise gains further momentum, runaway heating may well turn Earth into a lifeless planet, a danger that was discussed in this 2013 post, warning that, without anything stopping the rise, it will continue to eventually destroy the ozone layer and the ice caps, while the oceans would be evaporating into the atmosphere's upper stratosphere and eventually disappear into space.

At 5°C rise, most life on Earth will have gone extinct. A 2018 study by Strona & Bradshaw indicates that most life on Earth will disappear with a 5°C rise (see box on the right). As the temperature keeps rising, chances are that all life on Earth will go extinct, as Earth would be left with no ozone layer to protect life from deadly UV-radiation. Furthermore, Earth would no longer have water, an essential building block of life. Soil moisture, groundwater and water in oceans would evaporate and eventually disappear into space, as discussed in an earlier post.

Much of the above was discussed in 2019 posts such as When will we die? and Most Important Message Ever.

Beyond a 5°C rise

The image below, from Song et al. (2021), shows how major mass extinctions over the past 541 million years (the Phanerozoic) are linked to temperature rises higher than 5.2°C and rates of change higher than 10°C/Myr.

The image below, also from Song et al. (2021), shows the magnitude versus the rate of temperature change for 45 defined climate events. The color indicates the timespan of each event. 

The image below, from an earlier post, sums up our predicament, highlighting the rapidity of the current temperature rise and its potential magnitude. 

As illustrated by the image below, the temperature has been rising for a long time and, as said, the temperature rise is accelerating, as discussed in posts such as this one and this one

[ from earlier post ]

This accelerating is one of several reasons why the temperature will keep rising well beyond a 5°C rise, the same way that Venus went, back in history, as discussed below.

Could Earth go the same way as Venus?

[ Earlier version posted at Most Important Message Ever and discussed at facebook ]

Earth did experience high temperatures before, but it cooled down and some species did survive the mass extinctions in the past. This time, however, temperatures could keep rising, due to:
  • Brighter Sun - The sun is now much brighter than it was in the past;
  • No sequestration - The rapidity of the rise in greenhouse gases and of the associated temperature rise leaves species little or no time to adapt or move, and leaving no time for sequestration of carbon dioxide by plants and by deposits from other species, nor for formation of methane hydrates at the seafloor of oceans;
  • No weathering - The rapidity of the rise also means that weathering doesn't have a chance to make a difference. Rapid heating is also dwarfing what weathering (and vegetation) can do to reduce carbon dioxide levels; and 
  • Methane, water vapor, loss of sea ice & heat sinks and further feedbacks - As the temperature rises, feedbacks increasingly kick in, such as emissions from decomposing vegetation and fires, while methane erupts from hydrates with little or no time for it to get decomposed.

A very small increase in solar irradiation – leading to an increase of the global Earth temperature, of only a few tens of degrees – would be enough to trigger an irreversible runaway process on Earth and make our planet as inhospitable as Venus, as a recent study concludes.

In conclusion, Earth could go the same way as Venus soon, considering that there could be a rise from pre-industrial of more than 18°C as early as 2026, as discussed in an earlier post and at the extinction page. Also consider the following, from a 2013 post

Long-term scenarios foresee Earth eventually becoming uninhabitable for mammals, even if mammals would survive the current temperature rise. The image below, from Farnsworth et al. (2023), depicts Solar System bodies in accordance with their Earth Similarity Index (ESI), which is based on data such as mass, radius, and temperature, versus the Planetary Habitability Index (PHI), which is based on the presence of a stable substrate, available energy, appropriate chemistry, and the potential for holding a liquid solvent.

The above image points out that eventually (in ~250 Myr) a supercontinent, Pangea Ultima, will form, resulting in higher carbon dioxide (CO₂) concentrations due to changes in volcanic rifting and outgassing. The image shows Earth on the right under pre-industrial and several Pangea Ultima (PU) CO₂ conditions. This, combined with higher solar energy (approximately +2.5% W m⁻² greater than today) and continentality (larger range in temperatures away from the ocean) will lead to increasing warming that would drive mammals into extinction, if they would still be present then. 

Earth is on the edge of runaway warming

The old picture, with Earth well within
our solar system's habitable zone
How well is Earth's orbit around the sun positioned within the boundaries of the habitable zone? The illustration by the Wikipedia image on the right would give that impression that Earth was comfortably positioned in the middle of this zone.

What is the habitable zone? To be habitable, a planet the size of Earth should be within certain distances from its Sun, in order for liquid water to exist on its surface, for which temperatures must be between freezing point (0° C) and boiling point (100° C) of water.

In the Wikipedia image, the dark green zone indicates that a planet the size of Earth could possess liquid water, which is essential since carbon compounds dissolved in water form the basis of all earthly life, so watery planets are good candidates to support similar carbon-based biochemistries.

If a planet is too far away from the star that heats it, water will freeze. The habitable zone can be extended (light green color) for larger terrestrial planets that could hold on to thicker atmospheres which could theoretically provide sufficient warming and pressure to maintain water at a greater distance from the parent star.

A planet closer to its star than the inner edge of the habitable zone will be too hot. Any water present will boil away or be lost into space entirely. Rising temperatures caused by greenhouse gases could lead to a moist greenhouse with similar results.

The distance between Earth and the Sun is one astronomical unit (1 AU). Mars is often said to have an average distance from the Sun of 1.52 AU. A recent study led by Ravi Kopparapu at Penn State mentions that early Mars was warm enough for liquid water to flow on its surface. However, the present-day solar flux at Mars distance is 0.43 times that of Earth. Therefore, the solar flux received by Mars at 3.8 Gyr was 0.75 × 0.43 = 0.32 times that of Earth. The corresponding outer habitable zone limit today, then, would be about 1.77 AU, i.e. just a bit too far away from the Sun to sustain water in liquid form. Venus, on the other hand, is too close to the Sun (see box below).

Kopparapu calculates that the Solar System’s habitable zone lies between 0.99 AU (92 million mi, 148 million km) and 1.70 AU (158 million mi, 254 million km) from the Sun. In other words, Earth is on the edge of runaway warming.

Image by Kopparapu et al. New calculations show that Earth is positioned on the edge of the habitable zone
green-shaded region), boundaries of which are determined by the moist-greenhouse
(inner edge, higher flux values) and maximum greenhouse (outer edge, lower flux values)

Kopparapu says that if current IPCC temperature projections of a 4 degrees K (or Celsius) increase by the end of this century are correct, our descendants could start seeing the signatures of a moist greenhouse by 2100.

Kopparapu argues that once the atmosphere makes the transition to a moist greenhouse, the only option would be global geoengineering to reverse the process. In such a moist-greenhouse scenario, not only are the ozone layer and ice caps destroyed, but the oceans would begin evaporating into the atmosphere's upper stratosphere.

Venus' runaway greenhouse effect a warning for Earth
by Sam Carana - first posted November 28, 2007, at:

Venus was transformed from a haven for water to a fiery hell by an runaway greenhouse effect, concludes the European Space Agency (ESA), after studying data from the Venus Express, which has been orbiting Venus since April 2006.

Venus today is a hellish place with surface temperatures of over 400°C (752°Fahrenheit), winds blowing at speeds of over 100 m/s (224 mph) and pressure a hundred times that on Earth, a pressure equivalent, on Earth, to being one km (0.62 miles) under the sea.

Hakan Svedhem, ESA scientist and lead author of one of eight studies published on Wednesday in the British journal Nature, says that Earth and Venus have nearly the same mass, size and density, and have about the same amount of carbon dioxide. In the past, Venus was much more Earth-like and was partially covered with water, like oceans, the ESA scientists believe.

How could a world so similar to Earth have turned into such a noxious and inhospitable place? The answer is planetary warming. At some point, atmospheric carbon triggered a runaway warming on Venus that boiled away the oceans. As water vapour is a greenhouse gas, this further trapped solar heat, causing the planet to heat up even more. So, more surface water evaporated, and eventually dissipated into space. It was a “positive feedback” -- a vicious circle of self-reinforcing warming which slowly dessicated the planet.

“Eventually the oceans began to boil”, said David Grinspoon, a Venus Express interdisciplinary scientist from the Denver Museum of Nature and Science, Colorado, USA. “You wound up with what we call a runaway greenhouse effect”, Hakan Svedhem says. Venus Express found hydrogen and oxygen ions escaping in a two to one ratio, meaning that water vapor in the atmosphere the little that is left of what they believe were once oceans is still disappearing.

While most of Earth's carbon store remained locked up in the soil, rocks and oceans, on Venus it went into the atmosphere, resulting in Venus' atmosphere now consisting of about 95% carbon dioxide.

“Earth is moving along the curve that connects it to Venus”, warns Dmitry Titov, science coordinator of the Venus Express mission.


- Venus Express - European Space Agency (ESA)

- Venus inferno due to 'runaway greenhouse effect', say scientists

- Probe likens young Venus to Earth

- European mission reports from Venus

The video below, Science Snippets: Loss of All Life on Earth Explained ... Again - by Guy McPherson, describes our precarious situation.


• What the IPCC impacts report is hiding

• When Will We Die?

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

• Accelerating Methane Rise

• Earth is on the edge of runaway warming

 Habitable zones around main-sequence stars: new estimates - by Ravi Kumar Kopparapu et al. (2013)

 Habitable Zone - Wikipedia

 Earth is closer to the edge of Sun's habitable zone (2013)

 Updated model for identifying habitable zones around stars puts Earth on the edge

• Co-extinctions annihilate planetary life during extreme environmental change, by Giovanni Strona and Corey Bradshaw (2018)

 Tardigrades have a fatal weakness after all (2020)

 Thermotolerance experiments on active and desiccated states of Ramazzottius varieornatus emphasize that tardigrades are sensitive to high temperatures - by Ricardo Neves et al. (2020)

 The projected timing of abrupt ecological disruption from climate change - by Christopher Trisos et al. (2020)

 Extreme Space-Weather Events and the Solar Cycle - by Mathew Owens et al. (2021)

 Ancient volcanic eruption destroyed the ozone layer

 The Toba supervolcano eruption caused severe tropical stratospheric ozone depletion - by Sergey Osipov et al. (2021)

 President Niinistö in Arkhangelsk: If we lose the Arctic, we lose the whole world

 Thresholds of temperature change for mass extinctions - by Haijun Song et al. (2021).

 Climate extremes likely to drive land mammal extinction during next supercontinent assembly - by Alexander Farnsworth et al. (2023)
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