Wow. Now, every intelligent 10-year-old kid must know why this possibility is non-existent, why the statement is nonsense. Some scientists including Roy Spencer have pointed out how absurd these Hawking's statements were from a scientific viewpoint.
But lots of the scientists who have paid lip service to the lies about the so-called global warming or climate change in the past have remained silent and confirmed that their scientific dishonesty has no limits. I despise all the climate alarmists who know that statements like that are absurd but who hide this fact because a lie like that could be helpful for their profits or political causes. You know, what these jerks and the people who tolerate these jerks' existence haven't quite appreciated is that it is only lies that may be helpful for them.
Now, there are exceptions. Zeke Hausfather, a US Berkeley climatologist, has been an alarmist but he has pointed out that he realizes that Hawking's statement is just junk:
However, I disagree with Hausfather's assertion that this statement by Hawking's is outside Hawking's field of expertise. It is some rather basic physics combined with the basic knowledge of the outer space that should be known to 10-year-old boys who attend physics lectures at the elementary school. It isn't or shouldn't be outside Stephen Hawking's expertise because Hawking is a physicist and one who has studied the outer space. I think it's right to say that Stephen Hawking has shown a rudimentary ignorance about his field, physics.
A reader has asked me "why Venus is special". But Venus isn't special in any general sense. Or if we said that Venus is special, almost every planet would be special. A more sensible assertion is that every planet is completely different. It has a completely different chemistry than others. It has a completely different temperature than others, mostly due to the completely different distance from the Sun.
I really think that it's a shame that kids and even adults don't reliably know these basic things.
First, look at the distances of the planets from the Sun, e.g. in this table. Mercury, Venus, and Mars have 38%, 73%, and 152% of the Earth's distance while Neptune, the most distant planet from the Sun, has 3,000% of the Earth's distance.
Planets are just rocks that ended up there. But the positions have consequences. The greater the distance is, the cooler the planet will be, at least approximately. Why? Because the amount of solar radiation per unit area goes down as 1/R2. This incoming radiation has to be equal to the outgoing one which scales like σT4 where T is the absolute temperature of the planetary surface (i.e. temperature in kelvins). I am neglecting albedo and greenhouse effects and other details. You may see that T∼1/√R.
So Venus whose distance from the Sun is 0.73 times greater than the Earth's ("k times greater" means "smaller" for k<1) should have the temperature that is 1/√0.73∼1.17 times the Earth's. If the albedo and greenhouse effect were the same, that would be 1.17×288=336 kelvins or so. That would be 63 °C or so on the surface and Venus could be a bit warmer but habitable. But the composition of the atmosphere and the albedo etc. are different so Venus ends up much higher than that, well above the boiling point of water. Due to the chemistry and the greenhouse effects etc. that result from it, it's largely unavoidable.
That's why we say Venus is barely out of the habitable zone. People usually conclude that Mars is barely inside the habitable zone. The habitable zone is the region of the parameter space, mostly but not necessarily only as a function of the distance from the Sun or another star, where liquid water survives on the surface. Water is good for life.
While Earth and Venus may look like siblings (the radii and distances from the Sun are comparable) and they're sometimes described in this way, they differ in all the details - especially chemistry - dramatically. In particular, the atmosphere of Venus is almost 100 times denser. Around 95% of it is carbon dioxide so the total mass of Venus' carbon dioxide is almost 200,000 times greater than the mass of carbon dioxide in the Earth's atmosphere. There's just no way to pump this much CO2 into the Earth's atmosphere because there's not enough burnable carbon we could access in any imaginable way. At most, if we tried really hard, we could perhaps quintuple the CO2 concentration in the air - which would be a good thing for life on Earth and our economies - but it would be extremely difficult.
Again, the extra greenhouse effect on Venus that adds over 100 °C to the planetary temperature results from the amount of CO2 that is almost 200,000 times greater than that on Earth. Even if we double the CO2 in the atmosphere relatively to now, the ratio would still be almost 100,000. Note that the greenhouse effect due to CO2 on Earth contributes of order several °C so it is significantly greater than the 1/200,000 times the greenhouse effect from CO2 on Venus. It's because the dependence isn't linear. It's sublinear, approximately logarithmic. The more greenhouse gas you have, the less another molecule matters.
If you have never studied the diverse temperatures of the Sun's eight planets, you are encouraged to spend at least minutes by looking at the Wikipedia pages about these atmospheres:
Mercury: hydrogen, helium, oxygen, sodium, ...You see that there are numerous planets - both the distant ones as well as Mercury, the closest one to the Sun (it may be surprising to get it at both extremes) - whose atmospheres are dominated by hydrogen followed by helium - it's like the early elements in the Cosmos. But the precise compositions are totally different, the following trace elements are different, and the overall pressures of the atmospheres differ by many orders of magnitude.
Venus: carbon dioxide, nitrogen, sulfur dioxide, argon ...
Earth: nitrogen, oxygen, argon, water vapor, ...
Mars: carbon dioxide, argon, nitrogen, ...
Jupiter: hydrogen, helium, methane, ammonia, ...
Saturn: hydrogen, helium, traces of volatiles, ...
Uranus: hydrogen, helium, water, ammonia, methane, ...
Neptune: hydrogen, helium, methane, ...
The atmospheres of our neighbors, Venus and Mars, happen to have carbon dioxide as the dominant contribution of the atmosphere. But even though some alarmists are working hard to make all the people forget the composition of the Earth's atmosphere, well, Earth is not a planet where CO2 is important in the atmosphere. It doesn't make it to the top three. On Earth, the main gases are nitrogen, oxygen, argon, and water vapor - although the concentration of water vapor is highly variable, sometimes above and sometimes below that of argon. Carbon dioxide is only the fifth gas.
Also, carbon dioxide fails to be the dominant greenhouse gas on Earth, too. By far, it's the water vapor that plays this role. Water's greenhouse effect is stronger than that from the carbon dioxide by more than one order of magnitude.
There are lots of differences. One may run some reconstructions of the chemistry and behavior of the planets to find out why these particular gases ended up dominant in the atmosphere. These explanations have lots of parts. In particular, you could ask why Venus has no water. Well, solar wind has probably stolen water and even hydrogen in any form from Venus' atmosphere.
But I don't want to drown in the detailed mechanisms especially because I am no planetary expert. But there are some basic qualitative conclusions. And one of them is that the chemistry of planets is naturally extremely diverse. Why is it diverse? Because the atmospheres above planets look e.g. like a distillation equipment. You heat a mixture of gases and liquids to some temperature, some of them get up, some of them condense and drop down, some of them may chemically change and react with something else, and so on. What you end up with on the surface sensitively depends on the temperature of your distillation equipment you started with and other choices.
It's enough for the temperature to drop beneath the boiling point of some gas and the gas drops down as a liquid and may be removed from the atmosphere. And vice versa. New gases may appear in the atmosphere if the temperature jumps above a threshold. Some reactions may get vastly faster when the temperature moves in some interval. Some elements may escape from the planet or be stolen by the solar wind. Now, add the geological activity similar to one we know on the Earth. Different rocks have diverse composition. The processes are complex and numerous and so are the possible outcomes.
Despite the complexity, we know certain things, and one of them surely is that CO2 isn't a major gas in the Earth's atmosphere. The alarmist fraudsters have clearly succeeded in brainwashing a big stupid part of the human population which must have accepted the faith that CO2 is a very important gas in the Earth's atmosphere. But CO2 represents just 400 ppm i.e. 0.04% of the volume of the Earth's atmosphere, or 1/2,500 of it. You just can't get any qualitative changes of the Earth is such a minor gas were doubled because 0.08% would still be tiny. A doubling of CO2 - which takes a century if the economy keeps on growing - only adds some 1 °C to the temperature of the planet. Even if it were 2 or 3 °C, it's still nothing compared to the hundreds of Celsius degrees that you would need to make the Earth a bit more similar to Venus.
But the connection between Venus and Donald Trump is yet another level of Hawking's stunning stupidity. Donald Trump may be the U.S. president but he's not a dictator controlling life on Earth, not even life in the U.S. The Americans are increasing or decreasing their consumption of fossil fuels in various ways - some people grow the economy, others are unhinged green lunatics, and so on - in ways that don't depend on the identity of a guy in the White House much.
What one U.S. president may do is to change the U.S. emissions by 5% in one direction or another during his 8-year tenure. But the U.S. is just about 1/5 of the world so this would amount to the change of the world emissions by 1% during these 8 years. During these 8 years, 4 ppm per year times 8 = 32 ppm is being emitted by the mankind to the atmosphere. 1% of that, as I just explained, which Trump may affect is just 0.32 ppm. The greenhouse effect from 120 ppm that we've added since the industrial revolution could have been 0.7 °C of warming. But 0.32 ppm is 375 times less than 120 ppm so you expect 375 times less warming than 0.7 °C from that, about 0.002 °C.
A U.S. president like Donald Trump has the capacity to change the temperature of the Earth by 0.002 °C in one way or another, not by hundreds of degrees that would be needed to make Earth more similar to Venus. Can you see the difference between 0.002 °C and 200 °C? It is the same five damn orders of magnitude that I have mentioned as the ratio of CO2 in the atmospheres. Is Stephen Hawking or the hacker of his computer unable to distinguish the numbers 200 and 0.002?
I think that just a few decades ago, a scientist who would say something like that would mock himself so much that he would completely lose all credibility and become a joke that everyone laughs at. But these days, things like that are apparently normal. What you say may be arbitrarily insane, arbitrarily contradict the things that 10-year-old kids should reliably know. Nevertheless, if this plain absurd statement of yours is positively correlated with the interests of the far left movement that has hijacked an important part of the public discourse, you won't be finished. In most cases, you will even not be criticized. In some cases, you will even be reported and praised.
It's the deceitful far left intellectual contamination that is turning us into brain-dead structures similar to those on Venus, and not carbon dioxide, that needs to be removed from the face of Earth.
And that's the memo.
The real Stephen Hawking died in the 1980's. His animatronic replacement is just a visual puppet. Perhaps the typist behind the curtain is having some fun, mocking the unthinking who eagerly gobble up anything that this pretend genius pretends to say.