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 whether CO2 causes warming

Together with water vapour, CO2 keeps our planet warm so that it is not covered in ice, too hot or devoid of liquid water.

Temperature and CO2 are not connected.

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 El Nino

El Nino lasts for 1 to 2 years.

El Nino most commonly occurs in late December, lasts for a month or so and results from an intrusion of warm ocean waters replacing normally cold waters in the eastern Pacific.

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 past CO2 levels

The early Sun had a luminosity of some 30 per cent less than now and, over time, luminosity has increased in a steady state. The low lumunosity of the early Sun was such that the Earth's average surface temperature would have been below 0°C from 4500 to 2000 million years ago. But, there is evidence of running water and oceans as far back as 3800 million years ago. This paradox is solved if the Earth had an enhanced greenhouse with an atmosphere of a lot of carbon dioxide and methane.

Over geological time, there is no observed relationship between global climate and atmospheric CO2. At times, CO2 was up to 25 times higher than at present.

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 water vapour

Water vapour tends to follow temperature change rather than cause it. At higher temperatures there is more evaporation and higher water vapour concentrations. At lower temperatures, the opposite occurs. Water vapour is an amplifier rather than a trigger.

Contrary to popular belief, the carbon cycle does not control climate. It is the water cycle that does and water vapour is the main greenhouse gas in the atmosphere.

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 CO2 warming (again)

...massive outpourings of volcanic rocks suddenly degassed the Earth's mantle and . . . atmospheric carbon dioxide rose from 0.06 to 0.21 per cent. This . . . would have caused a 4°C temperature rise...

Furthermore, atmospheric CO2 follows temperature rise - it does not create a temperature rise.

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 low CO2

At 800,000 and 650,000 years ago, atmospheric CO2 dropped below 180 ppmv yet temperature was unchanged.

The current CO2 content of the atmosphere is the lowest it has been for thousands of millions of years, and life (including human life) has thrived at times when CO2 has been significantly higher.

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 climate sensitivity to doubled CO2

The variation in CO2 shows that a climate sensitivity of greater than 1.5°C has probably been a robust feature of the Earth’s climate system for over 420 million years.

If the current atmospheric CO2 content of 380 ppmv were doubled to 760 ppmv, there would be a minuscule impact on the radiation balance and the temperature. An increase in air temperature of 0.5°C is likely.

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 sea level rise

During the last interglacial (130,000-116,000 years ago), global mean surface sea temperature was at least 2°C warmer than at present and mean sea level was 4 to 6 metres higher than at present.

The most alarmist predictions of sea level rise from ice sheet melting caused by global warming need to be substantially scaled back. Ice persisted for much longer on Earth when the Earth was much hotter than today.

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 CO2 warming (yet again)

The global warmth of the Cretaceous has been attributed to elevated levels of CO2 in the atmosphere.

The proof that CO2 does not drive climate is shown by previous glaciations.

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 species extinctions

Some 95% of all plant species and 50% of all land animals perished in this mass extinction. Large-leafed plants were replaced by small or multi-lobed leafed plants. Carbon dioxide-induced overheating of the atmosphere appears to have destroyed land plants and the animals that lived off them. This is the earliest geological clue that extreme global warming can be a killer.

Some species extinctions result from cooling, whereas global warming and high CO2 do not lead to extinction.

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 sources of CO2

There has been a progressive increase in the C12 to C13 ratio in the modern atmosphere, showing that the biological contribution of carbon to the atmosphere is increasing. This can be from a great diversity of sources, including the burning of fossil fuels.
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The C14 proportion of total carbon in the atmosphere is decreasing, suggesting that there is an increased biological contribution of CO2 to the atmosphere. Isotope chemistry tells us what we know: human activities such as deforestation, coal burning, animal husbandry and cropping add CO2 to the atmosphere.
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If we humans burn fossil fuels and biomass, then the atmospheric oxygen content should be decreasing. The oxygen/nitrogen ratio shows that this is the case and is not consistent with outgassing of CO2 from oceanic or crustal sources.

Volcanoes produce more CO2 than the world’s cars and industries combined.

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 migrating plants

Replacement of high altitude forests by mixing with low altitude forests to create greater species diversity has happened in previous times of warming and would be expected in another warming event.

Even if the planet warms due to increased atmospheric CO2, it is clear that plants will not feel the need to migrate to cooler parts of our planet.

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 CO2 warming (I know, getting repetitive)

The Sun and atmospheric carbon dioxide were certainly major factors that controlled ancient climate. The Earth would not have received as much solar energy from the faint Sun as now and that energy received had to be held in a thick greenhouse atmosphere otherwise all water on Earth would have frozen. Fortunately, at that time, the Earth's atmosphere was very high in carbon dioxide and methane and the Earth did not enter a permanent icehouse.

Modern global temperature trends are doing their best to show us that CO2 is not a driver of climate.