The Earth's climate regulates itself

Weathering removes carbon dioxide from the atmosphere and delivers it to the ocean, where it combines with calcium to form limestone. Limestone is drawn under the Earth’s crust by the movement of tectonic plates — a process known as subduction. Heat separates carbon dioxide from limestone. Carbon dioxide is ejected into the atmosphere through volcanic eruptions. Source: William Ruddiman

From NexusMedia

Life on Earth has survived vast changes in climate, from a warm period 450 million years ago, when most of the present-day United States was underwater, to the last ice age 20,000 years ago, when New England was buried beneath a mile-thick glacier. Though climate change trigged mass extinctions, life went on. 

This is something of mystery. Runaway climate change turned Venus into a scorching hellscape, but Earth never grew so hot or cold that life failed to endure. Even in its most turbulent moments, our tiny planet remained a refuge, a blue-green lifeboat adrift against the vast hostility of space. Why? 

Scientists have long speculated on the possibility of a planetary thermostat keeping climate change in check.  

Here’s how it works: Carbon dioxide traps heat, keeping the Earth nice and cozy. A dip in CO2 can bring about an ice age. A spike can make the planet sizzle. Earth regulates this greenhouse gas through weathering. Atmospheric carbon dioxide dissolves in rainwater and combines with rocks to form bicarbonate. 

The global thermostat responds to hot and cold. Heat speeds up chemical reactions, causing rocks and rainwater to draw down carbon dioxide levels more rapidly, thereby cooling the planet faster. Cold temperatures slow down this process, preventing the planet from getting too chilly.

Weathering is the reason that Earth is not like Venus, where rising levels of carbon dioxide rendered the planet inhospitable to life. Today on Venus, where the atmosphere is almost entirely carbon dioxide, the average temperature is more than 800 degrees F. On Earth, the average temperature is closer to 60 degrees F.

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It sounds as if we could just go on spewing CO2 into the armosphere without worrying, doesn't it?  The problem is that the natural processes of weathering take thousands of years.  If we stopped emitting CO2 now, it would take 100,000 years before atmospheric CO2 went back to the pre-industrial level:

“It’s some degree of liquid water interacting with rock that keeps the Earth’s climate stable over long time periods,” said Pogge von Strandmann. As he noted, this is of little comfort when it comes to human-caused climate change. Weathering changes the climate gradually, over many thousands of years. 

“We know that weathering will increase [as the planet gets warmer],” he said. “We know that it will remove carbon dioxide, but it will be at least 100,000 years or so before it would allow the climate to recover back to pre-industrial conditions.” By burning coal, oil and natural gas, humans are transforming the climate on the scale of decades.

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