Climate myth number 1-the earths climate has changed before

 
eudemonia
 
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eudemonia
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18 February 2013 19:28
 

Climate’s changed before

Climate is always changing. We have had ice ages and warmer periods when alligators were found in Spitzbergen. Ice ages have occurred in a hundred thousand year cycle for the last 700 thousand years, and there have been previous periods that appear to have been warmer than the present despite CO2 levels being lower than they are now. More recently, we have had the medieval warm period and the little ice age. (Richard Lindzen)

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A common skeptic argument is that climate has changed naturally in the past, long before SUVs and coal-fired power plants, so therefore humans cannot be causing global warming now. Interestingly, the peer-reviewed research into past climate change comes to the opposite conclusion. To understand this, first you have to ask why climate has changed in the past. It doesn’t happen by magic. Climate changes when it’s forced to change. When our planet suffers an energy imbalance and gains or loses heat, global temperature changes.

There are a number of different forces which can influence the Earth’s climate. When the sun gets brighter, the planet receives more energy and warms. When volcanoes erupt, they emit particles into the atmosphere which reflect sunlight, and the planet cools. When there are more greenhouse gases in the atmosphere, the planet warms. These effects are referred to as external forcings because by changing the planet’s energy balance, they force climate to change.

It is obviously true that past climate change was caused by natural forcings. However, to argue that this means we can’t cause climate change is like arguing that humans can’t start bushfires because in the past they’ve happened naturally. Greenhouse gas increases have caused climate change many times in Earth’s history, and we are now adding greenhouse gases to the atmosphere at a increasingly rapid rate.

Looking at the past gives us insight into how our climate responds to external forcings. Using ice cores, for instance, we can work out the degree of past temperature change, the level of solar activity, and the amount of greenhouse gases and volcanic dust in the atmosphere. From this, we can determine how temperature has changed due to past energy imbalances. What we have found, looking at many different periods and timescales in Earth’s history, is that when the Earth gains heat, positive feedbacks amplify the warming. This is why we’ve experienced such dramatic changes in temperature in the past. Our climate is highly sensitive to changes in heat. We can even quantify this: when you include positive feedbacks, a doubling of CO2 causes a warming of around 3°C.

What does that mean for today? Rising greenhouse gas levels are an external forcing, which has caused climate changes many times in Earth’s history. They’re causing an energy imbalance and the planet is building up heat. From Earth’s history, we know that positive feedbacks will amplify the greenhouse warming. So past climate change doesn’t tell us that humans can’t influence climate; on the contrary, it tells us that climate is highly sensitive to the greenhouse warming we’re now causing.

 
 
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18 February 2013 22:20
 

There is something else the change skeptics either forget or ignore - while the climate has indeed fluctuated in the past, the difference today is the speed at which it has changed.  The amount of climate change we’ve seen in the past 100 or so years has usually taken tens of thousands of years.

 
eudemonia
 
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eudemonia
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19 February 2013 12:15
 

Exactly right Skip. This short term sudden warming, and extreme, as looking at the Poles and Greenland would tell us, has human fingerprints all over it.

 
 
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22 February 2013 02:00
 
Epaminondas - 19 February 2013 11:15 AM

Exactly right Skip. This short term sudden warming, and extreme, as looking at the Poles and Greenland would tell us, has human fingerprints all over it.

The fingerprints also include carbon isotopes that exist only in oil, but they are now being found in the atmosphere.  Guess how they got there?

These isotopes also don’t show up in ice cores.  Guess why not?

 
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SkepticX
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22 February 2013 11:13
 

Just a couple notes of technical accuracy ...

  - The fact the Earth’s climate has naturally changed significantly in the past isn’t a myth. The actual issue is that it’s misused/misrepresented (intentionally “misunderstood”) to dismiss the findings that clearly indicate it’s now changing differently due to human influences.

  - General skepticism is the proper mindset by which to develop a sound understanding of the cosmos, including the Earth and its climate—precisely the mindset that corrects for the actual issue here. Climate change skepticism (or denial) is the problematic mindset at issue.

These may seem like pedantic issues, but only if you don’t really consider it very carefully. Calling the fact that the Earth’s climate has changed significantly in the past is, in fact, wrong. Wording it too strongly like that suggests an emotional agenda is in play here (whether it really is or not). It compromises credibility. Promoting proper skepticism is precisely what the OP is trying to accomplish. Calling skepticism out for climate change denial without qualifying the term to specify that’s the form of pseudo-skepticism at issue confuses the issue and undermines skepticism—again, a credibility issue, but for the notion of skepticism.

Ultimately I’d say it really is pretty trivial, but mostly in the same sense that the “noises” we make in here are inherently trivial, given that it’s an online forum that about 14 people or so are gonna read. But I’d argue that clarity and accuracy are important issues—one of the best functions/benefits of participating in a more overall skeptically healthy forum like this one.