Climate cycles

First off, a big thank you to Reasic for linking to this blog.
His words were very kind and I can only gabble 'thanks' in return, as well as urge others to visit his blog.

One rather pertinent subject to climate change is that of climate cycles, large shifts in the Earth's climate occurring over several centuries in the short-term and several tens of thousands of years on the more long-term basis.

These shifts cycle between warming periods and cooling periods, normally to an extreme extent (as much as 6 degrees Celsius from the mean), and we are currently in the middle of a warm period.

A graph of the natural cycles

Warming cycles are often held up as a disproof of anthropogenic global warming theory.
However, this is misunderstanding a basic principle of the theory of man-made climate change; not that the temperature is at the highest it has ever been but that the rate of change of temperature is higher, which can be much more dangerous (compare slowly easing oneself on to a bed of nails and then dropping on to it from a height of several metres).

The Earth and its ecosystems can adapt to extremes, given time. They cannot adapt well to large changes within a short amount of time, as the dodo faced when humans along with the things which humans brought (cats).

So, back to its supposed status as a disproof.

There are many misunderstandings concerning climate change. One of those is the idea that proponents of the theory claim that temperatures today are the highest they've ever been and then hold this up as evidence of warming.
This is wrong.

It is claimed only that the current rate of change is at an unprecedented high1; 0.76 degrees Celsius in a century and a half.

And this, as far as we know, is an unprecedented rate. The Vostok data doesn't show anything this rapid. The EPICA data doesn't.
Neither do tree rings, sea shells or any other common long-term temperature proxies.

The current warming could be part of a natural cycle, although we should really be cooling or at least remaining stable at this point in time.
However, the rate of warming leads us to believe that this may not be the case.

References:

1. http://www.global-greenhouse-warming.com/global-temperature.html

The graph was produced by myself using the Vostok ice core temperature data.
It uses a reversed axis for time (the present is on the left) and, due to some quirk of OpenOffice.org Calc, changes in time-scale further back (something which I'm currently trying to fix).
It is necessarily shrunk to fit on the page.
The mean is approximately 4 degrees below the modern value of -55.5 degrees Celsius (remember, this is Antarctica).

New possibilities

Feedback mechanisms can, as already stated, lead to a whole range of new possibilities which we never considered before.

If we suppose that we have a 'perfect' planet; one in which there is no atmosphere other than carbon dioxide and the star around which it orbits with no change in angle never changes in its activity then, by adding carbon dioxide, we will increase the temperature (to be more accurate, it increases the radiative forcing of carbon dioxide in the atmosphere; the effective additional wattage of energy in or out provided by its presence).

The forcing given by additional carbon dioxide is positive (it effectively increases the energy coming in or, at least, not leaving) logarithmic in scale; if we continue adding the same absolute amount then it will have less of an effect each time. After a while we will reach a theoretical 'maximum' at which point any additional carbon dioxide will have a negligible effect, negligible in this case meaning 'so close to zero it doesn't really matter any more'.

In our hypothetical planet, then, carbon dioxide can only provide so much heating before it makes no difference to add any more, and it will probably end at some reasonable temperature.

However, this is when we strip out any factors which might change things. When we take into account other factors, such as feedback mechanisms, it looks a little different.

Suppose we have a few trillion (10^18) tonnes of methane in a frozen form on this planet. They will have little or no effect on radiative forcing when frozen, so there's little need to worry if the temperature either remains stable or decreases.

However, if the temperature increases enough then we may see this methane being unfrozen and reverting to gaseous form.
It will then enter the atmosphere and cause a further positive shift in radiative forcing; methane is a very powerful greenhouse gas.

We then see a higher temperature as a result of this methane than we would see from carbon dioxide or the methane alone; we have the radiative forcing effect of first carbon dioxide and then the methane on top of it.
We have a scenario which couldn't have been arrived at without the methane feedback mechanism, hence the new possibilities.

Of course, it works both ways. For example, an increase in carbon dioxide which could cause an explosion in the plant population sufficient to withdraw all carbon dioxide from the atmosphere; this would cause a massive cooling as the carbon dioxide's forcing effect is lost.
This is another scenario which can't be arrived at if feedback mechanisms are not considered.

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Post changes

Having been criticized for not referencing all my sources (not to mention being called biased in the process, as well as being compared to a pro-EU BBC (haven't people had enough of bashing the Beeb?)), I'm currently in the process of adding references. Therefore, some posts might change from one visit to the other; they shouldn't change in content, just have references added.

Also, for the record, I'm not particularly anti-EU. Anti-its-current-implementation, but the principle is good.

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Feedback mechanisms

Greenhouse gases offer a direct forcing of our climate, but perhaps more important are processes called feedback mechanisms, which can serve to multiply a climate shift manyfold or, alternatively, blunt it.

A simple example of a feedback mechanism is the melting of ice.
If we take a bit of ice covering a bit of ground and then start directing heat energy at it then it will melt eventually, of course.

Now, ice reflects most of the energy directed at it back towards the sources. However, the ground doesn't; it tends to absorb more heat than it reflects.
Therefore, once a bit of ice melts, the ground beneath it warms more. This will warm any nearby ice as well and thus eventually reveal some more ground to warm, which will help melt more ice, which will warm more ground, and so on and so forth.

This begins a cycle whereby the effect of a little thing at the start - a small piece of ice melting - can be amplified to have potential effects far beyond its actual scale.

This particular example is an example of a positive feedback cycle.
There are two types of feedback mechanisms: negative and positive.
A positive feedback cycle reinforces a trend; as the amount of ice goes down in the example, the warming trend quickens as less ice is available to reflect energy.

A negative feedback cycle blunts a trend; an example is the increase in vegetation caused by larger quantities of carbon dioxide in the atmosphere. The vegetation takes advantage of the bountiful carbon dioxide and withdraws some from the atmosphere, helping keep carbon dioxide levels stable.

Feedback mechanisms vary in strength and time-scale. The melting of ice tends to happen slowly at first and then at an ever-increasing rate; the vegetation growth takes much longer and is variable in speed from then onwards.

Sometimes a feedback mechanism of such magnitude and speed can occur that it can't be blunted until it's run its full course; an example would be the clathrate gun hypothesis, in which essentially solid methane at the bottom of the seabed is released by warming temperatures in such massive quantities that warming increases manyfold.

Feedback mechanisms are almost inevitably blunted at some point, though; when the ice runs out, when vegetation becomes overwhelmed with carbon dioxide or when the methane runs out.
However, by the time they stop, the effects are usually all manifested, although some mechanisms can have effects which take years to come into play.

Feedback mechanisms can spawn new possibilities which wouldn't even be considered otherwise; they can kick-start other feedbacks as well.

And the new possibilities will be the topic of the next post.

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Quick update - a post full of links

I'm a bit busy at the moment, so my post on feedback mechanisms will be a bit longer yet.

In the meantime, though, I invite you to help spread the blog by clicking either the Technorati 'Fave this blog' or the 'digg it' button, which as of the time of posting shows two diggs. I did the first to originally submit it; thanks to whoever did the second! :-)

Whilst you wait, perhaps you could go visit my forum at real-democracy.co.uk?
We're a small community of politically-minded individuals, but we're also very friendly and spend a lot of our time debating less serious subjects as well. In fact, a majority of our time really.
The Energy & Environment section contains a lot of useful information in the various threads, although generally unsorted at the moment. Sorry.

Alternatively you could visit realclimate.org.
It's a website/blog which goes into the more technical side of global warming theory, although it doesn't make any active attempt to give both sides of the argument, being written by strong proponents (who are also real scientists, including several working at NASA).
It's well worth the look, assuming you're not an extreme skeptic.

I'll get a new post about the science up ASAP! Sorry about that!

Edit: posted the feedback mechanisms earlier than I thought I would, but the quality probably suffered.
Please comment. :-)