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. :-)

Greenhouse gases and clouds

Many of you will have seen Al Gore's An Inconvenient Truth and Martin Durkin's The Great Global Warming Swindle, probably leaving you confused over whether man really does have anything to do with global warming or not.

The official answer: no-one's really sure.
The real answer: probably.
The first incorrect answer: definitely.
The second incorrect answer: definitely not.

Double the incorrectness if the 'definitely not' is followed by conspiracy theory rambling.

The main reason that man is suggested as a cause is due to his greenhouse gas emissions.
Humans and human industry emit thousands of millions of tonnes of various gases each year, considerably affecting the composition of the Earth's atmosphere.
As an example, carbon dioxide, the most commonly cited of these emissions, is up to a concentration of 385 parts per million (ppm)1, or 385 molecules of carbon dioxide in every million molecules of the Earth's atmosphere (or,alternatively, 0.0385% of the atmosphere).
Prior to the Industrial Revolution, when human industry began to grow in earnest, the levels
were around 280 ppm (and had remained below 290 ppm for at least 400,000 years prior to today)2.
Methane, another commonly cited emission, has grown by about 150% since 1750,
around the beginning of the early Industrial Revolution. It is, however, still present in much smaller quantities than carbon dioxide (approximately 1,750 parts per thousand million (ppb) in 1998)3.

Several gases that we emit are categorised as 'greenhouse gases', gases which retain heat radiation from the Sun in our atmosphere.
Naturally occurring greenhouse gases keep our planet significantly warmer than it would otherwise be, making it suitable for life such as our own.4

It has been shown that greenhouse gas concentrations remained relatively stable for several hundred millennia, although when we go back further we see that there were much higher concentrations in the atmosphere than today.
In particular there were extremely large amounts of carbon dioxide and, more importantly, methane, in the atmosphere around the time of the Permian extinction event, approximately 250 million years ago.5
There is strong evidence to suggest that the temperatures around the equator increased by five or more degrees Celsius at this time, meaning that temperatures at other latitudes would have increased by higher amounts.6

That these greenhouse gases, which include water vapour, carbon dioxide and methane, increase temperatures on the Earth is undoubted. However, what is disputed is the extent to which additional amounts other than the natural will affect the Earth's present climate.

This may seem a simple question - well, if they increase temperatures, then more will increase them still further, obviously - but it is actually quite complicated.
For one, not all factors affecting climate are known or are understood well enough to produce perfect mathematical models of climate.
Clouds are a particularly big unknown; logically, more are formed when there is a higher concentration of water vapour in the atmosphere, but how do clouds affect us?
At night they appear to retain heat by reflecting outgoing radiation back to the Earth, but at
day they do both this and they reflect incoming radiation from the Sun.7
Which one is dominant? How exactly does the amount of water vapour affect their formation? A controversial one, do cosmic rays affect their formation (the answer seems to be 'not really')?8
Even worse, computers are not powerful enough to answer this for us. The most powerful supercomputers designed for climate models cannot handle anything but cells on the Earth about a thousand times bigger than the average cloud, so any effect has to be guessed at by scientists and an approximation fed into the machine.9
Clouds are not the only great unknown. Also unknown are many things about the Earth's oceanic circulatory systems, which have a large effect on climate. Only the simplest of models for these can be produced, and any inaccuracies are likely to be quite large and will multiply in scale with each time-step as the models are run to predict future climate.

There are many other things which also affect the climate, including positive and negative feedback loops. These will be the main topic of the next post (note how in this post we have not arrived at a conclusion as to whether man is causing any warming. The science of climatology is relatively young as a science and there are too many uncertainties to arrive at any definite conclusion, only probabilities).

References:

1. http://www.esrl.noaa.gov/gmd/webdata/ccgg/trends/co2_mm_mlo.dat
2. http://cdiac.ornl.gov/ftp/trends/co2/vostok.icecore.co2
3. http://www.epa.gov/methane/scientific.html#atmospheric
4. http://www.physicalgeography.net/fundamentals/7h.html
5. http://www.astrobio.net/news/print.php?sid=582
6. http://en.wikipedia.org/wiki/Permian-Triassic_extinction_event#Methane_hydrate_gasification
7. http://www.giss.nasa.gov/research/briefs/rossow_01/
8. http://environment.newscientist.com/channel/earth/climate-change/dn11651
9. http://www.aip.org/history/climate/GCM.htm

First, the reasoning

Many of you may be wondering what justification we have for believing that global warming is occurring.
That's what this post will attempt to explain: the reasoning behind the assumption that the Earth is warming.

We have direct measurements of quasi-global temperature going back to about 1850 or so.1
In Central England we have records going back to 1659, the furthest far back instrumental records go.2

From 1850 to about 1940 we measured, on average, an increase in global temperatures; from 1940-1970 a cooling and from 1970 onwards a heating again.3

This can be shown in a graph, like so:



This is a graph from the BBC, by the way; in future I'll try to make my own.

It can be seen quite clearly that, on average, temperatures have increased.
However, climate is a long-term thing; a mere century and a half of data isn't really evidence enough.

We have indirect measurements of temperature going back around eight hundred thousand years, however, contained in the ice cores of Antarctica.4

Here is a graph showing temperature deviation from the average going back four hundred thousand years.



It was created by James Hansen of NASA.

So nothing special, you might say. Temperatures have been higher in the past than they are now.
Except that we haven't taken into account rate of change.

Within the past century and a half average temperatures have risen by 0.76 degrees Celsius. 5
This is an unprecedented rate.

Something must be causing it, and that's what we'll come back to in the next post.

References:

1. http://en.wikipedia.org/wiki/Instrumental_temperature_record
2. http://hadobs.metoffice.com/hadcet/
3. http://en.wikipedia.org/wiki/Instrumental_temperature_record#Warming_in_the_instrumental_temperature_record
4. http://www.esf.org/activities/research-networking-programmes/life-earth-and-environmental-sciences-lesc/completed-esf-research-networking-programmes-in-life-earth-and-environmental-sciences/european-project-for-ice-coring-in-antarctica-epica-page-1.html
5. http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_SPM.pdf