Is the climate chaotic?

I'm not sure about decadal detection of chaos in climate. We know weather is chaotic, and there have been some crazy changes in the past (eg Younger Dryas), so maybe.

Even if it _is_ chaotic, does that make prediction impossible? Well, yes, but you can predict things _within uncertainty_.

Weather is chaotic; I can't tell you what the temperature of Earth will be in a year, but I can tell you that the mean temperature will be within a handful of degrees from today (and most likely within a degree C).

Chaotic behavior is often bounded. Solar System objects undergo chaotic motion when, thanks to things like resonances perturbing their Hamiltonian, they cross phase space separatrices. But if they ever leave the region of phase space close to the separatrix, then the motion is no longer chaotic. Depending on the properties of the phase space, this may well mean that the outcome is predictable.

It is also commonly detected using the Lyapunov Characteristic Exponent, which states that close paths in phase space exponentially diverge. But the LCE is a measurement of _local_ divergence, and doesn't apply across the entire phase space; once your particles are sufficiently far apart they no longer necessarily diverge and may well be predictable. (eg think of the 3 body problem, once one of the bodies is ejected you no longer have a 3 body problem and the entire system is analytically solvable).

This probably explains why climate model projections diverge massively on the short term (<30yrs), but tend to come out with the same range of results in the longer term.

It also probably explains why climate models do multiple runs with a range of initial conditions and why outputs such as climate sensitivity are commonly reported as a probability distribution function - which is a perfectly sensible way of modeling and handling chaotic behaviour.

EDIT: Might'n't stochastic resonances still lead to chaotic outcomes? Depends on the precision of our measuring capacity - after all, the level of 'chaos' we see depends entirely on our measuring capacity! A lot of the apparent chaos in the solar system comes from orbital resonances.

Climate and weather are two of the most chaotic systems there are. It was from meteorology that Chaos Theory was born.

Imagine climatology as a jigsaw – a huge one with thousands of pieces. At the moment we have the edges in place and enough small blocks assembled to know what the overall picture is. However, it appears at the moment that quite a lot of pieces may be missing, there are some that appear to be from a different jigsaw, some seem to be duplicated and there’s even a few tiddlywinks, chess pieces and marbles that shouldn’t be there at all.

There are numerous cyclical events which have an effect on our climate – the obvious ones are the day and the year but there are others relating to the Sun and the motion of Earth in space that have frequencies of between 11 years and 430,000 years.

The cyclical nature of these phenomena mean that they’re entirely predictable and we can calculate the net warming or cooling occasioned by each cycle. Summing up all the values gives us an overall forcing – either warming or cooling.

But these cycles alone can not account for the warming and cooling that is being observed or has been observed. Nor does it fully account for the 542 million years of climatic change reconstructed through oxygen isotope analysis and multi-cellular organism analysis and other techniques.

In the long term (tens of thousands of years and beyond) then there is a good correlation between temps and cycles with a few anomalies thrown in. If we focus in on time periods of a few thousand years or less then there is a lot of noise, the temperature chart moves up and down contrary to the cyclical forcings.

We know that some of these deviations are attributable to oceanic and atmospheric changes and the most obvious one is the changing concentration of greenhouse gases within the atmosphere. Even without any human involvement the levels of greenhouse gases constantly fluctuate, the changes are comparatively small over periods of up to a few thousand years but there are significant variations when we look at frames of millions of years.

We can reconstruct past atmospheric and oceanic composition and behaviour and factor this in to the equations, but there are still many unaccounted for peaks and troughs.

In terms of Earth’s history there can be sudden and dramatic changes. On four occasions the planet has been a hot desert with average temperatures slightly higher than the hottest place on Earth today. Conversely there have been times the entire planet has frozen, most notable of which was the Snowball Earth event of 630 million years ago. The only lifeforms to survive this event were extremophiles.

Quite what triggered these catastrophic changes isn’t understood nor is the trigger mechanism which switches from warming to cooling and visa versa (the end of Snowball Earth is one event we do understand - it was volcanoes breaking through the ice and releasing greenhouse gases that caused the planet to warm). Just to set anyone’s mind at ease, these events occur slowly (in human terms) so it’s not something to worry about.

When we remove the known, the quantifiable, the qualifiable, what we’re left with is a lot of unknowns and a good deal of inexplicable chaos. Slowly more is being learned and our knowledge is advancing but it will be a long, long, long time before we can say that we fully understand the climate (if ever).

It is not completely chaotic. There are apparently feedbacks. Otherwise you can't explain how the Earth's climate has been relatively constant throughout its life. We get 30% more energy from the sun today than when the earth was young. The periodicity of the ice ages is strong evidence that it isn't completely chaotic. It also indicates that some of the feedbacks aren't completely predictable and there must be interactions between them.

I think so. Dr Reid Bryson, in 1974 said that the erratic weather was caused by man's emissions of Co2 and that this would lead to a pronounced cooling trend, but subsequent rises in temperature have proven him wrong, which shows how hard it is to predict climate.

http://news.google.com/newspapers?nid=1951&dat=197...

I really hope this is going to be the lead-in to some diatribe about climate being deterministic?