Climate is complicated. There are so many feedbacks affecting each other that it’s hard to sort out the muddle of cause and effect. To try to get a better handle on the problem of understanding which variations are more fundamental and important, we need to start from some simple observations and work outwards into the problem of understanding the interaction of all the myriad phenomena vying for our attention.
Nutshell: Energy comes from the Sun to the Earth, most of which is covered in oceans. The oceans absorb short wave solar energy and emit long wave radiation which heats the atmosphere and the ‘greenhouse gases’ it contains. The atmosphere bounces the radiation down and up then loses the heat to space. A change in global temperature could have four basic causes, or a mixture of them.
1) A change in external forcing such as an increase or decrease in solar activity, or variation in cloud seeding cosmic rays due to the motion of the solar system through the local interstellar clouds, a nearby supernova or possibly the changing orbital configurations of the outer planets affecting the shape of the heliospheric current sheet.
2) An increase or decrease in greenhouse gases such as water vapour or carbon dioxide. (However, Miscolczi thinks an increase in co2 will cause a decrease in water vapour to re-equilibriate the system)
3) An increase or decrease in albedo, principally cloud cover, wind patterns raising dust, and volcanic activity emitting particulates (aerosols), ozone destroying gases and ‘greenhouse’ gases.
4) Changes in Earth’s orientation parameters, orbital parameters, length of day, frequencies of anomalous motions (Chandler wobble) etc.
More detail: The amount of energy that reaches the Earth from the Sun, the Total Solar Irradiation (TSI) is modulated by the Earth’s albedo (amount of reflectivity) which varies with changing cloud cover, ice area, flora colouration etc. This changes the amount of solar energy that actually makes it into the oceans, the Insolation at the surface.
The oceans are the biggest thing acting as a heat-energy battery on the Earth, or as Anthony Watts puts it, they are “One big assed heat flux capacitor” :)
There is as much heat capacity in the top two fathoms of the ocean as there is in the entire atmosphere above it. The tail does not wag the dog, because the long wave radiation bouncing back down from the atmosphere can’t penetrate the ocean beyond it’s own wavelength. The global ocean is the big dog on the climate block. However, the atmosphere does play a big role in redistributing the heat the ocean emits into it. Along with the ocean currents, the atmospheric currents move heat away from the equator towards the poles, and carry cold water and air from the poles down to lower latitudes. The Earth is a big heat engine, and much of the ‘internal’ climate action is due to the way the Earth (and more importanly ocean-atmosphere) is constantly trying to equilibriate the energy it is recieving from the Sun.
There are various ways of looking at the way heat-energy gets around the Earth climate system. Some new and fresh insights have been provided by people like Ferenc Miscolczi, Erl Happ, Stephen Wilde and Willis Eschenbach, describing various ways the Earth’s climate system checks and balances itself in response to changing conditions. Miscolczi for example, demonstrates mathematically why the Earth climate system is in dynamic equilibrium, with a ‘saturated grenhouse effect’. Eschenbach describes how thunderstorms transport heat to the upper atmosphere, bypassing the ‘greenhouse layer’ and shading Earth from the Sun’s irradiance.
So if the Earth tends towards equilibrium, why does the temperature fluctuate and precipitation vary so much over centuries? Well the first thing to observe here is that the temperature hasn’t actually varied all that much, maybe a degree or two over the last thousand years. And precipitation, although there decade long droughts in places, has been pretty stable globally too. Let’s look at some of the things which are affecting the sytem from the outside, before we consider internal variation.
Because it is subject to outside influences in the interplanetary space weather, the earth reacts to try to equilibriate with it’s surroundings as well as balance it’s internal energy budget. The Sun varies it’s output of radiations and particle emissions over it’s various cycles, the ~11 year Schwabe cycle of rising and falling sunspot numbers. It’s ~22.1 year Hale cycle of reversing magnetic polarity. It’s ~205 year de Vries Cycles, and other longer periods we can see from looking at proxy records such as the C14 tree ring series and the Be10 deposits modulated by galactic cosmic rays, which are more or less repelled by the Sun’s varying activity. These longer cycles coincide with long term resonances in the orbits of the gas giant planets, an example is the 2245 year cycle of the changing synodic period of Uranus and Neptune, which is caused by the cycle of Jupiter-Saturn conjunctions. UV from the sun has altered by 15% recently, and the speed of the solar wind varies considerably with the waxing and waning of solar cycles and the coronal holes which emit the particles. We are still learning about the effects these variations have on our planet and it’s climate system.
Also, the motion of the Earth itself as it approaches nearer to and retreats from the sun during it’s yearly orbit causes a big change in the proportion of TSI recieved at the surface. At this point in it’s ~25,000 year precessionary cycle, the Earth gats around 80W/m^2 more incoming solar radiation at the top of the atmosphere above the southern hemisphere’s vast oceans in it’s summer than the northern hemisphere gets. These seasonal variations drive a huge energy difference between different parts of Earth. As well as all this, our nearest celestial neighbour, the Moon, which has the largest variance in gravitational effect on our planet, follows a complex cycle of Lunisolar conjunction and opposition, changing maximum declination, nodal procession and other longer cycles which at times in the history of the solar system have been in strong resonance with the motions of other planets, vastly amplifying their effects on the motion of Earth’s molten core and it’s associated magnetic field, as well as shifting ocean currents and tidal actions.
There are many more aspects to climate not even touched on yet, volcanos and earthquakes, thunderstorms and atmospheric waves, el Nino and la Nina, geomagnetism and the global electrical circuit, ocean salinity and overturning. I’ll start weaving them into part 2, along with extra details provided by people who visit and leave snippets of info in comments. Please join in so that we can create a fully inclusive “holistic theory of climate”.