Climate is an accumulation of long term trends in weather - usually a picture built up over at least 30 years from wide ranging weather data.
It's now established beyond doubt that our climate is changing at an unprecedented rate after a long period of stability. To understand these changes we have to look at the "greenhouse effect".
About 30% of the energy arriving from the sun is reflected back out to space. Were there no other influence on how energy is absorbed on the planet's surface average temperatures on earth would be about -18 degrees C, 33 degrees lower than the balmy 14 Celsius that makes our life here tenable.
The explanation for this difference lies in certain gasses, mainly,Water Vapour, Carbon Dioxide, Methane, Ozone, Nitrous Oxide and CFC's, and their ability to absorb long wave radiation reflecting from the surface of the earth and re-radiate some of it as heat into the Earth's atmosphere.
These gasses make up only a tiny fraction of the atmosphere - leaving water vapour aside for the moment they represent less than 0.038% by volume - but they do have a huge effect on regulating the earth's average temperature. It's called the greenhouse effect but that's a poor analogy - Greenhouses work by allowing energy in but stopping it from escaping by convection - the greenhouse gasses are a bit more like a thermal blanket, but that's only a good analogy because it's way better than Greenhouses.
I like to look at them in another way - I'm possibly completely off the map with this idea, but my instinct tells me that even talking about warming creates a barrier to popular understanding of climate change, Scepticism is underpinned because after thirty years of talk about warming it still gets cold. It's a view driven by ignorance but it's one that's growing. The global temperature increases are still very small - may 0.6 of a degree Celsius - but the energy that rise represents is huge and may be it's better to talk about energy.
Is it better to visualise the earth's atmosphere as a giant heat engine, and Greenhouse Gasses as a form of throttle or regulator? Reduce their concentration and there is less energy available to drive the great movements of air masses and ocean currents and the cycles of condensation and evaporation that drive our climate - increase it and the system is driven harder.
Look at system this way and it's easy to see how climate change works. Take on single greenhouse gas as an example. Man made (anthropogenic) carbon dioxide emissions have risen from a pre-industrial age 230 parts per million (ppm) to 400 ppm in 2013. We've almost doubled the concentration of one of the most important components of a phenomenon that keeps our planet 30 degrees warmer than it would be if the greenhouse effect didn't exist.
We've effectively floored the throttle. There's more energy available to the climate system so it acts in a less stable more extreme way - much like a car driven at high speed. The average temperature has risen slightly - but it's the extra energy in the system that's pushing the climate into overdrive. It's difficult to conceive just how much more energy goes into the system. Veteran climate scientist James Hanson likens it to the equivalent of 400 thousand Hiroshimas worth a day, suddenly, in less than a hundred years, we have a climate system running on amphetamine - hardly surprising that there's been a host of record breaking weather events over the last few years!
The world's climate emerges from great planet wide systems. for example. the water cycle - where vapour from the hydrosphere, seas and open water, and from plants in the biosphere form clouds, to precipitate as rain and eventually return to the sea, or as snow, accumulating as glaciers on mountains or sea ice.
The ability of greenhouse gasses to make more energy available to these systems means more evaporation and more rain, cloud, and snow. And here is where water vapour comes into the equation - it's the single most important greenhouse gas but it's concentrations vary widely - and it creates it's own special self-fulfilling prophecy. As the planet warms, it's concentrations will rise, which will again amplify warming meaning more water will be vaporised which means more warming which means....
.... positive feedback - and it's another important factor in climate change.
A good example of positive feedback for an ageing rocker like me is Jimmy Hendrix getting his amazing feedback howl long before the day of digital effects. He'd stand with his guitar pick-ups close to his speakers and hit a note. They would pick up the sound from the speakers and feed it back to the amp - along with the signal from the still vibrating string. These would re-emerge from the speaker - louder and wilder and be fed back again - building that soul rending howl - or - if you're not careful - blowing up the speaker!
These feedbacks are only positive in the mathematical sense - they increase the intensity of the cycle. Confusingly, in terms of climate change they have a negative effect because they increase the amount of warming. Another example of howling rocking and rolling climate feedback is the earth's albedo, or reflectivity. This has a big role to play in how much of the sun's energy bounces back into space. Darker surfaces absorb heat - so the sea has a low albedo and warms more easily than the land. Lighter surfaces reflect more heat back into space so ice on mountain tops and in the high latitudes has a very high albedo. As it melts, the earth's albedo will fall, and more heat will be absorbed amplifying warming - and more ice will melt. These positive feedbacks - and a host of others including methane locked into tundra and "Frozen methane" on the sea floor of cold oceans, raise spectres of runaway climate change and a Venus like climate. Happily, gloomy as the climate change prognosis may be, there are negative feedbacks (good things for the climate!) most especially, according to Stefan-Boltzmann law, (and the link is only for those with a strong constitution - it's pages of equations!) which says if temperature doubles, radiated energy increases by a factor of 16, in other words - if the planet gets hotter it loses heat more quickly. Hopefully this means "Venus Earth" is another sci-fi nightmare!
What I've gained from the week -
I enrolled in the course because, although I'm already reasonably knowledgeable about climate issues, I'm very much self taught and think a bit of contact with proper scientists will do me no harm at all. I've had an almost lifelong interest in environment, sustainability and politics and climate is obviously the single most important variable in any thinking about sustainability. I'm really interested in accurate but simple ways of communicating climate issues but too busy with other things to sit down and do the work - I can't honestly say the week has increased my understanding much (that's not a criticism - I wasn't expecting too much from week one - I'm sure my massive ego will be well and truly dented as the course progresses) - but it has made me write this blog - which has been the hardest thing I've had to do so far. I am so insecure about my own writing and I'm trying to develop a style that covers the technicalities well enough but retains a degree of humour simplicity - Not sure I've succeeded, I don't really know for sure I've even answered the questions but at least i'm trying - looking forward to week 2!
Useful sites
Wikipedia is a great starting point with sections on Global Warming , Climate Change, etc - and while I'd never use a wiki entry as a serious reference it's good for links and more reading. Climate Progress has a USA bias and is a bit messianic at times but for an insight into the politics surround climate it's invaluable, Skeptical Science is the place to go for answers to the rubbish talked by men in the pubs and the Daily Mail, with a check list/debunk of favourite climate denier myths.
