Monday 27 January 2014

past climates

this weeks lessons!


This week has been a journey through time, back to the earth's origins almost 4.5 billion years ago, to examine the way the earth's climate has changed on a geological timescale, and  the techniques used to identify the processes that brought those changes about. Geological specimens can give clues about early climate - sediments as old as 3.8 billion years have been found.

In the early history of the earth the sun was weaker - delivering 25% to 30% less energy than today. Paradoxically, the geological record shows a climate suitable for the evolution of life at a time when the planet should have been frozen. In fact it was probably warmer than today - almost certainly because CO2 concentrations were far higher than those found in our atmosphere now.

Carbon pools in the major reservoirs on earth.[2]
PoolQuantity (gigatons)
Atmosphere720
Oceans (total)38,400
Total inorganic37,400
Total organic1,000
Surface layer670
Deep layer36,730
Lithosphere
Sedimentary carbonates> 60,000,000
Kerogens15,000,000
Terrestrial biosphere (total)2,000
Living biomass600 - 1,000
Dead biomass1,200
Aquatic biosphere1 - 2
Fossil fuels (total)4,130
Coal3,510
Oil230
Gas140
Other (peat)250
The geological record has allowed insights in natural cyclical changes to the earth's climate. There's a great slow carbon cycle in which carbon dioxide, highly soluble in water,  forms carbonic acid - which reacts with exposed rocks to leach out soluble bi-carbonates.

These eventually find their way to the sea and are used by marine animals as a building-block for their shells - made of insoluble calcium carbonate. Eventually they settled to the sea floor, and, over millennia, gradually lockaway free CO2 into the lithosphere - reducing atmospheric concentrations and cooling the atmosphere.

This process of fixing carbon has removed vast quantities of carbon from the active carbon cycle - If I've interpreted the table correctly, all the carbon in the atmosphere, dissolved in the oceans, stored in the biosphere and, amazingly, in the worlds fossil fuel reserves, is only a tiny fraction of the carbon accumulated in the lithosphere, around 1/20,000.

We learned that at one point so much CO2 was locked away that the earth cooled to a point where an irreversible feedback mechanism tipped the climate into a prolonged frozen phase.

This "snowball earth" may have arisen from a combination of decreased greenhouse gas, leading to more extensive ice cover and higher albedo, and perhaps one of the cyclical variations in the earths's orbit, known as the Milankovitch cycles or an event that increased dust content in the atmosphere, reducing the energy arriving at the earth's surface to a point where so much ice formed that its high albedo triggered an irreversible spiral of cooling.

the process led to "20 million year winters", with global temperatures as low as those of modern Antarctica. In the frozen state all the natural carbon sequestration was halted - there was no liquid water to form carbonic acid and probably little exposed rock. The icy conditions did not stop vulcanism and gradually CO2 levels reached a level where warming restarted a new phase of warming and cooling.

As we came closer to "modern times" we looked at the way climatologists are able to use a range of techniques to work out climatic change in fine detail - using:
  •  dendrochronology (study of tree rings)  - involves gathering many cores of trees and relating growth patterns to current and historic weather records. This data can then be compared with tree ring samples from older living trees and also from trees preserved in buildings and in fossils to build a picture of historic weather patterns
  • Ice core samples - As snow falls it traps air - year on year new snow falls - compressing earlier layers - eventually turning them into ice - trapping the air permanently. By drilling through deep ice in the places like the Antarctic and  Greenland air samples from ice as old as 800,000 years have been obtained - allowing air samples to be analysed for greenhouse gasses,  and also yielding other variables that can affect climate like ash and dust and other climate indicators like pollen.
  • Core samples of sediments - which yield samples of fossil micro flora, pollen etc that can be used as proxies to deduce climatic conditions in the past - the most spectacular example of this is work done was at Lake El'gygytgyn - Known as Lake E, in eastern Siberia, which give an unbroken sediment record of over 3 million years.
This evidence has allowed climatologists and geologists to build a more detailed picture of the cyclical reduction of CO2 levels and periods of glaciation known as ice ages over the last 4 million years. We are technically in a warm "interglacial" at the moment - with ice retreating from the far north of Britain only 12 thousand years ago 

From these very accurate tools we know that the pre industrial CO2 concentrations of around 220 parts per million (ppm)  have been the norm for a  very long time - and that since the late 19th century, levels have risen to 400 ppm due to human activities, mainly burning coal and oil and deforestation. This a CO2 concentration, according to the Lake E results,  not seen for 3.5 million years, and one that lead to Arctic temperatures 8oC warmer than today.

There is a growing body of evidence to suggest that the extra energy high levels of greenhouse gasses pump into the world's climate systems cause more frequent and more severe weather events, reducing sea ice cover, and will lead to sea level rises, that could threaten many of the world's major cities and population centres. 

Learning experiences

I didn't find anything especially difficult this week - probably the hardest thing for me was watching the "Snowball Earth" Video - which I found over-dramatic and a poor way of absorbing information - and sorry course leaders - also populist science 13 years out of date.

It was good to get a more structured view of the tools used to research past climates but the thing I found most interesting was the number of students who were a tad sceptical about climate change - I'm no scientist, but I've been delving deeply into the political context of climate change denial, in particular in the USA, for the last 4 years. There were a lot of people on the course who felt we needed to listen to "the other side of the story" - not realising the "other side" is not an alternate scientific view but  a propaganda exercise. If I have the time I plan to blog about this at some point through the week.

I've been researching and using other web sites through the week - I've linked to a few of them in this and my previous post  - but there are a few links that ~I've found invaluable.

Skeptical Science is a denial myths debunk site but also carries a wealth of info.Science Daily have e-mail a daily bulletin of all environmental stories that report new developments in climate research as they are published and Carbon Brief issue a weekly e-mail bulletin on political and technological developments, news etc.







Monday 20 January 2014

reflections on albedo and climate change - week one of the climate change course

Climate Change Explained - er  maybe?

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.