A tale of two poles

Today I found out a number of interesting things about the Earth’s poles and their ice:

1) The Antarctic is colder than the Arctic.  Since ice has not melted there yet, it is not currently contributing to sea level rise.

2) The melting of sea ice (as with much of the Arctic) does not contribute to sea level rise, as the floating ice already displaces the volume of water it would occupy if it melted.  Therefore only the melting of land ice can raise sea levels (small glaciers and Greenland ice sheet).

3) In our warming world, temperature rises have been most marked in the polar Arctic regions.  “Since 1980, the surface area of the Arctic sea ice in summer has formed from around four million square kilometres to about one and a half million square kilometres. The Arctic is a microcosm of climate change. It’s a place where changes in the Earth’s temperature have been felt most keenly.” (Mat Collins, University of Exeter).

Another key difference is that in September 2012:

  • The Arctic had the smallest area of sea ice ever recorded by satellite
  • The Antarctic had the largest area of sea ice ever recorded by satellite




400 parts per million

On Thursday May 10th 2013 the Mauna Lao Observatory in Hawaii recorded the concentration of carbon dioxide in the Earth’s atmosphere passing the 400 parts per million mark for the first time since records began in 1958.  What the records (known as the Keeling Curve after the scientist who devoted his life to collecting them) show is that concentrations of carbon dioxide in the Earth’s atmosphere have been climbing steadily in that time.

Ice core data, obtained from analysis of the gases trapped bubbles in polar ice, go back 800,000 years, and in this time the planet has not experienced this level of carbon dioxide.  Analysis of carbon isotopes present in compounds made by tiny marine phytoplankton preserved in ancient ocean sediments suggests that the last time the planet experienced 400 parts per million was in the Pliocene, between 5.3 and 2.6 million years ago.

In the mid-Pliocene warm period, 3.3 to 3 million years ago, the Earth had several other key similarities with the contemporary Earth – a similar intensity of sunlight reaching the Earth; similar global geography; similar parameters of the Earth’s orbit; and the fact that many mid-Pliocene species are still extant.

There are also some key differences between these two Earth phases.  Sea levels were higher (estimates range from 5 to 40 meters higher than today); the Greenland and Antarctic ice sheets were smaller than today; the jet stream was sluggish, if it existed at all – the planet existed in a permanent El Nino.  Average temperatures were 3 or 4 C higher than today, and possibly 10 C higher at the poles.

For these key reasons, many scientists consider the mid-Pliocene to be a key climate analog for the Earth’s future.  However, there is one key reason that makes this analogy so particularly significant for climate science:  in the mid-Pliocene, the levels of carbon dioxide in the atmosphere were decreasing. Today they are increasing at an unprecedented rate.  During ancient climate change, an increase of 10 parts per million might have taken 1,000 years or more to happen. Now, if emissions continue to increase as predicted, the planet is set to reach the 1,000 ppm level in only 100 years.




How do volcanoes affect climate change?

There are a number of natural forcing factors at work on the earth’s climate, causing short-term changes to weather patterns and longer-term climate change.  It is against this backdrop of natural variability that the effects of human-induced climate change must be measured.   Of these, volcanoes are a key forcing mechanism, which have had large impacts on human civilization in the recent past.  For example, in northern Europe, the medieval Little Ice Age corresponded with a period of high volcanic activity, whilst the Medieval Warm Period occurred at a time of low volcanic activity.  Solar variation was also a key factor in these climate changes.

Volcanic forcing can have both short-lived and longer-term impacts on global climate.


  • Sulphuric aerosols injected up into the stratosphere reflect back nearly all the sun’s energy that they encounter, sending it back into space and preventing it from reaching the planet’s surface.  This is a short-lived effect that can be measured in terms of years.
  • Volcanic ash, a form of black carbon, can be deposited on snow fields, glaciers and other reflective bodies, reducing their albedo.  Hence they reflect less of the sun’s energy and absorb more of it.  This would result in a short-term warming, until the deposits are covered by further snowfall.


  • The volcanoes inject carbon dioxide and other long-lasting blanket gases into the atmosphere, and their effect can be measured in centuries.  This have a warming effect on global climate.

The effect of volcanoes on climate in the short and long term has been used by some climate change sceptics to attempt to undermine the credibility of climate science.  However, as the British Geological Survey puts it:

“The contribution to the present day atmospheric CO2 loading from volcanic emissions is … relatively insignificant.”

…especially when compared with the effects of anthropogenic carbon dioxide pollution.  Volcanoes contribute c.100–300 million tonnes of CO2 each year; which is only 1% of the annual anthropogenic carbon dioxide load.



The carbon cycle – warm blankets and snowballs

During the earth’s very early history, around 4 billion years ago, the sun radiated 25 – 30% less heat than it does today.  If the earth had the same blanket of gases as it does today, the earth should have been c.20C colder.  However, there is evidence (the presence of water and the development of life, 3.8 billion years ago) that the earth was not this cold, and was in fact warmer than today.  The reason for this lies in the carbon cycle.

The early earth was apparently covered by a warm blanket of carbon dioxide gas, acting as a blanket, trapping a proportion of the heat of the sun and re-radiating it back to the surface of the earth.  This carbon dioxide was itself part of a carbon cycle: carbon dioxide was dissolved in rainwater to become carbonic acid; this rained down to the earth’s surface; it weathered silicate rocks to make bicarbonate ions; which in turn entered the sea water as bioavailable calcium taken up by shellfish to make their shells; these in turn were deposited at the bottom of the seas as limestone.  This carbon cycle was triggered by the enlargement of the continents, making more material available to be weathered by the carbonic acid and thus more carbon to be taken out of the atmosphere and deposited in the earth’s crust.

As the continents continued to expand, the reduction of carbon dioxide in the atmosphere caused the planet to cool and more polar ice to be created, in a negative feedback loop.  As the continents continued to expand, so the planet contiuned to cool, and the ice expanded further away from the poles.  When the ice reached the tropics, the planet entered into a tipping point, and the ice closed over the entire planet, meeting at the equator.  This has happened twice in the earth’s history, at 2.2 billion and 700 million years ago, during periods known as ‘snowball earth’. 

Again the carbon cycle played a key role here, this time as a positive feedback loop, reversing the earth’s snowball.  Volcanoes continued to spew carbon dioxide into the atmosphere, but the time the land was so covered by ice that the carbonic acid could not weather the rock and be deposited in the earth’s crust.  The carbon dioxide thus built up in the atmosphere, developing as a warming blanket that eventually absorbed and re-radiated enough energy back to the earth’s surface to start to melt the ice and reverse the snowball. 

I find it fascinating that the lime products I am using to renovate my house are in fact carbon stores from billions of years ago, in the same way that coal is a carbon store.  However, there is a key difference between these two materials.  When coal is burnt to produce heat, the carbon inside it is released as carbon dioxide which serves to warm the planet as a blanket gas.  When limestone is burnt to produce lime, carbon dioxide is also produced, however, the lime reabsorbs this carbon when it is used, and allowed to harden. 

Reflections at the end of week one

The big surprise for me this week was realising how little I know about the earth systems mechanics of climate change.  I have long been concerned by climate change, beginning as a direct activist against tropical logging, new roads and other climate damaging developments in the early 1990s. This activist experience, combined with many conversations, books read, internet research and 25-year old GCSE chemistry, had led me to be fairly confident that I knew what I was talking about when discussing human-made climate change.  Now I find I was wrong, that the greenhouse effect does not operate the way I thought and that carbon dioxide is not the main climate altering gas.

I am delighted to have my assumptions challenged, and my knowledge realigned.  In this way I can become a more effective communicator and campaigner.  Which I still need to be. Because, as my peer group and internet research is continuing to tell me, while I may have been wrong about the earth science, I am not wrong about the devastating potential of human-induced climate change.  I may not have understood the mechanics, but I understand the effects all too well.


Climate vs weather

On the surface this is a simple matter to define:  ‘weather is what you get, …climate is what you expect’ ( http://www.nasa.gov/mission_pages/noaa-n/climate/climate_weather.html).  Weather is what happens now; it is an immediate experience. Climate is what happens over space and time; it is an observation. By general consensus, climate is observed over 30 years, or longer.

An example of a weather change is a sudden thunderstorm on a sunny day. An example of climate change is the year on year warming of the polar regions, resulting in the melting of the polar ice caps.

However, the objection to the popular interchangeability of these two terms is more important than simply pedantry.  There are two main reasons for this common misconception between weather and climate: the first is ignorance; the second is wilful misunderstanding, as with the recent media discourse surrounding the stranding of the MV Akademik Shokalskiy (see http://www.newstatesman.com/future-proof/2014/01/weather-and-climate-change-are-not-same-thing for a discussion of this).

This confusion between, or worse, obfuscation of weather and climate, strikes at the core of much of the media and everyday discussion about climate change denial.  ‘Climate change is not real because…’: ‘we’re having a cold winter snap’; ‘it’s a miserable summer’s day today’ – that’s not climate change, that’s weather.  And a climate change sceptic media can use weather events such as the trapping of the MV Akademik Shokalskiy as a way of reducing climate-related concern in the minds of a public already embracing climate change denial.

The climate system

Our planet’s climate is a complex system powered by solar radiation.  “There are three fundamental ways to change the radiation balance of the Earth:

1) by changing the incoming solar radiation (e.g., by changes in Earth’s orbit or in the Sun itself);

2) by changing the fraction of solar radiation that is reflected (called ‘albedo’; e.g., by changes in cloud cover, atmospheric particles or vegetation); and

3) by altering the longwave radiation from Earth back towards space (e.g., by changing greenhouse gas concentrations).”


Components of the climate system:

At the planet level our climate system comprises five key components and the interactions between them:

  • The atmosphere (the gases that surround the planet);
  • The hydrosphere (dominated by the oceans but also including fresh water, rivers, lakes, and groundwater);
  • The biosphere (all living things and soils);
  • The cryosphere (ice sheets; sea ice and mountain glaciers);
  • The lithosphere (the surface of the earth’s crust).

These five elements are linked by a series of dynamic cycles, such as the water cycle, which together generate our climate and weather.  Affecting these cycles are a number of feedback mechanisms (both positive – accumulative; and negative – dampening) and external forcings.

It has been suggested by another student on the course that we could separate out humanity as a sixth key component in the system, as the ‘anthroposphere’, as we enter into the anthropocene (with thanks to Paul Price).

Feedback mechanisms: positive (amplifying) and negative (diminishing)

Within the climate system are a series of feedback mechanisms, which directly affect the planet’s climate.  They three key ones are:

  • Water vapour feedback (positive feedback – increased planetary temperature causes more water vapour to evaporate from the hydrosphere and travel to the atmosphere, where it acts as a blanket gas, causing the planet’s temperature to again increase).
  • Ice albedo feedback (positive feedback – increased temperature causes more ice to melt, which reduces the area of heat reflective ice and increases the area of heat absorbing dark sea, in turn increasing planetary temperature)
  • Radiation feedback (negative feedback – when a planetary element such as the lithosphere is warm, it radiates heat, causing it to lose energy, causing it to cool down.)

External forcings:

External forcings are factors that are external to the climate system that have the capacity to alter it.  They include:

  • Volcanic eruptions ejecting aerosols high into the atmosphere;
  • Solar variations sending increased or diminished quantities of solar radiation to the earth’s surface;
  • Human-made gases, namely carbon dioxide, methane, nitrous oxide, ozone and CFCs entering the atmosphere