Climate vs weather

On the surface this is a simple matter to define:  ‘weather is what you get, …climate is what you expect’ (  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 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

Albedo (not libido)

Albedo is the reflection of heat by the earth back into space.  Once heat arrives through the atmosphere to the earth’s surface, variable amounts of that heat is reflected back up into the atmosphere, and eventually into space.  Surfaces such as ice and snow that reflect a high amount of heat have a high albedo.  Surfaces that absorb rather than reflect heat, such as sea and rock, have a low albedo.

Overall, the Earth reflects about 30% of the sunlight that reaches it from space; it has an albedo of around 0.3. The other 70% is absorbed.  Without any blanket gases around the earth, this alebdo of 0.3 would give us an average temperature across the globe of -18C.
The more ice melts at the poles, the less heat is reflected by ice and snow, and the more heat is absorbed by water.  In this way the albedo of the earth is decreased.
And I don’t think I need to define libido…

Blankets not greenhouses

Already I find this course is doing its job.  There was I with my memories of GCSE chemistry 25 years ago (gulp!) thinking that at least I understood the way greenhouse gases work.  Oh no….  Turns out that the term ‘greenhouse gases’ is not at all the best way to conceptualise our planet’s temperature systems.

The short-wave heat radiation entering the greenhouse, and the long-wave heat radiation  partially leaving the greenhouse (which I’d learnt about at school) are only a very small part of the story.  In a real greenhouse, the main heating mechanism is in fact the trapping of air inside the structure, preventing the escape of heat.  Whereas for our planet, the key heating mechanism is the presence of certain gases in the atmosphere.  These gases act as a blanket, trapping heat and re-radiating some of it back to the surface of the planet.

Without these blanket gases our planet would be, on average, a not very cosy -18C.  However, as these gases are present, we have instead an average of 15C – much better for life.  So, until the anthropocene, these blanket gases were doing a very important job, moderating the temperature of the planet and thus facilitating life.

So what are the key gases?  Again, my chemistry GCSE let me down.  CO2 is important, but not as important as H2O (as water vapour).  Water vapour, it turns out, is the main blanket gas.  CO2, methane, ozone, nitrous oxide and human made CFCs are also key contributors.  Molecule for molecule, methane is a more active blanket gas than CO2, but it is also far less abundant in the atmosphere.

Why am I doing the course?

At the start of the 8 -week course I thought it worthwhile to jot down some thoughts about why I’m doing this.  I could simply state that climate change is the key issue of the age, and I want to make sure I’m up to date on the facts, figures, theories and approaches.  But whilst this provides part of the picture, it isn’t 100% honest.

As someone who has been an  environmental activist in the past; an academic and professional archaeologist in more recent times,  and now a full-time mum, this course provides me with a number of opportunities to:

  • engage my brain;
  • make sure my understandings about climate change are up to date and accurate;
  • assess the narrative about climate change that is being delivered by courses such as these;
  • build contacts;
  • use it as a springboard to launch myself into a new campaigning field.

I’m intrigued to see which of these aspirations are fulfilled and what evolves through the next 2 months.

Starting the course

Today I started the FutureLearn course on Climate Change, provided by the University of Exeter.  The 8-week course consists of a combination of short video presentations; text; discussions on the site’s discussion board, Facebook and Twitter; and a series of tests to review your knowledge.  The first video recommended starting a blog as a way to develop reflective learning skills.  I’ve not tried this as a technique (I left university many years ago!), so am trying it out for size…and here I am!