Climate Change Week 1

I have started an online course from FutureLearn - https://www.futurelearn.com.  The course is 'Climate change: challenges and solutions', led by the University of Exeter in the UK.  It is my first experience of an online course and I am thoroughly enjoying it.  The course lasts eight weeks and at the end of each week the students are required to reflect on what they have learned.  So for the next eight weeks, my blog posts will record my reflections.

The greenhouse effect is fundamental to understanding climate change but the greenhouse metaphor isn't a good one.  The heat in a greenhouse escapes through the glass but a small amount gets trapped.  The greenhouse actually warms up because of prevention of airflow, which stops the loss of heat by convection.  This is a similar effect to the heat in an unventilated car on a hot day, which is why it is a dangerous place to leave your pets.  This contrasts with the earth that is kept warm by a 'blanket' of gases.  The most significant gas is water vapour, but the others are carbon dioxide, methane, ozone and nitrous oxide.  The earth reflects about 30% of the sunlight that it receives, which means it has an albedo of 0.3.  Ice and snow have high albedos, i.e. reflect a lot of the radiation, whereas the oceans have low albedo, i.e. absorb a lot of the radiation.  If there was no reflection, the earth's average temperature would be around -18 deg C, but the blanket of gases warms the earth's surface to an average of around +15 deg C.

Climate can be thought of as a highly complex system with feedback mechanisms that produce self-regulation.  The key system components are the atmosphere, the hydrosphere (oceans, rivers, lakes), the biosphere (living things), the cryosphere (ice and glaciers) and the lithosphere (surface of the earth's crust).  Heat from the sun causes water to evaporate from the hydrosphere and biosphere.  Clouds are formed, which precipitate (rain and snow) and water returns to the earth's surface.  Water then returns to the hydrosphere, or if it is frozen snow it can enter the cryosphere.  Sunlight on the cryosphere can transform it into vapour by a process called sublimation.  The water cycle can be affected by many factors involving human activity.

There are many feedbacks in the climate system - closed loops of cause and effect.  Some feedback loops have the mathematical terminology of positive, because they are reinforcing.  Some feedback loops are termed negative because they are balancing.  Here are three examples of feedback in action within the climate system:

The first example is when water evaporates in the atmosphere, the molecules of water vapour absorb radiation from the earth and vibrate.  They then re-emit heat radiation, resulting in further warming.  This is positive, reinforcing feedback.

Another example of positive feedback is when solar radiation hits sea ice, most is reflected because of the ice's high albedo.  The ocean's surface, on the other hand, has low albedo and absorbs most of the radiation.  So as the system warms up, the sea ice melts, which increases absorption by the oceans, warming the sea water, causing more ice to melt, and so on.

The final example is negative feedback.  All bodies give off radiation and the warmer the body the more radiation it gives off.  When it gives off more radiation, that cools it down.  This is known as the Stefan Boltzmann effect or the Planck feedback.

So this complex climate system has a multiplicity of positive and negative feedback loops that self-regulate.

That's my summary of the first week's theoretical aspects from the course.  But one other aspect that really registered with me was appreciating the difference between weather and climate.  Weather is really the day-to-day elements that we experience such as temperature, rain and wind.  Climate change on the other hand, looks at long-term (30 years+) changes in weather.  Where I live in Turkey, the climate is temperate Mediterranean, the characteristics being long hot and dry summers, cooler and wetter winters.  We have all been around long enough to experience all sorts of weather conditions but even in my advancing years, I don't think I could seriously make objective judgements on climate change like, for example, increases in average temperatures in some parts of the world.  So weather is all about short-term conditions that are easy to measure and evaluate.  Whereas climate variations are all about long-term changes, which are assessed by averaging and probabilities.  This really wasn't obvious to me until I started the course.

So it's been very informative and good fun so far.  My only mistake was that I rushed into the test for the week, which was foolish because I dropped a few points.  Next week I won't be so hasty!