Week 3 – Signs of Climate Change

Ships of the desert

Do the 'discussions' work for you?
Okay, so one of the core ideas on this course is that we watch a video, or read something off the web then enter into a discussion via posts on the course forum.

Trouble is you end up with literally hundreds of posts to trawl through for each discussion. It just doesn't work.

The problem is the sheer number of people on this course (and over 500 more have joined since it started). If the majority try to make contributions, the discussions become too unwieldy.

It would be better if the course organisers either limit the numbers or, run the course for everyone at once (as now) but divide them into separate groups running in parallel.

Longer videos?
I must admit I was a bit disappointed that the video 'lectures' weren't a lot longer. Instead there's more emphasis on discussions (which don't work - See above).

I think I've worked out what they wanted to do here though. The videos are just a quick heads-up on a given theme, whilst the research/discuss sections are meant to be the main method of education: You look at the data and you work out what it means e.g. I was really surprised this week when I discovered that the UK's wettest year (2012) was part of a 40 year trend towards wetter weather. I just thought we'd had a bit of bad luck lately!

The difference between Obliquity and Precession

Earth (with axis shown) orbiting the Sun

I don't know about you but I was confused by week 2's video description of Obliquity (Axial tilt) and Precession.

The video's description made them sound the same with only the period of time different.

So, after much research, here's the actual difference:

Obliquity is about the angle of tilt of the Earth's axis relative to it's orbit round the Sun. This tilt gives us our seasons e.g. In June to August, the northern hemisphere leans towards the Sun giving us Summer. In December to February, the southern hemisphere tilts towards the Sun giving them their Summer.

If you ignore all other effects, this tilt changes from 21.5 to 24.5 degrees over a 41000 years period. The more the angle, the more pronounced the seasons


Precession is a wobble the axis gets from the pull of the Moon and the Sun. If you ignore all other effects, this wobble makes the Earth's axis trace out a circle over a 23000 year period. On it's own it would also give us our seasons.

So yes, Obliquity and Precession are very similar but subtly different.

What makes a gas a greenhouse gas?

A water molecule

Something the course hasn't gone into yet is why certain gases behave as greenhouse gases (GHGs). So I thought I'd have a go at it myself :)

There are 2 requirements for a GHG:

1) The gas needs a frequency of vibration mode that matches the frequency of infra red light (IR). In other words it needs to be capable of vibrating in tune when IR hits it.

2) The vibration needs to perturb the gas molecule's electric field, creating a dipole. Dipoles are where a molecule has a positive and negative pole (like a battery).

When you accelerate and decelerate a dipole (i.e. vibrate it) electro-magnetic radiation - in this case IR - is created.

In summary, IR hits a GHG, the gas vibrates in tune with it and therefore fires off IR in all directions including back to the ground.

More here.

Week 2 - Palaeoclimate

Home

Palaeoclimate (past climates) is a particular interest of mine as a geology graduate, so I was especially pleased about this week's content.

The use of 'Snowball Earth' was particularly clever as it expanded upon the ideas of feedback mechanisms and a self-regulating planet from last week.

I was already aware of Snowball Earth as I'd already seen the Horizon program featured when it first aired (and from various sources since), but it was good to see more detail on how the planet managed to escape it (Nice work you volcanoes!).

I was also aware that the sun had been less bright in the past but didn't realise how our self-regulating planet had scaled back the CO2 (through chemical weathering and sequestration in the oceans) as the sun got brighter. Wow.

Goldilocks zone: Another concept I knew but it was interesting to know that Earth will have a runaway greenhouse effect eventually like Venus. I thought the physics were all wrong (Must dig out a reference for that some time).

Again, proxy climate data and the effects of the Earth's orbit and axial tilt weren't news to me but it was great to get more detail.

The proxy data allows us to learn lessons from the past whilst the influences on solar input help us understand the climatic changes they show us. All very clever stuff.

Week 1 - Principles of Climate Change

Jack Russells: Aren't they great?!

As mentioned in my previous post here are my reflections on the first week of the course based on the Uni's suggested questions:

What are the key scientific principles that explain climate change including the greenhouse (blanket) effect?
When the sun's light hits the Earth, about 30% is reflected back into space and the rest of the energy is absorbed and radiated back into the atmosphere as heat.

Greenhouse gases like water vapour, CO2, methane, ozone, and nitrous oxide, in turn, absorb this heat and re-radiate it in all directions including back towards the ground.

As a result, heat is trapped in the lower atmosphere. This is the greenhouse effect.

The climate system of our planet is made up of 5 elements:

• Atmosphere.
• Cryosphere (Snow & ice)
• Lithosphere (Solid rock)
• Biosphere (Living things)
• Hydrosphere (Water )

These all interact with each other to provide our ever-evolving climate. These are influenced by external factors known as 'forcings' (e.g. volcanoes, solar variation, and we humans).

Closed loops of cause and effect can develop called feedbacks. For example, when temperature rises, more water evaporates, which traps heat in the atmosphere, so raising the temperature and so on. This amplifying effect is called positive feedback. The opposite effect, which reduces the temperature, is called a negative feedback.



What are the key feedback mechanisms that help to explain why our climate is able to “self-regulate”? 

• water vapour feedback (described above)
• ice albedo (a positive feedback)
• Radiation (a negative feedback)

How can our climate be conceptualised as a system containing a series of components that interact with one another?
See my answer to the first question.

What are the most important themes you have learned this week?
That the climate is a very complex, constantly evolving and self-regulating system. And we humans are unbalancing it.

What aspect of this week did you find difficult?
Finding the time to fit in reading through all the forum comments.

What did you find most interesting? And why?
Seeing how all the elements of the climate fit together and feed off each other.

Was there something that you learned this week that prompted you to do your own research?
I started looking at some of the chapters in the latest IPCC report and noticed they had one on palaeoclimate i.e. climate in the past. Apparently climate models can be tested against palaeoclimate and successfully 'predict' the past.

Beginnings

Our cat: Not a happy bunny

I'm doing what's called a 'Massive Open Online Course' with Exeter University at the moment. It's the one called Climate Change: Challenges and Solutions. And it's free, which is always a bonus.

As part of the course, you're asked to 'reflect' on what you've learnt through something like a blog. So here we are.

The course lasts 8 weeks and every week you're set up (online) with a new bunch of videos, course material, and questions that allegedly take between 2 and 3 hours to complete. Well, yeah, but if you want the full social media experience, you need to read through all the comments posted by your classmates. That kind of takes a while. Lucky they're worth reading then.

Why am I doing the course? Well, as I commented on the course forum "I'm doing this course because I'm concerned about the sort of world my kids will be growing up in. Will they be part of the first generation to KNOW their world is in decline, or part of one that's finally going to turn it all round? Or will climate change turn out to be nonsense, and the joke will be on us".