Climate over time

I convinced my not-so-humble friend, Julien, to sign up for the MOOC and last week he kept saying, “who actually takes this course? I learned all of this in high school!” Well, I ran into him on Monday morning and he confessed that he had attempted the quiz without going through the material and to no one’s surprise he didn’t do so well.

“Things got challenging!” he said. You don’t say.

But that’s what’s exciting about this week. How can two ten-minute videos condense so many theories and tools scientists use to develop an evidence-based timeline of the Earth’s past climate? My learning process for this week was definitely not linear so stay with me and we’ll try to untangle a couple of important questions together.


In climate science, time frames are like a pair of glasses you can wear to look at the same circumstances and draw different conclusions – I learned that this week.

Onto my first source of confusion:

Professor Tim Lenton is talking about how the positive ice albedo feedback loop is usually contained but that if cooling is sufficient, if it surpasses 30 degrees of latitude on both hemispheres (the tropics), a ‘tipping point’ is reached and the amplification of the ice albedo feedback loop becomes so strong that it can end up covering the equator with ice and voila! Snowball Earth.

Wait, but why? Why the tropics? What’s so particular about this latitude?How do we know that 30 degrees latitude from either hemisphere is a tipping point?

I saved this question for the weekly feedback session with Tim and he rephrased it to give it more accuracy: “Why does the ice albedo feedback runaway at 30 degrees?”

“It comes down to the Earth’s geometry as a sphere” he explained. Let’s see why with a visual aid. The sphere shown below is highlighting four circumferences in blue (60ºN, 30ºN, 30ºS and 60ºN). These circumferences are called parallels of latitude because they are parallel to the equator. This image is awesome because it allows us to see straight away that these circumferences are biggest near the equator and smallest near the poles.


Latitude is a measurement to indicate a distance from the equator to either hemisphere, it is taken by projecting a line from the center of the Earth to a point on the surface and recording the angle from the horizontal.

Now, use your imagination and start picturing that the circumference is made out of ice, lots and lots of circumferences together give us surface area. When you’re ready, remember the ice albedo feedback loop we learned about in week 1: more ice, more sunlight reflected away from the Earth, less heat, less temperature and more ice. Imagine ice circumferences creeping up towards the equator from both poles, each one bigger than the last and adding a little bit more of ice cover: 34°, 33°, 32°, 31°…

As Tim explains in the feedback video, it just happens to be that the increasing ice surface as we travel further down to the equator paired with the ice albedo feedback effect together become so powerful near the 30° latitude on both hemispheres that each extra ice circumference is enough to generate as much additional ice cover. Aaaaand that’s how a positive feedback loop can destabilise the Earth’s temperature for those of us who were wondering in week 1 how can the positive feedback loops take over and push the Earth into a different state.

Onto my second question, the volcano query, which is probably my favourite because as a child I had a completely unjustified fear of dying in the middle of the night by being suddenly covered with lava. It began right after I saw the famous human-shaped casts of romans from the extinct city of Pompeii, I mean, can you really blame me? This fear, however, was resolved when I learned that I didn’t even live in a place that could be reached by a volcano eruption. Ha. Ha.

So back to the volcano and climate change question: in the first video, Snowball Earth melts because volcanoes start pumping out carbon dioxide into the atmosphere creating a thick gas blanket. But then in the second video, it is noted that in the short term, volcanoes usually have a cooling effect due to ash clouds spreading aerosols all around the globe and reflecting solar radiation back into space.

I lift my eyebrow and take a pause? So volcanoes can do both? Melt the Earth and also cool it?

Well Liam, one of the other assistants for the course and first year geography student, asked precisely this during the feedback video and Tim explained that it’s all about thinking in different time scales:


How does volcanic activity affect the Earth’s temperature in the long and short term.

I have a couple of questions on the carbon cycle which I hope I can gain some insight on next week:

What creatures capture carbon in the ocean and how do they turn it into shells? How did creatures start grabbing carbon from the ocean and onto their bodies from an evolutionary perspective? And let’s get wild and silly: can we humans develop special features out of excess carbon dioxide in the atmosphere since we’re adaptive creatures that respond to our environment?

I am also very positively surprised by how helpful everyone is. It seems that the BBC videos on Snowball Earth did not work for participants outside the UK, this was quickly amended by other participants sharing a link to the full documentary on YouTube I think I’m learning just as much about climate change as I am about the advantages and limitations of social online learning.

Thank you for reading and I’ll see you next week.




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