Relative to the rest of Earth’s history, the climate at the moment is pretty cold as Earth is just coming out of an ice age. So over time the gradual increase in temperature is quite normal. The Earth’s climate has undergone these ups and downs in global temperature throughout its entire lifetime with different species flourishing at different times. But even with these ups and downs the Earth’s temperature has been pretty stable and consistently habitable when compared to Venus or Mars.
So how does Earth maintain this consistent habitability?
It’s all about the exchange of elements and molecules! And this is what I learnt last term in the geochemistry module.
CO2 is important: Too much in the atmosphere and Earth’s gets too warm (like Venus) and not enough in the atmosphere and it freezes (like Mars). Earth is like the ‘Goldilocks planet’ not too hot, not too cold, but just right
How to maintain CO2 (a very basic model): Earth produces a lot of CO2, from respiration, volcanic emissions, dissolving limestone in the ocean etc. You’d think the latter was of least importance, but really it is the crux of the matter – limestone (CaCO3) is where the Earth stores most of the CO2 so as not to have it catching the sun’s rays in the atmosphere and warming the Earth up. As global temperatures increase more weathering occurs, shaving off bits of mountains and sending more elements, such as Calcium into the oceans. If there is more Calcium (Ca) in the oceans the Earth can make more Limestone (CaCO3) and thus remove more CO2 from the atmosphere which in turn decreases global temperatures. Et voila: a perfect self-sustaining global temperature cycle (which happens much the same the other way around too).
Obviously lots of other things factor into this cycle as well such as photosynthesis of trees and algae, ocean pH, how many mountains there are, the changes in shape of the orbital path the Earth takes around the sun, how quickly the tectonic plates are moving and much more.
So the Earth is very good at dealing with CO2 when considering only natural sources – the question is; do human emissions thrust the amount of CO2 out of the manageable range? Will we spiral into a global oven complex from which there is no return?
Perhaps when we consider that normal CO2 concentration in the atmosphere (what the Earth system strives for) is around 270ppm and the number we have today is 400ppm, there is cause for concern.
So to answer whether or not humans are causing global warming is: no we are certainly not causing it as it is a natural cycle and would be warming anyway. BUT we are in grave danger of meddling with it too much for Earth to recover and do need to think seriously of how not to further upset the preciously delicate balance of the Earth’s global temperature system.