I know, this is a biology blog. But, well, all organisms live on Earth and have always been influenced by climate (how do you think humans managed to spread across the Earth?). In this series, we will look at the history of Recent climate (since 1 Ma ago) and its future (and perhaps later, I’ll do the entire history – I’ve already done the Neoproterozoic anyway). In this post, I just want to introduce the very basics of climate science, the prerequisites that you need to know to understand the rest of the series; chances are you already know all the info in this post.
The first thing to understand is the difference between climate and weather. Both of them study the state of the atmosphere – temperature, winds, precipitation, etc. The difference is in the scale: meteorology, the study of weather, looks at them on a short time scale up to several weeks. Climatology, the study of climate, looks at them at the year- to million year scale.
What this means is that when someone tells you that bad weather has nothing to do with global warming, he is, at face value, correct, because global warming is a climatic phenomenon, not a meterological one. The flipside is that global warming will lead to instabilities in the climatic cycles of the Earth, leading to higher frequencies of bad weather. In palaeoclimate, except in unique cases which we won’t cover, we are looking at past climates, not weather.
To understand this link between climate and weather, first we need to look at how these climate cycles are generated and what forces influence them.
The first factor is, of course, the Sun, the main provider of energy into the Earth system. Without energy (heat), none of the phenomena we see on Earth would function. Then we have the various terrestrial factors stemming from the atmosphere, hydrosphere (oceans), biosphere (organisms), cryosphere (ice caps, permafrost) and geosphere (rocks). These all interact together to influence climate in processes we refer to as “climate forcing“.
The quantification of climate forcing is referred to as radiative forcing, and has the units Wm–² (Watt per m²), and is the change in energy between 10 km in altitude over a certain period of time. If it’s positive, then warming is happening. If it’s negative, then cooling is happening.
Now that these basics are done, let’s look at how climate is actually generated. The most important thing to understand is that climate is a very dynamic system, full of feedback loops. Even an infinitessimal change in one of the factors listed above will have repercussions; there are no exceptions. Just as in biology, there are positive feedback loops and negative feedback loops. Positive ones enhance and encourage the change, leading to climatic instability. Negative feedback loops are regulatory ones and keep the climate stable.
An example of a positive feedback loop is an increase in greenhouse gases. This leads to higher temperatures and melting of ice caps. The white ice caps are replaced by darker patches of land/ocean, thus affecting the albedo: white reflects light and the associated energy back into space, while dark retains the energy (it’s why you should wear light colours in summer and dark ones in winter!). This means that not only did the increase in greenhouse gas lead to higher temperatures, they also led to the decrease in albedo, resulting in even more warming. It’s like a domino effect.
On the other hand, there are the negative feedback loops. Take the increase in greenhouse gases and the associated increase in temperature again. This may have a negative effect with respect to the cryosphere, but it’s the opposite when we consider the hydrosphere: higher temperatures lead to more evaporation from the oceans. Evaporation = cloud formation, and clouds are white, meaning that the albedo is increased again, counteracting the loss of ice sheet albedo.
As you can see, even with such simple examples, climate can already be seen as a very difficult concept to grasp. In this case, a climatologist has to calculate whether the extra clouds will compensate for the ice sheet loss in terms of energy radiated back into space.
I mentioned greenhouse gases already, as if they’re something special. In fact, the entire atmosphere acts like a greenhouse: when energy hits the Earth, some of it gets retained and some gets reflected back; the atmosphere re-reflects some of that reflected energy and stops it from escaping into space – this is the greenhouse effect. Unlike the uniform glass of a greenhouse though, the atmosphere is composed of many different molecules, some of which cause a stronger greenhouse effect than others. The main culprits in Earth’s case are water vapour, carbon dioxide, methane and various nitrogen oxides, even though they are found in trace amounts in the atmosphere (compared to the oxygen and nitrogen bulk). The more of them there are, the more effective the greenhouse effect.
As I said, those are the extreme basics. If you want to know more (and are too shy to ask), all Intergovernmental Panel on Climate Change (IPCC) reports are available here. The 2007 one is the 4th, with a 5th currently being worked on for 2014. Check out especially the Working Group I Report on the physical science basis of global warming, for all the technical details on climate, with numbers to boot. The synthesis report has good summaries too.
Up next will be another introductory post on how we do palaeoclimatology. Then we will look at the actual data :)
Jump to: Palaeoclimatology; Climate at: 1 Ma, 100 ka, 1 ka; historical; future.