Week Three - Past and Present Climates

One of the key elements to combat climate change is understanding what forcing are behind. Many people are aware of the numerous human activities that contribute to climate change but not very many have a grasp on the natural processes that also cause our climate to change. All possible climate change causes need to be taken into account when trying to figure out if the changes we are seeing are natural and if they are not, how to combat them at the source.

Some of the natural processes that have been causing our climate to change over the past 4 and a half billion years have been our distance from the sun (orbital cycle), the suns strength, earths reflectivity (albedo), and greenhouse gas emissions (GHG emissions). Each of these have occurred in constant cycles throughout our history but one in particular, GHG emissions, has been amped up with advances in technology by humans.  We know this by looking at proxies of past climate change that allow us to measure the relative amounts of GHGs in the atmosphere at different time periods.

The reason we can know that none of the other climate change causes are causing our climate to change is because of the time scales that they work on. Orbital cycles occur at very regular intervals. The earth rotates around the sun in an ellipse type path that grows and stretches as times goes on. When it comes to affecting climate change though, these changes happen over a span of thousands of years and are too long to account for the changes we see from them.

Similarly to the changes in our orbit, the sun has also been getting steadily brighter and hotter. This though has been happening since the earth first formed and would not account for the sudden increase that we have seen in average global temperatures in the fast few decades. The sun goes through a sun spot cycle as well but that happens every 11 years.

Earth reflectivity has been changing throughout time as well and controls how much energy from the sun is radiated back out into space. If albedo is high, more energy is reflected back into space, if it low, more energy is absorbed. Many things affect albedo such as particles in the atmosphere, ice sheets on the poles, and the different structures or plants that occupy different land areas. If we have more ice masses and reflective aerosols in the atmosphere, more incoming solar radiation is reflected and the earth cools. But if ice melts and leaves fresh soil exposed or trees are cut down for fields that exposed more dirt, these things can cause our albedo to go down and our temperature to rise. This can also cause a negative feedback because more ice melting causes more soil to be exposed and warmed by incoming radiation. This warmed soil causes more ice to melt and so on and so forth.

Lastly we have GHG emissions. These emissions have steadily been increasing since the existence of humans. Before our time, these gases were emitted by volcanoes and wild fires. Since nothing was able to control these processes we can and say that they occur at somewhat frequent times throughout history. What we can’t ignore though is that there has been an increase in the presence of these gases in the past few decades. The only factor that has differed through their semi-constant occurrences is humans. We have essentially sped up the process of GHG emissions into the atmosphere way beyond something we have ever seen in the past thousands of years.