Climate scientists are almost unanimous in the understanding that the bulk of th

Question

Climate scientists are almost unanimous in the understanding that the bulk of the warming observed in the 20th and 21st centuries can be attributed to human activities. This scientific conclusion can be summarized as follows: Humans industrial activity has led to emissions of large amounts of carbon dioxide (CO2) and other greenhouse gasses (such as methane, nitrous oxide, and halocarbons). The resulting increased atmospheric concentrations of these greenhouse gasses has caused a strengthening in the Earth’s greenhouse effect. In class we have called this “the perturbed greenhouse effect”. This strengthening of the greenhouse effect in the Earth’s atmosphere has warmed the planet’s surface. This warming is what we observed when we look at instrumental records of past temperature and see that the Earth has warmed. Despite this strong scientific consensus, the belief exists in parts of popular culture that the global warming that occurred in the 20th and early 21st centuries is natural variability. In this reflection, we ask you to consider the question of how we might distinguish natural climate variability from anthropogenic (human-caused) warming. Put more simply, “how do we know it’s us?”. We don’t expect you to know what all the pieces of the scientific argument are (we will cover some of them later in the term), but we would like you to discuss what types of observations or evidence we would need to settle the question. You might think of this problem another way -- if you had as many resources as you needed, what observation, analysis and simulations would you want in order to settle the question “what caused the global warming of the last 100 years?”

Explanation / Answer

We can distinguish natural climate variability from anthropogenic (human-caused) warming by measuring and examining the ration of carbon isotopes that is present in current atmosphere as the signature of carbon in CO2 emitted from buring of fossil fuels is different from those produced from living plants and hence this can be used as a tool for diffentiating between natural climate variability and anthropogenic activity. As most of the world population lives in Northern Hemisphere as the CO2 levels out there are very high as compared to southern hemisphere this also reflects the anthropogenic warming of earth. We also have the knowledge of how much atmospheric CO2 is produced per unit of fossil fuel, this can also assist us in knowing about the source of warming.

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