Global Warming and Ice Core Analysis

The Earth is rapidly warming-up. This is what the news media telling us everyday. The scientific journal also presents scientific data that shows the Earth temperature has increased about 1.5 C over the last 100 years.

Being a chemistry professor, I am very curious on how this data is collected and why this 1.5 C temperature rise is such a big deal

First, this is about data analysis: How do scientist know the Earth temperature profile over thousand or hundred of thousand years ? It turns out their data are based on ice-core isotope ratio analysis. Let me explain how this is done.

First, they drill and take ice core over a frozen lake out of Greenland. The depth of the ice core will correspond to the years-past that the ice were formed; assuming the ice never melted and new snow would cover over the old ice and snow-ice were accumulated over million years. Then take the ice sample at a particular depth which corresponds to the years that the ice were formed, scientists measured their hydrogen isotope ratio. Well, a question is what this isotope ratio is going to tell us about the temperature.

This has something to do with the difference of the vapor pressure-temperature profile between H2O and D2O. Being heavier than H2O, at a given temperature, the vapor pressure of D2O is lower than that of H2O. So, there will be more H2O vapor than D2O vapor at any given temperature. As the Earth temperature gets warmer, then H2O vapor will be even more abundant than D2O vapor; thus a smaller H/D ratio in the condensed phase of the ice core sample. Thus by measuring the H/D ratios over different ice core depth, scientist can reconstruct Earth temperatures over million of years of past history.

This would be a great problem exercise for a physical chemistry student to put their knowledge of vapor pressure concept into the context of the real-world problem-solving.