365 Days of Climate Awareness 9 - Intro to Paleoclimatology

365 Days of Climate Awareness

9 - Intro to Paleoclimatology

Paleoclimatology is defined as the study of Earth climate for which there are no direct measurements. Potentially this includes even the the twenty-first century in parts of the world where scientific work was seldom done, but many historical methods do not work for too-recent time. Temperature records were kept by scientists from the 1700's on, and institutions like the British Navy logged data such as temperature and magnetism (via compass combined with lat/long observations) which have added significantly to our understanding of the earth system. Preceding those, however, and in parts of the world where records like those were not kept, we are forced to use proxy data.

Proxy data are observations which can stand in for direct observations. The observed proxy has a physical relationship (sometimes horrifyingly complicated) to the target data which can be quantified theoretically. With this mathematical relationship, generally established by extensive testing and experiment, the proxy data can be analyzed and converted into the target quantity. Critical information including global temperature and atmospheric composition can be determined this way.

It goes without saying that having as clear and detailed an idea of the Earth's climatic history is very important for understanding the scope and causes of current climate change. With accurate historical data for comparison, we can judge the magnitude and quickness of temperature and greenhouse gas concentration increases in recent centuries. The most recent and high-resolution set of records uses tree rings from around the world. With knowledge of the species and changing growth rates in response to temperature, we can infer aspects of the climate for the past several thousand years. This data set is especially valuable because it overlaps modern observations and other proxy methods.

A way to look into the further past is via ice cores from Greenland and Antarctica. Antarctic ice is much thicker and older than Greenland's, and provides us with a much longer record: up to 800,000 years, versus about 130,000. Most of the information we want is locked inside of tiny air bubbles trapped in the ice as it froze, like so many miniature samples.

Looking back further than this, into the span of millions and then billions of years, we look at chemical signatures in sediment and sedimentary rock. (The other rock types, igneous and metamorphic, have been subjected to heat and pressure to the point that any prior chemical properties have been altered or lost.) The rock record is the lowest-resolution, with precisions of 2-5% of the sample age (going back into billions of years old). But it is our only window into the planet's distant past. [Note: the precision statement was edited as my original was for a best-case of younger samples.]

Tomorrow: the temperature record in paleoclimatology.

Be well!