Science or Speculation? The Uncomfortable Truth About Climate Proxies

How One Cave’s Data Challenges the Narrative of Unprecedented Climate Change

During my time as a graduate student, my advisor and I often steered clear of climate science discussions due to the increasingly politicized and contentious nature of the field. However, we frequently engaged in philosophical debates about science itself. My advisor had a habit of beginning every qualifying exam with a deceptively simple yet profoundly challenging question: “What is science?” This question wasn’t just a test of knowledge, it was a probing inquiry into the very foundation of our work. I vividly recall being asked this question during my exam, and though I likely flubbed the answer, it left a deep impression on me. It made me question whether I truly understood the field I was dedicating my life to.

This question stuck with me, particularly when we ventured into discussions about climate science. One paper that consistently came up in our conversations was an analysis of speleothems from Moondyne Cave in southwest Australia. This study became a focal point because it so clearly illustrated the inherent challenges in reconstructing past climates using proxies. The discrepancies between the speleothem’s isotopic record and actual measured temperature data always left me questioning: How well do we truly understand the climate of the past?

These discussions highlighted the limitations and uncertainties inherent in using proxies like speleothems to reconstruct historical climates, and they raised a fundamental question: Are these reconstructions truly scientific? If science is about creating logically defensible knowledge through rational investigative methods, then how do we reconcile these inconsistencies? This lingering skepticism about the reliability of proxies has deeply shaped my perspective on climate reconstructions, intensifying my doubts about the certainty with which we claim to understand historical climate variations, and, by extension, modern climate change.

My advisor’s insistence on questioning the very nature of science became even more relevant as I delved deeper into paleoclimatology. His approach forced me to confront the uncomfortable reality that the field, like many others, is not immune to subjectivity, bias, or the pressures of consensus. This realization deepened my skepticism about the certainty of past climate reconstructions, particularly when they rely on proxies that can be so easily misinterpreted or influenced by factors other than the ones we aim to measure. The question “What is science?” continues to resonate with me as I explore these complexities, reminding me that true scientific inquiry requires constant questioning, even of the methods and assumptions we hold most dear.

How Speleothems Form and Their Use in Climate Reconstruction

Speleothems, such as stalagmites and stalactites, form over centuries or millennia as water seeps through the soil and drips into caves. As this water evaporates, it leaves behind minerals like calcium carbonate, which build up layer by layer to create these impressive formations. The key to using speleothems as climate proxies lies in the isotopic composition of the oxygen and carbon within these layers. The ratio of oxygen isotopes (δ18O) in the calcite is thought to reflect the temperature at the time the water was deposited, warmer temperatures should result in lower δ18O values, while cooler temperatures should lead to higher ones.

For a refresher on oxygen isotopes check out…

How do scientists estimate past temperatures from ice cores?

However, this process is not as straightforward as it might seem. The Moondyne Cave study revealed that the δ18O variations in the stalagmite were not primarily driven by temperature changes.