Note to Yarns from the Farm readers: this is the third instalment of a series on climate change that I’m writing for our local monthly newsletter. The first article is here, and the second here. The image above is today’s satellite-derived sea surface temperature for the Indian Ocean, courtesy of the Australian Bureau of Meteorology
Like Mozart, Galileo is often credited for things he didn’t do. However, he really did invent the first thermometer in the last decade of the 1500s. In 1654, Ferdinand II, the Grand Duke of Tuscany (a devout Catholic who was Galileo’s friend and patron despite the censure of Galileo’s work by the church) improved on Galileo’s concept, sealing alcohol into a glass tube with small coloured globes containing fluids of different density that are allowed to float freely. You can buy its modern equivalent as a decorative art thermometer for your desk.
A modern version of the Galilean thermometer.
Galileo Galilei is arguably my favourite scientist. He was endlessly curious about the way the world and the cosmos works, doggedly determined to find mathematical explanations for matter and motion, and adamant in his refusal to accept flawed logic even to the extent of facing imprisonment by the Roman Catholic Church for heresy. He is a fitting scientific ancestor for climate scientists of our time.
As I discussed in the first two episodes of this series, rising CO2 from burning fossil fuels is the cause of climate change. Rising temperature is the primary symptom of the impact of rising CO2. Rising temperature, in turn, causes a suite of what we might call secondary symptoms of rising CO2, like rising sea level and changes in wind and rainfall patterns.
Because less than 1% of the atmosphere is made up of greenhouse gases, relatively small additions of carbon dioxide, methane, nitrous oxide and water vapor have an outsize influence on heat in the atmosphere.
While accurate temperature measurements were made in the centuries that followed Galileo’s invention, good global temperature coverage did not begin until the mid 1800s. The science community has settled on 1880 as the start of modern global record-keeping for temperature.
Over the past 50 years, satellite measurements of global surface temperatures using infra-red scanners have steadily improved in accuracy, resolution and coverage. Satellite temperature observations are used in conjunction with ground-based data to create global temperature maps with an accuracy estimated by NASA to be within 0.1 deg C, in a study published in 2019.
Because long-term changes in global temperature are on the order of 1 deg C, knowing the accuracy is critical to interpreting the results.
And because the signals are small, scientists use temperature differences (called anomalies) as a way to make changes over time more clear. Anomalies can be from any baseline that makes sense. NASA uses the mean from 1951 to 1980 and reports a 1 deg C rise from that baseline for global data averaged over the five years from 2015-1019. Averaging reduces statistical noise in the data, improving accuracy.
NASA’s temperature anomaly varies geographically, approaching 2 deg C in the polar regions where it is causing glaciers and permafrost to melt, and changing ecosystems reliant on polar ice packs. Rising sea surface temperatures are implicated in coral bleaching and changes in ocean circulation like the Indian Ocean dipole, which influences rainfall over Australia.
Physical and biological systems are complex, making it a challenge to observe and predict secondary effects of CO2 rise. Temperature will remain the gold standard variable because it is relatively bulletproof. But most of what we want to know about the future is tied to variables like rainfall, which are much harder both to measure and to predict.