Hand written temperature observations by Thomas Jefferson.
Humans have been observing the physical world around them long before the notion of a “scientist” was even considered. Our inherent desire to find answers to that which we do not understand has fueled the discovery of many things and continues to push scientific understanding even today. But when did we become so interested in the weather and climates around the world? More importantly, how long have we actually been recording these observations?
Marking the beginning of the Instrumental Period, the Central England Temperature (CET) dataset is the longest running temperature record in the world. The CET began in 1659 with mean monthly temperature data, then daily temperature records began 113 years later in 1772. In 1878 the CET was once agin updated to include mean maximum and minimum daily and monthly temperature data. The CET covered a triangular area in the United Kingdom which included London, Lancashire, and Bristol. Although the longest observational record begins in the U.K. (and continues to this day) other people from around the world also started to pay attention to their local patterns in climate and weather.
In the young and blossoming America’s, Thomas Jefferson established himself as a renaissance man, and was known to keep meteorological diaries, with the oldest surviving diary dating back to 1776. His diaries included records from the America’s, Europe, and the mid-Atlantic. Benjamin Franklin began recording his observations in 1724 and he spent a great amount of time theorizing about storms and weather patterns, and even making sea surface temperature readings as he joined voyages across the Atlantic Ocean. Other contributing scientists of the 18th century include Gabriel Fahrenheit and the mercury thermometer (1724), George Hadley and a theory on global wind circulation (1735), Daniel Bernoulli and his kinetic theory of gases (1738), and Swedish astronomer, Anders Celsius, who brought us today’s celsius temperature scale (1742).
In the late 1700’s, discovery knew no bounds as the scientific community quickly began understanding the world in a whole new light following the scientific revolution. The Instrumental Era was a major milestone for what has become the climate sciences, laying the groundwork for understanding climate change. Entering the 19th century, record keeping only improved, and so did our methods of collection. As science and technology progressed exponentially, humanity was thrust into a new period.
Figure 1: The CET is the worlds longest running observational temperature record. The illustration shows annual temperature anomalies as blue bars, with a 10-year running average in red.
By the time the 20th century rolled around, temperature data was being collected in every region with the exception of the poles, which began in the 1940’s and 50’s, and by the 1970’s the first geo-synchronous and sun-synchronus satellites began collecting data about our Earth. The now continuous monitoring of Earth’s environment allow us to see data almost instantly, and contributes to more than just the climate sciences. From GPS mapping, to following weather patterns and checking sea surface temperature and color, to mapping the world, satellites have proven to be invaluable to Earth scientists. Temperature is not the only metric that has been of interest to scientists, though. Understanding that the abundance of carbon dioxide and other greenhouse gases in our atmosphere are the leading cause of climate change, we have also been monitoring atmospheric gas concentrations. The Mauna Loa Observatory (MLO) is an atmospheric research facility, located in Hawaii, that has continuously logged atmospheric data since 1958. Since then, 5 more research facilities have been built from the northern to the southern hemisphere to monitor the condition of our Earth’s atmosphere. We now have nearly 400 years worth of global climate data which includes modern data combined with instrumental records from the 18th century. If 400 years of data doesn’t quite seem like enough to discern a trend, scientists have an additional ~65 Million years worth of climate data from global sediment and ice cores! (click here to learn more)
Figure 2: Global illustration displays the location of all six atmospheric observation stations that are operated by the National Oceanographic and Atmospheric Administration (NOAA) and the ESRL Global Monitoring Division.
Trends and Observations
The data is clear. Our global climate is changing, and it is not due to any natural variability or causes (See: Milankovitch Cycles: The Sun’s Role in Climate). The current shift in climate is a result of our interaction with the environment, and the changes we are beginning to see around the world are not necessarily good. So what does the climate record show? Maybe you’ve never seen global temperature and CO2 graphs or never really paid attention to the shear amount of information found in these types of illustrations, or, you could be a fellow scientist actively criticizing my work. Whichever category you fit into, here is a breakdown of the modern data:
Figure 3: CO2 levels, in ppm, as measured by the Mauna Loa Observatory from 1958 to 2017. The red line represents daily values, while the black line represents values corrected for seasonality.
You may notice that this graph is a bit different from Figure 1, mainly because we now have CO2 levels in parts per million on the y-axis, instead of temperature. Moreover, you’ll notice this graph only goes back to 1958, the first year that the Mauna Loa Observatory started collecting data. The most obvious result is the steady increase in atmospheric levels since measurement began nearly 60 years ago, growing approximately 1.5 ppm/year. If you’re wondering what the temperature and CO2 data look like plotted together from 1958 to the present, go no further!
Figure 4: Mean global land and ocean temperature anomalies and atmospheric CO2 levels from 1958 to 2016. *temperature stops at 2015, while CO2 stops at 2016 (Modified from Keeling, NASA GIS)
Each line in Figure 4 is a running average of the data collected. This allows the smoothing of data and displays the gradually increasing trend in both global temperatures and carbon dioxide levels. One thing I would like to point out, is that while the temperature data is using global land and ocean temperatures, the carbon dioxide data is only coming from the Mauna Loa observatory in Hawaii. At first you might think this is problematic: global temperature station data being compared to atmospheric data from a single location near the equator in Hawaii. However, what we find is that no matter where we measure atmospheric greenhouse gas levels, they are all pretty close to each other. This is because once these gases become detectable in the atmosphere, they have already become well mixed, meaning no layering or stratification has occurred. (See: Greenhouse Gases) Furthermore, atmospheric observation stations are located in remote areas at high elevations, avoiding urban areas with relatively higher concentrations of CO2 closer to the ground.
No matter which way we illustrate the data, one thing is very evident: global temperatures are rising, and so are greenhouse gas levels. Arguments exist which explore the possibility of temperature changes leading carbon dioxide changes, however, new research is showing that this is not the case. While recent data only gives us enough information to evaluate the last 400 years, paleoclimatologist have developed ways to look further into our Earth’s past. The larger perspective given to us by ice core and global sediment core data enables us to compare recent warming with what we have experienced in the past to determine if today’s warming is within reason, or a global anomaly. To learn more about the paleoclimate record, how the data is collected, and too see visualized data covering the past ~65 million years, click here!
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Tans, P., 2017: ftp://aftp.cmdl.noaa.gov/products/trends/co2/co2_annmean_mlo.txt (accessed March 2017)