Part #1 of my exploration of Global Warming
There are a lot of emotions surrounding the issue of Global warming and Climate Change but in order to start to unwind this issue, I have decided to explore the facts and scientific body of evidence that has been developed through the scientific principles of observation, experimentation, theorizing. As usual, I will link most of my sources at the bottom of the page.
My first installment will look at the issue if the Earth is really warming and how do we know. I will not in this installment look at cause an effect of any changes, simply the result of the measurements that science has been able to make. I will save the rest for future writings.
How do we take the earth’s Temperature?
The earth’s temperature is recorded in several different ways.
- Surface Air Temperature (SAT) has been measured by reliable equipment all over the world since the 1850s. In the US for example, The US Historical Climatology Network (USCN) maintains a network of 1,219 overseen by the National Oceanic and Atmospheric Administration (NOAA) They use a systematic approach to collect, process and catalog temperatures all over the Unites states. Similar networks exist in every country in the world.
- Marine Air Temperature (MAT) were formerly monitored by tossing a bucket over the side of the ship and putting a thermometer in the bucket. Today several more accurate methods are used. We measure the intake water temperature on ships Sea-surface water temperature (SST), And we use satellites to measure surface temperatures, as well as other methods of acoustic and microwave measuring.
- Atmospheric temperatures used to be measured by weather balloons, but today we use a system called GRAS – the Global Navigation Satellite System Receiver for Atmospheric Sounding. This system uses radio waves to measure the temperature and humidity with a very high accuracy.
- Underground temperatures – Cataloging temperatures of deep groundwater wells, and deep oil and gas wells (Borehole measurements) gives us a reliable record of how the earth’s crust is warming. This is less accurate, but does show changes buffered against current short term changes at surface level.
150 years of measuring temperature accurately has shown the following:
- Late 19th Century – A constant temperature with only slight fluctuations
- Early 20th century – A steady rise in temperature
- Mid 20th Century – A leveling off or small decline in temperature
- Late 20th century until today – A steep rise in temperature increase
All told, Data shows an average global temperature increase of 0.65°C since the start of the 20th century.
How do we measure temperatures in the distant past?
In my reading and discussions on the Climate change issue, I encounter many arguments that a 150-year window of direct temperature measurement is just too small of a time slice to make any sort of climate predictions.
Too answer that we look at the several indicators that can predict past temperatures by “proxy”
- Annual rings of trees – examining the annual rings on the oldest of living trees and further back, fossilized trees, we can see changes in the growth rates that can indicate patterns of climate. This works best in regions that have distinct winter/summer variation.
- Growth layers in coral reefs – Like tree growth rings, the growth layers of coral show climate changes in tropical regions.
- Lake sediments – sedimentary material in lakes can show volume of water in the layers of thickness of runoff and can also show types of pollen and other organic matter that is indicative of warmer/colder climate changes.
- Ice Core studies – Examining the oxygen trapped in Polar Ice cores can indicate past temperatures. The Ratio of the oxygen Isotopes present indicates past temperatures. Oxygen comes in two forms, Oxygen-16 and Oxygen-18, the Oxygen 16 has two less neutrons than Oxygen 18 and thus evaporates easier. In a colder climate, less Oxygen 18 is evaporated and precipitated to glaciers.
These Proxy methods of determining temperatures in our past beyond the age of thermometers allow us to reconstruct the temperatures of our climate back millions of years, not necessarily with the granularity of actual measurements like today, but enough that we can see the trends going back far enough to see the long-term trends.
In conclusion, the answer to the question of “Is our planet warming” is yes. Direct measurement of our last 150 years shows a dramatic increase starting late in the 20th century and Reconstructive temperature trends long term by proxy indicators reaffirms that the velocity of the increase in temperature does not meet the past patterns of our pre-industrial age.
Part #2 will come soon and will deal with Greenhouse Gasses, the Carbon Cycle and the Earth’s energy cycle as it relates to temperature.
“The Earth’s Changing Climate” by Professor Richard Wolfson, The Teaching Company