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Since there has been a lot of debate here at 13.7 (and everywhere) about global warming, and what is or isn’t factual or good science, I thought it would be a good idea to bring out some of the basic science behind what we know and what we don’t know about this important issue. Of course, this is not intended as an official document or as a thorough analysis, but as a primer for those who are interested in facts.

1. The Earth is a finite system, which receives most of its energy from the Sun. A small amount of heating also comes from radioactive decay and release from the interior.
2. The Sun emits radiation mostly in the visible spectrum, peaking at about 500 nm, closely corresponding to yellow light. Some of the radiation is reflected back into space, and some is absorbed and then reemitted back into space as lower-energy infrared radiation. Warming occurs when a larger fraction of the absorbed radiation is trapped near the surface. Think of your car, parked under the sun. With windows closed it gets much hotter inside.
3. The trapping of heat is caused mainly by what are called greenhouse gases: water vapor, carbon dioxide, methane, and ozone are the main ones. Without these gases in the atmosphere, the average temperature would be approximately 59 ºF lower.
4. During the past 100 years, the average global temperature has increased by 1 degree Fahrenheit. Global sea levels have risen 4 to 8 inches.
5. These numbers are not disputed. What is disputed is the cause behind the increase: natural vs. anthropogenic (i.e., caused by human activity).
   There have been many periods of naturally-occurring warming in Earth’s past history. Evidence going back hundreds of thousands of years has been uncovered with, e.g., the Vostok ice core samples from Antartica. (Petit, J.R. et al, Nature 399 (1999): 429–436). The findings show that global warming is directly correlated with an increase in carbon dioxide (CO2) and methane in the atmosphere. The peak temperatures corresponded to the highest accumulation of CO2 at about 280 parts per million by volume (ppmv).
6. This number should be contrasted with the readings of CO2 during the past 50 years, which shows a steady linear increase—after averaging for seasonal fluctuations (with amplitude of 20 ppmv)—from 310 ppmv (1958) to 385ppmv (2008)— and thus well above the peaks during previous heating periods in Earth’s history for the past 400 thousand years. This increase in the concentration of greenhouse gases is directly related to an increase in population and industrialization linked to fossil fuel consumption.
7. There have been small regional temperature fluctuations in recent history, known as Medieval Warm Period (about AD 950-1250) and the Little Ice Age that affected the North Atlantic region. The variation in temperature, measured from botany data and temperature records in England, was of about 0.2 degrees (up and then down), although global data indicates an overall cooling during the period. (See, e.g., Michael Mann et al, Nature 460 (2009): 880-3.)
8. The Sun has a natural cycle where its irradiance oscillates periodically every 11 years. As the Sun irradiates more, the Earth receives more radiation and it could conceivably get warmer. However, there is no obvious periodic warming of Earth in sync with the solar cycle. Recent research on this issue leads to contradictory results due to the different action of greenhouse gases at different heights in the atmosphere, some even concluding that there could be cooling associated with a solar maximum. Also, even though the past decade has been warmer than average, the Sun has remained at a relatively low activity level, being actually late in climbing to its max.
9. Models attempting to quantify the increase in global temperature for the next 100 years are extremely complex, being sensitive to different assumptions about the coupling of heat flow between oceanic currents and the atmosphere, projected greenhouse gases outputs, deforestation rate and other factors. Hence, results vary broadly, predicting an increase between 2 and 5 degrees Celsius. No model predicts a decrease in global temperature. Even taking the lowest predicted value, the consequences would be devastating, especially to coastal communities.

Our accelerated growth has fed from fossil fuels for about 200 years. It’s time we embrace different energy sources that have a more sustainable relationship with the environment. We must change our ways, from parasitic to symbiotic.

Also please read Scientists speak on climate change: Science and independence:

To politicize [climate research], to persecute and scrutinize individual scientists as if they were corrupt politicians, is not only misguided but useless. Not all scientists are virtuous (and not all doctors, lawyers, bankers, or teachers either), but the whole point of the scientific process is to free itself from such personal flaws: sooner or later, fraudulent or wrong data is uncovered and the path toward certitude is restored. Errors may persist for a while, but not for a very long while.

So, we must wonder what’s behind all these attempts to denigrate scientists working on climate change. One of us here at 13.7, Ursula Goodenough, asked in May what motivates climate change deniers.

I can’t say I know, and there probably are many answers, but one is surely ignorance of how science works. Another is manipulation by politicians, talk-show hosts with clear political agendas and the oil industry. Another must be a culture that feeds on the humiliation of the other for its own self-gratification.