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Climate in Context

Figure 1: A blackbody source is a model for a hot object that emits light across a broad region of the electromagnetic spectrum. The Sun can be modeled as a blackbody at nearly 10000 Fahrenheit. (In this figure the model is shown in blue and the solar spectrum at the top of the atmosphere is presented in red). The most intense part of the Sun's spectrum is in the visible between 0.4 and 0.8 micrometers (illustrated with the rainbow bar). The Earth also acts as a blackbody source whose emission is much weaker and is emitted at much longer wavelengths, in the infrared. In both cases, molecules in the atmosphere can reduce the amount of solar radiation that reaches the Earth's surface at particular wavelengths. For example, ozone molecules in the stratosphere reduce the amount of ultraviolet light that reaches sea level. (a good thing!). Similarly, most molecules absorb some of the infrared light emitted from the Earth's surface.

The acceleration of global warming is one of the greatest scientific and political issues of the 21st century. The most recent data shows that the world average concentration of carbon dioxide (CO2) in the atmosphere is around 407 ppm (parts per million). In other words, of every million molecules that make up the Earth's atmosphere 407 of them are CO2. At the start of the industrial revolution (generally thought to be in the early-mid nineteenth century), CO2 levels were close to 250 ppm and have been rising ever since as seen by the measurements started in the Mauna Loa observatory in the 1950s. The average global temperature has increased by about 2.0 degrees Fahrenheit in that time and is threatening to continue increasing based on global temperature models.

How does carbon dioxide affect temperature?

The sun emits  light over a broad range of colors from the ultraviolet into the infrared. (The most intense portion of the solar spectrum is in the visible, between 0.4 and 0.8 μmeters. See Figure 1.).  The Earth's surface also emits light over a wide range of colors, albeit much less intense and emitting at longer wavelengths in the infrared into the cold of space.  Components of the atmosphere,

Figure 2: According to the IPCC from 1995 to 2005, atmospheric CO2 concentrations increased by 19 ppm, the highest average growth rate recorded for any decade. Carbon dioxide concentration data extract from the Siple ice core in west Antarctica, in addition to direct measurements starting in the 1950's at the Mauna Loa observatory in Hawaii.

including water and carbon dioxide, absorb some of that radiation, preventing its release into space.  Other molecules such as methane and nitrous oxide, that are present in the "natural" environment but at higher concentrations due to human activity, participate in this heat-trapping known as the greenhouse effect, and we refer to these chemicals as Greenhouse Gases (sometime abbreviated as GHG.  The concentrations of all of these GHGs have risen over the past 150 years.  The concentrations of CO2, in particular, have risen very quickly over the last 50 years especially when considered in the context of the past 100 millennia (As revealed through analysis of trapped air in ice core samples, see Figure 2).

What's causing carbon dioxide levels to rise?

The consensus among most global scientists is that anthropogenic sources, or human activity, such as the burning of fossil fuels have been the leading cause of increasing CO2 levels. When oil or coal are burned, carbon  that has been trapped for millions of years is released into the air. According to the Intergovernmental Panel on Climate Change (IPCC) 2014 Synthesis Report, "emissions of CO2 from fossil fuel combustion and industrial processes contributed about 78% of the total GHG emissions increase from 1970 to 2010."

What do the marker colors on the maps mean?

It is a bit subjective, but we have chosen green to represent a desirable (and sustainable) global concentration of CO2 and anchored that to be 350 ppm.  We have also set red to represent, well, a red line that may have disastrous consequences for the Earth's population and have set that to be 500 ppm. (We are working on an article on these choices). If you visit the map on the home page often, you will find that we never see levels as low as 350 ppm in the inhabited areas that the sensors are located.  In fact, most sensors read values higher than the current global average of 407 ppm.   How should we think about that?  If a sensor near you  is reading 450 ppm, that indicates that your local air is contributing to a larger global average.   This might be because of GHG emissions from a local factory, a nearby highway, or it might be because wind is blowing in air with more combustion emissions from 100s of kms away. Almost certainly it means that one of many types of human activity is increasing CO2 in the atmosphere.

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page last edited February 8, 2018 by JHM