Introduction

Background

Since the Industrial Revolution in the 1700s, human have substantially increase the amount of greenhouse gases into the atmosphere by burning fossil fuels, cutting down forests, and conducting other activities When greenhouse gases are enters the atmosphere, many remain there for long time periods ranging from a decade to many millennia. Over time, these gases are removed from the atmosphere by chemical reactions or by emissions sinks, such as the oceans and vegetation, which absorb greenhouse gases from the atmosphere. However, due to increasing human activities, these gases are emitted into the atmosphere more quickly than they are being removed, and thus increasing in concentrations.

As seen in Figure 1,2,3,4,5,6 and 7, the global atmospheric concentrations of carbon dioxide, methane, nitrous oxide, and certain manufactured greenhouse gases have all increase significantly over the last few hundred years.

Greenhouse effect – pros and cons

Image result for green house effect

(National Academy of Sciences, 2017)

The Earth is constantly bombarded with enormous amounts of solar radiation that enters the Earth’s atmosphere in the form of visible light, ultraviolet (UV) or infrared (IR) radiation.

About 30 percent of the radiation striking Earth’s atmosphere is immediately reflected back out to space by clouds, ice, snow, sand and other reflective surfaces, according to NASA. The remaining 70 percent of incoming solar radiation is absorbed by the oceans, the land and the atmosphere. As they heat up, the oceans, land and atmosphere release heat in the form of IR thermal radiation, which emitted into the atmosphere.

This equilibrium of incoming and outgoing radiation (greenhouse effect) makes the Earth habitable, with an average temperature of approximately 15 degree Celcius, according to NASA. Without this atmospheric equilibrium, Earth would be as cold, lifeless and inhabitable.

Greenhouse gases such as Carbon dioxide, Methane and Ozone act like a blanket, absorbing IR radiation and preventing it from escaping into outer space. The net effect is the gradual heating of Earth’s atmosphere and surface, resulting in a  global warming.  Global warming can result significant climate change such as  rise in sea levels, increasing ocean acidification, extreme weather events and other severe natural and societal impacts.

Trend of Greenhouse gases 

Carbon Dioxide

Figure 1:Concentrations of carbon dioxide in the atmosphere from hundreds of thousands of years ago through 2015, measured in parts per million (ppm). The data come from a variety of historical ice core studies and recent air monitoring sites around the world. Each line represents a different data source.

Since the beginning of industrialization, Carbon dioxide concentrations have increased substantially, rising from an annual average of 280 ppm in the late 1700s to 401 ppm as measured at Mauna Loa in 2015—a 43% increase (see Figure 1). Almost all of this increase is due to human activities1.

 

Methane

Figure 2 shows concentrations of methane in the atmosphere from hundreds of thousands of years ago through 2015, measured in parts per billion (ppb). The data come from a variety of historical ice core studies and recent air monitoring sites around the world. Each line represents a different data source.

The concentration of methane in the atmosphere has increased by two-fold since preindustrial times, reaching approximately 1,800 ppb in recent years (see the range between 2014 and 2015 Figure 2). This increase is said to be mainly due to agriculture and fossil fuel use2.

Nitrous Oxide

Figure 3: concentrations of nitrous oxide in the atmosphere from hundreds of thousands of years ago through 2015, measured in parts per billion (ppb). The data come from a variety of historical ice core studies and recent air monitoring sites around the world. Each line represents a different data source.

For the past 800,000 years, concentrations of nitrous oxide in the atmosphere rarely exceeded 280 ppb. However, since the 1920s the levels have risen and peaking at a new high of 328 ppb in 2015 (Figure 3). This increase is predominately due to agriculture3.

Ozone

Figure 4:  the average amount of ozone in the Earth’s atmosphere each year, based on satellite measurements. The total represents the “thickness” or density of ozone throughout all layers of the Earth’s atmosphere, which is called total column ozone and measured in Dobson units. Higher numbers indicate more ozone. For most years, Figure 5 shows how this ozone is divided between the troposphere (the part of the atmosphere closest to the ground) and the stratosphere. From 1994 to 1996, only the total is available, due to limited satellite coverage.

The total amount of ozone in the atmosphere generally declined by about 3% between 1979 and 2014 (Figure 4). All of these decrease happened in the stratosphere, with most of the decrease occurring between 1979 and 1994. Variations in stratospheric ozone over the years reflect the effect of ozone-depleting substances. These ozone-depleting chemicals have been released into the air for many years.Globally, the amount of ozone in the troposphere increased by about 3 percent between 1979 and 2014 (Figure 4).

 

Chlorofluorocarbon (CFCs)

Figure 5.

Following the increasing awareness of the detrimental effect of CFCs on the ozone layer and the international and domestic efforts to work to decrease the emission of CFCs across the world. Ever since, the role of CFCs on global warming has been small. The atmospheric energy rise is the first step to warming. The atmospheric energy rise of CFCs since 1750 has been about 0.34 Watt/m2. From figure 5, CFC-11 started to decline from 1990 and since 1998, CFC-12 levels levelled and tapered off.

 

Water Vapor

Figure 6

As the Earth’s troposphere warms, it is able to “hold” more water vapor without the vapor condensing into clouds and then rain.  Assuming the relative humidity remains constant, the amount of extra water vapor is governed by the Clausius-Clapeyron relationship, and is about 7% more water vapor per degree Kelvin increase in temperature.    The global increase in water vapor is easy to see in Figure 6, which shows the global mean time series of total column water vapor over the worlds oceans, expressed in percent change from average. This increase can be formally attributed to human-induced climate change — see Santer et al, 2007.

 

Figure 7: a map of water vapor trends over the 1988-2012 period.

Although there is a significant overall increase in water vapor, it is by no means spatially uniform.  As seen in figure 7, despite much of the world shows moistening to various degrees, there are regions of very substantial drying in the central tropical Pacific Ocean on either side of the equator.

What If All The Ice Melted On Earth?

That’s right. You watch a video with Bill Nye in it.

 

References

  1. IPCC (Intergovernmental Panel on Climate Change). 2013. Climate change 2013: The physical science basis. Working Group I contribution to the IPCC Fifth Assessment Report. Cambridge, United Kingdom: Cambridge University Press. www.ipcc.ch/report/ar5/wg1.
  2. IPCC (Intergovernmental Panel on Climate Change). 2013. Climate change 2013: The physical science basis. Working Group I contribution to the IPCC Fifth Assessment Report. Cambridge, United Kingdom: Cambridge University Press. www.ipcc.ch/report/ar5/wg1.
  3. IPCC (Intergovernmental Panel on Climate Change). 2013. Climate change 2013: The physical science basis. Working Group I contribution to the IPCC Fifth Assessment Report. Cambridge, United Kingdom: Cambridge University Press. www.ipcc.ch/report/ar5/wg1.
  4. Climate Change Indicators: Atmospheric Concentrations of Greenhouse Gases | Climate Change Indicators in the United States | US EPA. (2016). Epa.gov. Retrieved 24 March 2017, from https://www.epa.gov/climate-indicators/climate-change-indicators-atmospheric-concentrations-greenhouse-gases
  5. Glikson, A. (2013). Are CFCs responsible for global warming?The Conversation. Retrieved 24 March 2017, from http://theconversation.com/are-cfcs-responsible-for-global-warming-14962
  6. Santer, B. D., Mears, C., Wentz, F. J., Taylor, K. E., Gleckler, P. J., Wigley, T. M. L., … & Klein, S. A. (2007). Identification of human-induced changes in atmospheric moisture content. Proceedings of the National Academy of Sciences104(39), 15248-15253.
  7. Climate Analysis | Remote Sensing SystemsRemss.com. Retrieved 25 March 2017, from http://www.remss.com/research/climate#vapor

    8. Marc Llallalina (2016). What is the Greenhouse Effect? | Global Warming. [online] Available at: http://www.livescience.com/37743-greenhouse-effect.html [Accessed 21 Mar. 2017].

 

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