Climate Change: The Smoking Guns for Humans

It is well established that increasing greenhouse gases such as carbon dioxide and methane will warm the earth's lower atmosphere (troposphere). It is also well established that present day concentrations of these two greenhouse gases have been measured at higher levels than those observed over the previous hundreds of thousands of years. Furthermore, the concentration rate is increasing. Where is all of this carbon dioxide coming from? According to Mann & Kump (2009), the IPCC (2007), Ghosh & Brand (2003), Ruddiman (2001), and others:

• Carbon in the air is made up of ¹²C (99%), ¹³C (1%), and ¹⁴C (1 per trillion)
• Plants prefer ¹²C over ¹³C. The ¹³C/¹²C ratio in plants is 2% lower than the atmospheric ¹³C/¹²C ratio
• Fossil fuels are derived from ancient plants so they have same low ¹³C/¹²C ratio
• Therefore, fossil fuel emissions (burning ancient plants) releases more ¹²C resulting in a DECREASED ¹³C/¹²C ratio
• Ocean carbon has a net zero ¹³C/¹²C ratio
• Since the Industrial Revolution, ¹³C/¹²C has been decreasing -- fossil fuels and land clearance are the primary sources for the extraordinary carbon levels in the atmosphere. Oceans cannot be the source for these emissions.

Volcanoes also outgas carbon with low ¹³C/¹²C ratios. Low ¹³C/¹²C ratios from volcanic activity have been observed by Cartigney et al. (2009), Mastalerz, de Lange, Dählmann, & Feseker (2007), Castrillo et al. (2004), Erdelyi, Richter, & Title (2002), and others. So could volcanoes be causing the observed decreasing atmospheric ¹³C/¹²C ratios? NO.

As discussed in Global Warming Misinformation - Volcanoes Emit More CO2 Than Humans, emissions from humans dwarf those of volcanoes. According to the IPCC (2007) WGI Report Chapter 2:

...when CO₂ from fossil fuel combustion enters the atmosphere, the ¹³C/¹²C isotopic ratio in atmospheric CO₂ decreases at a predictable rate consistent with emissions of CO₂ from fossil origin.

Scientists have calculated that volcanoes emit between about 130-230 million tonnes (145-255 million tons) of CO₂ into the atmosphere every year (Gerlach, 1991). This estimate includes both subaerial and submarine volcanoes, about in equal amounts. Emissions of CO₂ by human activities, including fossil fuel burning, cement production, and gas flaring, amount to about 27 billion tonnes per year (30 billion tons) [ ( Marland, et al., 2006) - The reference gives the amount of released carbon (C), rather than CO₂, through 2003.]. Human activities release more than 130 times the amount of CO2 emitted by volcanoes--the equivalent of more than 8,000 additional volcanoes like Kilauea (Kilauea emits about 3.3 million tonnes/year)! (Gerlach et. al., 2002)

Figure 3.1: Since the Industrial Revolution, ¹³C/¹²C has been decreasing (Zhao et al., 2006)

Figure 3.2: More recent CO₂ global emissions vs. ¹³C/¹²C ratios (IPCC, 2007)

Figures 3.1 and 3.2 show that as global CO₂ emissions are rising, the ¹³C/¹²C ratio is decreasing (larger negative values) due to human emissions of carbon dioxide.

¹⁴C is radioactive and is measured in tree ring data. Measured decreases of ¹⁴C/¹²C since the Industrial Revolution show that ¹²C is increasing (Figure 3.3, Mann 2009). This increase cannot be from volcanoes or deep oceans – only from fossil fuel emissions and land clearance. Because of above ground atomic bomb testing in the late 1940s continuing through 1963, ¹⁴C concentrations greatly increased. Therefore, ¹⁴C/¹²C ratios since the late 1940s cannot be used to infer carbon increases from human emissions.

Figure 3.3: Since the Industrial Revolution, ¹⁴C/¹²C has been decreasing

Figure 3.4 (Ruddiman, 2001) shows a time series of the two main sources of anthropogenic carbon in the atmosphere. One can see that since the Industrial Revolution carbon emissions have dramatically increased.

Figure 3.4: Measured Carbon Emissions vs. Time

Figure 3.5 shows that since 1751 approximately 329 billion tons of carbon have been released to the atmosphere from the consumption of fossil fuels and cement production. Half of these emissions have occurred since the mid 1970s. The 2006 global fossil-fuel carbon emission estimate, 8230 million metric tons of carbon, represents an all-time high and a 3.2% increase from 2005. (Boden, T.A., G. Marland, and R.J. Andres, 2009)

Figure 3.5: Since the Industrial Revolution, ¹⁴C/¹²C has been decreasing

Figure 3.6 (Ruddiman, 2008) shows where the carbon emissions end up. Fossil fuel burning and land clearance are sources of carbon while the oceans and land (primarily due to vegetation) are sinks for carbon. One should note that the measured amount of carbon in the atmosphere is only 55% of what is actually being emitted into the air.

Figure 3.6: Where do Carbon Emissions Go?

Figure 3.7 (IPCC, 2007) reveals that the rate of carbon sources is larger than the rate of carbon sinks which is why carbon in the atmosphere has been dramatically increasing. Plants and the oceans are not able to keep pace with industrial output and land clearance.

Figure 3.7: Carbon Source and Sink Rate

Carbon dioxide levels in the atmosphere are currently at unprecedented levels and the source for this additional carbon is primarily from human activities. There are no other known plausible arguments to explain modern carbon levels without humans being the main cause of the increase.

Could the increasing carbon in the oceans and ocean acidification be due to volcanic outgassing? NO. Figure 3.8 (Ruddiman, 2001) shows that deep ocean ¹³C/¹²C ratios (δ¹³C) have varied only slightly (between -1.2 and +1) over the last two million years. Submarine volcanoes emit carbon with δ¹³C values of -4 or less so their contribution must be insignificant. IPCC WGI Chapter 7 (2007) and Ruddiman (2001) show that carbon stores in the ocean are primarily driven by alternating phases of glaciations. During glacial climates, there is less land vegetation so the ¹²C would have to be stored in the deep ocean resulting in higher δ¹³C values. During warmer climates there is more land vegetation, so more ¹²C would leave the oceans to be stored inside the vegetation. This process lowers δ¹³C values in the oceans.

Figure 3.8: Deep water δ¹⁸O and δ¹³C values in the past 2 million years

Figure 3.9 (IPCC, 2007) is arguably the "smoking gun" for the anthropogenic (human) cause of climate change. As the figure clearly illustrates, when climate models consider only natural causes of climate change (blue color), the actual recorded climate (black line) cannot be predicted. However, when human forcing is added to natural forcing the pink curve matches very well with the observed climate across the globe. Simply stated, the climate observed today could NOT have happened if humans did not exist - it is impossible for natural forces alone to have caused today's climate. Furthermore, in the past few decades, climate models have shown that human factors are the dominant cause of climate change.

Figure 3.9: Climate models with and without human activities

Tropospheric warming with stratospheric cooling is essentially another "smoking gun" for anthropogenic global warming. There are no known natural forcing mechanisms that result in this coupling. Solar forcing, cloud cover, ENSO, PDO, NAO, etc. cannot explain a cooler stratosphere even when ozone depletion is accounted for. Increasing greenhouse gases explain this coupling very well and climate models predict a warmer troposphere and a cooler stratosphere with increased greenhouse gases.

Next: Natural Causes of Climate Change

• Introduction
• The Scientific Consensus
• Determining the Climate Record
• Impact of Greenhouse Gases
• Natural Causes of Climate Change
• Global Cooling?
• Climate Models & Accuracy
• Modern Day Climate Change
• The Global Warming Denial Machine
• Global Warming Misinformation
• Reasons for the Misinformation
• How to Talk to a Conservative about Climate Change
• Summary of Key Points
• Suggested Reading
• Works Cited

Last updated: 04/19/10