Causes of Present Climate Change

Question 1

How are scientist using carbon isotopes to more accurately determine the atmospheric CO2 emitted from fossil fuels?

Answer 1

Scientists use carbon isotopes to more accurately determine the atmospheric CO2 emitted from fossil fuels. The basis for this method is that fossil carbon contains low amounts of the carbon isotope (carbon-13) and none of the radioactive isotope (carbon-14), with its half-life of 5730 years. As the concentration of CO2 produced from fossil fuels rises, the proportions of 13C and 14C drop measurably. Scientists first discovered the decreasing proportion of 14C within atmospheric CO2 in the 1950s; regular measurement of this carbon isotope began in 2003. These data show that most of the CO2 increase comes from the burning of fossil fuels.

Question 2

How dose the contribution of each greenhouse gas towards the atmosphere vary?

Answer 2

The contribution of each greenhouse gas toward warming the atmosphere varies depending on which wavelengths of energy the gas absorbs and on the gas’s residence time, the length of time that it resides in the atmosphere.

Question 3

What are earths primary greenhouse gasses and which one is the most abundant?

Answer 3

In Earth’s atmosphere, the primary greenhouse gases are water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and halogenated gases. Of these, water vapor is the most abundant.

Question 4

Which greenhouse gasses have the longest/shortest residence time?

Answer 4

However, as discussed in Chapter 7, water vapor has a short residence time in the atmosphere (about 90 days) and is subject to phase changes at certain temperatures. Carbon dioxide, in contrast, has a longer residence time in the atmosphere and remains in a gaseous state at a larger range of temperatures.

Question 5

How dose present CO2 concentration differ from the last 800 000 years?

Answer 5

The present concentration of CO2 in Earth’s atmosphere is higher than at any time in the last 800 000 years, and perhaps longer. The record shows CO2 ranging between 100 ppm and 300 ppm over that time period, while never changing 30 ppm upward or downward in any span of less than 1000 years. Yet in May 2013, atmospheric CO2 reached 400 ppm after rising over 30 ppm in only the previous 13 years (having hit 370 ppm in May 2000).

Question 6

What is the residence time of carbon dioxide?

Answer 6

Carbon dioxide has a residence time of 50 to 200 years in the atmosphere; however, rates of uptake vary for different removal processes. For example, the uptake of atmospheric CO2 into long-term carbon sinks such as marine sediments can take tens of thousands of years.

Question 7

What is the second most prevalent greenhouse gas after CO2 and what is its rate of increase?

Answer 7

After CO2, methane is the second most prevalent greenhouse gas produced by human activities. Today, atmospheric methane concentrations are increasing at a rate even faster than carbon dioxide.

Question 8

How has methane levels changed in the past 800 000 years?

Answer 8

Reconstructions of the past 800 000 years show that methane levels never topped 750 parts per billion (ppb) until relatively modern times, yet in Figure 11.22a we see present levels at 1890 ppb.

Question 9

What is the residence time and efficiency at trapping longwave radiation of methane compared to CO2

Answer 9

Methane has a residence time of about 12 years in the atmosphere, much shorter than that of CO2. However, methane is more efficient at trapping longwave radiation.

Question 10

What are the long and short term effects of methane on trapping atmospheric heat compared to CO2?

Answer 10

Over a 100-year time scale, methane is 25 times more effective at trapping atmospheric heat than CO2, making its global warming potential higher. On a shorter time scale of 20 years, methane is 72 times more effective than CO2.

Question 11

What happens to methane after about a decade?

Answer 11

After about a decade, methane oxidizes to CO2 in the atmosphere.

Question 12

What is the largest source of atmospheric methane and how can that be divided up?

Answer 12

The largest sources of atmospheric methane are anthropogenic, accounting for about two-thirds of the total. Of the anthropogenic methane released, about 20% is from livestock (from waste and from bacterial activity in the animals’ intestinal tracts); about 20% is from the mining of coal, oil, and natural gas, including shale gas extraction ; about 12% is from anaerobic (“without oxygen”) processes in flooded fields, associated with rice cultivation; and about 8% is from the burning of vegetation in fires.

Question 13

What are some natural sources of Methane?

Answer 13

Natural sources include methane released from wetlands (associated with natural anaerobic processes, some of which occur in areas of melting permafrost, as described in Geosystems Now) and bacterial action inside the digestive systems of termite populations.

Question 14

What is the effect of permafrost on methane levels?

Answer 14

Scientists suggest that methane is released from permafrost areas and along continental shelves in the Arctic as methane hydrates thaw, potentially a significant source.

Question 15

What is the third most important greenhouse gas produced by humans?

Answer 15

The third most important greenhouse gas produced by human activity is nitrous oxide (N2O), which increased 19% in atmospheric concentration since 1750 and is now higher than at any time in the past 10 000 years

Question 16

What is Nitrous oxides lifetime in the atmosphere?

Answer 16

Nitrous oxide has a lifetime in the atmosphere of about 120 years—giving it a high global warming potential.

Question 17

What human activities contribute to the increase of N2O in the atmosphere?

Answer 17

Although it is produced naturally as part of Earth’s nitrogen cycle, human activities, primarily the use of fertilizer in agriculture but also wastewater management, fossil fuel burning, and some industrial practices, also release N2O to the atmosphere.

Question 18

What do scientists mainly attribute the rise in N2O with?

Answer 18

Scientists attribute the recent rise in atmospheric concentrations mainly to emissions associated with agricultural activities.

Question 19

What are the halogenated gases?

Answer 19

Containing fluorine, chlorine, or bromine, halogenated gases are produced only by human activities.

Question 20

What are the fluorinated gases?

Answer 20

Of this group, fluorinated gases, sometimes called F-gases, comprise a large portion. The most important of these are chlorofluorocarbons (CFCs), especially CFC-12 and CFC-11, and hydrochlorofluorocarbons (HCFCs), especially HCFC-22.

Question 21

What is Radiative Forcing/

Answer 21

Radiative forcing
The amount by which some perturbation causes Earth’s energy balance to deviate from zero; a positive forcing indicates a warming condition, a negative forcing indicates cooling; also called climate forcing.

Question 22

What is the dominates gas effecting earths energy budget?

Answer 22

Scientists have measured the radiative forcing, quantified in watts of energy per square metre of Earth’s surface (W · m−2), of greenhouse gases on Earth’s energy budget since 1979. Figure 11.23 (page 334), which compares the radiative forcing (RF) exerted by 20 greenhouse gases, shows that CO2 is the dominant gas affecting Earth’s energy budget.