2.5: Future Geographies - Predicting Atmospheric Composition

Prediction versus Projection 

It is undeniable that the climate of Earth has seen numerous changes over time. Our current climate is undergoing changes in unprecedented ways for modern times. Measurements of atmospheric temperature show a clear upward trend while many regions are gripped in years-long drought. Most geoscientists concur that the current warming trend is related to human activities. Some disagree and suggest it is a natural fluctuation similar to that which the earth has experienced in the past.

To understand how climate has changed in the past, and more importantly, what will happen in the future, geoscientists must rely on models. Models are merely representations of the real world and are constrained by our understanding of earth processes. Scientist must make assumptions to fill in gaps where understanding or data is lacking. As a result, the output of a model inherently has a degree of uncertainty associated with it.

Predicting the changes in gaseous composition of the atmosphere is a difficult exercise. How the gaseous composition of the atmosphere will change in the future depends a great deal on the impact of human activities and our ability to control emissions. In addition to changes brought about by humans, increasing temperatures as a result of an enhanced greenhouse effect will impact the concentration of various gases in earth's atmosphere.

Uncertainty over how population will grow, economies develop, and technological advancement makes it difficult at best to predict the future composition of the atmosphere. Bodies like the Intergovernmental Panel on Climate Change (IPCC) make projections based on models. Though quite sophisticated, models of earth systems are constrained by our knowledge of environmental processes. The unpredictability of human advancement and the state of our understanding of climate dynamics leaves uncertainty in these projections. Thus geoscientists use statistics and their expert judgment for factors that elude quantification to determine the likelihood for the outcome of their model projections.

Future concentrations will not necessarily be geographically defined due to the fluid nature of the atmosphere. The exception may be water vapor, due to the unequal distribution of available water to evaporate into the air. However, the sources of future contributions to the gaseous composition of the atmosphere are certainly geographically distributed, especially those from human activities. The race toward economic development will shift the largest contributors to the developing world.

Figure \(\PageIndex{1}\): This graph shows that while developed countries increase emissions gradually, developing countries experience faster growth and become the dominant contributors over time. (CC BY-SA 4.0 ; Michael Ritter via The Physical Environment).

Figure \(\PageIndex{1}\) is a line graph, titled Total Greenhouse Gas Emissions by Region, compares greenhouse gas emissions in developed countries and developing countries from 2000 to 2030.

The horizontal axis shows years from 2000 through 2030. The vertical axis shows emissions in carbon dioxide equivalent units, with values ranging from about 10 to 35.

The line for developed countries starts at about 18 in 2000 and rises gradually to about 24 by 2030. This shows a slow, steady increase over time.

The line for developing countries starts at about 14 to 15 in 2000 and rises more quickly, reaching about 30 by 2030. The increase becomes steeper after about 2010.

At the beginning of the period, developed countries have higher emissions than developing countries. Around 2015, the two lines meet at about 21, showing that emissions are approximately equal at that point. After 2015, developing countries surpass developed countries and continue to increase more rapidly.

Overall, the graph shows that developed countries experience modest emissions growth, while developing countries show faster growth and become the higher-emitting group by the middle of the period.

Figure \(\PageIndex{1}\) illustrates a stacked area graph illustrating the trend of global greenhouse gas emissions (or carbon dioxide emissions) over time, broken down by contributing world region (such as the United States, East Asia, and Europe). The graph visually represents how the total global emissions have increased and how the primary geographical source of these emissions has shifted over the decades. 

IPCC Storylines and Scenarios

The Intergovernmental Panel on Climate Change (IPCC) is recognized by many as the foremost authority on climate change. Their most recent analysis of climate change (2007) utilized four different "storylines" that represent the range of driving forces and emission behind climate change. Each storyline posed several different scenarios, grouped as "families" to examine the outcome of models that use similar assumptions about the driving forces, and some that do not.

A1 Storyline (Homogeneous World - market focus) 

1. Very rapid economic growth.
2. Substantial reduction in regional per-capita income.
3. Global population peaks mid-century then declines.
4. Rapid introduction of new, and efficient technology.

A2 Storyline (Heterogeneous World -market focus) 

1. Emphasis on self-reliance & preserving local identities.
2. Slow per-capita economic growth and technological change.
3. Continuously increasing global population.

B1 Storyline (Heterogeneous World - environmental focus) 

1. Global population peaks mid-century then declines.
2. Rapid change to information & service economy.
3. Reduction in material intensity.
4. Introduction of resource-efficient and clean technologies.

B2 Storyline (Heterogeneous World - environmental focus)

1. Continuously increasing global population, slower than A2.
2. Less rapid creation of new energy technologies than B1 & A1.
3. Local and regional emphasis on environmental and social justice issues.

Ultimately, the IPCC's use of these four diverse Special Report on Emissions Scenarios (SRES) storylines—A1, A2, B1, and B2— provides a framework for conversations about climate change. The scenarios provide tools to test climatic models by providing the framework to understanding diverse human choices about technology, population growth and resource management that impact green house gas emissions. 

Projected increases in greenhouse gases

Projected increases from the four story lines are shown in Figure \(\PageIndex{2}\). All but the A2 show an increase in CO₂ followed by a decrease or leveling in CO₂ emissions the coming century. The A2 scenario show an increasing rate of emissions through time. In some sense, this is the "worst case scenario" with a continuously increasing population using more resources, slow technological change, and lack of global unity in tackling these issues.

At the opposite end of the spectrum is the "utopian" B1 scenario. The B1 scenario assumes low fertility with low mortality and central migration rates, global population peaks mid-century, then continually decreases toward 2100. Resource-efficient and renewable technology adoption diffuses rapidly through the world economy. The greening of material production and energy use helps lower carbon dioxide emissions from industry and transportation.

Figure \(\PageIndex{2}\): Projected carbon dioxide emissions compares possible future emission pathways, showing that global greenhouse gas trends depend on human choices about energy use, development, and climate policies. (Source: IPCC)

 Figure \(\PageIndex{2}\) contains four panels labeled A1, A2, B1, and B2, each showing a projected pathway of global greenhouse gas emissions from 1990 to 2090.

In all four panels, the horizontal axis shows time from 1990 to 2090. The vertical axis shows global carbon emissions, ranging from near 0 to about 40 units.

Panel A1 shows emissions rising rapidly from about 2000 to around 2050. After the middle of the century, emissions peak and then decline slightly. Shaded regions indicate variation within the scenario. This panel represents a high-growth pathway with eventual stabilization or modest reduction.

Panel A2 shows emissions increasing continuously across the entire period from 1990 to 2090. There is no visible peak or decline. This panel represents sustained growth in emissions over time.

Panel B1 shows emissions rising moderately until about 2050 and then declining steadily after mid-century. This panel represents a pathway in which emissions are reduced after an initial period of growth.

Panel B2 shows emissions increasing gradually and then leveling off near the end of the century. Growth is slower than in A1 and A2. This panel represents moderate growth followed by partial stabilization.

Overall, the figure compares four different future emissions pathways. A2 shows the most continuous long-term increase. A1 also rises strongly but eventually peaks. B1 rises and then declines, while B2 rises more slowly and levels off. Together, the panels show that projected emissions can differ substantially depending on the scenario assumptions.

The A2 and B1 scenarios represent two ends of the spectrum of possible outcomes. But in both cases, the importance of global population change and attendant demand for resources has a strong impact on emissions of greenhouse gases and stress on the physical environment. It may be just as likely for the changes in the composition of the atmosphere to lie somewhere between these extremes. The A1 market-driven scenarios of decreasing population growth coupled with rapid expansion of technology can yield reductions of greenhouse gases as well.

The IPCC does not suggest the likelihood of any particular outcome. They should be seen for what they are, scenarios, what could happen given particular conditions. Thus they serve policy makers with a kind of roadmap to the future, however uncertain it might be.

Assess you understanding of the preceding material by Looking Back at the Greenhouse Effect, and Future Geographies or skip and continue reading.

Looking Back at the Greenhouse Effect and Future Geographies \(\PageIndex{1}\)

Describe how the greenhouse effect works.

Answer

Gases such as carbon dioxide and methane absorb radiation emitted by the earth and warm, raising the temperature of the air.

List the four IPCC Scenarios and their world type/focus.

Answer

A1- Homogenous world - market focus. A2 - Heterogeneous world - market focus. B1 - Homogenous world - environmental focus. B2 - Heterogeneous world - environmental market focus.