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Motivation | Climate Change
Climate Change | Sustainable Building
It has been accepted by the vast majority of the scientific community that human activity is warming our planet. Climate models that have been developed which only account for natural effects agree well with climate data collected from before the Industrial Revolution. This means that it is highly likely that these models are capturing all of the important climate forcings during this pre-Industrial Revolution time period. When these models are applied to times after about 1950, however, they consistently underpredict the temperatures that have been observed increasing around the globe. This is a very important and significant finding. Many who have cast doubt onto global warming cite normal variations, changes in solar cycles or other natural explanations for the warming that has been observed recently. The fact that climate models that have shown good agreement with all natural phenemenon over a period of thousands of years fail to account for the recent increase in temperatures indicate that other, un-natural, effects become significant after 1950. The source of these un-natural effects, or forcings, can begin to be understood by studying
Figure 1: IPCC Summary of Global
Climate Models1
Figure 1 to the left. It shows the original models mentioned above as the blue plot on each graph. Updated models that account for anthropogenic, or human derived, climate forcings are shown in red. Actual observed temperatures are shown with the black line. Note that after about 1950 the previous models do not capture the recent rise in temperature, but the updated models that account for human activity do. This fact indicates that the source of the recent warming trend is human activity. Knowing that human activity is responsible is only a small piece of the puzzle, however. The next task will seek to understand what emissions or activities have lead to these temperature increases.
Carbon dioxide is widely known to be
a "green house gas" (GHG), that is a gas that helps trap heat beneath the atmosphere. There are many other gasses that act as GHGs besides carbon dioxide, however.
Figure 2: Global
Warming
Potentials 2
Many of these gasses are shown in Figure 2, which displays the global warming potential (GWP) with the effects of CO2being normalized to one. Notice the extremely high values of many other gasses besdies CO2. Methane, CH4, is often mentioned as a major source of emissions from agriculture, and with a GWP of 21, it is understandable that mitigating methane emissions should be a priority. Hydro-fluro-carbons (HFCs), which are used as refrigerants in HVAC systems, have even greater GWP than methane or carbon dioxide. Analyzing the GWP of emissions is only one part of the human activity that effects global climate change. The other forcings will now be discussed.
To more fully understand how human activity is affecting climate change, one must look more broadly at the forcings that are behind the changes. Figure 3 displays a table that showcases the important anthropogenic forcings. The error bars represent the
Figure 3: Radiative forcings for various
anthropogenic effects
uncertainty expressed for each respective effect. Note that some anthropogenic activities tend to decrease the radiative forcing, meaning that they contribute to cooling. However as can be seen by the total net anthropogenic plot on the last row of the table, the net effect of the anthropogenic effects included in this analysis are to warm the planet.
At this point, it has been established that the planet is warming. It has been further shown that the cause of this warming is, at the very least, being accelearted by human activity. The disasterous effects predicted for our new climate if temperatures continue to rise will not be discussed in detail, but in short: droughts will be more severe, storms will be stronger, sea levels will rise and the very fabric of our society will be stretched to its limit.
How does sustainable construction and operation of buildings effect the global climate change challenge? It transforms it instead into a global climate change opportunity. Read about the opportunity here.
References:
1. IPCC Fourth Assesment Report : Climate Change, 2007
2. IPCC Second Assesment Report: Climate Change, 1995