People and Climate: Modeling and Impacts

Earth Science Extras

by Russ Colson

 

Modified from artwork by Russ Colson published in "Topics for Debate", Issues in Earth Science, Vol 11, Aug 2019, http://earthscienceissues.net/topics_for_debate

 

Computational Modeling of Climate Change

Prior to doing this exercise, it might be worthwhile to review the previous lessons on world energy balance and greenhouse warming at:

http://EarthSci4Teachers/ESE/Telling_Stories_of_the_Present/Stories_of_the_Atmosphere/Energy_Balance_of_Worlds/Energy_Balance_of_Worlds--Text/index.html

and

http://EarthSci4Teachers/ESE/Telling_Stories_of_the_Present/Stories_of_the_Atmosphere/Energy_Balance_of_Worlds/Energy_Balance_of_Worlds--Text/index.html

Here are a couple of the high school earth science standards addressing climate modeling from the Next Generation Science Standards (2013):

• HS-ESS3-6 Earth and Human Activity --- Use a computational representation to illustrate the relationships among Earth systems and how those relationships are being modified due to human activity.

• HS-ESS3-5 Earth and Human Activity --- Analyze geoscience data and the results from global climate models to make an evidence-based forecast of the current rate of global or regional climate change and associated future impacts to Earth systems.

Given how difficult it is for people to predict weather even a week or more out, it should be apparent that predicting changes in climate over years or decades of time will be fraught with complexity. Thus, despite the fact that the Next Generation Science Standards include climate modeling in the high school earth science expectations, the nitty-gritty of climate change modeling is going to be difficult for even the informed-non-specialist scientist to understand.

Its unclear from the standards above exactly how deep into the models high school students are expected to dig, however, it seems reasonable that college students can engage at least a little bit with these models, given the expectations of high school students! Thus, we are going to look at a couple of climate modeling papers, one from 1975 (just so the complexity of more modern modeling doesn't overwhelm us!) and then a more recent survey of how good a job climate models have done over the past 50 years at predicting changes in global temperatures. Our goal in examining these research papers is to infer the implications of what they are saying, a key scientific communications practice.

 

The Effects of CO₂--A Computational Model from the Mid 1970s

The first article we are going to examine is "The Effects of Doubling the CO₂ Concentration on the climate of a General Circulation Model" by Syukuro Manabe and Richard T. Wetherald, The Journal fo Atmospheric Sciences, Vol 32, 1975.

 Consider the abstract of their paper, below. An abstract of a research paper attempts to capture the key conclusions, constraints, evidence, limitations, and implications of the work. Read it several times to try to understand what it means before attempting the questions. In figuring out what it means, you may need to use your prior understanding of the nature of greenhouse warming, energy balance, and atmospheric structure.

An attempt is made to estimate the temperature changes resulting from doubling the present CO₂ concentration by the use of a simplified three-dimensional general circulation model. This model contains the following simplications: a limited computational domain, an idealized topography, no heat transport by ocean currents, and fixed cloudiness. Despite these limitations, the results from this computation yield some indication of how the increase of CO₂ concentration may affect the distribution of temperature in the atmosphere. It is shown that the CO₂ increase raises the temperature of the model troposphere, whereas it lowers that of the model stratosphere. The tropospheric warming is somewhat larger than that expected from a radiative-convective equilibrium model. In particular, the increase of surface temperature in higher latitudes is magnified due to the recession of the snow boundary and the thermal stability of the lower troposphere which limits convective heating to the lowest layer. It is also shown that the doubling of carbon dioxide significantly increases the intensity of the hydrologic cycle of the model.

 

A climate model, even one that is nearly 50 years old, includes a large number of components, including the condensation of moisture, the movement of air, the arrival and departure of electromagnetic energy from space, the movement of energy as both latent and sensible heat, the effects of the absorption and emission of energy (including by greenhouse gases), the thermodynamic equations that define the state of air (like compression, temperature, adiabatic cooling, and so on), and so on. The paper we are examining simplifies these many parameters into the following diagram (the red letters have been added for reference in the ensuing question).

Below is another conceptual diagram from the paper, this one showing the output results of the model (for both current CO₂ and an imagined future doubling of CO₂ in the atmosphere), compared to measurements made in the real world. Study the diagram, read through what each of the abbreviations refer to, and think about the implications of the output results of the climate model. When you have done this, work through the questions below, intended to get you to think about the meaning of the diagram and what it implies.

 

Hopefully you thought about the puzzling questions introduced in the feedback for the question above. Do you have an explanation? Noticing patterns in data or in modeling output is a first step in understanding your results. However, it is in finding and understanding the explanation for our experimental or modeling results that our activity in modeling gains scientific significance. What do the results mean?

Here, again, are those questions. Think about them in light of the modeling results, which are reproduced again below for your convenience.

The implications of these model results are more signficant than you might at first recognise. For example, if greenhouse gases intercept and absorb outgoing infrared radiation before it escapes into space, then why does the net NLR leaving the Earth system actually increase? Why is the biggest increase of all related to latent heat transport (LH) rather than anything related to infrared radiation that is absorbed by greenhouse gases? Why does the net incoming radiation from the sun increase with an increase in CO₂ (our CO₂ level can't effect the sun can it)? Thiink about it before attempting the question below.

 

Evaluation of Model Effectiveness (1970 to 2007)

The second article we are going to examine is "Evaluating the Performance of Past Climate Model Projections" by Zeke Hausfather, Henri F. Drake, Tristan Abbott, and Gavin A. Schmidt, Geophysical Research Letters, Vol 47, 2020.

Consider the chart below from this paper, showing the success of various models in predicting what were at the time of their publication future changes in globarl temperature.

 

Here is text from the paper:

The Hanson et al 1988 model, (H88) was featured prominently in congressional testimony, and the recent thirtieth anniversary of the event in 2018 focused considerable attention on the accuracy of the projection (Borenstein & Foster, 2018; United States. Cong. Senate, 1988). H88's "most plausible" Scenario B overestimated warming experienced subsequent to publication by around 54% (Figure 3).

To understand this over estimate of temperature change predicted by the H88 model (which resulted in considerable congressional conversation), the authors of this review break the accuracy of the model into two separate parts 1) the correctness of the underlying physics that models changes to Earth's future climate given different amounts of human-affected greenhouse heating (the greenhous heating is called "external forcing" ) and 2) the prediction of the amount of future external forcing (based on predictions of the future human production of amount CO₂, CH₄, etc..

To distinguish the effects of these two parts, the authors present the graphs below. The top graph shows how temperature was predicted to change by the H88 model for three scenarios, A being the highest reasonable forcing expected, B being most likely expected forcing, and C being the lowest reasonable forcing expected. These values are compared with the actual temperatures deviations that Earth experienced in the years after their forecast was made. The variation in the blue lines provides for an estimate of uncertainty. The dashed grey line shows when the forecast began (as opposed to fitting the model to past data). The bottom graph shows the same data, but shows the temperature deviations as a function of the actual external forcing that happened (thus taking any errors due to part 2, the prediction of the amount of future external forcing, out of the prediction). The dashed blue lines indicate the rough range of uncertainty. In both graphs, the blue represents actual observations of temperature, forcing, and year.

 

Climate Change Impacts--Discussion Prompts

Changes in climate, such as global warming, can impact people through

1) Changes in sea level that can submerge landscapes and farmland, flood coastal cities, cause increased periodic storm damage in coastal areas, increase salt water incursion into coastal wells, etc.

2) Changes in strength or number of severe storms (such as hurricanes, tornado outbreaks, or winter storms), causing loss of life and/or property damage.

3) Changes in local and regional climates, making areas wetter, drier, hotter, or colder, impacting ecosytems, agriculture, access to fresh water, drought frequency, wildfires, etc.

Any or all of these can impact infrastructure, human health, and quality of life.

 

Search online for sites, information, and opinions that address the following questions. Read several articles to get a sense of the range and scope of the problems and the perspectives on those problems.

1) What populations are most vulnerable to the effects of climate change? In what way(s) are these populations more vulnerable and how do you think this should affect government policy?

2) Read up on Minnesota Native American perspectives (e.g. Anishinaabe) on climate change: What are some of these perspectives and how should this inform our national perspective?

in considering the last questions, and in searching online for thoughts and perspectives, consider also the Minnesota State high school earth science benchmark:

9E.4.2.2.1 Apply place-based evidence, including those from Minnesota American Indian Tribes and communities and other cultures, to construct an explanation of how a warming climate impacts the hydrosphere, geosphere, biosphere, or atmosphere. (P: 8, CC: 4, CI: ESS3) Examples of cultures may include those within the local context of the learning community and within the context of Minnesota. Emphasis is on understanding and using American Indian knowledge systems to describe regional impacts of climate change to Minnesota. Examples may include the water cycle and how precipitation change over time impacts cultural practices related to nibi ("water" in the Ojibwe language); or the decline/species loss of wiigwaas ("paper birch" in the Ojibwe language and an important tree in Anishinaabe culture) due to climate stressors like drought or changes in snow cover.

 last updated 11/3/2022.   Text and pictures are the property of Russ Colson, except as noted.