top of page
  • Writer's pictureDr. Lee Anne Willson

Four Climate Scenarios for Ames

Updated: Feb 24, 2022

Unpacking the latest public input survey

Editors note: There was some miscommunication from the CAP consultants about the start date for the emission reduction targets below. The confusion was whether they started in 2005 or 2018. Here is a link to another post that explores the difference between the two and what it means for the state of the Ames CAP.

In a long session Tuesday evening, November 16 (available at ) the climate consultants Sustainability Solutions Group (SSG) presented four scenarios that they can use to guide development of a climate action plan for Ames. Three of the scenarios begin with a goal, and once the city has chosen, they will figure out how Ames can meet that goal, using a combination of their modeling and consultation with people in Ames. The fourth scenario is built up by looking at what people are confident can be done and adding that up to get a goal. A visualization of a plan is a wedge diagram, showing how various actions add up to bring about the needed change. You can construct one at . Here is an example from the SSG report:

Each color represents a different policy or change in practices; for example, the red wedge represents electric vehicles taking an increasing share of transportation. (You can download the council packet for November 16 from find this graph on page 42.) Cost or investment? One of the questions people have about all of these options is “what will it cost?” That is actually not an easy question to answer, because there are a variety of kinds of costs involved. All of the plans will involve some capital costs, that is, money spent up front to build or retrofit buildings, increase solar capacity, and so on. However, much of that is more investment than expense, because the changes will provide savings going forward. Just as we can now buy SunSmart shares (a capital investment), those shares lead to savings (rebates) that ultimately pay for the initial investment. Similarly, a homeowner can invest in a heat pump, geothermal heating/cooling, or other sustainable retrofits, and after the initial cost they will be getting lower energy costs into the future. It is likely that a big part of any of the plans will be to encourage homeowners to invest in emissions-reducing options. Since not all homeowners have the financial flexibility to invest a chunk of cash for this purpose, some cities have come up with ways to provide loans for the purpose. The loans can be paid back from the savings that result. The loans generally come from financial institutions but may be guaranteed by the city government. Because the improvement stays with the house, when the house sells the new owner assumes both the debt and the rebates going forward. Places where the city would need to invest directly include upgrading or replacing the power plant, continuing to make the city buildings and transportation fleet lower in emissions, and investing in public transportation. These are likely in all scenarios, and in fact the city has already been working on all of these areas. Taking action In terms of the kinds of actions that would need to be taken, all four scenarios are similar. The big difference is how fast these actions are pushed along. As the consultants pointed out, the net cost (investment minus return) after twenty years may be essentially the same for the faster vs. slower choices, because the faster choices also start seeing reduced costs much sooner. The big difference is whether ways can be found to move quickly – whether the capital costs can be covered without delay. Reducing net emissions – how much difference is there between scenarios? Of the four scenarios, the one that is most uncertain in its reduction of emissions is the one they call “evidence-based,” that is, where they look around for opportunities and add them up to see what the goals are. As SSG pointed out, this option has the disadvantage that it generally does not meet even the minimum standards for doing our share towards climate mitigation – in contrast to the “science-based” options. (I was puzzled by that label, but found a website explaining how this term is being used in the climate planning community: In this context, it means that the plan meets the stipulations of the IPCC for what needs to be accomplished world-wide.) Now for the math – comparing the three plans that contain goals.

Below is a plot of these three from the report compared with BAP (business as planned, that is, if no new initiatives occur, but just those already underway or funded).

Clearly, two of these scenarios (orange-science and purple-federal) are quite similar in terms of the total emissions that they allow – total emissions being the area under the curve. These are the two that are based on the assumption that everyone will do the same amount of reduction, so that the world as a whole can follow a path similar to the orange or purple lines in this plot. The emissions by these two similar cases is about 50% higher than the net emission by the yellow line. The yellow curve is some distance from the other two. The assumption here is that those countries that have the most resources – the biggest GDPs – are also, for the most part, those countries that have put most of the excess CO2 into the atmosphere and are therefore the countries that need to do more. The US, while not the biggest emitter now, is responsible for 24% of the excess carbon (greenhouse gases) in the atmosphere, because we have been a big emitter in the past, and because the CO2 stays in the atmosphere for a long time. Fair share calculations are explained here: The calculations for Ames follow the pattern set by the C40 Cities ( ). These give Ames a carbon budget – a net emissions budget – necessary to do our share to keep the temperature increase below 1.5°C. Using that as a guide, SSG created the following illustration of how we might meet this goal:

To recap: The two intermediate plans (orange-science and purple-federal from the first graph) make the assumption that everyone in the world can follow the same path. The “fair share” case takes into account that not every city or country has the ability to contribute equally, and that in most cases the ability to contribute more results from having, in the past, added more carbon to the atmosphere. The City Council has a responsibility to make sure that the City manages its resources with care, so they are asking questions to help them figure out the financial impact of the various options. That is appropriate. At the same time, we are in a situation where not taking action can end up more expensive than taking action. Let me end with a parable. A tale of three cities There are three cities below a dam. This dam was built many years ago, and the responsibility for maintaining it eventually rested with these three cities. They have been dealing with many local issues, and funding for repair of the dam has been set aside for more urgent needs. Now, the engineers are telling them “The dam is going to fail if it is not repaired soon. When it fails, your cities will be in harm’s way. We need to act.” The citizens of the cities gather to discuss what to do. Some of them are ready to put all the resources available into repairing the dam. Some say “We will only pay our share if the other two cities also do so.” Some say “I don’t believe we are really in danger” or “Maybe it’s real, but I can’t afford to pay more taxes.” Some say “Well, if it looks like it is about to fail we’ll just move somewhere else.” We can probably all recognize those reactions. The only difference, when it comes to climate change, there is no “somewhere else.” As to what happened to our three cities? For now, it is anyone’s guess.


bottom of page