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  • Writer's pictureDr. Lee Anne Willson

Science-based goals for Ames

What role does science play in the choice of a climate action plan goal for Ames? There are several parts of the process where the ability of science to tell us “if you do A, B will result” is essential. Business as usual The first place where science is needed is telling us what will happen if we do not make changes in what we are doing. This is the “business as usual” (BAU) scenario. The Intergovernmental Panel on Climate Change (IPCC - ) includes BAU projections in their reports; they lead to 2.5°C or higher increases in the global temperature compared to its value in the late 1800s, before industrialization started to drive it up.

The consultants for the Ames plan, SSG, have generated a “business as usual” (BAU) report for Ames, including what we are doing now, trends operating now, and changes that are expected in the near future if there are no additional decisions or policy changes by the City. The BAU report for Ames shows a decline in emissions in the near term, in part because ISU will be switching from coal to natural gas for its power plant. It then shows a rise back to roughly current levels by 2050, as the population of Ames gradually grows.

The reports and presentations by SSG to the City of Ames are available at What we need to accomplish The second use of science can tell us what we need to accomplish, in terms of reduced emission and other mitigation, to prevent the worst global outcomes. The science in the IPCC report tells us that, in short, the world needs to reach net-zero emissions by 2050 to keep the temperature increase below 1.5°C. The report details the climate changes and the consequences that come with increases in the global temperature of 1.5°C, 2°C or more. Science shows that, although the difference between 1.5°C and 2°C may seem small, the results are not small ( ). To keep the temperature increase below 1.5°C requires the world to reach zero net emissions by 2050. Most countries have committed to this goal; some have committed to accomplish this by 2030 (and two have already achieved this goal) or 2035 or 2040 or 2045; a small number are committing only to goals beyond 2050. (An interesting graphic, though now 5 months old, is at ) Where are we now? Climate Action Tracker ( ) keeps track of commitments made by countries and cities around the world, and compares those to what is needed. Their plot shows that current commitments are not enough, including commitments coming out of the Glasgow summit. How is this relevant to Ames? The science here shows that cities are responsible for about 2/3 of the greenhouse gas emissions. Because many key decisions are made at the city level, the adoption of climate action plans by cities is a vital part of the effort to mitigate climate change.

Creating scenarios The third place where science is needed is translating actions we can take into their impact in terms of reducing emissions. How big a difference does it make to use less concrete, replace more cars with electric vehicles, provide more public transportation, plant more trees? What steps could Ames take to reduce its use of natural gas? The SSG models focus on tracking what we actually emit, but may not consider all the things we might do to counter those emissions. Offsets can be doing something that reduces emissions that we are not producing – for example, paying someone else to stop emitting, or providing excess solar power to another community so they don’t need to burn as much natural gas. Offsets can also be doing something to remove carbon from the atmosphere – e.g. planting trees here, or paying for trees to be planted somewhere else, or using wood waste to produce biochar. When offsets are discussed in the context of the Climate Action Plan goals, it is good to remember that there are offsets that benefit the community by spending money locally, such as increasing the number of trees in Ames, or improving the soils in our parks or yards. Setting goals for Ames What the science doesn’t tell us is what goal Ames should choose, and how that relates to the world goal of zero by 2050. Other considerations include the costs and tradeoffs – if we do this, what can we then not do? If we build new, denser housing is it too expensive for the people who lived in the old houses? What is our fair share of the effort to counter climate change? That kind of decision is a community process – where people talk, and listen, and come together with common goals and compromises so that no one ends up paying more than their share in dollars or suffering. A goal is often a “zero by” date, or a pledge to reduce emissions by a certain percentage by a target date. If it is a “zero by” date then the actions needed do not depend on the previous history, only on how fast the city can reach net zero. A percentage reduction date depends on what the initial date is that you compare to, and this does depend on the history – it is a lot easier to reach 50% reduction if you include a recent past change that reduced emissions by 25% than if you start counting after that change. Therefore, it is much harder to compare city-by-city when the goals are % reduction, and much easier to compare when they are “zero by” dates. What I expect for the Ames Climate Action Plan in its final form is that there will be both a zero-by date and some intermediate goals. Those goals may be a mixture of “this source should be reduced to zero by” dates and “overall emissions should be reduced by X% by” goals. These will be informed by the detailed report that the city will get from SSG, but the city may also consider what other kinds of offsets it may be able to do that will allow us to achieve net-zero as soon as possible. A bit more math Starting reductions as soon as they are possible can have a big impact on the total emission that we put into the atmosphere. For example, suppose we have the technology to reduce the emissions from one source to zero within five years. Then the total emission that is released by that process is the area of the dark grey triangle in the first panel (below). If, on the other hand, we are focusing on a “zero by” date that is 15 years out, and we first concentrate on starting slower processes, only starting this one 5 years before the goal date, then the total emissions from that process will be the area of the five dark-grey triangles in the right-hand panel – five times as much. This important aspect of reducing greenhouse emissions is not captured in a simple “zero-by” date.


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