When the countries of the world meet for climate negotiations in Copenhagen this month, they will discuss how to prevent global temperatures from increasing more than 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels. This warming limit, accepted in principle by the leaders of the G8 countries in July, is more than just a number—it represents a way to think about the climate problem that can help us develop and evaluate options for solving it.
The current trajectory for greenhouse gas emissions would move the Earth by the middle of this century well outside the temperature range in which humanity evolved, marked by the 2-degree limit. This trend increases substantially the risk of dangerous, irreversible, and, perhaps, catastrophic changes in the global life support systems upon which we all depend. As the White House Science Advisor John Holdren aptly puts it, we’re “driving in a car with bad brakes towards a cliff in the fog.” The 2-degree limit is like a road sign warning us to avoid the cliff ahead.
Defining a warming limit implies a greenhouse gas budget, which is an upper limit to our cumulative emissions over the next 50 to 100 years. Such a budget encapsulates our scientific understanding of how emissions interact with the Earth’s climate and affect global temperatures. Some of the most significant greenhouse gases, like carbon dioxide, stay in the atmosphere for many decades, which is why the budget is defined over the long term.
Acceptance of an emissions budget should focus the climate talks because it encourages discussion of how to allocate that budget among countries. Many argue that developing countries like China can legitimately claim much of the emissions budget because they have large populations and have consumed relatively small amounts of fossil fuels thus far. But developed countries like the United States can’t phase out greenhouse gases overnight. In addition, many emissions from emerging economies are attributable to the manufacture of exported goods. Discussion of a specific budget will help negotiators balance more effectively these complex issues of feasibility and equity.
The warming-limit approach is analogous to how businesses conduct planning under uncertainty: Set a long-term goal, then work backward to determine how to achieve it, modifying plans dynamically as developments dictate. It’s operationally much more useful than a target for a single year. In fact, it can be used to derive such targets over many years, once the budget is allocated to developed and developing countries. It also has advantages over conventional, forward-looking policy analyses, which are hamstrung by the inherent limitations of economic forecasting models in accurately predicting the future.
Using a warming limit in this way prompts us to ask questions like “What are the least expensive options for meeting the target?” or “How many emission-free power plants must be built per week to meet the target, and how much capital would that require?” or “How fast must energy efficiency improve to meet the target given projected economic growth?” The answers to such questions help us identify the options that are most cost-effective, feasible, and desirable, and allow us to envision the kind of world we want to create.
The 2-degree warming limit is demanding—it implies halting growth in absolute global greenhouse gas emissions within the next decade, with reductions of at least 50% by 2050 compared to 1990 levels, and larger reductions soon afterward. It also has other implications that most policy makers do not yet fully appreciate:
(1) We shouldn’t wait: Delaying action only eats up the emissions budget, locks in emissions-intensive infrastructure, and makes the required reductions much more costly and difficult later. Early action also brings the costs of technologies down through economies of scale and learning-by-doing, a fact usually ignored by ill-informed climate skeptics.
(2) We need to move quickly on many fronts: The rate of change in energy systems needed to stay within the budget will require broad societal mobilization, rapid innovation, and major investments in science, technology, and education not unlike those undertaken by the United States after the USSR launched Sputnik in 1957. One key to rapid change will be the development of new technologies that consumers prefer even if they initially carry a higher price—much like early fossil fuels, such as kerosene, were preferred to whale oil for lighting in the mid-1800s;
(3) We can’t burn it all: More than half of the Earth’s remaining economically recoverable fossil fuel reserves must be kept in the ground to achieve climate stabilization (or, if burned, their carbon emissions will need to be stored securely). A price on carbon and significant reductions in the costs of low carbon technologies are the two most important means for achieving this difficult goal.
The 2-degree warming limit provides guideposts for a real solution to the climate problem, yielding insights available from no other approach. We’ll need to apply these insights, invest in a large portfolio of promising options, fail fast, and learn as rapidly as we can. There’s simply no more time to waste.
Jonathan Koomey is a Visiting Professor at the Yale University’s School of Forestry and Environmental Studies, and Florentin Krause is a researcher living in Richmond, California. Krause was the principal investigator and Koomey was one of two other coauthors of the first systematic attempt to evaluate the implications of a warming limit-based approach to addressing the climate problem (Florentin Krause, Wilfred Bach, and Jonathan G. Koomey. 1989. From Warming Fate to Warming Limit: Benchmarks to a Global Climate Convention. El Cerrito, CA: International Project for Sustainable Energy Paths. http://files.me.com/jgkoomey/9jzwgj). It was republished in 1992 as Florentin Krause, Wilfred Bach, and Jonathan G. Koomey. 1992. Energy Policy in the Greenhouse. NY, NY: John Wiley and Sons.
This post was reposted from Climate Progress. That posting includes footnotes and references which you may find useful.